Effect of Musculista senhousia mats on clam mortality and growth: much ado about nothing?

Abstract

By means of manipulative experiments, growth and mortality of the clams Tapes decussatus and Ruditapes philippinarum were assessed in the presence and absence of Musculista senhousia (Mytilidae) in its mats. The experiment was arranged as a randomized complete block design, with eight blocks of nine cages each: four blocks contained T. decussatus, and four blocks R. philippinarum. The experimental units received one of the following treatments: T. decussatus (or R. philippinarum) with no mats, with mats of M. senhousia in high density, with mats in low density. The experiment ran for 100 days. The growth of both clam species was not affected by the presence of mussel mats. Mortality was higher for T. decussatus than for R. philippinarum, but the presence of mats, both in high and low density, seemed to exert no significant effect on clam mortality. It is hypothesized that deeper-dwelling species, as the carpet-shell and the Manila clam, are much less affected than other bivalves by mussel mats.