The 'maximum growth/optimal food condition' hypothesis: a test for 0-group plaice Pleuronectes platessa in the Dutch Wadden Sea

Abstract

A test of the 'maximum growth/optimal food condition' (MG/OFC) hypothesis is described for 0-group plaice Pleuronectes platessa L. in the western Dutch Wadden Sea. The MG/OFC hypothesis assumes optimal food conditions (i.e. no competition for superfluous food and hence no negative density-dependent growth) and consequently a maximum growth rate only determined by prevailing water temperature conditions. Growth of 0-group plaice subpopulations was determined for a number of areas differing in food abundance and composition (benthic biomass of potential food items) and density of 0-group plaice in both the intertidal and the sublittoral. Growth showed a positive relationship with food abundance, in both the intertidal and the sublittoral, falsifying the MG/OFC hypothesis. At similar food abundance, growth in the intertidal was always higher than in the sublittoral due to the presence of the lugworm Arenicola marina in the intertidal only. In the intertidal, growth was positively related to density of A. marina. The assumption of the MG/OFC hypothesis of no negative densitydependent growth was confirmed both in the intertidal and in the sublittoral, although it did not result in maximum growth rate for 0-group plaice everywhere in the field Differences in growth rate therefore do not necessarily reflect competition for food and density-dependent growth, but they might reflect differences in food composition and availability (searching and handling time).

Shifts in nursery habitat utilization by 0-group plaice in the western Dutch Wadden Sea

“…For juvenile plaice, the ecological function of each habitat type, in this region has been previously established showing that intertidal flats were the primary nursery habitat during plaice first year of life (Zijlstra et al, 1982;Van der Veer & Witte 1993). Despite performing tidally movements onto and off the intertidal to deeper areas associated to feeding (Kuipers, 1973;van der Veer & Bergman, 1986), migrations were considered of minor importance up till August and no severe decline in abundances were seen before September (Zijlstra et al, 1982;van der Veer, 1986;van der Veer & Witte, 1993).…”

“…For juvenile plaice, the ecological function of each habitat type, in this region has been previously established showing that intertidal flats were the primary nursery habitat during plaice first year of life (Zijlstra et al, 1982;Van der Veer & Witte 1993). Despite performing tidally movements onto and off the intertidal to deeper areas associated to feeding (Kuipers, 1973;van der Veer & Bergman, 1986), migrations were considered of minor importance up till August and no severe decline in abundances were seen before September (Zijlstra et al, 1982;van der Veer, 1986;van der Veer & Witte, 1993). In agreement with recent observations for the Balgzand, a well-studied tidal flat area in western part of the Wadden Sea (van der Veer et al, 2011), this study shows that 0-group plaice also disappears from several other intertidal areas already in early summer and the high abundances found in subtidal and tidal channels suggest that deeper habitats nowadays can contain and support large populations of young-of-the-year plaice.…”

“…Previous diet studies in various nursery areas have shown that juvenile plaice can be considered as opportunistic omnivorous benthic feeders (e.g. Edwards & Steele, 1968;Kuipers, 1977;de Vlas, 1979;Poxton et al, 1983;Pihl, 1985;van der Veer & Witte, 1993). Therefore, food availability for 0-group plaice was not based on detailed, time consuming stomach content analysis, but on estimates of potential available benthic prey biomass (c.f.…”

“…A number of different intertidal, subtidal areas and channels in the western Dutch Wadden Sea were extensively studied in the late 1980s (results partly published in van der Veer & Witte, 1993). Therefore, this extensive depth-stratified survey was repeated in 2009 and the hypothesis that a shift in habitats within main nursery areas had occurred was tested by comparing the spatial and temporal patterns in distribution and abundance of 0-group plaice.…”

“…Studies in the western Dutch Wadden Sea helped to elucidate patterns of habitat use by juvenile plaice (Zijlstra, 1972;Kuipers, 1973Kuipers, , 1975Kuipers, , 1977de Vlas, 1979) and to evaluate plaice population dynamics in relation to variation in habitat quality (van der Veer et al, 1990;Karikiri et al, 1991;van der Veer & Witte 1993;van der Veer et al, 2010). It was established that plaice settlement is mainly restricted to tidal flat areas (Zijlstra et al, 1982;van der Veer & Bergman, 1986) and that 0-group plaice remain in this primary nursery habitat until autumn, before moving to deeper waters offshore as suggested by increasing densities in coastal waters (> 3 m depth) (Zijlstra et al, 1982;van der Veer et al, 1990).…”