Oxygen uptake by wrack- and driftwood-acclimated populations of Platorchestia platensis (Amphipoda, Talitridae) during feeding and fasting


Oxygen uptake rates were measured in fasted and fed Platorchestia platensis (Krøyer, 1845) to estimate the energy required for ingestion, digestion, absorption, assimilation and growth. A modified population specific dynamic action model (SDApop) was compared between two populations fed either wrack or driftwood. Results reject the null hypothesis: that both populations have equal energy requirements during digestion, as might be the case if native enzymes alone were involved. The alternate hypothesis that driftwood-fed P. platensis have a significantly lower SDA than wrack-fed ones was supported. Our oxygen uptake measurement experiments could not distinguish between two possible causes of the lower energetic costs associated with driftwood-fed P. platensis: driftwood as a poor-quality food and/or a microbial subsidy effect. Preliminary microbiological studies of P. platensis do support the subsidy effect, because cellulose-degrading bacteria and filamentous fungi were present in whole body tissues from the animal. Wrack and driftwood culture treatments of P. platensis supported a different cellulose-degrading microbiome between the two treatments.