Active and passive processes associated with initial settlement and post-settlement dispersal of suspended meiobenthic copepods
Settlement by suspended meiofaunal copepods into shallow depressions was investigated in a large, recirculating laboratory flume. Initial settlement was examined under various near-bottom flow regimes, and the interaction of flow with post-settlement behavior was investigated. Cylindrical depressions of constant depth were constructed with a range of aspect ratios (diameter and depth combinations) to mimic natural microtopographic features. Copepods were released into the flume (at nominal flows of 2, 5 and 7 cm sec−1), and settlement/ distribution in the mimic pits was observed. Four experiments were conducted using a total of five species. The first tested for copepod substrate preferences in still water. The second tested for passive settlement into azoic sediment using predictions, based on hydrodynamics, of the ability of depressions of different aspect ratios to act as passive collectors. The patterns of initial settlement of living, freeze-killed and bead-mimic meiofauna were compared. Algal-enriched sediment (to test for active habitat selection) was used in two experiments; one to test for active choice upon initial settlement and the other to test for active habitat selection via post-settlement dispersal into closely-paired pits. Although copepods were capable of active habitat selection in still water, no species tested was able to initially select the preferred habitat in moving water. Moreover, the same copepod species tested in moving water were generally deposited among depressions in the same manner as passive particles. Post-settlement behavior influenced copepod distribution at a low nominal current velocity (2 cm sec−1) as more individuals of both species located (and remained in) algal-enriched depressions after four hrs. Under high flow (8 cm sec−1), copepods were unable to select enriched over non-enriched depressions, either because they did not re-emerge from non-enriched pits or because shear velocity was too high to permit active habitat selection.
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Document Type: Research Article
Publication date: 01 July 1995
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