Details

Autor(en) / Beteiligte

• Shanks, Alan L.
• Brink, Laura

Titel

Upwelling, downwelling, and cross-shelf transport of bivalve larvae: test of a hypothesis

Ist Teil von

• Marine ecology. Progress series (Halstenbek), 2005-01, Vol.302, p.1-12

Ort / Verlag

Oldendorf: Inter-Research

Erscheinungsjahr

2005

Link zum Volltext

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• Larval supply affects the structure of marine communities. Cross-shelf transport of larvae by upwelling and downwelling may cause variation in larval supply. We tested the hypothesis that slow-swimming bivalve larvae are swept offshore during upwelling and shoreward during downwelling. We sampled a transect at Duck, North Carolina during a period when currents shifted from upwelling to downwelling and back to upwelling. During each shift, nearshore water was exchanged with offshore water and currents were 10 to 100 times faster than larval swimming speeds. LarvalSpisula solidissimaandEnsis directuswere found below the thermocline and, contrary to prediction, were swept onshore during upwelling and offshore during downwelling. WhenS. solidissimalarvae were found above the thermocline, cross-shelf transport was as predicted. LarvalTellinaspp. andMulinia lateralisremained within 5 km of shore despite cross-shelf currents and the exchange of nearshore waters with offshore waters. They did not behave as passive particles; they were not swept offshore by upwelling or onshore by downwelling. For these taxa the hypothesis was rejected. These larvae may have remained close to shore by using behaviors analogous to those displayed by animals concentrated at convergent fronts. Given the relatively slow swimming speed of bivalve larvae, there is no reason to expect that any larval type is swept offshore by upwelling. The effect of upwelling and downwelling on larval distributions varies with larval behavior and vertical distribution. Without careful sampling, one cannot invoke offshore transport of larvae by upwelling as a cause of variations in larval settlement.