SEASONAL-CHANGES IN LIPID-CONTENT AND COMPOSITION IN THE BENTHIC AMPHIPODS MONOPOREIA-AFFINIS AND PONTOPOREIA-FEMORATA

Seasonal variation in lipid content and composition was studied in deposit-feeding amphipods from a Baltic archipelago. In Monoporeia affinis, which is more active and has a higher respiration rate, lipid levels were low in winter and early spring, rose to 27% of the dry mass in late summer, then declined in autumn. In Pontoporeia femorata, which regulates its oxygen consumption, lipid levels were 20-23% of the dry mass. In October, maturing male P. femorata had a significantly lower lipid content than females. Triacylglycerol and phospholipid accounted for approximately 90% of lipids. Phospholipid dominated in M. affinis in March, but triacylglycerol accumulated and became the main lipid after the spring bloom. Triacylglycerol was always the main lipid in P. femorata. but also accumulated after the spring diatom bloom. Both species seem to assimilate and store food resources from the diatom bloom. The higher feeding rate of M. affinis may explain its greater accumulation of lipid. Lower metabolic costs in P. femorata may allow it to maintain steady lipid levels for most of the year.