Feeding ecology of capelin (Mallotus villosus) in a fjord impacted by glacial meltwater (Godthåbsfjord, Greenland)

Abstract

Capelin (Mallotus villosus) is an important trophic node in many Arctic and sub-Arctic ecosystems. In Godthabsfjord, West Greenland, the zooplankton community has been shown to change significantly from the inner part of the fjord, which is impacted by several glaciers to the shelf outside the fjord. To what extent this gradient in zooplankton composition influences capelin diet during their summer feeding in the fjord is yet unknown. To investigate this, we analysed stomach content of capelin (8–14 cm) sampled using a pelagic trawl at three stations in outer (GF3), mid (GF7) and inner (GF10) part of Godthabsfjord in May and August 2013. In May, the copepod nauplii numerically dominated the diets, but euphausiids contributed > 92% by carbon mass at all stations. In August, calanoid copepods were the most important prey numerically and by carbon mass. Smaller copepod species became more important towards the inner stations, whereas the large Calanus species dominated in the outer stations. There was also a trend in decreasing stomach carbon content towards the inner stations, and on the individual level, variation in stomach content was strongly negatively related to the proportion of small copepods in the diet. This suggests that the inclusion of small copepods in the diet cannot compensate for the absence of larger euphausiids and copepods. Therefore, any change in the ecosystems that favours these at the expense of larger zooplankton and euphausiids is likely to impact capelin feeding negatively with consequences for the whole ecosystem.