Effects of larval swimming behavior on the dispersal and settlement of the eastern oyster Crassostrea virginica

Abstract

Hydrodynamic model coupled to a larval behavior model which incorporates an increased downward swimming speed in response to elevated turbulence. Turbulence and flow measurements over oyster reefs, oyster restoration sites, and bare seafloor were quantified using velocimeters. Hydrodynamic cues were input into the larval behavior model to determine how changes in swimming behavior due to turbulence influence settlement patterns. Results indicate that alterations in settlement velocity, specifically maintaining approximate neutral buoyancy until larvae are both mature and over an existing reef, substantially increased the probability of settling on suitable substrate. We also found that oyster reefs in low velocity regions have a higher probability of self-colonization, while reefs found in less sheltered higher velocity environments receive comparatively little of their own larvae and depend upon connectivity with other areas. Data from in situ larval settlement plates agree with model results and indicate that rates of settlement are ∼1.5 to 3× greater over existing reefs composed of primarily vertically oriented oysters than over restoration reefs that are less topographically complex. Large-scale efforts to restore oyster (Crassostrea virginica) habitat rely on the creation of high-relief hard substrate to improve the natural recruitment of larvae originating from existing oyster populations. Delivery of competent larvae to reefs is influenced by larval behavior, which respond to elevated levels of turbulence by a downward swimming behavior. To determine the geographic dispersal of populations of oyster larvae and how swimming behavior of larvae alters settlement patterns within Virginia (USA) coastal bays, this study utilized a depth-averaged Delft3D