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The European oyster Ostrea edulis is a keystone species that is internationally recognised as ‘threatened and declining' in the North-East Atlantic and several nations have adopted strategies for its conservation and restoration. The overall goal of the present work was to inform conservation and restoration efforts. The purpose of this thesis, therefore, was to study the larval behaviour and ecology of O. edulis in as much as is relevant to the dispersal of this species. Specifically, the larvae's vertical distribution, swimming speeds, settlement preferences and pelagic duration were studied in laboratory experiments. Most larvae concentrated at the bottom of the aquarium, independently of the developmental stage, light, food or temperature. In addition, larvae behaved actively in ~50% of all bottom observations, indicating a behavioural function other than resting. Advection close to the seabed is known to be slower than in any other part of the water column. The observed demersal behaviour would therefore most likely reduce dispersal from natal populations and enhance self-recruitment. At the surface, larvae frequently formed aggregations. In the water column, larvae swam with high vertical directionality and their distribution was homogenous. Swimming speeds ranged from 0.001 mm/s to 9.07 mm/s. O. edulis larvae settled preferentially among conspecifics (100% in < 24h), and if conspecifics were absent, larvae also settled in response to habitat-associated biofilms (81% of settlement after a 45h delay). Sterile shells and terrestrial stones did not induce more settlement than control treatments (0-14% settlement). Pelagic duration was strongly dependent on temperature, food and a suitable settlement cue. In the absence of an appropriate settlement cue, 80% of larvae delayed metamorphosis for up to 14 days, when the experiment was terminated. In contrast, 95-100% of larvae delaying their metamorphosis settled when presented with a conspecific. Such a delay in metamorphosis enhances the risk of predation and, ultimately, of losing most larvae to mortality if target habitats are absent. The results of this thesis provide strong evidence that O. edulis larvae are targeting their own beds, and that the behaviour of larvae plays a crucial role in their dispersal and successful recruitment. Restoring European oyster beds at a scale that is large and dense enough to promote the retention of larvae may be crucial to the success of restoration efforts.

There is currently worldwide pressure to establish Marine Protected Area (MPA) networks which are self-sustaining and will persistently protect habitats and species. In order for MPA networks to be effective, the species targeted for conservation must be able to disperse between protected areas and maintain a gene-flow necessary for population sustainability and persistence. This warrants new research on how to quantify and map faunal dispersal to ensure that protection will be effective and sustainable. Population genetic methods have merit, with the ability to track parentage and gene flow between areas directly. However the costs, quantity of samples, and time required to genetically quantify dispersal for multiple species make these approaches prohibitive as the only method of assessment, especially in relatively inaccessible offshore waters. Dispersal modelling is now becoming more accessible and may fulfil immediate needs in this field (although ground truthing will be necessary in the future). There have been very few dispersal modelling studies focussed on deep sea or offshore areas, predominantly due to the lack of high resolution hydrodynamic models with sufficient geographic extent away from shore. Current conclusions have been drawn based on shallow water coastal studies, informing offshore MPA network size and spacing. However the differences between these two environments may mean that dispersal abilities are not comparable. Deep water receives less influence from wind and weather, and the scales are vastly different in terms of a) the depth ranges covered, b) the planktonic larval durations (PLDs) of animals, and c) the geographic areas concerned as a consequence. Global hydrodynamic models with reasonable resolution are now becoming more accessible. With the outputs from these models, and freely available particle simulators, it is becoming more practical to undertake offshore deep water dispersal studies. This thesis aims to undertake an analysis of these accessible modelling tools within a deep sea context. The guidelines which are currently available to dispersal modellers are yet to encompass the needs of deep water modellers which may require some additional considerations given the extended depth range covered and the different hydrodynamic drivers away from the air/sea interface. Chapter 1 reviews the larval dispersal process, the factors which may affect dispersal success, and those which should be incorporated into future predictions of dispersal. The current methods for assessing larval dispersal are explored covering genetics, elemental tagging and modelling approaches with an extended look at modelling considerations. Existing marine conservation policy is also touched on in the context of connectivity and larval dispersal. Chapter 2 is designed to inform future deep sea modellers on how to parameterise and understand a dispersal model. As models appear as a ‘black box’ to the majority of users, sensitivity tests can offer a way of scaling model inputs and tempering expectations from model outputs. A commonly used model pairing (the HYCOM hydrodynamic model and the Connectivity Modeling System) is assessed, using parameters which link to the temporal and spatial scales of mixing in the modelled system: timestep of particle tracer, horizontal and vertical positioning of release points, release frequency of larvae, and temporal range of simulation. All parameters were shown to have a decreased sensitivity with depth, with patterns reflecting local watermass structure. Future studies observing similar hydrodynamic conditions seeking to optimise their model set up would be advised to stratify their model release locations with depth. A means to incorporate all sensitivity test results into optimal input parameters for future studies is demonstrated. Chapter 3 investigates whether dispersal models provide any advantage over a “sphere of influence” estimate based on average current speeds and PLDs: there is no use pursuing dispersal modelling if the outputs are too erroneous to provide any advantage over a back-of-the-envelope calculation. This chapter examines the outputs of two dispersal models driven by two different hydrodynamic models in order to observe the variability in prediction between models. This model comparison revealed a greater disparity between hydrodynamic model predictions than has been previously understood by ecologists. The two models compared (POLCOMS and HYCOM) may equally be considered as suitable to promote realism in the study region, but slight differences in resolution and numerical error handling resulted in dispersal predictions from which opposing conclusions can be drawn. This chapter therefore emphasises the necessity for model ground truthing before predictions can be trusted. Chapter 4 assimilates the findings of the previous chapters and applies their advice to a study of MPA network dispersal connectivity. Using the hydrodynamic model which performed best in chapter 3 (HYCOM), a simulation was undertaken for cold water coral (Lophelia pertusa (Linnaeus 1758)) larval dispersal between already established MPAs in the NE Atlantic. As larval characters have only been observed ex situ, dispersal was simulated using two null models (passive and active vertical migration) and averaged to provide an intermediate prediction. A method for assessing dispersal within MPAs and MPA networks is offered based on the intermediate prediction, as well as a network wide assessment of the difference in dispersal patterns for passive and active larvae. It was found that the existing network performs well at supplying larvae to non-networked sites, but performs poorly at supplying other MPAs. The ‘best’ MPAs were central to the network and facilitated the traverse of regional gaps in suitable habitat. The ‘worst’ MPAs were peripheral to the network and small in size. Network-wide passive and active dispersal matrices had no significant difference between them. However site specific variability in the effect of vertical migration was detected subject to variability in local topographic barriers to dispersal, only some of which could be surmounted with vertical migration. All chapters aim to inform future deep sea dispersal modellers, and encourage exploration of this tool in other contexts, as well as marine conservation. The thesis cautions against the transplantation of shallow water assumptions to deep water environments, and advocates region specific studies and mandatory ground truthing of predictions. An upcoming study will ground truth the findings of this thesis with both genetic and oceanographic data, allowing the accuracy of study results to be quantified.

Abstract: Coral reefs are essential to the marine ecosystem, and provide some of the most diverse habitats in the world. Coral reef fisheries contribute 6.8 billion to the economy a year globally. However, coral reefs are under significant threat because of human activities such as overfishing, ocean pollution, and habitat destruction. Overfishing leads to shrinkage of the herbivorous fish population, and ocean pollution results in the rapid growth of nutrients in the water. These activities give rise to macroalgae, since herbivorous fish eat many algae and excessive nutrients provide macroalgae with abundant necessities to grow. Macroalgae constantly compete with coral for living space. Adult coral and algae can grow by overgrowing other functional groups or available space. Coral larvae and algae propagules can recruit into adult coral and algae by dispersal and settlement onto available space. Existing literature mainly treats the whole coral reefs as one big patch and focused on one functional group overgrowing other functional groups. However, that is rarely the case in nature. Coral reefs are composed of hundreds of coral skeleton patches and between each patch are sand and rocks. Living coral, macroalgae, and turf algae grow on the coral skeletons. The mechanism of how coral, macroalgae, and turf algae occupy available space while competing; and how macroalgae invade coral and turf algae spatially through larval or propagules dispersal and settlement is still poorly understood. We develop several differential equation models from the first principles and a solid biological background to answer those two questions in chapters 2 and 3. We also give conditions under which coral will retreat or expand. The interactions between macroalgae and coral were widely studied, but how turf algae interact with other benthic groups is still poorly understood. We also generate some insights into the role of turf algae from the analysis from chapters 2 and 3. In chapter 2, we develop a one-patch ordinary differential equation model by introducing available space explicitly and incorporating larval dispersal. We undertake bifurcation analysis to understand the effect of grazing on the coral-algae dynamics. We show coral persist under high grazing pressure. We show reasonable fishing helps maintain the herbivorous fish population, and a healthier herbivorous fish population can support a higher level of coral cover. We find coral are more resistant to the decline of larval recruitment when the rate of turf algae occupying available space is high. In the chapter 3, we consider multiple patches and derive a weakly-coupled network of ordinary differential equations and a reaction-diffusion equation model for the continuous space case from the first principles for modelling brooding coral dynamics. We use the spatially explicit reaction-diffusion equation model to understand the spatial dynamics of the coral-algae ecosystem, and we simulate travelling waves to explain how the macroalgae invade coral spatially through larval dispersal at different grazing levels.

Pomatomus saltatrix is a globally distributed pelagic mesopredator which is exploited heavily throughout its range. Despite the implementation of strict management strategies, the southwest Pacific Ocean (eastern Australian) population has limited published information about the life history of this important fishing species. This thesis has 4 main chapters which investigate growth and mortality, diet, juvenile habitat use and the reproductive biology of the southwest Pacific Ocean population of P. saltatrix, locally known as tailor. By validating a whole otolith ageing technique and using a model selection process with 8 candidate growth models, I showed that the Schnute growth equation provided the best fit and yielded parameter values of a = 0, b = 2.49, size at age 1 = 25.46 cm fork length (FL) and size at age 4 = 46.34 cm FL. P. saltatrix in the southwest Pacific had a similar growth rate to other global populations, with the exception of the northwest Atlantic population which shows a considerably faster growth rate. Using a length frequency representative of harvested P. saltatrix and a catch curve analysis, instantaneous total mortality rate (Z) for the southwest Pacific population was estimated to be 1.62. Comparison with other global populations showed the northwest Atlantic population to have both the lowest natural mortality (M) and Z, together with the largest maximum biological age (14 y). All other populations were similar with higher mortality and maximum ages of 6 10 years. Z was driven largely by M for most populations, although fishing mortality (F) was highest in the east Indian and southwest Pacific populations. The dietary niche of P. saltatrix in eastern Australia was explored using a classification tree analysis to identify key factors driving diet variation. P. saltatrix was shown to be an opportunistic generalist predator which exhibited increased baitfish consumption, and decreased crustacean consumption, with increasing size. The classification tree analysis showed that body size and latitude had the greatest influence on the diet of P. saltatrix, with significant ontogenetic diet shifts occurring at 8 and 30 cm fork length (FL). While piscivory is evident in the majority of P. saltatrix diets by ~8 cm FL, crustaceans are almost entirely absent from the diet after ~30 cm FL. The importance of latitude was likely related to the broad-scale oceanography in the study region, including the East Australian Current and its separation from the continental shelf. Otolith chemistry was used to evaluate the use of estuaries and the coastal marine environment by juvenile P. saltatrix in eastern Australia. Otolith chemical signatures of juveniles from 12 estuaries, spanning 10° of latitude, were characterised using laser ablation-inductively coupled plasma-mass spectrometry. Based upon multivariate otolith elemental signatures, fish collected from most estuaries could not be discriminated from one another. This was attributed to the varying influence of marine water on otolith elemental composition in fish from all estuaries. Using a reduced number of estuarine groups, the multivariate juvenile otolith elemental signatures and univariate Sr:Ca ratio suggest that between 24 and 52 % of adult P. saltatrix had a juvenile period influenced by the marine environment. Elemental profiles across adult (age-1) otoliths highlighted a variety of life history patterns, not all consistent with a juvenile estuarine phase. Furthermore, the presence of age-0 juveniles in coastal waters was confirmed from historical coastal trawl data. Combining multiple lines of evidence suggests considerable plasticity in juvenile life history for P. saltatrix in eastern Australia, through their utilisation of both estuarine and coastal nurseries. A reproductive biology survey across the whole population and an analysis of historical larval fish abundance, found a second distinct spawning period in late summer in NSW in addition to the recognised spring spawning in QLD. Ovaries displayed asynchronous oocyte development suggesting fish spawn multiple times per season. Fecundity showed an exponential relationship with fish length with estimates of batch fecundity ranging from 99,488 to 1,424,425 eggs per fish. When combined with a length frequency of the population, the majority of eggs were produced by fish < 40 cm fork length. Length at 50 % maturity (L50) was estimated at 30.2 and 31.5 cm FL for male and female tailor respectively, suggesting that raising the NSW minimum legal length (MLL) from 30 cm total length TL to 35 cm TL to match the QLD MLL could significantly improve recruitment. The sex ratio was found to have shifted in the last 40 years to a female dominated population (1.58 females :1 male). An oceanographic particle tracking model revealed that larvae from the different spawning events are dispersed differently, with the late summer spawning period supplying the most recruits to the southern portions of the species distribution, suggesting that the multiple spawning periods have developed as a result of selection over time as surviving larvae from the different spawning periods are transported differently by the ocean currents. P. saltatrix in the southwest Pacific (eastern Australia) show a life history pattern generally consistent with most other global populations of P. saltatrix except the northwest Atlantic population which grows larger, older and matures later.

Larval dispersal is consequential for the structure and dynamics of populations and the distribution of species. Most benthic marine species inhabit patchily distributed habitat and larval dispersal is often the primary means of population connectivity. Studies suggest that gene flow is the product of conduits and barriers to dispersal, including oceanic and geographic features and a combination of physical and behavioral mechanisms that effect the relationship between larval supply and settlement. Tracking larval dispersal in the ocean is considered one of the great logistical challenges in marine ecology, with a substantial history of using genetic markers to study dispersal. Although most studies apply indirect methods that integrate information across generations, in highly dispersive populations and across fine spatial scales, genetic parentage analysis has seen increasing use, but with limited examples from temperate environments or along open-coastlines where currents dominate and larvae may be advected offshore. Here, I describe larval dispersal of nearshore rockfishes across a network of marine reserves along the open-coastline of central California, a temper- ate current-driven ecosystem and the site of a network of marine protected areas (MPAs). Rockfishes of the genus Sebastes form a marine species flock of more than 100 species and are a prominent component of the ichthyofauna in temperate ecosystems. Kelp rockfish (S. atrovirens) are part of this species flock and one of >50 species present in the Monterey Bay, California region. In Chapter 1, I describe the development of a novel set of statistically powerful microhaplotype markers for efficiently performing pedigree relationship inference in the kelp rockfish and demonstrate that the false positive rates for single parent-offspring and full-sibling analyses are orders of magnitude lower than relying on the most informative single nucleotide polymorphism (SNP) in the same short-read sequence. In Chapter 2, I apply these new genetic markers to identify eight single parent-offspring pairs and 25 full siblings from thousands of samples of adult and juvenile rockfishes collected inside and outside of marine reserves. Dispersal between reserves and areas where fishing is allowed demonstrates the efficacy of the MPA network. Chapter 3 applies these microhaplotype markers to species identification of >50 rockfishes from the Northeast Pacific. Genetic assignment accuracy exceeds 99% and the species for which accuracy does not reach 100% are gopher (S. carnatus) and black-and-yellow (S. chrysomelas) rockfishes, sister species with evidence of ongoing gene flow. Phylogenetic analyses recovers relationships among species and subgenera concordant with previous studies. Finally, in Chapter 4, I analyze additional species of rockfishes obtained for the larval dispersal study and identify full siblings among juvenile gopher/black-and-yellow and copper rockfishes. Combining these data with results from Chapter 2, I compare the proportions of full sibling pairs among the species, finding the greatest proportion of full siblings sampled in the kelp rockfish. Collectively, these chapters provide valuable new genetic resources for studying rockfishes, describe the first direct observations of dispersal in rockfishes, and provide insight into the efficacy of a network of MPAs along an open-coastline.

Dispersal of the majority of large benthic marine invertebrates relies on a planktonic phase of the life cycle dispersed by ocean currents. Patterns and spatial scales of larval dispersal drive biogeographic distributions, genetic connectivity and population and community dynamics. Biological parameters that drive dispersal potential include larval traits such as the onset and length of competence, the ability of larvae to metamorphose in response to a specific environmental cue, and the rate of energetic storage depletion. This dissertation examines complex larval traits of a reef-building coral, Acropora millepora, giving insight into how larval trait variation and molecular pathways may contribute to the propensity to disperse. First, I examined whether or not light color (wavelength) acts as a cue to influence the likelihood of settlement and metamorphosis in two species of reef-building coral. I found that exposure to different colored lights impacts the propensity to metamorphose when exposed to chemical settlement cues, and these differences in behavior reflect wavelengths of light roughly associated with their respective habitats. Second, I characterized gene expression differences between three larval fluorescent color morphs in order to elucidate the functional significance of color variation in larvae. I found that red fluorescent larvae have gene expression profiles that correlate with gene expression profiles associated with coral larval thermal tolerance and diapause in other organisms. This suggests that red fluorescent larvae may be physiologically able to exist in the water column longer, potentially dispersing longer distances. Third, I described patterns of gene expression through development and correlated these patterns to competence and fluorescence. This revealed that larval maturation associated with competence is correlated with gene expression of neuropeptide signaling, ion transport and GPCR signaling. Environmental perturbation, such as temperature, may affect these pathways, which could alter larval dispersal dynamics in the sea. Finally, to complement these correlative studies, I developed the first method of genomic manipulation in reef-building corals. Utilizing the CRISPR/Cas9 system induced targeted mutagenesis in candidate genes associated with larval dispersal traits. This work is foundational to study gene functions in an ecological context, which will greatly improve our understanding of coral biology.

Abstract: Reef-forming glass sponges are ecosystem engineers that provide habitat for a diverse assemblage of benthic marine species. Sixteen glass sponge reefs have recently been discovered at 100-200 m depth off the coast of British Columbia, Canada and are of conservation interest. Nothing is known of the genetic diversity or connectivity of these glass sponge populations or the extent of clonality, details that would better inform the design of protected areas. Previous work on the primary reef-forming species in the Strait of Georgia (SoG), Aphrocallistes vastus, has faced challenges in developing non-duplicated (diploid) markers. Here I develop a panel of single-copy, informative single nucleotide polymorphism (SNP) markers using a novel technique involving next generation sequencing (NGS). I examine the genetic structure of A. vastus at both reef and non-reef sites at multiple scales: 1) across individuals sampled within and between clumps in reefs, 2) between reefs, and 3) between sites within and outside the SoG. I show that the reefs are formed through sexual reproduction. Within a reef, and even within the SoG basin, genetic distance between individuals does not vary according to geographic distance, suggesting the presence of larvae that disperse throughout the SoG. Importantly, populations within the SoG are genetically distinct from populations in Barkley Sound, west of Vancouver Island. These results highlight the effectiveness of a new NGS methodology for overcoming problems posed by genomic duplication in some invertebrates, emphasize genetic mixing across reefs, and provide a baseline of connectivity that can provide insight into the management requirements of marine protected areas currently under discussion.

Nearshore populations have been depleted and some have not yet recovered. Therefore, theoretical studies focus on improving fisheries management and designing marine protected areas (MPAs). Depleted populations may be undergoing an Allee effect, i.e. a decrease in fitness at low densities. Here, I constructed a marine metapopulation model that included pre- and post-dispersal Allee effects using a network theory approach. Networks represent metapopulations as groups of nodes connected by dispersal paths. With this model I answered four questions: What is the role of Allee effects on habitat occupancy? Are MPAs effective in recovering exploited populations? What is the importance of larval dispersal patterns in preventing local extinctions due to exploitation and Allee effects? Can exploitation fragment nearshore metapopulations? When weak Allee effects are included, habitat occupancy drops as larval retention decreases because more larvae are lost to unsuitable habitat. With strong Allee effects habitat occupancy also drops at high larval retention because more larvae are needed to overcome the Allee effect. Post-dispersal Allee effects seem more detrimental for nearshore metapopulations. MPA effectiveness seems also lower in a post-dispersal Allee effect scenario. In overexploited systems, local populations that go extinct are also less likely to recover even after protecting the whole coastline. In exploited nearshore metapopulations with Allee effects, local occupancy or the recovery of local populations depends not only on larval inflow from neighbor populations, but also on larval inflow for these neighbors. Nearshore metapopulations with intense fishing mortality and Allee effects may also suffer a decrease in dispersal strength and fragmentation. Population fragmentation occurs when large populations are split into smaller groups. A tool for detecting partitioning in a network is modularity. The modularity analysis performed for red abalone in the Southern California Bight showed that exploitation increases partitioning through time before the entire metapopulation collapses. These findings call for research effort in estimating the strength of potential Allee effects to prevent stock collapse and assess MPA effectiveness, evaluating the predictability of local occupancy by centrality metrics to help identify important sites for conservation, and using modularity analysis to quantify the health of exploited metapopulations to prevent their collapse.

A contemporary challenge in marine ecology is understanding population connectivity driven by transport during early life stages. Connectivity results from a complex combination of biological traits and physical mechanisms. This dissertation begins by investigating the influence of physical mechanisms on particle transport around the Island of Hawaiʻi. Particle dispersion was determined by using an individual-based model (IBM) and the flow fields derived from a global and a regional implementations of an ocean circulation model. To understand the underlying physical processes of transport, coherent structures were located in the flow field, recurrent physical features were identified, and how particle transport related to them was observed. Results showed that the eddying flow increased connectivity and influenced retention, as well as that both the flow field and dispersal patterns were highly variable. In this scenario, eddy events influenced transport in distinct ways, and the timing of release played an important role in the dispersal and resulting connectivity. Differences were found in the transport of particles and emerging connectivity patterns when comparing the two model implementations, highlighting that modeling studies should use hydrodynamical model flows representing the scales of variability affecting dispersion. Then, the IBM was adapted for fish species, and connectivity patterns along the Hawaiian Archipelago of three bottomfish: E. coruscans, E. carbunculus, and P. filamentosus were investigated . These species appeared to share common features in their connectivity patterns driven by larval transport, as follows: i) limited connectivity between the Papahānaumokuākea Marine National Monument (PMNM) and the Main Hawaiian Islands (MHI); ii) greater connectivity among islands in the PMNM than in the MHI; iii) existence of four, mostly self-contained, dispersal zones along the Archipelago; and iv) islands from Kauai to Necker connected the PMNM and the MHI through larval dispersal, acting as ecological corridors. When the MHI's bottomfish restricted fishing areas (BRFAs) were considered, it was found that these reserves are potentially replenishing depleted fishing areas by larval export, but rely on larval subsidy from the fishing sites to sustain their populations. Thus, the efficiency of the reserve network could be improved by the protection of additional bottomfish habitat, distributed in new or expanded reserves. Finally, dispersal characteristics of yellowfin tuna (T. albacares) around the MHI were investigated. The physical environment appeared favorable for retention of yellowfin tuna larvae. However, retention is not the main factor optimizing the spawning season of this species in the archipelago, and other factors, such as favorable water temperature and food availability, are likely contributing to spawning seasonality. The distribution of larvae by the time evolving eddying field was highly variable. Apart from nearshore regions, no additional persistent dispersal pathways or accumulation zones were observed.

A critical component to understanding connectivity of spatially-separated populations of marine organisms is quantifying hydrodynamic paths of dispersal, and variation in the strength of these hydrodynamic connections. We mimicked larval dispersal of the Eastern oyster (Crassostrea virginica) by replicating wind-driven circulation patterns in Pamlico Sound (PS), NC using a numerical hydrodynamic model (ADCIRC, ADvanced CIRCulation) to produce 3-dimensional flow-fields, followed by predicted trajectories of virtual larvae using a particle-tracking model (PTM). Predicted larval trajectories were then used to estimate a larval connectivity matrix for PS to help guide oyster restoration efforts via a network of no-take oyster broodstock reserves. To force the ADCIRC model, we used wind observations during the time that oyster larvae would have been dispersing in PS, and used velocity observations from two bottom-mounted ADCP (Acoustic Doppler Current Profiler) instruments to validate velocities predicted from ADCIRC. Field observations of trajectories from 12 Pacific Gyre surface drift buoys released during the summer of 2007 were used to validate the paths of virtual larvae produced by the PTM. The 3D ADCIRC model reliably predicted variation in velocities at different locations in PS, especially currents near-surface. The PTM also reliably simulated trajectories of surface drift buoys under varying wind regimes, thereby providing confidence in qualitative predictions of dispersal of virtual larvae, and potential larval connectivity in PS. Potential oyster larval connectivity was not uniform among broodstock sanctuaries in PS, ranging from 20 to 65% connectivity from a given sanctuary. Moreover, potential self-recruitment to a given broodstock sanctuary also varied spatially. Thus, when spatial variation in the degree of potential oyster larval connectivity in PS identified in this study is combined with the results of related studies on spatial dynamics of oyster populations in PS (see below), there is strong evidence for an oyster metapopulation and possibly source versus sink population within PS.

Dispersal of marine organisms has generally been assumed to be demographically open with planktonic larvae exploiting ocean currents to travel long distances. However, recent studies report evidence of local larval recruitment. In this study, I hypothesized that populations of the temperate coral, Oculina arbuscula, are maintained primarily by local recruitment off the Georgia coast because: 1) suitable substrate for settlement is patchy and 2) O. arbuscula's branching morphology is conducive to asexual reproduction by fragmentation. To address this hypothesis, I combined data from allozyme electrophoresis, histocompatibility assays, and despersion of established colonies. Results indicated substantial local recruitment maintained primarily by sexual reproduction rather than asexual fragmentation. Sexually produced planulae are not only philopatric, but also show evidence of some migration among populations. In this temperate species, local recruitment primarily maintains aggregated populations of O. arbuscula.

Author's abstract: The Atlantic sand fiddler crab, Uca pugilator, is an extremely abundant fiddler crab found along the eastern and Gulf coast of the United States. Fiddler crabs have a life cycle with an obligatory planktonic larval phase of 30-90 days, which might be expected to lead to widespread larval dispersal and consequent genetic homogeneity over considerable distances. However a large amount of morphological and behavioral variation is found between northern and southern populations along the eastern coast. This study was undertaken to determine the population genetic structure of U. pugilator and to determine whether these differences may have a genetic basis. The population structure of the fiddler crab was analyzed using 576 individuals collected from 12 sites along the eastern coast. PCR-base single stand conformation polymorphism (SSCP) was used to analyze segments of the mitochondrial 16S rRNA and the nuclear internal transcribed spacer 1 (ITS1) genes of these individuals. The ITS1 marker did not prove to be informative when screened by SSCP for this study. The 16S marker revealed a moderate amount of population structure (FST = 0.292) between populations. The results of this study reveal frequent gene flow between nearby localities, but reduced levels between populations separated by large distances. Despite the potential for high dispersal by planktonic larvae, population differentiation and isolation by distance was found between populations U. pugilator. Northern and southern regions are separated by a genetic distance of 0.3866 suggesting the potential for morphological and behavioral differentiation across the species range. INDEX WORDS: Uca pugilator, Fiddler crab, Population structure, Gene flow, Larval dispersal, Single-stand conformational polymorphism, 16S rDNA, ITS-1