Although food quality is thought to play an important role in the survival of marine organisms, the extent of natural variability in food quality over long time scales remains poorly characterized. We present a 6 yr time series of fatty acid data from the calanoid copepod Neocalanus plumchrus, an important contributor to mesozooplankton biomass in the Strait of Georgia and the northeast Pacific Ocean. Fatty acid profiles indicate significant spatiotemporal differences in the diet of this copepod. Spatially, oceanic specimens display fatty acid signatures characteristic of omnivorous copepods while coastal animals display primarily herbivorous, diatom-based signatures. Temporally, the fatty acid profiles of coastal N. plumchrus shifted from an omnivorous oceanic diet to an herbivorous, diatom-based diet between 2001 and 2006. The ratio of diatom to flagellate fatty acid markers increased over time, peaking from 2005 to 2006. The composition of flagellate markers also changed from primarily dinoflagellate markers (rich in docosohexaeonic acid) to green algal markers (poor in this essential fatty acid). The diet of N. plumchrus as deduced from fatty acids correlates with phytoplankton community composition. The abundance of coastal N. plumchrus in the Strait of Georgia was strongly correlated with the ratio of docosahexaeonic acid to eicosapentaeonic acid in the lipids of these copepods. We also discuss the potential for an imbalance of essential fatty acids supplied by a diatom-rich diet to limit the growth and survival of N. plumchrus in the Strait of Georgia.KEY WORDS: Copepod · Diapause · Diet · Docosahexaeonic acid · Eicosapentaeonic acid · DHA · EPA · Fatty acids · Food quality · Neocalanus
Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 382: [151][152][153][154][155][156][157][158][159][160][161] 2009 which are retained in their zooplankton predators and can be used as qualitative tracers of dietary source (Dalsgaard et al. 2003). Diatoms, for example, are characterized by high concentrations of eicosapentaeonic acid (EPA,, 16:1n-7 and by the presence of polyunsaturated fatty acids (PUFA) containing 16 carbon chains (16PUFA), whereas dinoflagellates are characterized by high concentrations of the essential PUFA docosahexaeonic acid (DHA, and PUFA containing 18 carbons (18PUFA, specifically, 18:4n-3) (Thompson et al. 1992, Viso & Marty 1993, Graeve et al. 1994, Stevens et al. 2004a. Essential PUFAs such as DHA and EPA are important for the physiology of marine copepods and have been shown to affect the efficiency by which energy is transferred in food webs (Müller-Navarra et al. 2000, St. John et al. 2001. Other examples of fatty acid trophic markers of phytoplankton, microzooplankton, bacteria and calanoid copepods are provided in Table 1.The use of fatty acid trophic markers in calanoid copepods has been verified in the laboratory and the field, and has succeeded in establishing trophic relations among and within different species of copepods and...