Reproduction, growth and early life history of the Antarctic gammarid amphipod Paramoera walkeri

The gammarid Paramoera walkeri is one of the most abundant amphipods in near-shore Antarctic waters. There has been increasing interest in P. walkeri as a test species for ecotoxicology studies and bio-monitoring for contaminants in Antarctica, but further information is needed to improve understanding of its biology including reproduction, growth and early life history. Female P. walkeri brooding late-stage embryos were collected in summer from coastal waters in the Vestfold Hills region, East Antarctica, and were maintained in the laboratory. Timing of neonate release, brood size and early post-marsupial survival and growth (total length) of juveniles were recorded. Brood size ranged from 26 to 86 neonates per female, and juvenile survival rates were high (96 %). The increase in body length of juveniles ranged from 0.017 to 0.043 mm/day with a mean growth rate of 0.028 mm/day (0.94 % per day) over 11 weeks with strong evidence for exponential growth over time. The body lengths of laboratory-raised juveniles were not significantly different to those of wild-caught juveniles with the same number of segments (15) in the first antennae, indicating that growth may have progressed at a similar rate in vivo and in situ. Juvenile growth was similar when modelled over time or by addition of first antennal segments. This study provides new information on the reproductive biology and early life history of P. walkeri, with further evidence that Antarctic amphipods exhibit slow growth, even when food is not a limiting factor, compared with species from lower latitudes.