VARIABILITY IN GROWTH-RATES OF JUVENILE FISHES IN DIFFERENT ESTUARINE HABITATS

Estuaries are vital nursery grounds for many marine fishes. During initial estuarine residence, juvenile fishes presumably benefit greatly from rapid growth, which can diminish susceptibility to size-selective predators. To measure the degree of variability in growth rates across different estuarine sites and habitats, I conducted caging experiments with 3 species (Pseudopleuronectes americanus, Tautoga onitis, and Gobiosoma bosci) at 4 sites in New Jersey, USA, estuaries. Two sites were in an estuary with dense eelgrass Zostera marina beds (Little Egg Harbor) and 2 were in an estuary lacking eelgrass but supporting patchy accumulations of the macroalgae Ova lactuca (Great Bay). Experiments were conducted in vegetated (either Zostera or Ulva) and unvegetated habitats at each site. Relative differences in growth rates among the 4 sites and between the 2 habitats were generally maintained across experiments within species, suggesting a consistency in foraging value. For all 3 species, growth was highest at a Great Bay site and generally lowest at a Little Egg Harbor site. The presence of vegetation (either Zostera or Ulva) was beneficial to growth only for T. onitis. Observed patterns in water temperature, sediment structure, and food availability were potential factors effecting the observed differences in growth rates. Natural densities of the 3 fish species were quantified and compared to the results of growth experiments to determine if there were trade-offs between rapid growth and other attributes of habitat quality. P. americanus and T. onitis were more abundant in areas supporting faster growth, but the complete absence of tautog from unvegetated substrates suggested some degree of habitat avoidance. A clear trade-off between habitat selection and foraging quality occurred for G. bosci; gobies were most abundant inside eelgrass beds, which supported the poorest growth rates.