RELATIONSHIPS BETWEEN THE BIVALVES MYTILUS-EDULIS L AND CERASTODERMA-EDULE (L) IN A SOFT-BOTTOM ENVIRONMENT - AN EXAMPLE OF INTERACTION AT SMALL SPATIAL SCALE

On the Neuharlingersieler Nacken tidal flat in the east Frisian Wadden Sea, Mytilus edulis spat settle and develop on Cerastoderma edule she lls, thereby establishing mussel clumps or proper beds. Frequency of o ccurrence of individual C. edule bound in M. edulis clumps represented 0-22% of total conspecifics and was particularly high at the low shor e distribution limit of C. edule. Postulated small scale interactions between M. edulis and C. edule were investigated in experimental cages in the field. Shell growth of C. edule was slower in the presence of M. edulis. In contrast, effects on survival were not detected during t he 6 months experimental period. Slower cockle growth may be explained by a combination of mechanisms involving both exploitative competitio n for food, interference competition via byssal attachment and smother ing by biodeposits.