The yellow clam Amarilladesma mactroides (Deshayes, 1854) is considered a vulnerable species since the mid-1990s. Populations have experienced mass mortalities throughout their entire range of distribution (23–41°S) along exposed sandy beaches of Atlantic South America. Detrimental anthropogenic impacts have further contributed to failure of populations to make a recovery. To determine the factors involved in these events, density prior to a mortality event was calculated and live yellow clams encompassingmost of its geographic range distribution were analyzed histologically to describe parasites and pathologies. Moreover, moribund specimens were analyzed by molecular techniques to test for the presence of the virus OsHV-1. A mortality event was recorded after a maximum density of 127 clams/m2 was attained. No clear pattern was found between the prevalence and intensity of infection and localities, mortality events, or sampling season. Although OsHV-1 was not observed in any of the yellow clams t...

The yellow clam Amarilladesma mactroides (Reeve, 1854), is an intertidal species that prospers mainly on dissipative sandy beaches along the temperate Atlantic coast of South America, from Brazil to Argentina (24–41° S). This large clam is considered a fast burrower, which lives buried in the sediment, migrating seasonally into the intertidal zone. The present study explores the effect of sediment grain size on the burrowing performance of this species, to elucidate the influence of granulometry on the alongshore distribution of the A. mactroides population. Laboratory trials were performed with clams of different sizes, to study the influence of grain size on the burial rate. Clam distribution was analyzed along a 32 km coastal fringe whose granulometric composition varies from very fine to coarse sand. The values of the mean burrowing rate index, a measurement of clam mobility, suggest that burrowing is fast to very fast in fine and medium sand and becomes slower toward areas with extreme parti...