Effects of environmental conditions on planktonic abundances, benthic recruitment and growth rates of the bivalve mollusc Ruditapes decussatus in a Portuguese coastal lagoon

Controlling environmental parameters for the early stages of marine invertebrates have received little attention, particularly in field studies. This study involves measurement of abundances and growth rates of the bivalve Ruditapes decussatus Linnaeus 1758 during its planktonic larval and early benthic life stages in a coastal lagoon: Ria Formosa, Portugal. Measured abundances were compared with tidal amplitude, water temperature, salinity, wind velocity and direction, and a food availability indicator (chlorophyll a). Data were obtained on abundance and prodissoconch length of the larvae, measured two to three times per week, and of post-larval stages individuals that had settled in artificial collectors over 10 months. Larval and juvenile cohorts were identified using size-frequency distributions and larval ages estimated by larval shell growth lines. Data were fitted to linear, exponential, and Laird-Gompertz growth models. Larval growth rates best matched a linear model: 3.78 +/- 0.55 per day, r(2) = 0.75, p < 0.001. Early benthonic growth rates best matched a Laird-Gompertz model: 3.97 +/- 0.15 per month, r(2) = 0.98, p < 0.001. It was concluded that there was a significant relationship between planktonic and recruitment abundances. Water temperature (as a coarse factor) and advection (as a fine factor) effects were inferred to be the prime environmental factors affecting early life stages of this species in this coastal lagoon system. (C) 2001 Elsevier Science B.V. All rights reserved.