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 exper imentally deployed at 15, 50 and 100 cm above the bottom in an eelgras s (Zostera marina) meadow in Vellerup Vig, Denmark. Daily water sampli ngs at deployment height showed that concentrations of total suspended material were decreasing and concentrations of chlorophyll a increasi ng with distance from the bottom. A close correlation between chloroph yll a concentration and growth rates in ascidians and mussels was foun d, showing highest growth rates above the eelgrass canopy. There was g ood agreement between growth rates measured in situ and in the laborat ory for mussels when compared to previous reports, while ascidians had lower in situ growth rates. The results indicate that dead organic ma tter is of little nutritional value to C. intestinalis and M. edulis t hough the mussel, due to its ability to sort particles, is better suit ed to the turbid environment of an eelgrass meadow. (C) 1997 Elsevier Science B.V.