Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2005. / Includes bibliographical references.

Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2005. / Includes bibliographical references.

Coastal hydrodynamics regulate population dynamics through the distribution and dispersal of the meroplankton of many benthic invertebrates. I examined the hydrodynamics at four different sites on the south-east coast of South Africa and coupled them with larval sampling done at high temporal and spatial resolution. Day and night sampling was done at all four sites and a continuous 24 hour study was done in one site, both forms of sampling were carried out in autumn and spring. Samples were taken at two stations, 900 metres offshore and 300 metres apart, within each site. Water properties measured were depth, temperature and current velocity and direction. Plankton samples were collected using a plankton pump at various depths, from the surface, bottom and either side of the thermocline when present. A wide range of taxa (mostly bryozoans, bivalves, barnacles and decapods) was examined. 2-way ANOVAs were used to test the effects of time and depth on each taxon. In addition, multiple regression analyses were performed on each taxon to investigate the effects of hydrodynamics on the distribution of larvae. Bryozoanlarvae proved to be positively phototactic whilst bivalve veligers, barnacle larvae and decapod zoeae performed diel vertical migration. Turbulence and temperature had an effect on the vertical distribution/migration of decapod zoeae. These results highlight the role of taxon-specific responses to flow and the potential differential effects on larval retention and ultimately connectivity of benthic populations.

Thesis (Ph. D.)--Joint Program in Biological Oceanography (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2005. / Includes bibliographical references. / The overarching goal of this thesis was to investigate marine benthic invertebrate phylogenetics and population genetics, focused on the phylum Annelida. Recent expansions of molecular methods and the increasing diversity of available markers have allowed more complex and fine-scale questions to be asked at a variety of taxonomic levels. At the phylogenetic level, whole mitochondrial genome sequencing of two polychaetes (the deep-sea tubeworm Riftia pachyptila and the intertidal bamboo worm Clymenella torquata) supports the placement of leeches and oligochaetes within the polychaete radiation, in keeping with molecular evidence and morphological reinvestigations. This re-interpretation, first proposed by others, synonomizes "Annelida" and "Polychaeta", and lends further support to the inclusion of echiurids, siboglinids (previously called vestimentiferans) within annelids, and sipunculans as close allies. The complete mt-genome of C. torquata was then rapidly screened to obtain markers useful in short timescale population genetics. / (cont.) Two quickly evolving mitochondrial markers were sequenced from ten populations of C. torquata from the Bay of Fundy to New Jersey to investigate previous hypotheses that the Cape Cod, MA peninsula is a barrier to gene flow in the northwest Atlantic. A barrier to gene flow was found, but displaced south of Cape Cod, between Rhode Island and Long Island, NY. Imposed upon this pattern was a gradient in genetic diversity presumably due to previous glaciation, with northern populations exhibiting greatly reduced diversity relative to southern sites. These trends in C. torquata, combined with other recent short time scale population genetic research, highlight the lack of population genetics models relevant to marine benthic invertebrates. To this end, I constructed a model including a typical benthic invertebrate life cycle, and described the patterns of genetic differentiation at the juvenile and adult stages. Model analysis indicates that selection operating at the post- settlement stage may be extremely important in structuring genetic differentiation between populations and life stages. Further, it demonstrates how combined genetic analysis of sub-adult and adult samples can provide more information about population dynamics than either could alone. / by Robert M. Jennings. / Ph.D.

Thesis (Ph. D.)--Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2005. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references. / The goals of this thesis were to quantify the behavior of gastropod larvae (mud snails Ilyanassa obsoleta) in turbulence, and to investigate how that behavior affects larval supply in a turbulent coastal inlet. Gastropod larvae retract their velums and sink rapidly in strong turbulence. Turbulence-induced sinking would be an adaptive behavior if it resulted in increased larval supply and enhanced settlement in suitable coastal habitats. In laboratory experiments, mud snail larvae were found to have three behavioral modes: swimming, hovering, and sinking. The proportion of sinking larvae increased exponentially with the turbulence dissipation rate over a range comparable to turbulence in a tidal inlet, and the mean larval vertical velocity shifted from upward to downward in turbulence resembling energetic nearshore areas. The larval response to turbulence was incorporated in a vertical advection-diffusion model to characterize the effects of this behavior on larval supply and settlement in a tidal channel. Compared to passive larvae, larvae that sink in turbulence have higher near-bed concentrations throughout flood and ebb tides. / (cont.) This high larval supply enables behaving larvae to settle more successfully than passive larvae in strong currents characteristic of turbulent tidal inlets. A study was conducted at Barnstable Harbor, MA to estimate the responses of larvae to turbulence in the field. Gastropod larvae from different coastal environments had genus-specific responses to turbulence, suggesting that larvae use turbulence for large-scale habitat selection. On ebb tides, mud snail larvae had a similar response to turbulence as in the laboratory, with greater sinking velocities in strong turbulence. Behavior estimates differed for flood and ebb tides, indicating that additional physical cues influence behavior. Turbulence-induced sinking behavior would enhance retention and promote settlement of mud snail larvae in habitats like Barnstable Harbor. / by Heidi L. Fuchs. / Ph.D.

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2005. / Includes bibliographical references. / The geographic distribution and dynamics of coastal benthic populations are shaped by physical - biological interactions affecting larval dispersal and the demography of juvenile and adult individuals. This thesis focused on nearshore patterns of larval distribution and regional patterns in demography of intertidal barnacles in Southern and Baja California. Horizontal and vertical distributions, and the mortality rates of larvae, were assessed from short term (i.e. days) small- scale observations (0.1-1 km) in nearshore waters. Observations on spatial variability of adult barnacle demography were gathered over 1.5 years at scales of hundreds of kilometers. Stage-specific horizontal distributions and nearshore current measurements suggested that larvae of Balanus g-landula and Chthamalus spp. may experience limited dispersal. High mortality rates could further limit travel distances and the exchange of individuals among disjunct populations. Data on vertical distributions indicated that nauplii and cyprids of Balanus nubilus and Pollicipes polymerus occur at different depths. Nauplii remained near the surface at all times, whereas cyprids occurred in the bottom half of the water column. / (cont.) Such distributions, combined with vertical variability in horizontal flows, might cause the observed horizontal segregation of nauplii and cyprids. Differences in survival, growth rate, size structure, and per capita fertility of adult Balanus glandula were observed between Dana Point (Southern California) and Punta Baja (Baja California), a site located near the species' southern limit of distribution. Effects of spatial differences in demography on population persistence were assessed with a stage-structured matrix model. Model analyses indicated that the Punta Baja population is more susceptible to environmental stochasticity and more prone to local extinction than populations located further north. This thesis emphasizes the importance of characterizing factors that affect the dynamics of benthic populations at multiple spatial-temporal scales, and the usefulness of small scale high- frequency observations of nearshore phenomena, especially in relation with the dispersal of larvae. / by Fabián J. Tapia. / Ph.D.