Infection levels of eastern oysters by the unicellular pathogen Perkinsus marinus have been associated with anthropogenic influences in laboratory studies. However, these relationships have been difficult to investigate in the field because anthropogenic inputs are often associated with natural influences such as freshwater inflow, which can also affect infection levels. We addressed P. marinus-land use associations using field-collected data from Murrells Inlet, South Carolina, USA, a developed, coastal estuary with relatively minor freshwater inputs. Ten oysters from each of 30 reefs were sampled quarterly in each of 2 years. Distances to nearest urbanized land class and to nearest stormwater outfall were measured via both tidal creeks and an elaboration of Euclidean distance. As the forms of any associations between oyster infection and distance to urbanization were unknown a priori, we used data from the first and second years of the study as exploratory and confirmatory datasets, respectively. With one exception, quarterly land use associations identified using the exploratory dataset were not confirmed using the confirmatory dataset. The exception was an association between the prevalence of moderate to high infection levels in winter and decreasing distance to nearest urban land use. Given that the study design appeared adequate to detect effects inferred from the exploratory dataset, these results suggest that effects of land use gradients were largely insubstantial or were ephemeral with duration less than 3 months.

There have long been concerns about the negative impacts of recreational boating activity in the Indian River Lagoon system (IRL), especially in Mosquito Lagoon (ML), the northernmost part of the IRL. My research is focused on the impacts of boat wakes on intertidal reefs formed by the eastern oyster, Crassostrea virginica. There has been a 24% loss of oyster habitat in ML since 1943, where natural oyster reefs have been replaced by dead oyster reefs which do not serve the same ecological function. While there is anecdotal and correlative evidence that this loss is a result of boat wakes, no studies to date have confirmed dead reefs can be a direct result of boat wakes. Therefore, I addressed the following questions: (1) What wake heights are generated by a range of boat types, and (2) What amount of oyster movement and erosion occurs as a result of these boat wakes? A series of boat pass experiments addressed the first question; these results were utilized in experiments at Florida Institute of Technology's wave tank to observe sediment erosion and oyster movement as a result of specific wake heights. Model selection was used for both the field and wave tank experiments to determine which variables contributed most to explaining the wake heights, erosion, and oyster movement that occurred. Wake heights ranging from 0.05 cm to 20.80 cm were documented contacting the oyster reefs from the boat passes, with a mean of 2.95 cm. Boat type was less important than speed or distance when determining wake height. My wave tank results document that wake heights as small as 2 cm contacting oysters are capable of moving individual and clusters of oysters. Minimum distances for boats to travel in order to maintain wakes smaller than 2 cm at reefs are suggested for management purposes based on regression equations. This could minimize the amount of movement that occurs when oysters are subjected to boat wakes. The results of this study can help resource managers implement boating policies in Mosquito Lagoon, and contribute greatly to conserving this important ecosystem engineer.

Populations of Crassostrea virginica within Mosquito Lagoon, Florida have recently undergone significant die-offs, which are a subject of major concern. Restoration efforts within Mosquito Lagoon are focusing on reconstructing the three-dimensional reef habitats. Before effective protocols can be established, however, important questions about the sources of juvenile and adult oyster mortality must be answered. Potential causes of Crassostrea virginica mortality in the Indian River Lagoon system include sediment loads, competition, predation, and disease. My research focused on the interactions between oysters and the competitors that may affect the settlement, growth, and survival of Crassostrea virginica. The four objectives of my thesis research were to: 1) identify potential oyster competitors in Mosquito Lagoon, 2) determine if the sessile species recruiting to oyster shells have changed over time, 3) determine how the dominant competitors, barnacles, affect oyster settlement, growth and survival, and 4) determine if oyster or barnacle larvae are better able to settle in increased sediment and flow conditions that are associated with high levels of recreational boating. Lift nets were deployed within Mosquito Lagoon to determine available competing species. I collected species inventory data at six sites to determine the sessile invertebrate species (competitors) present on oyster reefs. Nets were deployed intertidally, just above mean low water, on living oyster reefs. One and a half liters of live and dead oysters were placed within the nets upon deployment. The nets were picked up monthly and surveyed for all fauna. Upon retrieval, all oysters within each net were brought back to the lab where all sessile organisms were immediately identified and returned to the lagoon. This survey began June 2004 and continued for one year. Shells from historic shell middens (up to 15,000 years old) were examined to determine if the sessile species settling on oyster reefs have changed over time. Similar species were found on both shells of historic and extant reefs. One notable exception was the appearance of Balanus amphitrite, an invasive barnacle, on the extant reefs. Balanus amphitrite is thought to have invaded Mosquito Lagoon approximately 100 years ago. This has resulted in a five fold increase in barnacle abundance per oyster shell. Balanus spp. were identified as important potential competitors and thus my research focused on spatial competition between C. virginica and native versus invasive barnacles of the area. Over 300 barnacles, including a native species, Balanus eburneus, and an invasive, Balanus amphitrite, have been counted on a single oyster shell. To determine how Balanus spp. affected settlement, growth, and survivorship of C. virginica, laboratory and field experiments were conducted in which densities of Balanus amphitrite and Balanus eburneus were manipulated. Density treatments included: no barnacles (control), low, medium, and high coverage of barnacles. Laboratory settlement trials with cultured oyster larvae were run in still water and flow (recirculating flume) using all barnacle density treatments. Additionally, all treatments with 7-day oyster spat were deployed in the field to follow oyster spat growth and survivorship. Settlement was counted by microscopy, and growth and survivorship were measured every 3 days for 4 weeks. Settlement of oysters was affected by barnacle presence only in flowing water. Still water trials showed no oyster preference related to any barnacle density or species. The presence of barnacles affected the growth and survivorship of oyster spat. However, there were no species specific differences. Studies suggest that recreational boating activities, especially boat wakes that cause sediment resuspension, may decrease recruitment and this may then provide an advantage to sessile competitors less affected by flow and sediment loads. To address these issues, replicated laboratory trials were run in a laboratory flume to quantify the effects of water motion (0, 5, 10 cm/s) and sediment loads (0, 8, 16 g/ml) on oyster recruitment and the recruitment of an important, relatively new competitor in the system, the barnacle Balanus amphitrite. If B. amphitrite settles in a wider variety of flow rates and sediment conditions, it may have a competitive advantage over the native oyster in this space-limited habitat. I found that high flow and sediment loads reduced larval settlement of C. virginica. Alternatively, settlement of cyprids of B. amphitrite did not differ among treatments. Thus, continuous boat traffic during settlement times should favor recruitment of the invasive barnacle Balanus amphitrite over the native oyster Crassostrea virginica. Determination of the competitive interactions of Crassostrea virginica in Mosquito Lagoon gives us important insights into the ecological conditions necessary for reestablishment of these oyster populations. Crassostrea virginica in Mosquito Lagoon was significantly impacted by barnacles; settlement, growth, and survivorship were all reduced by Balanus spp. This information will help resource managers in planning restoration techniques to minimize oyster and barnacle competitive interactions and increase Crassostrea virgininca success.

Karenia brevis, le dinoflagellé produisant des brevetoxines (PbTx), est la principale espèce d’efflorescences d’algues toxiques dans le Golfe du Mexique. Les effets de cette algue sur Mercenaria mercenaria et Crassostrea virginica sont méconnus tandis que les efflorescences coïncident avec la période de reproduction de ces espèces. Ce projet avait pour but de déterminer les effets i) d’une exposition à K. brevis en laboratoire et naturelle de terrain sur les processus physiologiques associés à la reproduction de M. mercenaria et C. virginica, et ii) d’une exposition à K.brevis sur la qualité et le développement des gamètes, embryons et larve de ces espèces. Suite à l'exposition des adultes de clams et d’huîtres à K. brevis, les paramètres physiologiques de la reproduction ont été affectés. La présence de PbTx dans les tissus des gamètes et le potentiel transfert maternel de PbTx à la progénie via les ovocytes, pourraient avoir entraîné les effets négatifs observés lors du développement larvaire.Les effets négatifs similaires causés par l'exposition des stades précoces à différentes préparations de cellules de K. brevis suggèrent que d'autres composés toxiques, en plus de PbTx, pourraient être impliqués dans la toxicité et, que la majorité des effets délétères se produisent durant les divisions embryonnaires.Le clam et l’huître américaine sont sensibles à K. brevis. Les effets négatifs sur les adultes et jeunes stades de vie, combinés à une exposition quasi-annuelle aux efflorescences de K. brevis, pourraient engendrer des perturbations majeures sur le recrutement des populations de ces espèces importantes, et avoir des répercussions environnementales et économiques. / The brevetoxin (PbTx) producing dinoflagellate, Karenia brevis is the most prevalent harmful algal bloom species in the Gulf of Mexico. The effects of this alga on Mercenaria mercenaria and Crassostrea virginica are poorly understood yet, blooms typically overlap with periods of reproduction and spawning in these species.The aims of this project were to determine the effects of i) laboratory and field exposure of K. brevis on the reproductive and related physiological processes of adult M. mercenaria and C. virginica and the quality of the offspring that were produced and ii) K. brevis exposure on gamete, embryo and larval development in these species.Following exposure of adult clams and oysters to K. brevis, negative effects were recorded on reproductive and physiological parameters. PbTx was recorded in gamete tissues, and maternal transfer of this PbTx to the offspring via the oocytes, may have resulted in the significant negative effects recorded on larval development up to the end of the lecithotrophic phase.The similar dose-dependent negative effects caused by direct exposure of gamete and early life stages to different cell preparations of K. brevis suggests that other toxic compounds in addition to PbTx may be involved in toxicity and, that the majority of negative effects occur during embryonic divisions.Hard clams and eastern oysters are susceptible to K. brevis exposure. The negative effects on adult and early life stages combined with the near- annual exposure to blooms of K. brevis could cause significant bottle-necks on the recruitment and population dynamics of these important species and, have wider reaching environmental and economic impacts.

Native oysters have been promoted as a means to improve water quality in Chesapeake Bay. This project added important insights into the potential of oyster aquaculture to process and remove nutrients from Bay waters. Results clarified that nutrient removal of nitrogen (N), phosphorous (P), and carbon (C) through harvest of cultivated oyster biomass can be quantified and modeled with high levels of statistical confidence. A simple, yet accurate, method is now available for estimating the amount of nutrients removed via harvesting aquacultured oysters. Based on model estimates, 106 harvest sized oysters (76 mm TL) remove 132 kg TN, 19 kg TP, and 3,823 kg TC. Previous work suggested that potentially substantial quantities of N may be removed through enhancement of the coupled nitrification-denitrification pathway in sediments as a result of oyster biodeposition. Using 15N and N2/Ar methods to measure N2 production in sediments, encompassing direct denitrification (DNF), coupled nitrification- denitrification, and anaerobic ammonium oxidation (anammox) pathways, at two oyster aquaculture sites and two reference sites (no aquaculture), we found that oyster biodeposition did not accelerate sediment N removal. We estimate sediment N removal rates via N2 production at an oyster cultivation site producing 5 x 105 oysters (1750 m2) to range from 0.49-12.60 kg N yr-1, compared to 2.27-16.72 kg N yr-1 at a reference site of the same area; making the contribution of oyster cultivation to N removal via sediment N2 production inconsequential as a policy initiative for Chesapeake Bay eutrophication mitigation. Molecular approaches and direct abundance measures have improved our understanding of the sediment microbial community response to oyster biodeposition. Overall, sediments impacted by oyster biodeposition had a significantly different denitrifying community composition than sediments a few meters away or at the non-aquaculture reference sites. Bacterial abundance in sediments was determined by site rather than by oyster biodeposition. No apparent effects of oyster biodeposition were evident in nitrifying bacterial abundance patterns at either site, indicating that oyster biodeposition does not enhance coupled nitrification-denitrification by increasing the abundance of nitrifiers in sediments.

The objective of this project was to document the status of oysters, Crassostrea virginica, from non-reef habitats throughout Tampa Bay, Florida, and assess the ecosystem contributions of those populations relative to reef-dwelling oysters. The aspects of oyster ecology studied here include condition, prevalence and intensity of disease (Perkinsus marinus - dermo), reproductive activity (including stage, fecundity, and juvenile recruitment), adult oyster density, and the faunal community associated with the oysters. The predominant source of variation was seasonal, with lesser contributions among sites, and in most cases, little or no effect of the habitat type. Oysters populations from each habitat recruit juvenile oysters, produce mature individuals, and contribute viable gametes at the same magnitude with similar seasonality. The associated faunal communities were also largely similar between habitats at any given site. Measures of oyster density, combined with estimates of the total available habitat, suggest that natural oyster reefs may represent only a small portion of the total oyster community in Tampa Bay, while oysters associated with mangrove habitats and seawalls are probably the most abundant in the bay. Additional mapping and quantification of these habitats would help to define their bay-wide ecosystem-services value. Restoration projects, though small in size relative to other habitats, do provide alternative and additional habitat with comparable value to other oyster-bearing habitats.

An artificial oyster reef constructed in Boca Ciega Bay, off of the War Veteran's Memorial Park, St. Petersburg, Florida, in 2005, was used to compare a mined shell material to the typical oyster shell substrate used in artificial reef projects as an alternative substrate and cultch material. Half of the reef's veneer was the fresh oyster shell and the other half was mined material. Experimental trays were deployed on top of the sediment along the leeward reef base and sampled quarterly to test the hypothesis that fresh shell is the preferential cultch material of the Eastern Oyster, Crassostrea virginica, promoting more oyster and epifaunal community development than the mined material. Monthly field observations along the reef face monitored the oyster community development on both substrates. The unanticipated influence of the reef's presence on the local current flows resulted in significant sediment loading on the reef. The sediment inundated and smothered the experimental trays over the course of the study, thereby converting the trays from hard substrate to soft bottom habitats. Any influence the different substrates might have had on community development was overwhelmed by sediment burial. Monthly field observations revealed positive oyster community development on both substrates. Live oyster abundance was significantly dissimilar between June and December 2006 on the fresh shell compared to the mined material (R = 0.241, p = 0.001). Epifaunal abundance showed even greater dissimilarity over the same time period (R = 0.474, p< [or] = 0.001). Greater abundances of large oysters were found on the fresh shell substrate due to an instability and deterioration of the larger pieces of mined material. A low replicate sample size of n = 3 leaves results from between month and between quarter sampling analyses open to interpretation. Though no definitive conclusions were drawn, the data from the community analyses provides useful information on the species inhabiting and utilizing oyster reefs in the Tampa Bay area.

Oyster reefs provide valuable ecosystemservices that contribute to coastal resilience. Unfortunately, many reefs have been degraded or removed completely, and there are increased efforts to restore oysters in many coastal areas. In particular, much attention has recently been given to the restoration of shellfish reefs along eroding shorelines to reduce erosion. Such fringing reef approaches, however, often lack empirical data to identify locations where reefs are most effective in reducing marsh erosion, or fully take into account habitat suitability. Using monitoring data from 5 separate fringing reef projects across coastal Louisiana, we quantify shoreline exposure (fetch + wind direction + wind speed) and reef impacts on shoreline retreat. Our results indicate that fringing oyster reefs have a higher impact on shoreline retreat at higher exposure shorelines. At higher exposures, fringing reefs reduced marsh edge erosion an average of 1.0 m y-1. Using these data, we identify ranges of shoreline exposure values where oyster reefs are most effective at reducing marsh edge erosion and apply this knowledge to a case study within one Louisiana estuary. In Breton Sound estuary, we calculate shoreline exposure at 500 random points and then overlay a habitat suitability index for oysters. This method and the resulting visualization show areas most likely to support sustainable oyster populations as well as significantly reduce shoreline erosion. Our results demonstrate how site selection criteria, which include shoreline exposure and habitat suitability, are critical to ensuring greater positive impacts and longevity of oyster reef restoration projects.

No description available.

Widely regarded as a keystone species and ecosystem engineer, the eastern oyster Crassostrea virginica plays a vital role in estuarine environments. Complex, three-dimensional oyster reefs act as havens for biodiversity and contribute to ecological processes. Recently, concern for this resource has arisen in Mosquito Lagoon, Florida, the southernmost limit along the Atlantic coast for undisturbed, intertidal reefs of C. virginica. Since the 1990s, intense recreational boating activity has caused atypical dead margins (mounds of disarticulated shells) to emerge on the seaward edges of oyster reefs located along major navigational channels. Once dead margins are formed, little is known about their influence on biotic composition and interactions on oyster reefs. This study focused on the affect of dead margins on: (1) mobile species biodiversity and distribution, (2) reef architecture, and (3) the affect of structural variables on predation of juvenile oysters. To determine if dead margins influenced the biodiversity of mobile species on oyster reefs, lift nets (1 m2) were deployed within Mosquito Lagoon for one year (June 2004 - June 2005). These nets (5/site) were deployed on the back-reef areas of six reefs (3 reference reefs and 3 reefs containing dead margins). To simulate reef habitat, one and a half liters of live oysters were placed within each net. Lift nets were checked monthly and surveyed for all mobile species. The resulting data were assimilated into a species inventory containing 65 species of fishes, mollusks, crustaceans, worms, and echinoderms. The two most abundant species present on reefs in Mosquito Lagoon were the big-claw snapping shrimp Alpheus heterochaelis, a filter-feeder, and the flat-back mud crab Eurypanopeus herbstii, a predator of oyster spat. Contrary to expections, analyses of community metrics showed that dead margins did not significantly affect the biodiversity of back-reef areas on oyster reefs. Modified lift nets (0.25 m2) were placed on six different oyster reefs (3 reference reefs and 3 containing dead margins) to test if dead margins affected the distribution of mobile species inhabiting oyster reefs. Nine nets were arranged to cover three separate areas of each reef: the fore-reef (3 nets), mid-reef (3 nets), and back-reef (3 nets). Half a liter of oyster shells were placed inside each net. These nets were checked weekly, for five weeks and species richness, density, and biomass were recorded. Analyses revealed that all community metrics were significantly higher on reference reefs than reefs affected with dead margins. Further, a significant drop in all three metrics was seen on the mid-reef area of affected reefs. The absence of species on this area is hypothesized to be due to a lack of water, shade, and habitat complexity. To document architectural differences, two types of transects were run along five reference reefs and five reefs with dead margins. First, quadrat transects determined the percent of live oysters, the percent of shell clusters, topographic complexity (using chain links), and the angle of shells on each reef type. Transect lines were stretched parallel to the water line and covered all three reef areas (fore-reef, mid-reef, and back-reef). The results showed reference reefs to have approximately four-fold more live oysters, approximately twice as many shell clusters, and significantly greater topographic complexity. Numbers of live oysters and shell clusters were greater on the fore-reef and back-reef areas of both reef types. Second, laser transects were used to record reef profiles and the slope of fore-reef areas. Transect lines were stretched perpendicular to the water line and every 20 cm the distance between the lagoon bottom and reef top was measured. Vertical reef profiles and fore-reef slopes were significantly different between reference reefs and reefs with dead margins. Dead margins compressed reef widths, increased center peaks, and increased slopes on the fore-reef area by two-fold. Lastly, field experiments were conducted to determine the affect of dead margins on the vulnerability of oyster spat to predation. Structural variables (e.g. shell orientation, single versus shell clusters, reef slope) were manipulated and effects on oyster mortality were observed. Three predators were tested: the blue crab Callinectes sapidus, the common mud crab Panopeus herbstii, and the Atlantic oyster drill Urosalpinx cinerea. Structural variables did not have a significant influence on oyster mortality; however, a significant difference was established between predators. Panopeus herbstii consumed the most juvenile oysters, followed by U. cinerea and then C. sapidus. Together, these findings document ecological implications of dead margins on C. virginica reefs and reinforce the urgent need for enhanced regulations and restoration. If the intensity of recreational boating remains unregulated, dead margins will continue to increase. Thus, in order to maintain the diversity and productivity of Mosquito Lagoon, it is crucial to fully understand how dead margins alter the biogenic habitat and biotic communities of oyster reefs.