Diet overlap among flatfish species in the southern North Sea

Abstract

The diets of two non-commercial flatfish species (solenette Buglossidium luteum and scaldfish Arnoglossus laterna) and two commercial flatfish species (dab Limanda limanda and plaice Pleuronectes platessa) were compared in a study area in the German Bight (southern North Sea) to investigate prey-resource partitioning between these species. The diets of A. laterna and B. luteum mainly comprised crustaceans (harpacticoids, amphipods, cumaceans and decapods), whereas the diet of L. limanda and P. platessa consisted mainly of polychaetes. The Schoener index, calculated for different fish size classes between these flatfish species, showed a biologically significant diet overlap between small-sized L. limanda and P. platessa and B. luteum and A. laterna, using similar prey resources of smaller prey (e.g. amphipods, harpacticoids and juvenile bivalves). In contrast, with increasing body size, a change in the diet of L. limanda and P. platessa towards larger prey occurred (e.g. polychaetes and decapods), resulting in low diet overlap values with B. luteum and A. laterna. Due to these size-related differences in resource use, it is assumed that there is reduced interspecific competition for prey between larger L. limanda and P. platessa and both non-commercial flatfishes, probably facilitating resource partitioning within the same area. In contrast, smaller L. limanda and P. platessa may compete directly for the same prey resources with B. luteum and A. laterna. Furthermore, prey availability of most important prey items of the studied flatfishes was relatively low in the study area. Therefore, increasing abundances of B. luteum and A. laterna in the southern North Sea since the late 1980s, owing to fishing effects and climate change, might affect the population dynamics of L. limanda and P. platessa.

Meiofauna as food source for small-sized demersal fish in the southern North Sea

“…Confirming this, preferential feeding on macrofauna was also found in previous diet studies for both fish species (e.g. Gibson and Ezzi 1980;Bayan et al 2008;Schückel et al 2011) and furthermore, was already found in relatively small fish (L T 's \ 10 cm; Schückel et al 2012). …”

“…For details on fish predation on macrofaunal prey groups, see Schückel et al (2011) and Schückel et al (2012). Among different meiofaunal prey groups, harpacticoids were always of primary importance in the diet of each of the studied fish species during all seasons, whereas nematodes dominated the meiofauna community in the study area.…”

“…Similar to both fish species discussed before, juvenile bivalves became an important prey group in spring. On the basis of their mouth morphology, it can be assumed that A. laterna and L. limanda are able to feed on larger and hence more energetically valuable prey (Piet et al 1998;Schückel et al 2011Schückel et al , 2012. Consequently, mainly macrofaunal prey (e.g.…”

“…Gee 1989; Kovačić and la Mesa 2008;Schückel et al 2012). On the basis of the optimal foraging theory, smaller fish eat smaller prey and switch usually to larger prey to maximize their net energy gain as fish length increases (Schoener 1971).…”

Food-Web Structure in Four Locations Along the European Shelf Indicates Spatial Differences in Ecosystem Functioning

“…In recent years, however, ongoing climate change has impacted all compartments of the marine ecosystem, leading to regime shifts of phytoplankton and zooplankton communities (Beaugrand and Ibanez, 2004;Richardson and Schoeman, 2004;McQuatters-Gollop et al, 2007), distributional shifts of benthos Birchenough et al, 2015), and deepening of fish assemblages (Dulvy et al, 2008). Cod has disappeared almost completely from the southern North Sea due to overfishing and climate change (Daan et al, 2005;Beaugrand and Kirby, 2010), and the region has changed into flatfish dominated communities, including abundant commercial species (e.g., Pleuronectes platessa) and particularly high abundances of small, non-commercial, mesopredatory species (e.g., Buglossidium luteum) (Ehrich et al, 2007;van Hal et al, 2010;Schückel et al, 2012). Furthermore, mackerel is extending its range northwards into the sub-Arctic (Stenevik and Sundby, 2007;Utne et al, 2012).…”