A comparison of growth in two juvenile flatfish species in the Dutch Wadden Sea: Searching for a mechanism for summer growth reduction in flatfish nurseries

Summer growth reduction in juvenile flatfish has been observed in various temperate coastal areas, suggesting a general mechanism. One possible mechanism that might explain this phenomenon is related to trophic limitation. After the spring phytoplankton bloom macrozoobenthic infauna becomes less active above the sediment, thereby affecting the time spent by predatory flatfish on searching for prey and hence, causing a reduction in food intake and in growth. Here, our aim is to gather evidence to substantiate this so-called “summer growth reduction” hypothesis by analyzing summer growth for 0-group flounder Platichthys flesus at the Balgzand intertidal area in the western Dutch Wadden Sea, under the prediction that flounder, as a more epibenthic predator, would suffer less or not at all from summer growth reduction in contrast to 0-group plaice Pleuronectes platessa, a more benthic feeder. Summer growth was studied for three contrasting years with respect to preceding winter water temperature conditions (cold, average and warm year) to exclude possible irreversible non-genetic adaptation of growth to water temperature conditions. Growth performance was analyzed by combining information on individual growth based on otolith daily ring analysis with predictions of maximum growth (= under optimal food conditions) based on a Dynamic Energy Budget model. In line with expectations and in contrast to 0-group plaice, no trend in growth performance over time was found suggesting that 0-group flounder showed no growth reduction after summer, providing further basis for a future testing of the trophic limitation hypothesis