Reproduction and Recruitment of the Intertidal Clam Darina solenoides (Bivalvia: Mactridae) in Patagonian Sandy Shores, Argentina

Abstract

Darina solenoides (P. P. King, 1832) is an abundant clam of sandy shores of southern South America. It has an essential ecologic role as a main food source for marine predators, including migratory seabirds, and is an intermediate host in parasitic life cycles. We describe the reproductive cycle and recruitment of D. solenoides in relation to environmental factors in central Patagonia, Argentina. Histological analysis of gonadal stages and quantitative indicators such as the condition index (CI), oocyte density and relative oocyte area (ROA) were examined monthly for two years (2016-2017; n = 1,315) from clams collected from two sandy shores of the San Jorge Gulf (SJG). Recruitment pattern was followed at a single site. The shell lengths ranged between 25.2 and 42.8 mm and the sex ratio did not differ significantly from 1:1. The proportion of clams showing total or partial castration by digenean trematodes was low (< 5%). A clear annual reproductive cycle was found and was characterized by high synchrony between sexes, years and sites. Proliferation of gonia extended throughout the colder months and vitellogenesis occurred mainly during the spring increase of seawater temperature and shortly after the major phytoplankton bloom. Maximum development of oocytes (mean diameter, 32.1 ± 12.9 μm) and presumed spawning by both males and females occurred during the austral summer. Settlement was also highest (mean = 162.8 ± 47.1 ind.m-2) during summer and was coincident with a second phytoplankton bloom that might favour larval development and subsequent early recruitment. This is the first reproductive study of a mactrid bivalve from the southwest Atlantic Ocean and provides useful information on the population dynamics of this key species from Patagonian sandy shores.