Behavior and Settlement of Gastropod Larvae in Turbulence
Swimming Ilyanassa obsoleta larvae
The motivation of my thesis research is to understand how biophysical coupling between turbulence and settlement behavior affects the supply of gastropod larvae to coastal populations. Turbulence varies both spatially and temporally in the ocean, and could provide an initial settlement cue to the planktonic larvae of nearshore invertebrates. Coastal gastropod larvae alter their behavior in turbulence, suggesting a potential settlement response to this hydrodynamic cue. Many veliger larvae pull in their velums and sink rapidly when disturbed, e.g. by turbulence, and this behavior must affect larval sinking fluxes and near-bottom concentrations (larval supply). An increase in larval supply could enhance settlement in turbulent areas, therefore larval sinking behavior has the potential to influence the large-scale spatial patterns and periodicity of gastropod settlement. I am investigating the effects of turbulence-mediated behavior on mud-snail larval supply and settlement patterns for the Eastern mud snail (Ilyanassa obsoleta), through a combination of laboratory, modeling, and field studies.
Laboratory study
To understand the population-level effects of sinking behavior on larval fluxes, the behavior first had to be quantified in laboratory-generated turbulence. I exposed larvae to a range of turbulence conditions representative of tidal inlets, and measured the larval vertical velocities. I fitted a normal mixture model to the observed larval velocities, to estimate the proportions of larvae in three behavioral modes. Details in Limnology and Oceanography 49(6).
Modeling
I am incorporating mud snail behaviors (quantified in the lab) into models of larval concentration distributions and settlement in tidal currents, to predict temporal patterns of larval supply in tidal flow. Model predictions will be tested against larval concentration profiles in a tidal channel (see below).
Field study
I recently completed a field study at Barnstable Harbor, MA, to test whether turbulence-induced sinking behavior affects the distribution of veligers in complicated, real-world flows. I measured turbulence and Reynolds stresses (using ADV and ADCP) and collected plankton samples in high-frequency vertical profiles. The concentration profiles of gastropod larvae will be compared against model-generated predictions, and against profiles for other types of larvae. Funded by the Coastal Ocean Institute.