The significance of food web structure for the condition and tracer lipid content of juvenile snail fish (Pisces: Liparis spp.) along 65-72°N off West Greenland

Abstract

Plankton community structure was analysed during summer along 65-72°N off West Greenland. The south-north transect mimics a time span of months in the phytoplankton and zooplankton succession during the Arctic summer. In the south, the mixing depth was below the photic zone and the phytoplankton community was dominated by flagellates. North of Disko Bay (69°N), the water column was stratified due to melt water, and the phytoplankton dominated by flagellates and a small amount of diatoms, but with higher biomass and primary production. The copepod community was dominated by Calanus spp. and was more progressed in terms of developmental stage composition in the south. The biochemical lipid finger printing in the food chain phytoplankton-mesozooplankton-juvenile planktivorous snail fish (Liparis spp.) confirmed the qualitative composition of the phytoplankton, and revealed that the mesozooplankton >400 μm in body size contained lipids originating from a non-diatom diet in the south, whereas it showed mesozooplankton lipids originating from a diatom diet in the north. The C16:1(n-7)/C16:0 ratio increased from 0.3 to 3 for mesozooplankton along the transect, indicating feeding based on diatoms in the north. This ratio was reflected in Liparis spp. along the transect. The condition of the juvenile snail fish was generally good (high b exponent) along the entire transect based on the relationship: total fatty acids (mg) = 0.0008 x standard length (mm)2.35. However, the relationship triacylglycerol:cholesterol was much higher north of Disko Bay, indicating a much better condition and thereby potential starvation tolerance and survival in the north. We conclude that the plankton structure along the south-north transect reflected the yearly succession in phytoplankton with respect to tracer lipids and that juvenile Liparis spp. were in a better condition when foraging on wax ester-rich mesozooplankton, which in turn developed ontogenetically during a diatom-based spring bloom in the north.