Waves cue distinct behaviors and differentiate transport of congeneric snail larvae from sheltered versus wavy habitats

Proximate larval responses to turbulence, tilt-inducing vorticity, and waves. Included is the percentage of larvae sinking or diving (A–C, G–I, and M–O) and the propulsive force of swimming larvae normalized by the minimum value (D–F, J–L, and P–R) vs. dissipation rate ε in grid-stirred tank (A–F), vs. magnitude of tilt-inducing vorticity ξ in the cylinder rotating about a horizontal axis (G–L), and vs. magnitude of side-to-side acceleration α in shaker flask oscillating horizontally (M–R). Turbulence experiments produced large dissipation rates, strain rates, and vorticities, but accelerations were small; rotating-cylinder experiments produced large vorticities and moderate centripetal accelerations, but strain rates were negligible; shaker flask experiments produced linear wave motions with large accelerations, but vorticity and strain rate were negligible (SI Appendix, Fig. S2). Symbols are percentages or means ±1 SE of instantaneous observations within small bins (N=100 except N=300 in G, H, J, K) of ε, ξ, or α at larval locations. Solid lines are the fitted piecewise model, and vertical lines and shaded regions indicate threshold signal ±1 SE identified by piecewise model fit (SI Appendix, Table S3). For propulsive force, the model was fitted to log₁₀(|Fv|) (SI Appendix, Figs. S3, S6, and S8); here the fitted |Fv| is normalized by minimum observed |Fv|, and when converted from log10 to linear scale, the linear model fit is curved.

Frequency distributions of behavior-inducing physical signals in snail habitats (SI Appendix, Methods: Environmental Data Analysis). Included are dissipation rate (A, D, G, and J), vorticity SD (B, E, H, and K), and acceleration SD (C, F, I, and L) in the water column (A–C and G–I) and BBL (D–F and J–L) of Delaware Bay (A–F; T. obsoleta habitat) and the New Jersey continental shelf (G–L; T. trivittata habitat). Values are computed from hydrodynamic model (purple histograms and lines) and buoy data (blue histograms and lines). Dissipation rates (A, D, G, and J) and vorticities (B, E, H, and K) are turbulence generated; accelerations are generated by turbulence (T) or waves (W) as indicated by labels (C, F, I, and L). Accelerations are dominated by turbulence in the BBL of Delaware Bay (F; purple histogram) and by waves everywhere else (C, I, and L; blue histograms). Numbers indicate percentages of signals exceeding larval thresholds for increased sinking/diving (dotted lines) or swimming effort (dashed lines) of T. obsoleta in Delaware Bay (A–F) and of competent T. trivittata on the New Jersey continental shelf (G–L). For accelerations, text colors indicate above-threshold signal percentages associated with turbulence (purple) and waves (blue), and upper values in boldface type correspond to the dominant process.

Observed physical signals in snail habitats and behaviors of competent larvae, with reference to signals typical of their adult habitats. (A and B) Joint frequency distributions of vorticity SD and acceleration SD in Delaware Bay (A, T. obsoleta habitat) and on the New Jersey shelf (B, T. trivittata habitat). Shading indicates normalized frequency of signals in the upper 75% of the water column (SI Appendix, Methods: Environmental Data Analysis); black lines indicate theoretical signal range in isotropic turbulence. Colored polygons are convex hulls enclosing the 75% most frequently co-occurring signals in the water column (solid lines) and benthic boundary layer (dashed lines) of Delaware Bay (orange; A and C) and the New Jersey shelf (red; B and D). (C and D) Mean behavioral vertical velocities of competent larvae from inlets and estuaries (C, T. obsoleta) and from the shelf (D, T. trivittata) across gradients of co-occurring turbulence- and wave-generated signals. Instantaneous observations of larval velocity are combined from multiple experiments and averaged over bins of instantaneous acceleration and vorticity magnitude at larval locations. Colored lines are as in A and B.