A test of the larval retention hypothesis in seamount-generated flows

Distributions of larvai of benthic invertebrates in water column near Feiberling Guyot, a talls eamount in the eastern tropical Pacific, were compared with studies of physical oceanographic processes in an effort to test the hypothesis that larvae are retained in seamount-generated flows. Field measurements of currents during 1990 and 1991 had shown that flows near the seamount were driven by tidal rectification, resulting in anticyclonic circulation over the summit and a vertical-radial circulation cell characterized by downwelling at the seamount center, outwelling at the level of the rim, and inward return flows above the level of the rim. No persistent, bottom-trapped, stagnant region was detected on the seamount, but the tidally rectified vertical-radial circulation could theoretically retain larvae. Larval abundances quantified in net samples collected near the seamount in September of 1989 and 1990 were slightly higher near the seamount center than over the flank or base (far field), but did not show the distinct, bottom-trapped aggregation expected from retention in a classic Taylor cap. Larval abundance patterns over the broad region of the seamount (even at the far field sampling locations) were, however, consistent with retention in the tidally rectified circulation. Hydroid colonization on settlement plates suspended on moorings for 6- and 13-month periods (an indirect measure of hydroid larval abundance) was concentrated over a narrow depth range (450–650 m) but extended radially over 40 km away from the seamount center, a pattern also consistent with larval transport and retention in the tidally-rectified circulation cell.