Journal Article

Roles of tidal and wind-generated currents in transporting white shrimp (Penaeus setiferus) postlarvae through a South Carolina (USA) inlet

Elizabeth Wenner, David Knott, Jack Blanton and Charles Barans

in Journal of Plankton Research

Volume 20, issue 12, pages 2333-2356
Published in print January 1998 | ISSN: 0142-7873
Published online January 1998 | e-ISSN: 1464-3774 | DOI: https://dx.doi.org/10.1093/plankt/20.12.2333

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The temporal and spatial abundance of postlarval Penaeus setiferus was studied from plankton samples in oceanic and estuarine waters near the North Edisto Inlet, South Carolina (USA), during three cruises in 1993 and 1994 (May 1993, August/September 1993 and June 1994). Each covered a full cycle of neap-spring tides. On each cruise, bongo nets were towed at three stations across the inlet throat on nightly flood tides. During the first two cruises, tows were made at surface and near-bottom depths in the inlet, while sampling was confined to surface depths during the last cruise. Plankton tows were also made outside the inlet along transects extending in a cross-shelf direction and along an arcuate transect around the inlet mouth. Stations along the arcuate transect were intensively sampled over a full tidal cycle during the last cruise. Extensive oceanographic and meteorological observations were obtained from moored instrument arrays and shipboard sampling in order to relate fluctuations in tidal, lunar and wind phenomena to temporal changes in postlarval density. Densities of postlarvae were greater in the inlet throat than at stations offshore. A significant interaction of postlarval density among inlet stations and depth was noted in May. For other cruises, no significant differences in density were noted among stations across the inlet, but postlarvae were concentrated at the surface. The lack of a consistent horizontal salinity gradient and obvious pattern in water masses across the inlet may explain why postlarval densities did not consistently differ laterally in the inlet. Greater densities generally occurred during the first quarter moon, although a clear relationship of larval density to the spring-neap cycle was not observed. Highest mean densities of ingressing postlarvae in surface flood tide collections from the inlet were generally associated with downwelling onshore winds which generate onshore flow near the surface. The similarity between the time series curves of postlarval density and the tidal component of currents just offshore of the inlet suggests that tidal transport may facilitate movement into the estuary. Based on increased postlarval density at the surface during early strong flood tides and a reduced density at depth in the inlet, we hypothesize that postlarval P setiferus are utilizing selective tidal stream transport.

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Subjects: Marine and Estuarine Biology ; Zoology and Animal Sciences