Seasonal and developmental variation in the fatty acid composition of Mysis mixta (Mysidacea) and Acanthostepheia malmgreni (Amphipoda) from the hyperbenthos of a cold-ocean environment (Conception Bay, Newfoundland)

Fatty acid composition in different life-history stages of Mysis mixta (Crustacea, Mysidacea) and Acanthostepheia malmgreni (Crustacea, Amphipoda) from Conception Bay, Newfoundland, was examined throughout 1999 and 2000. The primary aim was to relate the seasonal fatty acid dynamics to each species’ life cycle and to published information on the occurrence and quality of the annual phytoplankton bloom. Divergent patterns in fatty acid composition and specific fatty acid marker ratios reflected different life styles, diets and critical periods of energy accumulation and utilization in M. mixta and A. malmgreni. Changes in fatty acids reflected the sequence of plankton taxa during and following the spring bloom, starting with diatoms and dinoflagellates and ending with copepods. Immature mysids exhibited a particularly rapid accumulation of diatom-associated fatty acids at the start of the spring bloom, probably owing to the high degree of motility of M. mixta and the broad range of prey types available to this species. In contrast, immature amphipods did not begin to accumulate significant amounts of phytoplankton fatty acids until after the spring bloom material had settled to the hyperbenthos in May. Differences in fatty acid composition indicated that A. malmgreni was restricted to a lower quality diet than was M. mixta and that the trophic connection between A. malmgreni and production in the euphotic zone was weaker.