The influence of environmental factors and nutrient contentrations in tissues of the seaweed <i>Ahnfeltia tobuchiensis</i> (Rhodophyta: Ahnfeltiales) on the primary production and dark respiration of its population
Complex investigations of the influence of environmental factors - temperature, photosynthetically active radiation (PAR), ambient seawater concentrations of ammonium (NH4) and orthophosphate (РО4), as well as contents of organic carbon (C), nitrogen, phosphorus, and chlorophyll a (Ch) in seaweed tissues on the rate of photosynthesis (Pn) and dark respiration (Rd) of the unattached red seaweed Ahnfeltia tobuchiensis (Rhodophyta: Ahnfeltiales) population were performed in summer 2000 and 2008 in Izmena Bay (Kunashir Island) under in situ conditions. The dependence of photosynthesis on PAR intensity (P-I dependence) is described by the equation of a hyperbolic tangent. The population of A. tobuchiensis forms a layer of up to 50 cm thick with an area of 23.3 km² and a biomass of 125 000 tons. The Pn rate of seaweed population during daylight hours varies within a wide range with an average of 1.04 mg О2/(gdry wt h) and largely depends on PAR intensity and availability (r = 0.70-0.98). The maximum photosynthesis rate (Pmax) is substantially defined by the ambient concentration of NH4 (r2 = 0.91, p d during the night is on average 0.1 mg О2/(gdry wt h) and mainly depends on the content of Ch in seaweed tissues (r2 = 0.83, p 4 (r2 = 0.86, p 2 or 1.8 kgdry wt/m2, the net primary production (Pn) of seaweed population is estimated to be on average 22.5 g О2/(m2 day) or 8.4 g C/(m2 day). Based on these indices, the investigated population is one of the most productive ecosystems of the World Ocean. It is supposed that such indices of the А. tobuchiensis population are attained due to the highly efficient use of weak light and a low light saturation level of photosynthesis, compared to other seaweeds.