Growth parameters of a benthic suspension feeder along a depth gradient across the pycnocline in the southern Kattegat, Denmark

Recent findings that a significant part of the pelagic primary production in the Kattegat may occur in the pycnocline raised the question of whether or not this causes increased input of energy to the benthos in the area where the pycnocline comes into contact with the bottom. With this question in mind, comparative studies were made of somatic growth, condition and gut content of the filter feeding bivalve Arctica islandica and of gross community variables of total fauna at stations along a transect across the area where the pycnocline usually has contact with the bottom. Gut content and condition were measured in March/April, May and September 1992, concomitantly with studies of hydrography and pelagic biology. Growth was estimated by measuring internal growth rings in the shells on individuals of different sizes, yielding average estimates from several years. Temporal variation of chlorophyll a in the bottom water and chlorophyll gut content in A. islandica showed a similar pattern with the highest values in March/April and the lowest in September. Growth rates in terms of shell size of premature individuals (100%. The data does not support the expectation of a direct simple relation between pycnocline production and A. islandica growth, and different reasons for this are discussed.