In situ growth of the ascidian Ciona intestinalis (L.) and the blue mussel Mytilus edulis in an eelgrass meadow

Ascidians (Ciona intestinalis) and mussels (Mytilus edulis) were experimentally deployed at 15, 50 and 100 cm above the bottom in an eelgrass (Zostera marina) meadow in Vellerup Vig, Denmark. Daily water samplings at deployment height showed that concentrations of total suspended material were decreasing and concentrations of chlorophyll a increasing with distance from the bottom. A close correlation between chlorophyll a concentration and growth rates in ascidians and mussels was found, showing highest growth rates above the eelgrass canopy. There was good agreement between growth rates measured in situ and in the laboratory for mussels when compared to previous reports, while ascidians had lower in situ growth rates. The results indicate that dead organic matter is of little nutritional value to C. intestinalis and M. edulis though the mussel, due to its ability to sort particles, is better suited to the turbid environment of an eelgrass meadow. (C) 1997 Elsevier Science B.V.