Abundance, growth and production of the bivalve Solemya sp., a food source for juvenile rock lobsters in a seagrass community in Western Australia

Abstract

The infaunal bivalve Solemya sp. is the most abundant mollusc (up to 2660·m −2) in seagrass meadows at Seven Mile Beach, which support juveniles of the western rock lobster Panulirus cygnus George. Solemya sp. becomes sexually mature at 5 mm and may grow to a lenght of 17.6 mm. Solemya sp. is found in the seagrass meadows throughout the year, at temperatures of 18–25°Cand at a mean annual density (± 1 se ) of 1140 ± 232· m −2 in dense seagrass. Its shell lacks external growth rings, and the population does not have distinct recruitment cohorts. Growth, recruitment and mortality were assessed from populations recruited to in situ growth chambers and then maintained in the field or in aquaria. Recruit to natural populations occurs year-round. Growth is 0.029–0.133 mm·day −1, with growth to maturity taking an average of 64 days in summer and 163 days in winter. Mortality rates in the field are estimated at 0.0097–0.051·day −1. Annual production of Solemya sp. in sparse and dense seagrass meadows was estimated at 15.4 and 31.2 g AFDW·m −2 respectively, with corresponding P:B ratios of 10.4 and 13.9. Patterns of length-frequency in samples from different population densities suggest the existence of density-dependent mortality; the high P:B ratios also indicate high mortality rates. Production by Solemya sp. at Seven Mile Beach is sufficient to supply up to 22% of the food requirements for ≥ 2-yr-old juveniles of P. cygnus.