Population dynamics of the yellow clam Mesodesma mactroides: recruitment variability, density-dependence and stochastic processes

Abstract

Recruitment of benthic marine invertebrates varies greatly at different spatio-temporal scales. For instance, population dynamics of the yellow clam Mesodesma mactroides at Uruguay exhibit large temporal fluctuations, mainly associated with recruitment. We used data from an 8 yr long-term study to develop an age-structured model to show that density-dependent and density- independent forces acting together can jointly explain the population fluctuations in a sandy-beach bivalve population of the yellow clam Mesodesma mactroides. The pure density-dependent deter- ministic model parameterised with empirical values estimated during the 8 yr study predicted stable dynamics. The dynamics of the deterministic skeleton was markedly influenced by the addition of a relatively small amount of stochastic variability to fertility rates. The yellow clam population dyna- mics seem to be driven by the combined forces of density-dependent and density-independent fac- tors operating together. A combination of (uncorrelated) stochasticity in reproductive rates and asym- metric intercohort interactions (density-dependent recruitment and density-dependent survival rates) seems to be the key process generating large variability in recruitment.