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Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2000, Recruitment variability in benthic invertebrate populations results from variability in planktonic larval supply and from processes occurring during and after larval settlement onto the seafloor. The focus of this thesis is on the temporal and spatial variability in larval supply, the extent to which planktonic larval distributions are determined by larval behaviors and physical processes, and how differentially distributed larvae are advected to potential adult habitats by inner-shelf circulation such as wind-driven upwelling and downwelling. This research capitalized on two sets of larval concentration time series, collected by moored zooplankton pumps, and complemented by synoptic hydrographic time-series data. High variability was observed in larval concentration time series, yet the variations were nonrandom. Within the context of the sampling regime, two dominant modes of variability existed. One source of variation was associated with the synoptic meteorological time scale, and the other with the diurnal time scale. Over relatively long time scales, larvae were associated with particular water masses, defined by temperature-salinity characteristics. Within a particular water mass, group-specific vertical patterns were observed over both long and short time scales. "Low frequency" temporal variations resulted primarily from wind-driven cross-shelf transport of water masses in which larvae were differentially distributed relative to the thermocline. "Higher frequency" variations were attributed to diel vertical migrations. These findings suggest that larvae were passive to the degree that they were horizontally advected with certain water masses, but active to the degree that they could alter their vertical position in the water column. Local hydrodynamics, larval associations with specific water masses, and the vertical structure of larvae resulted in differential larval transport to potential adult habitats. Larval data indicate the times and places of possib, This research was supported by grants from the National Science Foundation's Coastal Ocean Processes (CoOP) Program (OCE91-23514 and OCE92-21615 to Cheryl Ann Butman, and OCE96-33025 to Steven J. Lentz and Cheryl Ann Butman); the National Oceanic and Atmospheric Administration's National Sea Grant Program Office, Department of Commerce (Grant # NA46RG0470, Woods Hole Oceanographic Institution Sea Grant Project No. RB-132 and RB-139 to Cheryl Ann Butman and Elizabeth D. Garland); and the WHOI Education Program.

Patterns and rates of particle contact onto flat plates in steady unidirectional flows were investigated in a laboratory flume. Plates with three leading edge configurations (faired, bluff and split) were used to generate boundary-layer flows that differed in downstream patterns of plate-ward advection, turbulence and shear stress. Particle contact onto the leading edges of all plates was consistently low in 2,5, and 10 cm s-1 along-stream flow speeds. Contact was enhanced under separation eddies that formed over bluff and split plates, but was reduced at reattachment points. High contact rates appeared to correspond to a combination of local plate-ward advection, a thick boundary layer, and reduced shear stress. Surprisingly, particle contact rates in the "non-varying" flow region further downstream on the plates varied only slightly between plate types and between flow speeds. Contact rates did, however, vary strongly with particle abundance in the flume. These results were used to develop a predictive model of passive larval contact rate onto settlement plates in known larval concentrations and free-stream flows. The contact model, when combined with larval behavioral observations, provides the basis for a more objective, quantitative method of interpreting larval settement plates., Funding was provided by the Office of Naval Research under Contract Nos. NOOO14-89-J-1431 and NOO014-89-J-1l12.

Recruitment variability in benthic invertebrate populations results from variability in planktonic larval supply and from processes occurring during and after larval settlement onto the seafloor. The focus of this thesis is on the temporal and spatial variability in larval supply, the extent to which planktonic larval distributions are determined by larval behaviors and physical processes, and how differentially distributed larvae are adverted to potential adult habitats by inner-shelf circulation such as wind-driven upwelling and downwelling. This research capitalized on two sets of larval concentration time series, collected by moored zooplankton pumps, and complemented by synoptic hydrographic time-series data. High variability was observed in larval concentration time series, yet the variations were non- random. Within the context of the sampling regime, two dominant modes of variability existed. One source of variation was associated with the synoptic meteorological time scale, and the other with the diurnal time scale. Over relatively long time scales, larvae were associated with particular water masses, defined by temperature-salinity characteristics. Within a particular water mass, group-specific vertical patterns were observed over both long and short time scales. "Low- frequency" temporal variations resulted primarily from wind-driven cross-shelf transport of water masses in which larvae were differentially distributed relative to the thermocline. "Higher- frequency" variations were attributed to diel vertical migrations. These findings suggest that larvae were passive to the degree that they were horizontally adverted with certain water masses, but active to the degree that they could alter their vertical position in the water column., Prepared in cooperation with Woods Hole Oceanographic Institution, Woods Hole, MA. Additional contracts are: OCE-9633025 and NA46RG0470

Patterns and rates of particle contact onto flat plates in steady unidirectional flows were investigated in a laboratory flume. Plates with three leading edge configurations (faired, bluff and split) were used to generate boundary-layer flows that differed in downstream patterns of plate-ward advection, turbulence and shear stress. Particle contact onto the leading edges of all plates was consistently low in 2,5, and 10 cm s(-1) along-stream flow speeds. Contact was enhanced under separation eddies that formed over bluff and split plates, but was reduced at reattachment points. High contact rates appeared to correspond to a combination of local plate-ward advection, a thick boundary layer, and reduced shear stress. Surprisingly, particle contact rates in the 'non-varying' flow region further downstream on the plates varied only slightly between plate types and between flow speeds. Contact rates did, however, vary strongly with particle abundance in the flume. These results were used to develop a predictive model of passive larval contact rate onto settlement plates in known larval concentrations and free-stream flows. The contact model, when combined with Larval behavioral observations, provides the basis for a more objective, quantitative method of interpreting Larval settlement plates. Boundary-layer-flow, larval settlement, particle contact.