Environmentally mediated crowding effects on growth, survival and metabolic rate of juvenile American lobsters (Homarus americanus)

The geographic range of the American lobster spans a very large temperature gradient. The gradient’s effects on growth and the onset of maturity are well known, but young age classes restricted to nursery grounds tend to overlap more in cooler regions than in warm regions, and the resulting effects on growth and survival are poorly understood. In field experiments in enclosures, in Maine, USA, age-0+ lobsters grew more slowly at the cooler site, and growth was little affected by stocking treatment. At the warmer site, stocking treatment effects were more pronounced. Sites did not differ in per capita survival, and stocking treatment effects were equally pronounced at the two: survival of 0+ lobsters was unaffected by additions of 1+ lobsters, but was significantly adversely affected by the addition of 0+ lobsters. Mass-specific metabolic rates of similar sized lobsters averaged higher at the cooler site. Our results suggest that location and intercohort effects are likely to affect growth more than survival of newly settled lobsters and that juveniles compensate metabolically for cool temperatures but not enough to compensate completely for their growth-retarding effects. Spatial variability in temperature may complicate use of physiological age indicators for the American lobster and other temperate crustaceans.