Selective growth and mortality of juvenile 0-group plaice Pleuronectes platessa in the Dutch Wadden Sea:a consequence of irreversible non-genetic adaptation during early pelagic life

Abstract

In this paper, we have addressed the question of whether selective growth and mortality of juvenile 0-group plaice Pleuronectes platessa (L.) occurs in the Dutch Wadden Sea as a consequence of irreversible non-genetic adaptation to water temperature conditions during early pelagic life. As tracers, the number of vertebrae, and of dorsal and anal fin rays were used, since the variability in these characteristics reflects the phenotypic plasticity induced by differences in environmental conditions, and especially water temperature, during early pelagic life. From the onset of larval immigration in March 1995, the juvenile 0-group plaice population was sampled frequently and the variability in its meristic characteristics was analysed. The number of vertebrae appeared to be established by water temperature conditions during the egg stage, while the number of dorsal and anal fin rays seemed to be determined during the larval stage. As a consequence, the number of vertebrae was not correlated with either the number of dorsal fin rays or the number of anal fin rays, but the numbers of anal fin rays and dorsal fin rays were strongly correlated. Strong support was found for Kinne's (1962; Comp Biochem Physiol 5:265-282) 'irreversible non-genetic adaptation' hypothesis-that the variability induced by environmental conditions during early life still expresses itself later on in juvenile life-as there was a significant positive relationship in our study between growth and the number of vertebrae during the period April to July. Also, instantaneous mortality was positively related to the number of vertebrae. It is suggested that the relationship with mortality results from a correlation between vertebral number and some important characteristic involved in avoiding predators, such as locomotory performance. Also, mean growth rate during the growing season and instantaneous mortality rate were positively correlated for each meristic characteristic. It is argued that the relationship between growth and mortality will vary over the years and will depend on the combination of environmental conditions during egg and larval stage compared to those during the subsequent juvenile stage.