Hydroid colonies as substrata for recruits of the mussel Mytilus edulis platensis front off Mar del Plata, Argentina.

GABRIEL NESTOR GENZANO; EXCOFFON A.; ACUÑA F.; ZAMPONI M. O.

Ophelia

Año: 2003 vol. 57 p. 53 - 61

0078-5326

Abstract. In Buenos Aires province (Argentina), due to the occasional presence of algae, hydroid clumps appear as the main primary substrata for the settlement of epizoical mussels. The settlement and growth of Mytilus edulis platensis on Amphisbetia operculata and Plumularia setacea colonies during their first life stages was analyzed throughout the year and the double settling larvae phenomenon is discussed. Colonies of both species were frequently colonized by numerous spat, which reached a maximum value of 1370 and 1450 individuals g-1 of colony, respectively. Settlement of these Mytilus larvae on the hydroids occurred  mainly in November, decreasing in December and January. The plantigrade´s biomass on A. operculata increased from December until April in spite of a decrease in the number of individuals. In constrast, in P. setacea both the plantigrade´s number and biomass decreased from December and no individuals were found in February. The major abundance and permanency of plantigrades on A. operculata could be explained by its bigger size and more profuse branching in comparison with P. setacea. The competent Mytilus larvae also settle on mussel beds, but only the filamentous substrata seem to ensure a high probability of survival during the early benthic stages, because it provides protection from predators (sea urchins and sea stars).   Running title: Hydroid colonies as substrata mussels.