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Marine Ecology Progress Series

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MEPS 125:107-115 (1995)  -  doi:10.3354/meps125107

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

Josefson AB, Jensen JN, Nielsen TG, Rasmussen B

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 Arcticaislandica 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 (<6 yr) were higher at intermediate depths, immediately below pycnocline depth, suggesting enhanced growth conditions in this area. A part of the variation in shell size was apparently due to long-term variations in growth conditions. Data showed low growth rates in 1988 and 1991 and a higher rate in 1990. Enhancement of soft tissue production close to the pycnocline depth was >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.

Benthic-pelagic coupling . Pycnocline . Growth . Arctica islandica . Kattegat

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