Only a few key prey species fuel a temperate coastal fish food web

Abstract

The food web structure of a coastal fish community (western Dutch Wadden Sea) was studied based on stomach content data from samples collected between 2010 and 2018. In total, 54 fish species were caught and 72 different prey items were identified. Fish species consumed from only a few up to >30 different prey species, suggesting the presence of both opportunistic and more specialized feeders. We found no significant differences between years or switches in food source with fish size. The trophic positions of the Wadden Sea fish community ranged from 2.0 to 4.7, with most trophic positions above 3.0. In the past, (near)-resident species were the most abundant guild in spring, and juvenile marine migrants in autumn. At present, all guilds are present in similar but low abundances. The (near)-resident community consisted of about 20 species that fed primarily on amphipod crustaceans, brown shrimps and juvenile herring. There was only a slight overlap in diet with the group of juvenile marine migrants (5 species of juvenile flatfishes and clupeids), whose preferred prey were copepods, polychaetes and brown shrimps. About 15 species of marine seasonal visitors showed an overlap in diet with both the (near)-resident and the juvenile marine migrants, especially for brown shrimps and to a lesser extent herring and gobies. Our results illustrate (1) the pivotal position of a few key prey species (amphipod crustaceans, brown shrimps, juvenile herring and gobies) for the coastal Wadden Sea fishes and (2) that the substantial prey overlap in the diet of some predators cannot exclude intra- and inter-specific competition among these predators.

Historical trophic ecology of some divergent shark and skate species in the Dutch coastal North Sea zone

“…The data were extracted from the archive of the Royal Netherlands Institute for Sea Research (NIOZ). These reconstructions of the trophic position of different shark and skate species was done in line with a recent analysis of the present fish food web structure in the western Wadden Sea by Poiesz et al (2020).…”

“…Trophic position (TP j ) for each individual skate or shark j, was calculated in line with a previous study of the trophic structure of the Wadden Sea fish fauna (Poiesz et al 2020). as 1 + the mean value of the trophic positions of the different prey species found in a stomach:…”

“…From the data set of stomach content data of fish community of the Wadden Sea collected between 2010 and 2018 (Poiesz et al 2020), all individual fishes with at least two different prey species were selected. For these individuals (n = 5300), trophic position was estimated in two different ways:…”

“…FishBase (Froese and Pauly 2019) provide average trophic positions of individual sharks and skates, but these might not correspond with local observations as a recent analysis of the Wadden Sea coastal fish food web by Poiesz et al (2020) has shown. Therefore, the past role and trophic position of these lost sharks and skates in the Dutch coastal zone fish food web is unknown.…”

“…Since the historical data set only contained information on prey species found, trophic position was estimated based on the average trophic position of the various prey species, ignoring differences in mass between the various prey species. The potential bias of ignoring differences in prey mass was investigated with a recent data set of stomach content data of fish community of the Wadden Sea collected between 2010 and 2018 (Poiesz et al 2020). Lastly, the relative degree of specialization in the diet of the various shark and skate species was reconstructed and dietary overlap among species was quantified and the niche type for each species was determined.…”