Late autumn condition of Calanus finmarchicus in the northwestern Atlantic: evidence of size-dependent differential feeding

We report size, lipid sac volume and fatty acid composition of C5 copepodites of Calanus finmarchicus collected in late autumn 2007 on the Newfoundland Shelf and in slope waters in the Labrador Sea, to assess differences in feeding histories between these populations. Copepodites from the slope waters were generally relatively large and were mainly at depth and in diapause, whereas those from shelf waters were relatively small and were either in the surface layers or had only recently descended into the deeper layer. Multivariate analyses revealed a strong pattern of separation among the levels of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA), bacterial fatty acid markers and omega 3 PUFAs in copepods from the different areas. There was clear separation of diatom (16:1 omega 7, 16:4 omega 1 and 20:5 omega 3) from prymnesiophyte-dinophyte (18:1 omega 9, 18:4 omega 3 and 22:6 omega 3) fatty acid markers. Larger body size and greater energy reserves were associated with C5 C. finmarchicus from the slope waters and with increases in the proportion of fatty acid biomarkers for diatoms and omnivory. Smaller body sizes were associated with C5s on the shelf and with a greater proportion of fatty acid biomarkers for dinoflagellates and prymnesiophytes. C. finmarchicus collected near the coast had significantly higher levels of biomarkers indicative of terrestrial input in their diet.