85762510
Long-term seasonal and spatial patterns in mortality and survival of Calanus finmarchicus across the Atlantic Zone Monitoring Programme region, Northwest Atlantic
Plourde, S., Pepin, P., and Head, E. J. H. 2009. Long-term seasonal and spatial patterns in mortality and survival of Calanus finmarchicus across the Atlantic Zone Monitoring Programme region, Northwest Atlantic. - ICES Journal of Marine Science, 66: 1942-1958.The vertical life table method was used to estimate stage-specific daily mortality rates and survival from 1999 to 2006 for Calanus finmarchicus sampled in the Canadian Atlantic Zone Monitoring Programme, which covers the Newfoundland-Labrador Shelf (NLS), Gulf of St Lawrence (GSL), and Scotian Shelf (SS). Stage-specific mortality rates and survival showed significant regional and seasonal differences, with the largest signal associated with variations in temperature. Density-dependent mortality, associated with the abundance of C6 females, was the main factor influencing mortality in the egg-C1 transition during the period of population growth in spring on the SS, and in summer in the GSL and on the NLS. In autumn, mortality in egg-C1 was positively related to temperature and negatively related to phytoplankton biomass, with particularly high mortality rates on the SS. The integration of our results into stage-specific recruitment rates from egg to C5 revealed that C. finmarchicus populations experience their greatest loss (mortality) during the egg-C1 transition. Loss during development to C1 was greater in the GSL than in the other regions during the period of population growth, resulting in lower recruitment success in the GSL. In autumn, C. finmarchicus showed low stage-specific daily recruitment rates on the SS at high temperatures, and low phytoplankton biomass compared with those in the GSL and on the NLS. Our findings reinforce the necessity of describing regional and seasonal patterns in mortality and survival to understand factors controlling the population dynamics of C. finmarchicus.
128945722
Ecological Geography of the Sea
Preface. Introduction: The Inadequacy of Classical Biogeography in Ecological Analysis. The New Availability of Timely, Global Oceanographic Data. The Use of CZCS Images in This Study. The Choice of Schemes to Partition the Pelagic Ecology of the Oceans. Ecological Gradients: Fronts and the Pycnocline: Oceanic and Shelf Sea Fronts Are Ecotones and Leaky. The Ubiquitous Horizontal "Front" at Shallow Pycnocline. Biogeography of the Shallow Pycnocline: Both Habitat and Boundary. Physical Forcing of Biological Processes: Minimal Set of Predictive Factors for Ecology of the Pelagos. What Do We Really Mean by an Algal Bloom? Can We Specify Major Biomes in the Pelagos? Stratification and Mixing in the Open Ocean: The Consequence of Latitude. Regional Discontinuities in Resistance to Vertical Mixing in the Warm Oceans. The Limits of the Characteristic Conditions of Polar Seas. The Seaward Boundary of Processes along Ocean Margins. Conclusion: there Are Four Primary Biomes in the Ocean. Biomes: Primary Compartments in Ecological Oceanography: A Definition of the Primary Biomes. Polar Biome. Westerlies Biome. Trades Biome. Coastal Boundary Zone Biome. Exceptional Regions: Boundary Layers and the High-Nutrient, Low-Chlorophyll Areas. Oceans, Seas and Provinces: The Secondary Compartments: How to Group the Major Oceans, the Marginal Seas and Coastal Regions. A Method for Specifying Ecological Provinces in the Oceans. A Statistical Test of the Proposed Boundaries. Temporal Variability and the Adjustment of Boundaries: Scales of External Forcing: From Seasons to Centuries. Linking Seasonal to ENSO-Scale Events. Longer Scale Trends and Changes. Conclusion: A Map of Provinces for a Strong ENSO Event? The Atlantic Ocean: Atlantic Polar Biome. Atlantic Westerly Winds Biome. Atlantic Trade Wind Biome. Atlantic Coastal Biome. The Indian Ocean: Indian Ocean Trade Wind Biome. Indian Ocean Coastal Biome. The Pacific Ocean: Pacific Polar Biome. Pacific Westerly Winds Biome. Pacific Trade Wind Biome. Pacific Coastal Biome. The Southern Ocean: Antarctic Westerly Winds Biome. Antarctic Polar Biome. Bibliography. Index.
58910221
Macroecology of Calanus finmarchicus and C. helgolandicus in the North Atlantic Ocean and adjacent seas
Global climate change is expected to modify the spatial distribution of marine organisms. 
However, projections of future changes should be based on robust information on the ecological 
niche of species. This paper presents a macroecological study of the environmental tolerance and 
ecological niche (sensu Hutchinson 1957, i.e. the field of tolerance of a species to the principal factors 
of its environment) of Calanus finmarchicus and C. helgolandicus in the North Atlantic Ocean and 
adjacent seas. Biological data were collected by the Continuous Plankton Recorder (CPR) Survey, 
which samples plankton in the North Atlantic and adjacent seas at a standard depth of 7 m. Eleven 
parameters were chosen including bathymetry, temperature, salinity, nutrients, mixed-layer depth 
and an index of turbulence compiled from wind data and chlorophyll a concentrations (used herein 
as an index of available food). The environmental window and the optimum level were determined 
for both species and for each abiotic factor and chlorophyll concentration. The most important parameters 
that influenced abundance and spatial distribution were temperature and its correlates such 
as oxygen and nutrients. Bathymetry and other water-column-related parameters also played an 
important role. The ecological niche of C. finmarchicus was larger than that of C. helgolandicus and 
both niches were significantly separated. Our results have important implications in the context of 
global climate change. As temperature (and to some extent stratification) is predicted to continue to 
rise in the North Atlantic sector, changes in the spatial distribution of these 2 Calanus species can be 
expected. Application of this approach to the 1980s North Sea regime shift provides evidence that 
changes in sea temperature alone could have triggered the substantial and rapid changes identified 
in the dynamic regimes of these ecosystems. C. finmarchicus appears to be a good indicator of the 
Atlantic Polar Biome (mainly the Atlantic Subarctic and Arctic provinces) while C. helgolandicus is 
an indicator of more temperate waters (Atlantic Westerly Winds Biome) in regions characterised by 
more pronounced spatial changes in bathymetry.
128973502
Spatial and seasonal patterns in abundance and age-composition of Calanus finmarchicus in the Gulf of Maine and on Georges Bank: 1977–1987
The mean seasonal cycle and distribution of various life history stages of C. finmarchicus throughout the Georges Bank (GB)-Gulf of Maine (GOM) region were characterized based on 5966 MARMAP zooplankton samples collected during 106 surveys over a 10-year period (autumn 1977–autumn 1987). A high degree of seasonal and spatial variability in C. finmarchicus abundance throughout the region was evident in contoured portrayals of data, grouped into standard stations and 2-month “seasons”. 
 
Eight subareas of the Gulf of Maine-Georges Bank region were identified through cluster analysis of standard stations having similar seasonal patterns in mean abundance of C. finmarchicus stages C3, C4, C5 and adults. These were the northern Gulf of Maine (Northern GOM); southern Gulf of Maine (Southern GOM); Scotian Shelf-coastal Gulf of Maine (Scotian-Coastal GOM); Mass Bay; tidally mixed Georges Bank (Mixed GB); tidal front on the Bank separating mixed from seasonally stratified water (Tidal Front GB); seasonally stratified water on the Bank (Stratified GB) and the Continental Slope adjacent to Georges Bank (SLOPE). 
 
A distinct seasonal abundance cycle was present in all subareas, but, the magnitude and timing of annual maxima varied greatly among subareas. Peak abundance was reached early (March–April) in Mixed GB, Tidal Front GB and Mass Bay, and late (July–August) in Northern GOM and Scotian-Coastal GOM. Remaining subareas had maxima in May–June. Abundance increased 10-fold from January–February to March–April and decreased sharply from July–August to September–October in all areas except southern GOM and northern GOM. The amplitude of the annual cycle was weakest in northern GOM and southern GOM, where high concentrations of C. finmarchicus persisted year-round, and strongest in the tidally mixed shallow water on GB, where the sparsest densities of C. finmarchicus occurred most of the year. Abundance curves for the various areas converged in March–April, when C. finmarchicus was ubiquitously very abundant (> 104/10 m2), and diverged from September to December. 
 
C. finmarchicus stage distribution in the GB-GOM area was highly negatively correlated with mean water column temperature during the stratified season. This seemed more related to the hydrography of the region, which isolates warmer well mixed Georges Bank from the Gulf of Maine and the stratified areas on the Bank, than to temperature, because Calanus abundances decline on the Bank before water temperatures exceed their preferences. 
 
A large part of the spatial and seasonal variation in C. finmarchicus abundance and age structure appears to be tightly coupled to major hydrographic regimes and to major circulation patterns in the region. There was a sharp ecotone between well-mixed Georges Bank and the Gulf of Maine as defined by C. finmarchicus abundance patterns and life history distributions. The ecotone is present year-round but is most apparent during the stratified season (May–October), when thermohaline density gradients and the near-surface current jet along the northern flank are generally strongest. The Gulf of Maine had the highest abundances of C. finmarchicus, and lowest spatial and seasonal variation in the region, while tidally mixed Georges Banks displayed the opposite pattern. This indication of stable population centers in the Gulf of Maine would make it a major source of Calanus in the region, particularly during March–April. Distributional patterns also suggest a strong Calanus influence from Scotian Shelf water in northern Gulf of Maine and on the southern flank of Georges Bank.
84946330
Distribution of Calanus spp. on and around the Nova Scotia Shelf in April : evidence for an offshore source of Calanus finmarchicus to the central and western regions
Observations of hydrography and Calanus spp. abundance were made at stations on lines across the central and eastern Scotian Shelf (SS) in April 1995 and 1997 and on additional lines on the western SS and across Cabot Strait (CS) and the Laurentian Channel (LC) in 1997. Calanus finmarchicus was more abundant on the central and western SS than in the east, and Calanus hyperboreus was concentrated in the east and in areas influenced by the Nova Scotia Current. Calanus spp. on the eastern SS probably originated mainly from populations overwintering in the Gulf of St. Lawrence. High abundances of C. finmarchicus occurred at or beyond the shelf break when warm slope water was present, suggesting that they derived from a population overwintering in the deep water south of the SS. In both years, slope water was present in the near-surface layers at shelf stations of the Halifax Line (HL), but in 1997 the degree of intrusion was greater. Calanus finmarchicus abundances were also substantially higher at shelf stat...
84635007
Climate fluctuations and the spring invasion of the North Sea by Calanus finmarchicus
The population of Calanus finmarchicus in the North Sea is replenished each spring by invasion from an overwintering stock located beyond the shelf edge. A combincation of field observations, statistical analysis of Continuous Plankton Recorder (CPR) data, and particle tracking model simulations, was used to investigate the processes involved in the cross-shelf invasion. The results showed that the main source of overwintering animals entering the North Sea in the spring is at depths of greater than 600m in the Faroe Shetland Channel, where concentrations of up to 620m -3 are found in association with the overflow of Norwegian Sea Deep Water (NSDW) across the Iceland Scotland Ridge. The input of this water mass to the Faroe Shetland Channel, and hence the supply of overwintering C. finmarchicus, has declined since the late 1960s due to changes in convective processes in the Greenland Sea. Beginning in February, animals start to emerge from the overwintering state and migrate to the surface waters, where their transport into the North Sea is mainly determined by the incidence of north-westerly winds that have declined since the 1960s. Together, these two factors explain a high proportion of the 30-year trends in spring abundance in the North Sea as measured by the CPR survey. Both the regional winds and the NSDW overflow are connected to the North Atlantic Oscillation Index (NAO), which is an atmospheric climate index, but with different time scales of response. Thus, interannual fluctuations in the NAO can cause immediate changes in the incidence of north-westerly winds without leading to corresponding changes in C. finmarchicus abundance in the North Sea, because the NSDW overflow responds over longer (decadal) time scales.
55167921
Spatial demography of Calanus finmarchicus in the Irminger Sea
Continuous Plankton Recorder data suggest that the Irminger Sea supports a major proportion of the surface-living population of the copepod Calanus finmarchicus in the northern North Atlantic, but there have been few studies of its population dynamics in the region. In this paper, we document the seasonal changes in the demographic structure of C. finmarchicus in the Irminger Sea from a field programme during 2001/2002, and the associations between its developmental stages and various apparent bio-physical zones. Overwintering stages were found widely at depth (>500 m) across the Irminger Sea, and surviving females were widely distributed in the surface waters the following spring. However, recruitment of the subsequent generation was concentrated around the fringes of the Irminger Sea basin, along the edges of the Irminger and East Greenland Currents, and not in the central basin. In late summer animals were found descending back to overwintering depths in the Central Irminger Sea. The key factors dictating this pattern of recruitment appear to be (a) the general circulation regime, (b) predation on eggs in the spring, possibly by the surviving G0 stock, and (c) mortality of first feeding naupliar stages in the central basin where food concentrations appear to be low throughout the year. We compared the demographic patterns in 2001/2002 with observations from the only previous major survey in 1963 and with data from the Continuous Plankton Recorder (CPR) surveys. In both previous data sets, the basic structure of G0 ascent from the central basin and G1 recruitment around the fringes was a robust feature, suggesting that it is a recurrent phenomenon. The Irminger Sea is a complex mixing zone between polar and Atlantic water masses, and it has also been identified as a site of sporadic deep convection. The physical oceanographic characteristics of the region are therefore potentially sensitive to climate fluctuations. Despite this, the abundance of C. finmarchicus in the region, as measured by the CPR surveys, appears not to have responded to climate factors linked to the North Atlantic Oscillation Index, in contrast with the stocks in eastern Atlantic areas. We speculate that this may because biological factors (production and mortality), rather than transport processes are the key factors affecting the population dynamics in the Irminger Sea.
89299469
Population Dynamics of Calanus in the North Atlantic: Results from the Trans-Atlantic Study of Calanus finmarchicus
During the year from July 1992 we were privileged to work together in Oregon, giving us opportunity to discuss scientific issues surrounding the life history and ecological relations of Calanus finmarchicus, the dominant zooplankter of the subarctic North Atlantic. Thanks to the efforts of Sheina Marshall and a hundred others, ‘‘C-fin’’ is probably the best-studied plankton animal, which of course makes it the ideal subject for further study. The more you know, the more you can learn. At the same time, Peter Wiebe and other planners of the US GLOBEC Program were considering C. finmarchicus as a possible target species for a multi-year Georges Bank project, and we realized that many workers in Canada and Europe, including the EU-funded ICOS Program, were also actively studying the species. We decided to initiate, at the level of individual scientists, a trans-Atlantic interaction among those interested in C. finmarchicus, and named this exchange the ‘‘Trans-Atlantic Study of Calanus’’ programme, or TASC. At first it was informal, with a photocopied newsletter distributed from Oregon, but in April 1994 with support from the EU-Marine Science and Technology (MAST) Programme and the Norwegian Research Council we met in Oslo (ICES Document CM 1994/L:10; Ophelia, 44: 1-205). This led the European contingent to prepare a proposal to EU-MAST for funds to support an EU-TASC programme of rearing, modelling and sampling studies, focusing on a ‘‘Year of Calanus’’, 1997. That proposal was accepted. Meanwhile, the US GLOBEC work on C. finmarchicus in the vicinity of the Georges Bank continued with sampling studies from 1994 to 1999, as did studies at several Canadian agencies. In August 1999, with encouragement from ICES, a final TASC Symposium was held at Tromso, northern Norway, to exchange and discuss dozens of individual and group contributions to our knowledge of C. finmarchicus. Invaluable support was provided by members of the Scientific Steering Committee: Jan O. Backhaus (Germany), Bruce W. Frost (USA), Roger P.
1054372
Composite forces shape population dynamics of copepod crustaceans.
Understanding the processes that control species abundance and distribution is a major challenge in ecology, yet for a large number of potentially important organisms, we know little about the biotic and abiotic factors that influence population size. One group of aquatic organisms that defies traditional demographic analyses is the Crustacea, particularly those with complex life cycles. We used likelihood techniques and information theoretics to evaluate a suite of models representing alternative hypotheses on factors controlling the abundance of two copepod crustaceans in a small, tropical floodplain lake. Quantitative zooplankton samples were collected at three stations in a Venezuelan floodplain lake from June through December 1984; the average sampling interval was two days. We constructed a series of models with stage structure that incorporated six biotic and abiotic covariates in various combinations to account for temporal changes in abundance of these target species and in their population growth rates. Our analysis produced several novel insights into copepod population dynamics. We found that multiple forces affected the abundance of particular stages, that these factors differed between species as well as among stages within each species, and that biotic processes had the largest effects on copepod population dynamics. Density dependence had a large effect on the survival of Oithona amazonica copepodites and on population growth rate of Diaptomus negrensis.
3551231
Reproduction of the planktonic copepod Calanus finmarchicus in the Lower St. Lawrence Estuary: relation to the cycle of phytoplankton production and evidence for a Calanus pump
Due to the dynamic physical environment of the Lower St. Lawrence Estuary, the spring phytoplankton bloom in the Laurentian Channel occurs late in the season, typically in mid-June, but the high phytoplankton biomass is sustained throughout the summer months. In this study, relationships between the phytoplankton production cycle, water temperature, and the reproductive cycle of Calanus finmarchicus Gunnerus, a predominant planktonic copepod in the Lower Estuary, were investigated during spring-summer 1991. Field observations showed that the final stages of oocyte maturation in C. finmarchicus females did not begin until the onset of the spring phytoplankton bloom in midJune. High egg production rates, as estimated by the number of eggs released by females incubated immediately after capture, commenced 1 wk later and persisted until late August. Egg production rates were significantly correlated with an index of gonadal maturity in females and were consistent with a rectilinear or curvilinear relationship with chlorophyll a standing stock. Laboratory experiments showed that: (1) in presence of food (the diatom Thalassiosira weissfloggii), maturation of oocytes would proceed and females could spawn eggs at least 2 mo before the spring bloom; (2) without food, the oocytes did not develop past immature stages, except in a small minority of the population; and (3) colder temperatures in early spring would prolong the lag between the onset of the spring bloom and the start of egg production by less than 4 d. Combined with concurrent microscopic measurements of oil sac volume, the results do not rule out the possibhty that lipid reserves were used to support the early stages of oogenesis, but do show that the majority of females did not use lipid reserves for vitellogenesis prior to the spring phytoplankton bloom. It is suggested that the Lower St. Lawrence Estuary is an important region of C. finmarchicus production in summer which, because of the residual surface circulation, may act as a Calanus 'pump' to influence levels of zooplankton biomass in the Gulf of St. Lawrence and on the shelf off Nova Scotia.
84997897
Fecundity characteristics of Calanus finmarchicus in coastal waters of eastern Canada
Abstract Results of an earlier study of fecundity characteristics of the copepod Calanus finmarchicus from the shelf off Nova Scotia are combined with more recent observations from the Estuary and Gulf of St. Lawrence, where female Calanus are considerably larger. Maximum egg production rates of Lower Estuary females in laboratory experiments were consistent with predictions based on the previously-derived relationship between maximum egg production rates and temperature, in which a culture of Thalassiosira weissflogii was used as the food source. Clutch sizes varied considerably and were significantly related to body size. Within a given body size, clutch sizes were observed to differ by up to a factor of two, possibly associated with differences in food availability or female age. Clutch size of Calanus finmarchicus may represent the interaction between the egg production rate that can be supported by the contemporaneous food conditions and the constraint imposed by the diel spawning cycle. Measurement ...
84570719
Egg production rates of Calanus finmarchicus in the western North Atlantic : effect of gonad maturity, female size, chlorophyll concentration, and temperature
Egg production rates of Calanus finmarchicus were measured in the Labrador Sea (spring) and on the Scotian Shelf (spring, summer, and autumn), in conjunction with indices of gonad maturity and food availability, female body size, surface layer temperature, and surface nitrate concentrations. Egg production rates were often two to four times higher than any previously reported at similar temperatures. Estimates of egg production rates of populations were most closely related to the proportion of reproductively mature females (as measured by a gonad stage index) and female size. Specifically, the gonad stage index (proportion of females capable of spawning) was correlated with the proportion of females that spawned during 24-h incubations, and female size determined the clutch size (i.e., number of eggs produced). Although there were detectable effects of food and temperature on egg production rates, they were generally weaker than the effect of female gonad maturity. Thus, over the broad spatial and tempor...
53998917
Growth and development rates of the copepod Calanus finmarchicus reared in the laboratory
Development rates, nitrogen- and carbon-specific growth rates, size, and condition were determined for the copepod Calanus finmarchicus reared at 3 temperatures (4, 8, and 12°C) at non-limiting food concentrations and 2 limiting food concentrations at 8°C in the laboratory. Devel- opment rates were equiproportional, but not isochronal. Naupliar stage durations were similar, except for non-feeding stages, which were of short duration, and the first feeding stage, which was prolonged, while copepodite stage durations increased with increasing stage of development. Under limiting food concentrations at 8°C, development rates were prolonged but similar relative patterns in stage durations were observed. Body size (length and weight) was inversely related to temperature and positively related to food concentration. Condition measurements were not affected by tempera- ture, but were positively related to food concentration. Growth rates increased with increasing tem- perature and increased asymptotically with increasing food concentration. At high food concentra- tions, growth rates of naupliar stages were high (except for individuals molting from the final naupliar stage to the first copepodite stage, in which growth rates were depressed), while growth of copepodites decreased with increasing stage of development. Neither nitrogen nor carbon growth rates, the former a proxy for structural growth, were exponential over the entire life cycle, but rather sigmoidal. Carbon-specific growth rates were greater than nitrogen-specific growth rates, and this difference increased with increasing stage of development, reflecting an augmentation in lipid depo- sition in the older stages. However, nitrogen and carbon growth rates were more similar under food- limited conditions. Based on this study, we recommend that secondary production rates of Calanus finmarchicus and possibly other lipid-storing copepods not be estimated from egg production mea- surements alone, as has been suggested for other species of copepods, because growth, including structural growth, is not equivalent for all stages.
8960204
Obtaining birth and mortality patterns from structured population trajectories.
"A method is presented for unravelling the demographic equation for structured populations. A solution to the McKendrick-von Foerster equation is constructed using spline functions and this is fitted to stage-structured population data in such a way that the solution is smooth, positive, and does not imply negative death rates. The smoothness of the surface, and hence the complexity of the population model, is determined in a statistically optimum manner using cross validation. Time- and age-dependent death rates can be obtained as well as time-dependent birth rates. Confidence intervals are obtained for population size and death rates that give a 95% probability that the true population dynamics are within the intervals. Practical application of the method is demonstrated, and comparison made with three alternative methods."
4327291
Density-dependent mortality in an oceanic copepod population
Planktonic copepods are primary consumers in the ocean and are perhaps the most numerous metazoans on earth. Secondary production by these zooplankton supports most food webs of the open sea, directly affecting pelagic fish populations and the biological pump of carbon into the deep ocean. Models of marine ecosystems are quite sensitive to the formulation of the term for zooplankton mortality, although there are few data available to constrain mortality rates in such models. Here we present the first evidence for nonlinear, density-dependent mortality rates of open-ocean zooplankton. A high-frequency time series reveals that per capita mortality rates of eggs of Calanus finmarchicus Gunnerus are a function of the abundance of adult females and juveniles. The temporal dynamics of zooplankton populations can be influenced as much by time-dependent mortality rates as by variations in ‘bottom up’ forcing. The functional form and rates chosen for zooplankton mortality in ecosystem models can alter the balance of pelagic ecosystems, modify elemental fluxes into the ocean's interior, and modulate interannual variability in pelagic ecosystems.
42728179
Stage-specific mortality of Calanus finmarchicus, Pseudocalanus elongatus and Oithona similis on Fladen Ground, North Sea, during a spring bloom
We used Woods Population Surface Method to estimate stage-specific mortality rates for populations of Calanus finmarchicus, Pseudocalanus elongatus, and Oithona similis from abundance data obtained during the Fladen Ground Experiment (FLEX 1976) in the northern North Sea. Temperatures from the day and night depth distributions of each developmental stage were used to force temperature functions for the duration of developmental stages. In addition, we considered the influence of potential food-limitation of development, which had only minor effects on the mortality estimates. We show that the risk of mortality changes substantially over the life span of the animals, with notable differences among species. O. similis, in particular, shows negligible losses after naupliar stages 1 and 2, which may account for its numerical dominance in many ocean regions. Differences among taxa are poorly explained by allometry alone and are instead related to species- and stage-specific differences in behavior. The vertical migration behavior of late developmental stages of C. finmarchicus (i.e. their choice of habitat) might help to reduce mortality risk.
85656097
A vertical life table approach to zooplankton mortality estimation
Zooplankton mortality is commonly estimated from time series of abundances (horizontal life table approach) with the assumption that transport processes are of minor influence. This assumption is commonly violated in the marine environment. We provide equations appropriate for analysis of stage distributions in zooplankton samples at a single time (vertical life table approach) that, in certain circumstances, facilitate mortality estimation without requiring time series of abundances. A primary assumption is that daily recruitment to a particular stage should not be characterized by a strong upward or downward trend. To improve the accuracy of parameter estimates, however, knowledge about such trends may be taken into account. The accuracy and precision of mortality estimation were assessed with an individual-based simulation model. Results obtained from application of the vertical approach to the copepod Pseudocalanw newmani are comparable to those obtained independently by a horizontal method. We conclude that the vertical approach may provide mortality estimates under conditions in which horizontal techniques are inappropriate. In contrast to estimates obtained with horizontal techniques, vertical estimates represent snapshots of the population.
25668286
On birth and death in the sea
We present the first comparative study of the stage-specific patterns of mortality of Calanus and Pseudocalanus, two widely distributed genera that are representative of a relatively large-bodied, broadcast spawning calanoid copepod and a relatively small-bodied, egg-brooding calanoid. The study site is Georges Bank, a continental shelf locality in the Northwestern Atlantic with retentive circulation that renders it suitable for studies of population dynamics. Based on extensive mortality estimates from 30 cruises, we find that co-occurring Calanus finmarchicus and Pseudocalanus spp. have markedly different patterns of stage-specific mortality, the former bimodal and the latter relatively uniform with respect to developmental stage. Neither taxon exhibits a monotonic decline in mortality with developmental stage, nor are rates of mortality predictable in a useful manner by copepod body size or by ambient temperature. Young stages of the broadcast-spawning C. finmarchicus show conditional density-dependence of mortality rates, i.e. mortality rates are independent of population density when adult females are low in abundance but positively related to population density at high female abundances. This density-dependence, which is probably attributable to egg cannibalism, introduces a quadratic mortality term into population dynamic models. The egg-brooding Pseudocalanus spp., in contrast, show no evidence of density-dependent mortality. The two taxa illustrate a life history trade-off: the broadcast-spawning Calanus exhibits birth rates that are greatly elevated with respect to those of Pseudocalanus, but there is a compensatory cost in very low survivorship of the freely spawned eggs. Both the high fecundity, high mortality life history of Calanus and the low fecundity, low mortality life history of Pseudocalanus appear to have approximately equal fitness in this study site.
56215820
Spatial differences in mortality of Calanus pacificus within the California Current System
A vertical life table method was used to estimate patterns of mortality of late developmental stages of Calanus pacificus in the southern sector of the California Current System from seven California Cooperative Oceanic Fisheries Investigations (CalCOFI) cruises (three spring, four late autumn-early winter). Copepodid stage durations were described as a continuous function of both food concentration and temperature from reanalysis. This function was combined with vertical profiles of temperature and Chl a to estimate stage durations in the field and solve for instantaneous mortality rates of two stage pairs: C5/adult females and C5/adult males. Male mortality rates averaged two to three times higher than the corresponding female mortality rates. There was no significant difference between seasons (spring versus winter) in either male or female mortality rates. There was a consistent spatial pattern of higher mortality rates of both males and females in the inshore region relative to the offshore region. This inshore increase in mortality rates is the opposite of that expected from the effects of food limitation, but is correlated with an index of abundance of zooplanktivorous fishes obtained from the CalCOFI ichthyoplankton series (a fishery-independent data source). Elevated predation risk may mitigate the inferred benefits to zooplankton of increased food supply.
51987129
Seasonal dynamics and mortality rates of Calanus helgolandicus over two years at a station in the English Channel
The stage-specific abundance and egg production rates of Calanus helgolandicus were determined on a near-weekly basis over 2 yr at a 50 m deep station in the SW English Channel (Stn L4). Mortality rates were derived using a vertical life-table approach across eggs, nauplii and also the CV-adult stage pair. The results demonstrate strong seasonal patterns in the mortality rates of egg and nauplii and the CV-adult stage pair, but with different relative rates and somewhat dif- ferent seasonalities. Mortality was highest in the egg and egg-NI stages, averaging 6.1 and ~1.5 d -1 , respectively, with the percentage surviving through the egg-NI stage pair often <<10%. Although the instantaneous removal rate of eggs was significantly related to adult abundance (p < 0.001, r 2 = 0.221), densities of adult C. helgolandicus seemed too low to account for these rates. Examination of the relationship between CV-adult female mortality and the abundance of the dominant invertebrate predators revealed statistically significant relationships (p < 0.001 r 2 = 0.276 for chaetognaths; p < 0.001 r 2 = 0.125 for siphonophores); however, the variability explained by temperature was much higher (p < 0.001 r 2 = 0.652). The egg-NI and NI-NII stage pairs also showed a highly statistically significant positive relationship between mortality and temperature. For the first time we compared mortality rates for egg-NI using 2 vertical methods — one using measurements of egg and NI abun- dance (Method A) the other using egg production rates and NI abundance (Method B) — and found the two to be similar, although Method B gave higher values. Finally, as many mortality equations do not consider the bias resulting from the presence of eggs incapable of hatching in the field, we derived and applied new equations for mortality of eggs and egg-NI (Method A) that incorporated egg hatching success. At low hatching success or low mortality rates, this correction can alter esti- mates of mortality rates significantly.
55848140
Mortality and survival in early stages control recruitment in Calanus finmarchicus
We present a data set describing the seasonal climatology and the spatial pattern in mortality and recruitment in early stages of Calanus finmarchicus in the lower St Lawrence estuary (LSLE) and the Gulf of St Lawrence (GSL), respectively. Contrary to the common assumption of constant mortality, daily mortality during development from egg to N3 or N6 showed important seasonal and spatial variations mostly independent from patterns in population egg production. Patterns in recruitment rate to late naupliar stages were mainly associated with patterns in survival, and dictated patterns in abundance of nauplii N4‐6 (seasonal, LSLE) and early copepodite C1‐2 (spatial, GSL). Consequently, recruitment to late naupliar and early copepodid stages was largely independent from patterns in population egg production. A multiple regression model showed that phytoplankton biomass and female abundance exerted opposite effects in the control of mortality, illustrating the beneficial effect of high phytoplankton biomass on the survival due to a relaxation of the cannibalism pressure or mortality owing to food shortage. A sensitivity analysis using a stage-based model clearly showed variations in the amplitude and the timing in recruitment to late naupliar stages solely due to different mortality formulations. Moreover, our simulations suggested that temperature alone should not be of primary importance in determining patterns in survival because of its general scaling effect on metabolism. Our study reinforces the importance of an adequate description of mortality and survival in studies of population dynamics and illustrates the importance of developing dynamic mortality formulations integrating multiple effects for future use in models of C. finmarchicus.
90127124
Data Analysis Methods in Physical Oceanography
Chapter and section headings: Preface. Acknowledgments. Data Acquisition and Recording. Introduction. Basic sampling requirements. Temperature. Salinity. Depth or pressure. Sea-level measurement. Eulerian currents. Lagrangian current measurements. Wind. Precipitation. Chemical tracers. Transient chemical tracers. Data Processing and Presentation. Introduction. Calibration. Interpolation. Data presentation. Statistical Methods and Error Handling. Introduction. Sample distributions. Probability. Moments and expected values. Common probability density functions. Central limit theorem. Estimation. Confidence intervals. Selecting the sample size. Confidence intervals for altimeter bias estimators. Estimation methods. Linear estimation (regression). Relationship between regression and correlation. Hypothesis testing. Effective degrees of freedom. Editing and despiking techniques: the nature of errors. Interpolation: filling the data gaps. Covariance and the covariance matrix. Bootstrap and jackknife methods. The Spatial Analyses of Data Fields. Traditional block and bulk averaging. Objective analysis. Empirical orthogonal functions. Normal mode analysis. Inverse methods. Time-series Analysis Methods. Basic concepts. Stochastic processes and stationarity. Correlation functions. Fourier analysis. Harmonic analysis. Spectral analysis. Spectral analysis (parametric methods). Cross-spectral analysis. Wavelet analysis. Digital filters. Fractals. Appendices. References. Index. 8 illus., 135 line drawings.
54940374
Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments
A fluorometric method is described which provides sensitive measurements of extracted chlorophyll a free from the errors associated with conventional acidification techniques. Fluorometric optical configurations were optimized to produce maximum sensitivity to Chl a while maintaining desensitized responses from both Chl b and pheopigments. Under the most extreme Chl b:Chl a ratio likely to occur in nature (1 : 1 molar), the new method results in only a 10% overestimate of the true Chl a value, while estimates from older acidification methods are 2.5-fold low. Under conditions of high pheopigment concentrations (pheo a: Chl a = 1 : 1 molar), the new method provides Chl a estimates that are equivalent to those determined from the acidification technique. The new simple method requires a single fluorescence determination and provides adequate sensitivity for small sample sizes (<200 ml) even in the most oligotrophic marine and freshwater environments.
41815473
Eat and run? The hunger/satiation hypothesis in vertical migration: history, evidence and consequences
The study of vertical migrations in aquatic organisms has a long and colourful history, much of it to do with the effects of changing sampling technology on our understanding of the phenomenon. However, the overwhelming majority of such studies carried out today still depend on detecting differences in vertical distribution profiles during some course of time, or acoustic echoes of migrating bands of organisms. These can not distinguish migratory activity of individual organisms, but can only assess net results of mass transfers of populations, which may integrate many individual migrations. This is an important distinction, for without knowing the actual movements of individuals it seems unlikely that we will be able to understand their causes, nor the effects of vertical migrations on the environment or on the migrators themselves. This review examines evidence for individual vertical movements gathered from ‘tracers ‘, mainly gut contents, and reviews the evidence for the hypothesis that such movements are in fact driven by hunger and satiation. The more recently appreciated vertical migrations of phytoplankters and their similarities in form and driving forces to those of zooplankton and nekton are also discussed. Finally, the role of vertical migrators in vertical fluxes of materials is discussed, along with the consequences of satiation‐driven descent for such estimates.
4071491
Temperature and Living Matter
AbstractIN accordance with the general lines of this series of monographs, the author restricts himself almost entirely to cell physiology; ecology and behaviour are not dealt with.Temperature and Living Matter
 By Prof. J. Blehrádek. (Protoplasma-Monographien, Vol. 8.) Pp. x + 277. (Berlin: Gebrüder Borntraeger, 1935.) 18 gold marks.
85441990
Characteristics of Calanus finmarchicus dormancy patterns in the Northwest Atlantic
Johnson, C. L., Leising, A. W., Runge, J. A., Head, E. J. H., Pepin, P., Plourde, S., and Durbin, E. G. 2008. Characteristics of Calanus finmarchicus dormancy patterns in the Northwest Atlantic. - ICES Journal of Marine Science, 65: 339-350.Demographic time-series from four fixed stations in the Northwest Atlantic Ocean demonstrate variable timing of entry into and emergence from dormancy in subpopulations of the planktonic copepod Calanus finmarchicus. A proxy for timing of entry was established as the date each year when the proportion of the fifth copepodid stage (CV) in the subpopulation rose to half its overall climatological maximum CV proportion at that station. The proxy for timing of emergence at each station was set as the first date when adults were more than 10% of the total abundance of copepodid stages. An alternate emergence proxy date was determined by back-calculating the spawning dates of the first early copepodid stages appearing in spring, using a stage-structured, individual-based model. No single environmental cue (photoperiod, surface temperature, or average surface-layer chlorophyll a concentration) consistently explained entry or emergence dates across all stations. Among hypotheses put forward to explain dormancy in Calanus species, we cannot eliminate the lipid accumulation window hypothesis for onset of dormancy or a lipid-modulated endogenous timer controlling dormancy duration. The fundamental premise of these hypotheses is that individuals can only enter dormancy if their food and temperature history allows them to accumulate sufficient lipid to endure overwintering, moult, and undergo early stages of gonad maturation.
86226614
A comparative study of Calanus finmarchicus mortality patterns at five localities in the North Atlantic
Author(s): Ohman, MD; Eiane, K; Durbin, EG; Runge, JA; Hirche, HJ | Abstract: We compare the patterns of stage-specific mortality of Calanus finmarchicus at five localities across the North Atlantic Ocean during the spring-summer period of active population growth: Georges Bank, a continental shelf locality in the NW Atlantic, based on 30 broadscale survey cruises in the US GLOBEC program; the northern North Sea, studied during the historic FLEX program with sampling four times daily for 73 days; Ocean Station M in the central Norwegian Sea, based on an 80-day daily time-series; and Lurefjorden (sampled weekly in late winter-early summer) and Sorfjorden (sampled monthly), two fjords in southwestern Norway characterized by markedly different guilds of predators. The mortality estimation methods included Wood's Population Surface Method, the Vertical Life Table (VLT) method, and a modified VLT, according to the study site and copepod recruitment schedules. Contrary to assumptions implicit in many simulation models and indirect methods for estimating zooplankton mortality, both rates and stage-specific patterns of mortality of C. finmarchicus vary appreciably across the North Atlantic. Characteristics of local environments, including the predator field in particular, appear to strongly influence mortality schedules in different regions. In at least two sites (Georges Bank and Ocean Station M), mortality rates of early stages of C. finmarchicus are density-dependent. We attribute this density-dependent mortality to egg cannibalism, which introduces non-linear population responses to changing environmental conditions. Region-specific biological interactions can substantially modify the effects of physical climate variability and render simple linear relationships between climate and zooplankton abundance unlikely. © 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.
40383334
An evaluation of factors affecting vertical distribution among recruits of Calanus finmarchicus in three adjacent high-latitude localities
The vertical distributions of populations of Calanus finmarchicus are described in three different fjord areas near Tromse, northern Norway during May 1986. These localities (Malangen, Grøtsund and Balsfjorden) had characteristic differences in temperature, phytoplankton and population density of copepods. They probably are representative annual situations during the spring and summer period for coastal and fjord areas in northern Norway. Copepodite stage I and II C. finmarchicus are found in the surface waters (0–30 m) during a 24 h cycle, while the other stages appear to have a different diel depth distribution in Malangen. Pronounced differences in the depth distribution of the various copepodite stages and adult females were found in Grøtsund and Balsfjorden during the same period of the day on 20 and 21 May. The tendency for vertical overlap among CI–CV was clearly less pronounced in an environment with low phytoplankton standing stock and high population density of copepods. The patterns of vertical distribution are analysed by multidimentional scaling (MDS) and it is evident that the distribution pattern of C. finmarchicus is different at each locality. These preliminary results, are discussed in relation to ontogenetic vertical migration and aspects of resource partitioning and the possible importance of vertical separation for reducing competitive interactions between the different life stages of C. finmarchicus.
129298383
Vertical segregation of Calanus finmarchicus copepodites during the spring bloom
Abstract Factors influencing the vertical distribution of the most abundant grazer in the Norwegian Sea were studied in the open ocean. During May 5–14 2003 the upper 60 m of an oceanic area (10,000 km 2 ) in the northern Norwegian Sea were covered with a towed instrument platform collecting simultaneously in situ data on hydrography, chlorophyll a concentration and zooplankton abundance with high resolution in space and time. A consistent vertical distribution pattern of Calanus finmarchicus differing markedly from previously reported data was observed: CII–CIII copepodites were located below moderate to high chlorophyll a concentration, at depths below 30 m. CIV copepodites were located slightly higher in the water column and CV copepodites and adults were consistently found in the upper chlorophyll-rich layer. Partial constrained correspondence analysis revealed that the effect of physical factors and diel vertical migration was clearly secondary to chlorophyll a concentration in explaining the observed vertical segregation. The effects of toxic algae and predation are discussed in evolutionary context. These findings underline the importance of understanding stage-specific behaviour to build realistic models.
33620
Temperature-Dependent Production of Marine Copepods: A Global Synthesis
Estimating the production of marine copepods depends on measuring two key variables: biomass and growth rate. The major difficulty in estimating production of marine copepods and other zooplankton has been the inability to obtain precise, rapid measurements. In practice the variability in measurement of biomass greatly exceeds that in growth rate. It is shown here that individual growth rates of copepods can be accurately estimated from data on generation times and the weights of eggs and adults. Analysis of 181 separately published estimates of generation time for 33 species of copepods at environmental temperatures ranging from -1.7⚬ to 30.7⚬C shows that temperature alone explains more than 90% of the variance in growth rate. Temperature dependence of growth rate transcends species differences. Weight-specific growth rate appears to be independent of body size. We hypothesize that food may not be limiting to growth in nature; the impression that food is limiting may be due to sampling at the wrong scales. Another possible cause of the apparent maximum growth rates of copepods in nature is predation mortality, which could selectively remove slower-growing individuals from the population. The temperature-dependent model developed here predicts the phenomenon of decreasing body size with increasing environmental temperature, often observed for single species of copepods. A method is suggested for making more accurate estimates of secondary production by using modern instrumentation to make quasi-synoptic measurements of biomass and temperature and using the temperature-dependent model to estimate individual growth rates.
17514363
Growth of marine planktonic copepods: Global rates and patterns in relation to chlorophyll a, temperature, and body weight
We compiled a global data set of copepod in situ weight-specific fecundity and growth rates, together with measurements of their body weights, and the chlorophyll a and temperature of the natural water in which these animals were growing. Juveniles can achieve half-saturation of their growth (K m ) at chlorophyll a concentrations almost an order of magnitude lower than adult females can their weight-specific fecundity. Adult weight-specific fecundity rates in situ are correlated with temperature, but the Q 10 s of 1.59 and 1.43 in broadcast and sac spawners, respectively, are much lower than under food saturated laboratory conditions (Q 10 s of 2.75 and 3.98). By comparing the in situ and laboratory food saturated results we are able to assess food limitation in the environment. The degree of food limitation increases with increasing temperature for adults: in situ rates approximate food saturated rates at low temperatures (0-10°C), at 25°C they are on average only about one-fifth of those at food saturation. By contrast, in situ juvenile rates are more strongly temperature-dependent than their adults and close to food saturation even at high temperatures. Juveniles grow much more rapidly and closer to food saturation than do adults of a similar size. There are several possible reasons for this. Compounds needed for egg production may simply be more dilute than those used in somatic growth. However, it is also possible that food limitation acts very differently in adults than juveniles. Molting rates in juveniles are strongly temperature dictated, and if sufficient weight is not added between molts, these slower growing juveniles do not survive. Adults, by contrast, can survive for long periods without having sufficient food to produce eggs.
54855986
Fecundity of marine planktonic copepods: global rates and patterns in relation to chlorophyll a, temperature and body weight
Global rates and patterns of fecundity in marine epipelagic copepods were studied as a function of temperature, body weight of the female and concentration of chlorophyll a. We divided data into 3 groups: broadcast spawners, sac spawners (including calanoids, cyclopoids and harpacticoids) and poecilostomatoids; although the latter are sac spawners, they were treated separately, but data were too sparse to examine patterns. Fecundity was positively correlated with temperature and body weight in both broadcast and sac spawners. Michaelis-Menten relationships revealed that fecundity rates are significantly related to chlorophyll a (chl a) concentration for broadcasters, but not so for sac spawners. Broadcasting copepods have a maximum fecundity (f(max)) of 47 eggs female(-1) d(-1), with a half-saturation coefficient (K-m) of 2.4 mug chl a l(-1), for a body weight of 10 mugC individual(-1), when all data are adjusted to 15degreesC. In contrast, fecundity rates in sac spawners are ca. 5 eggs female(-1) d(-1). Of the broadcaster genera examined, Centropages spp. has the highest f(max) at 71 eggs female(-1) d(-1) (data corrected to 15degreesC), and Paracalanus spp. the lowest f(max) at 25 eggs female(-1) d(-1). In the sac-spawning Pseudocalanus spp. we found a significant relationship between fecundity and chl a, with an f(max) of only 7.8 eggs female(-1) d(-1), while for Oithona spp. no significant relationship was evident. By comparing in situ with laboratory food-saturated rates we were able to assess the degree to which fecundity is food-limited in the natural environment. The degree of food limitation increases with increasing temperature in sac spawners; at low temperatures (similar to5degreesC) in situ rates are similar to laboratory food-saturated rates, but at 25degreesC rates are 23% of laboratory food-saturation values. In nature, increasing food limitation with increasing temperature may be the result of greater food requirements to balance respiration demands, i.e. decreasing net growth efficiency in warmer situations. It may also be due to lower availability of suitable food in terms of quality or quantity with increasing temperature, possibly as a result of increased dominance of smaller phytoplankton size fractions (e.g. picoplankton) in warm waters. Food limitation in the environment may be more severe than these comparisons suggest, as laboratory food-saturated fecundity rates in broadcasters may be as low as 36% of the in situ maximum rates (fmax rates).
85797962
Predation by omnivorous copepods on early developmental stages of Calanus finmarchicus and Pseudocalanus spp.
Predation is thought to be an important source of mortality in the early life stages of fish and copepods on Georges Bank. Omnivorous copepods may be predators on copepod eggs and nauplii, but data on feeding rates or selectivity are scarce. As part of the GLOBEC Georges Bank program, we generated functional response curves for the omnivorous copepods Metridia lucens, Centropages typicus, and Temora longicornis feeding on the eggs and nauplii of Calanus finmarchicus or Pseudocalanus spp. in shipboard predation trials. Neither C. typicus nor M. lucens reached saturation feeding on Calanus eggs until prey concentration was >400 L−1. Individual M. lucens and C. typicus ingested up to 34 ± 9 (mean ± SD, n = 3) and 24 ± 14 eggs d−1, respectively (68C). T. longicornis was more abundant in late spring, when they ingested Calanus eggs at rates similar to those of C. typicus. At ambient prey concentrations, ingestion rates of Calanus nauplii were higher than rates of Calanus eggs for the predator M. lucens but were similar for C. typicus. Advanced naupliar stages were less susceptible to predation than young stages. Pseudocalanus nauplii moved faster and were ingested at lower rates than similarly sized Calanus nauplii. Predation rates increased with increasing temperature for the warm-water species C. typicus but decreased for the cold-water species M. lucens. These results may contribute to models predicting the development of copepod populations and their availability to larval fish.
85690351
Calanus the cannibal
Recent modelling efforts have suggested that cannibalism on eggs and young nauplii is an important factor controlling the population dynamics of Calanus. We measured cannibalistic feeding rates on eggs and nauplii of Calanus helgolandicus in the laboratory. Clearance rates on nauplii were � 102 mL ind. � 1 day � 1 , while generally higher on eggs (320 mL ind. � 1 day � 1 ). Female starvation did not affect ingestion rates of eggs. We discuss our results in light of published model predictions, cannibalistic feeding rates of other copepods, and field distributions of Calanus developmental stages.
84168723
Switching between herbivory and carnivory by the planktonic marine copepod Calanus pacificus
Adult females of the omnivorous copepod Calanus pacificus, collected from the plankton off La Jolla, California, USA (June, 1978), fed disproportionately on the prey in greatest relative abundance when given mixtures of diatoms (Thalassiosira fluviatilis) and copepod (C. pacificus) nauplii as food. This switch from herbivorous to carnivorous behavior may be significant in nature during the decline of phytoplankton blooms. More generally, the widespread omnivorous habit among pelagic animals suggests a responsive and flexible trophic organization which contributes to the resiliency of planktonic communities in a dynamic physical environment.
54708504
Cannibalism by female Calanus finmarchicus on naupliar stages
Cannibalism has been assumed to strongly affect population dynamics of the calanoid copepod Calanus spp. during the pre-bloom phase. We hypothesised that Calanus finmarchicus females cannibalise on nauplii until there is enough phytoplankton available to fulfil their energy demands. We tested this experimentally by exposing females to different concentrations of algae Thalassiosira weissflogii (0.08 to 22.58 µg chlorophyll a l -1 ) and nauplii (stages NI and NII, 0 to 20 nauplii l -1 ). Clearance rates on algae and on nauplii were high (221 and 689 ml ind. -1 d -1 , respec- tively), but were independent of algal concentration. Females ingested naupliar carbon at a higher proportion than was available, even when naupliar carbon accounted for <5% of the totally available carbon. Predation rates on nauplii increased linearly and significantly (p < 0.001) with increasing nauplii abundance. Compared with literature values, predation rates were considerably higher (up to 10 nauplii ind. -1 d -1 ) than predation rates of the sibling species C. helgolandicus and C. pacificus on their nauplii, and also higher than predation rates of the omnivorous copepod Metridia lucens on Calanus sp. nauplii. Based on our data, we estimated that as much as 20% d -1 of the nauplii popula- tion may be preyed on by adult females. Thus, during the pre-bloom period when abundance of nau- plii is small and that of females is large, cannibalism may prevent recruitment to the G1 population.
58894449
Feeding of Calanus finmarchicus nauplii in the Irminger Sea
Recent studies have shown that the passage from nauplius to copepodite is a key event in the population dynamics of Calanus finmarchicus. As a first step towards understanding if and how trophic interactions influence this event, we investigated the feeding of C. finmarchicus nauplii IV-VI in the Irminger Sea during spring and summer in a series of incubation experiments. Generally, feeding efficiencies were highest on large cells, whereas small flagellates were ingested at very low rates. Colonies of Phaeocystis sp. were not ingested. Among the larger cells, the diatoms Chaetoceros pelagicus and Tropodineis sp. and the ciliate Strombidium sp. were the main food sources. We observed a negative relationship between the percentage of diatoms in the food environment and the filtration rate on Strombidium sp. We therefore suggest that the combination of low feeding efficiency on small cells and the generally low concentrations of ciliates in oceanic waters explains why C. finmarchicus relies on phytoplankton blooms for recruitment from nauplius to the first copepodite stage.
86607086
Sustained fecundity when phytoplankton resources are in short supply: Omnivory by Calanus finmarchicus in the Gulf of St. Lawrence
Despite low ambient concentrations of phytoplankton, Calanusjkzmarchicus sustained relatively high rates of egg production (1 l-45 eggs female 1 d-l) in the open waters of the Gulf of St. Lawrence in late June-early July. These rates were comparable to egg production rates observed in high-chlorophyll waters of the lower St. Lawrence estuary. Contrary to classical, linear food-chain models, variations in egg production of C. jinmarchicus were therefore not prcdictablc from variations in standing stocks of autotrophic cells. Egg production rates wcrc independent of the concentration of chlorophyll in situ, the abundance of autotrophic microplankton cells, in situ gut fluorescence, and the rate of ingestion of autotrophic particles. Hctcrotrophic microplankton- including ciliates and dinoflagellates presumed to bc heterotrophic-constituted a disproportionate fraction of the ration of C. finmarchicus in the open Gulf of St. Lawrence, despite their relatively low cell densities. Evidence suggests that heterotrophic microplankton frequently provided a prey resource sufflcicnt for net lipid synthesis as well as for egg production. For several decades the dominant view in marine zooplankton ecology has been that population growth of suspension-feeding copepods is governed by fluctuations in the availability of phytoplankton, principally larger autotrophic diatoms and dinoflagellates. Variability in the abundance and composition of autotrophic cells has been translated into variability in ingestion, growth, and fecundity of planktonic metazoans in models of simple linear food chains. Even recent models (Marra and Ho 1993) have taken this perspective. The development of predictive indices for population growth of planktonic copepods, thus, has focused narrowly on the role of phytoplankton and assumed a nearly instantaneous translation of ingested cells into somatic growth and fecundity. More recently, as the structure and dynamics of pelagic microbial food webs have be
85087887
A high frequency time series at weathership M, Norwegian Sea, during the 1997 spring bloom: feeding of adult female Calanus finmarchicus
The feeding ecology of Calanus finmarchicus was investigated during spring 1997 at a permanent station in the Norwegian Sea (Stn M, 66"N, 2"E) as part of the TASC (Trans Atlantic Study of Calanus finmarchicus) project time-series investigations. The phytoplankton bloom began in mid May, coinciding m t h the onset of the stratification, and was mainly composed of d~atoms and prymnesiophytes. Daily Ingestion of phytoplankton by C. finmarchicus was about 2% of body carbon for the long period before the bloom, 30% during the bloom and 14 % after the bloom. Due to their low abundance, ingestion of ciliates represented only 2 to 6 O/o of the phytoplankton ingestion. Body carbon and carbon/nitrogen ratio decreased significantly before the bloom indicating a deficit in carbon ingestion and the use of storage lipid during this period.
54986845
A high-frequency time series at Ocean Weather Ship Station M (Norwegian Sea): population dynamics of Calanus finmarchicus
Between the end of March and mid-June 1997, net samples in the upper 100 m were taken almost daily on Weathership M (Norwegian Sea) to determine the abundance and stage com- position of Calanus finmarchicus. Biomass showed high day-to-day variability with several peaks, ranging from 0.05 to 6.3 g C m -2 , with an average of 0.84 g C m -2 . Consequently, stage abundances were also highly variable, but stage composition was consistent. Although population egg production was almost constant throughout the study period, a clear cohort was formed. During the pre-bloom period, nauplii and Copepodite Stage I (CI) were frequently abundant, but further stage development proceeded only during the short bloom. At the end of the bloom, no young nauplii continued to grow, but older stages did. Some specimens had reached CV at the end of the investigation period. The extended seasonal presence of some stages made estimates of stage duration and production diffi- cult. Three different numerical methods were applied to estimate productivity and production. All methods resulted in similar estimates of productivity, 0.031 to 0.055 d -1 , corresponding to a produc- tion of 30 to 56 mg C m -2 d -1 . These rates are considerably lower than optimum rates measured in the laboratory, suggesting strong food limitation of growth during most of the observation period.
46128542
Feeding and reproduction of Calanus finmarchicus during non-bloom conditions in the Irminger Sea
Simultaneous ingestion and egg production experiments were conducted with female Calanus finmarchicus in April/May and July/August 2002 in the Irminger Sea. Experimental animals were provided with natural microplankton food assemblages and incubated under in situ conditions for 24 h. The quantity of food consumed was significantly related to the concentration of prey cells, with total daily ingestion rates ranging from 0.6 to 8.1 µg of carbon female–1 day–1, corresponding to carbon-specific rates of 0.6–4.7% day–1. Egg production rates (EPRs) remained relatively low (0.3–11 eggs female–1 day–1) during both periods of investigation and were not influenced by food availability. The data were used to construct energetic budgets in which the microplankton carbon ingested, including ciliates, was compared with the carbon utilized for egg production and respiration. These budgets showed that ingestion alone could not provide the necessary carbon to sustain the observed demands for growth and metabolism. Although ciliates constituted >80% of the total material ingested at times, they were not sufficient to provide the metabolic shortfall. Indeed, the females were typically lacking 5 µg of carbon each day, 5% of their carbon biomass. Our study results highlight the possible importance of internal reserves in sustaining reproduction in C. finmarchicus during periods of food scarcity.
23807347
Mortality of marine planktonic copepods: global rates and patterns
Using life history theory we make predictions of mortality rates in marine epi-pelagic copepods from field estimates of adult fecundity, development times and adult sex ratios. Predicted mortality increases with temperature in both broadcast and sac spawning copepods, and declines with body weight in broadcast spawners, while mortality in sac spawners is invariant with body size. Although the magnitude of copepod mortality does lie close to the overall general pattern for pelagic animals, copepod mortality scaling is much weaker, implying that small copepods are avoiding some mortality agent/s that other pelagic animals of a similar size do not. We compile direct in situ esti- mates of copepod mortality and compare these with our indirect predictions; we find the predictions generally match the field measurements well with respect to average rates and patterns. Finally, by comparing in situ adult copepod longevity with predation-free laboratory longevity, we are able to make the first global approximations of the natural rates of predation mortality. Predation and total mortality both increase with increasing temperature; however, the proportion that predation makes of total adult mortality is independent of ambient temperature, on average accounting for around 2 ⁄3 to 3⁄4 of the total.
140161427
Modeling the formation and circulation processes of water masses and sea ice in the Gulf of St. Lawrence, Canada
[1] The seasonal cycle of water masses and sea ice in the Gulf of St. Lawrence is examined using a three-dimensional coastal ice-ocean model with realistic tidal, atmospheric, hydrologic, and oceanic forcing. The model includes a level 2.5 turbulent kinetic energy equation. A model simulation over 1997–1998 is verified against available data on sea ice, temperature, and salinity. The results demonstrate a consistent seasonal cycle in atmosphere-ocean exchanges and the formation and circulation of water masses and sea ice. The accuracy of radiative, momentum, and sensible heat exchanges at the sea surface, and the production of turbulent kinetic energy from winds and tides, are critical to the accuracy of the modeled circulation. The analysis of the mean error on near-surface temperature and salinity in the late summer and fall using standard bulk exchange coefficients and radiation (about 1°C too cold and 1 salinity unit too fresh) shows the tradeoff between tidal mixing at the head of the Laurentian Channel, and wind-driven circulation and mixing in the surface waters. The results suggest year-long stratification in the estuary and northwestern Gulf, with little mixing except near the head region, where relatively deep warmer waters are mixed to the surface during winter, and cold intermediate waters are efficiently withdrawn during summer. The results suggest that the summer cold waters found at intermediate depths in the estuary and northwestern Gulf are not formed in situ. A significant fraction of these waters enters through the Strait of Belle Isle in wintertime, eventually reaching the estuary within about 6 months.
53697943
Spatial and temporal variations in copepod community structure in the lower St. Lawrence Estuary, Canada
The lower St. Lawrence estuary (LSLE) is a narrow and deep basin under the influence of both estuarine and marine processes. As a result, the LSLE is characterized by strong spatiotemporal heterogeneity in biological and physical environmental conditions. Previous studies have indicated a bias in the summer composition of the copepod population for predominance of late-development stages of Calanus spp., in comparison with adjacent waters of the Gulf of St. Lawrence (GSL) and northwest Atlantic. In this study, we use a 22 mo spatial survey of the LSLE to determine spatial and temporal variations in the copepod community and the relative contribution of Calanus spp. (C. finmarchicus and C. hyperboreus). Multivariate analysis revealed 4 copepod assemblages associated with seasonal patterns in temperature and chlorophyll a. Calanus spp. dominated the early summer community whereas the seasonal increase in abundance of the more surface-dwelling species (Acartia spp., Oithona spp. and Pseudocalanus spp.) explained the mixed Calanus spp./surface species community observed in late summer-autumn and winter. Three recurrent geographic zones can be discriminated in the LSLE on the basis of specific composition and abundance. The copepod community in the upper-central Laurentian Channel was dominated by Calanus spp. Downstream, in late summer-autumn and winter, a mixed Calanus/surface species assemblage was observed. In the shallow region, a very low abundance of Calanus spp. resulted in dominance of surface species after the early summer period. The genus Calanus spp. was the dominant component of the copepod community in LSLE as a whole because of its consistently high abundance along the Laurentian Channel during different seasons. A change in environmental conditions in the 1990s associated with a decadal climate variation in the GSL-LSLE region appears to be related to a dramatic increase in abundance of midwater copepod species (mainly Metridia longa) and, subsequent decline in the relative abundance of Calanus spp. We develop the hypothesis that the observed patterns in copepod species composition in the LSLE are primarily a consequence of the combined effect of the export in the residual surface outflow of early life stages of Calanus spp. and small surface-dwelling species and the upstream advection of late-development stages of Calanus spp. and midwater species in the inflowing deep water of the Laurentian Channel.
129403091
Seasonal and depth-dependent variations in the size and lipid contents of stage 5 copepodites of Calanus finmarchicus in the waters of the Newfoundland Shelf and the Labrador Sea
Abstract We report on the variation in energy reserves of individual C5 copepodites of Calanus finmarchicus from the Newfoundland continental shelf and the Labrador Sea collected from surface and overwintering (or bottom) depths prior to, during and after the expected timing of the onset of diapause. Overall, the trend was for a decreasing average prosome length as the year progressed for all locations although the decline was smallest in the Labrador Sea and greatest in the deep waters of the continental shelf. The size of the oil sac was closely linked to the weight of the copepodite but the form of this relationship showed substantial variations with depth and season. We show a clear increase in the relative oil sac volume for C. finmarchicus between late spring and late summer, by which time some animals had descended to diapause depths. The progressive decrease in oil sac volume of animals sampled at depth in the Labrador Sea between September and December suggests a significant loss of energy reserves during diapause. From the distribution of volumes and body sizes in December we estimate that 23–53% of individuals would not be able to meet the energetic cost of moulting and early gonad development. Overall, some of our observations appear to invalidate earlier hypotheses concerning the governing role of lipids in the life history of C. finmarchicus . However, assessment of the factors that influence entry into dormancy should be based on the relative probabilities of alternative strategies for successful reproduction (e.g. entering dormancy vs. continuing into a second generation).
55514794
Comparative ecology of over-wintering Calanus finmarchicus in the northern North Atlantic, and implications for life-cycle patterns
Data from plankton net and Optical Plankton Counter sampling during 12 winter cruises between 1994 and 2002 have been used to derive a multi-annual composite 3-D distribution of the abundance of over-wintering Calanus finmarchicus in a swath across the North Atlantic from Labrador to Norway. Dense concentrations occurred in the Labrador Sea, northern Irminger Basin, northern Iceland Basin, eastern Norwegian Sea, Faroe–Shetland Channel, and in the Norwegian Trench of the North Sea. A model of buoyancy regulation in C. finmarchicus was used to derive the lipid content implied by the in situ temperature and salinity at over-wintering depths, assuming neutral buoyancy. The Faroe–Shetland Channel and eastern Norwegian Sea emerged as having the highest water column-integrated abundances of copepodites, the lowest over-wintering temperature, and the highest implied lipid content. The results are discussed in the context of spatial persistence of populations, seasonal patterns of abundance, and relationships between over-wintering and lipid accumulation in the surface waters.
54716730
Life cycle and distribution of Calanus finmarchicus in deep basins on the Nova Scotia shelf and seasonal changes in Calanus spp.
The deep basins on the Nova Scotia shelf contain high concentrations of Calanus finmarchicus, C. glacialis, and C. hyperboreus at depths below 200 m. From May to late fall these were as high as 20 000 m-3. The dominant specles by numbers was C. finmarchicus; however, its biomass was equalled or exceeded by C. hyperboreus. The life cycle of C. finmarchicus in the region of 2 of the largest basins showed that breeding started late in winter with a peak in April. High concentrations of Calanus suggested that the basins had higher levels of C. finmarchicus production than the adjacent shelf with mean depths less than 100 m. All 3 species of Calanus started to accumulate below 200 m in May as Stages CIV and CV C. glacialisand C. hyperboreusdid not reproduce in significant numbers on the NW half of the shelf but did accumulate in the basins as they were advected from the NE shelf region. Resting stages of Calanus resided at depths below 200 m in water at between 8.5 and 11 "C for an estimated 7 to 8 mo. The fate of these copepods is uncertain, but evidence suggested that a large proportion were preyed on by euphausiids in the deep regions of the basin. The deep basins on the shelf make it possible for C. finmarchicus populations to dominate the Nova Scotia shelf zooplankton community for most of the year; without the basins the shelf zooplankton would probably resemble that of the Grand Banks which has no deep basins, and is dominated by microzooplankton.
84749712
Processes controlling recruitment of the marine Calanoid copepod Temora longicornis in Long Island Sound: Egg production, egg mortality, and cohort survival rates
Three phytoplankton blooms were observed during our 6-month study period and each resulted in increased rates of egg production (EPR) by female Temora longicornis. An EPR of 50 eggs female −1 d −1 was observed during the first bloom (spring bloom, March). The maximum EPR observed during the other blooms (May and July) was 20 and 30 eggs female −1 d −1 . At all other times the EPR was nearly zero. Each pulse in egg production initiated a distinct cohort. Survivorship from egg to adult was low: 3% for the first cohort and 0.8% for the second. The third cohort did not reach maturity. Mortality was highest in the egg stage ― only 10% of the eggs produced survived to first nauplius. Rates of egg mortality were positively correlated with clearance rates of T. longicornis, suggesting cannibalism as a cause of high mortality. However, the clearance rates required would be ∼ 34-fold too high, suggesting a different density-dependent factor, such as disease, viruses, ecto-parasitism or consumption by dinoflagellates. Advection and resting egg production do not appear to explain high rates of egg loss