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Free Content Larval settlement in flocculated particulates

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Planktonic larval settlement can be a major determinant of population and community dynamics. Settlement templates of benthic invertebrates have been attributed to biological, chemical, and hydrodynamic mechanisms. Completely unexplored, however, is the role of patchy, but widespread, flocculated particulates (“floc”) that intermittently rest on substrate surfaces. Motivated by observations of very high (of order 106 m-3) larval/postlarval densities in floc from a coastal embayment, this study experimentally identified physical and behavioral mechanisms responsible for these associations. In annular-flume studies, sediment cores were mounted flush with the channel bottom, serving as the floc source. Larval (Capitella sp. I, a polychaete worm) distributions in the flume were consistent with predictions for transported particulates. Floc and larvae accumulated at the channel inner corner in high flows (shear velocities, u*, of 0.8 and 1.6 cm s-1), but not in low flows (u* of 0, 0.2 and 0.4 cm s-1). Inner-corner concentrations of larvae/floc resulted from a predictable, cross-channel, bottom flow in that direction. In still-water behavioral assays, there were no significant differences in percent metamorphosis among flocs fabricated from particulate-laden seawater, conspecific fecal pellets (compact floc) and organic-rich sediment. Surficial aggregates clearly were acceptable settlement substratum.

This study is the first to show that settling larvae associate with surficial aggregates via both physical and behavioral mechanisms. Floc may be a transient larval venue facilitating habitat search, providing nutrition, or offering protection from predators. Alternatively, it could confer high mortality, reducing larval flux to the bed. Associations between larvae and floc do not supersede established mechanisms of habitat selection. They just thicken the plot.

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Document Type: Research Article

Publication date: March 1, 2008

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  • The Journal of Marine Research publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. In the area of biology, studies involving coupling between ecological and physical processes are preferred over those that report systematics. Authors benefit from thorough reviews of their manuscripts, where an attempt is made to maximize clarity. The time between submission and publication is kept to a minimum; there is no page charge.
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