Growth and reproduction of two molluscs from an exposed sandy beach

Abstract

Populations of a gastropod, Bullia rhodostoma, and a bivalve, Donax sordidus, were monitored quantitatively over one year on an exposed sandy beach which supports a rich macrofauna. B. rhodostoma had a single reproductive season with copulation in early summer. Growth was slow and is described by a Von Bertalanffy growth curve. The annual mortality rate was very low, - 0,34. Production was estimated and a P/B ratio of 0,94 obtained. A minimum estimate for production by reproduction gave a P_R/B of 0,06. The average calorific value was 19,34 kJg ^-1. D. sordidus appeared to have two spawning seasons and settlements in late winter and late summer. Growth was rapid and mortality moderate - 0,72. Steady state P/B was estimated to be 1,78. The mean calorific value was 18,84 kJg^-1. All of these values for both species are compared to those obtained on a nearby sheltered beach which has a poor macrofauna.