Abiotic/Biological Interactions in Coastal Marine Communities: Insights from an Alaskan Fjord

Interactions among multi-scale coastal marine ecosystem processes can be expected to play large roles in and interact with biological processes as stresses increase, potentially allowing interfering processes (including biological interactions) to become more prevalent. Retrospective analyses of intertidal (1988–1992) and subtidal (1971–2012) species compositions from a long-term ecological research program in Port Valdez, Alaska evaluated associations between benthic community structure and physical conditions to better understand interactions between regional to local processes on flora and fauna. Low salinity, habitat structure (varying from mudflats to rocky shores over a distance of <18 km), and suspended sediments contributed to intertidal community structure via elimination of predators from low-salinity prey refugia. Subtidal communities demonstrate adjustments by macrofauna to sedimentation with smaller, disturbance-tolerant fauna towards the head of the fjord as well as effects from depth-related covariates. Shared ecological processes result in comparable community trends in subtidal and intertidal habitats among subarctic and arctic fjords and similarly among coastal environments of the North Pacific. Control exerted by interactions among climatic, oceanographic, and local processes interacting with biota contributes to the direction and length of recovery from disturbance events and environmental changes. Feedbacks, mediation of recovery by additional processes, and strengths of interactions also play important roles in determining interaction outcomes. Interactions among local, regional, and global-scale processes may become critical sources of change as global ecosystem transitions through new climate states.     

Patterns of Plant Diversity in Georgia and Texas Salt Marshes

A fundamental question in ecology is how biological interactions and biogeographic processes interact to determine the biodiversity of local sites. We quantified patterns of plant species diversity on transects across elevation at 59 salt marsh sites in Georgia and 49 sites in Texas. Although these regions have similar climates and floras, we anticipated that diversity might differ because of differences in tidal regime. Diversity was measured at global, regional, site, and plot scales to consider processes occurring at all levels. Species pools were similar between regions. Texas had greater diversity at the site and plot scales, suggesting that processes occurring at the site scale differed. The greater diversity of Texas sites and plots was associated with wider distributions of individual species across the marsh landscape and proportionally more middle marsh (a high diversity zone) and less low marsh (a low diversity zone) than in Georgia marshes. Preliminary data suggested that these differences were not due to differences in salinity regime or standing biomass between regions, leaving differences in tidal regime as the most plausible hypothesis accounting for differences in plant diversity. We speculate that the less-predictable tidal regime in Texas leads to temporal variation in abiotic conditions that limit the ability of any one species to competitively exclude others from particular marsh zones.     

Spatial differences in macroinvertebrate communities in intertidal seagrass habitats and unvegetated sediment in three New Zealand estuaries

This study investigated macroinvertebrate community composition in seagrass beds at a range of spatial scales, with an emphasis on the transition between vegetated and unvegetated sediment. At four intertidal sites in three New Zealand estuaries (Whangamata, Wharekawa, and Whangapoua Harbours), a large continuous bed of seagrass (Zostera capricorni) was selected with adjacent unvegetated sediment. Macroinvertebrate community composition and biomass, as well as sediment characteristics, were determined at sampling locations 1 and 50 m inside seagrass beds, and 1, 10, and 50 m outside seagrass beds. Analysis of univariate measures of community composition (total abundance, number of species, and diversity) and total biomass indicated significant differences among sites and sampling locations, but contrary to many previous studies these measures were not higher inside than outside the seagrass beds. Multivariate analysis indicated that sites with high seagrass biomass supported a similar community composition. The remaining sampling locations were clustered by site, but there were also significant differences in community composition among sampling locations within a site. There were distinctive communities at the edge of seagrass beds at sites with high seagrass biomass, and evidence that the effects of seagrass beds may extend into the unvegetated sediment. At the low seagrass biomass site there was no evidence of any edge effects, although community composition differed inside and outside the bed. Differences in community composition were driven primarily by small changes in the relative abundance of the dominant taxa. At high seagrass biomass sites the absence of deep-burrowing polychaetes and low numbers of bivalves suggests that one possible mechanism underlying the observed variation in community composition was inhibition by the dense root-rhizome mat. The results of this study emphasize the need to consider the linkages between habitats in heterogeneous estuarine landscapes and how those linkages vary among sites, if the structure and functioning of macroinvertebrate communities in seagrass habitats are to be understood.     

Recolonization of Intertidal Infauna in Relation to Organic Deposition at an Oyster Farm in Atlantic Canada—A Field Experiment

A field experiment was carried out to investigate the patterns of macrobenthic recolonization and to determine the effects of biodeposition on benthic communities at an intertidal oyster culture site in New Brunswick, Canada. Total organic deposition in azoic organic-free sediment trays was generally higher within the farm compared to reference sites. Two weeks after deployment of trays, total organic content had reached 1.1%. The abundance, species number, and diversity of the macrobenthic community were positively correlated with the total organic content in the experimental trays, but the correlations between community parameters and organic content were negative in the ambient sediment. The results suggest that organic matter in sediment may have positive effects on macrobenthic infauna at low levels as an additional food source but may be harmful to benthic animals at high levels. This study also indicates that location in the intertidal zone is a major parameter affecting the community structure of macrobenthic colonization.     

Historical Comparison of Fish Community Structure in Lower Chesapeake Bay Seagrass Habitats

Seagrass beds provide important habitat for fishes and invertebrates in many regions around the world. Accordingly, changes in seagrass coverage may affect fish communities and/or populations, given that many species utilize these habitats during vulnerable early life history stages. In lower Chesapeake Bay, seagrass distribution has contracted appreciably over recent decades due to decreased water clarity and increased water temperature; however, effects of changing vegetated habitat on fish community structure have not been well documented. We compared fish community composition data collected at similar seagrass sites from 1976–1977 and 2009–2011 to investigate potential changes in species richness, community composition, and relative abundance within these habitats. While seagrass coverage at the specific study sites did not vary considerably between time periods, contemporary species richness was lower and multivariate analysis showed that assemblages differed between the two datasets. The majority of sampled species were common to both datasets but several species were exclusive to only one dataset. For some species, relative abundances were similar between the two datasets, while for others, there were notable differences without directional uniformity. Spot (Leiostomus xanthurus) and northern pipefish (Syngnathus fuscus) were considerably less abundant in the contemporary dataset, while dusky pipefish (Syngnathus floridae) was more abundant. Observed changes in community structure may be more attributable to higher overall bay water temperature in recent years and other anthropogenic influences than to changes in seagrass coverage at our study sites.     

Patterns of seagrass community response to local shoreline development

Three quarters of the global human population will live in coastal areas in the coming decades and will continue to develop these areas as population density increases. Anthropogenic stressors from this coastal development may lead to fragmented habitats, altered food webs, changes in sediment characteristics, and loss of near-shore vegetated habitats. Seagrass systems are important vegetated estuarine habitats that are vulnerable to anthropogenic stressors, but provide valuable ecosystem functions. Key to maintaining these habitats that filter water, stabilize sediments, and provide refuge to juvenile animals is an understanding of the impacts of local coastal development. To assess development impacts in seagrass communities, we surveyed 20 seagrass beds in lower Chesapeake Bay, VA. We sampled primary producers, consumers, water quality, and sediment characteristics in seagrass beds, and characterized development along the adjacent shoreline using land cover data. Overall, we could not detect effects of local coastal development on these seagrass communities. Seagrass biomass varied only between sites, and was positively correlated with sediment organic matter. Epiphytic algal biomass and epibiont (epifauna and epiphyte) community composition varied between western and eastern regions of the bay. But, neither eelgrass (Zostera marina) leaf nitrogen (a proxy for integrated nitrogen loading), crustacean grazer biomass, epifaunal predator abundance, nor fish and crab abundance differed significantly among sites or regions. Overall, factors operating on different scales appear to drive primary producers, seagrass-associated faunal communities, and sediment properties in these important submerged vegetated habitats in lower Chesapeake Bay.     

Tidal Freshwater Marshes Harbor Phylogenetically Unique Clades of Sulfate Reducers That Are Resistant to Climate-Change-Induced Salinity Intrusion

Rates of sea level rise associated with climate change are predicted to increase in the future, potentially altering ecosystems at all ecological levels. Sea level rise can increase the extent of brackish water intrusion into freshwater ecosystems, which in turn can affect the structure and function of resident microbial communities. In this study, we performed a year-long mesocosm experiment using intact tidal freshwater marsh sediment cores to examine the effect of a 5-part per thousand (ppt) salinity increase on the diversity and community composition of sulfate-reducing prokaryotes. We used a clone library approach to examine the dsrA gene, which encodes an important catalytic enzyme in sulfate reduction. Our results indicate that tidal freshwater marshes contain extremely diverse communities of sulfate-reducing bacteria. Members of these communities were, on average, only 71 % similar to known cultured sulfate reducers and 81 % similar to previously sequenced environmental clones. Salinity and associated increases in sulfate availability did not significantly affect the diversity or community composition of sulfate-reducing prokaryotes. However, carbon quality and quantity, which correlated with depth, were found to be the strongest drivers of sulfate-reducing community structure. Our study demonstrates that the sulfate-reducing community in tidal freshwater marsh sediments appears resistant to increased salinity in the face of sea level rise. Additionally, the microorganisms that comprise this sulfate-reducing community appear to be unique to tidal freshwater marsh sediments and may represent novel lineages of previously undescribed sulfate reducers.     

Seagrass patches and landscapes: The influence of wind-wave dynamics and hierarchical arrangements of spatial structure on macrofaunal seagrass communities

The spatial arrangement of seagrass beds varies from scales of centimeters to meters (rhizomes, shoot groups), meters to tens of meters (patches), to tens of meters to kilometers (seagrass landscapes). In this study we examine the role of patch scale (patch size, seagrass % cover, seagrass biomass), landscape scale (fractal geometry, patch isolation) and wave exposure (mean wind velocity and exceedance) variables in influencing benthic community composition in seagrass beds at three intertidal sites in northern New Zealand (two sites in Manukau Harbour and one site in Whangapoua Harbour). Analysis of univariate community measures (numbers of individuals and species, species richness, diversity and evenness) and multivariate analyses indicated that there were significant differences in community composition inside and outside of seagrass patches at each of the three sites. Partialling out the spatial and temporal components of the ecological variation indicated that seagrass patch variables explained only 3–4% of the patch scale variation in benthic community composition at each of the sites. The temporal component was more important, explaining 12–14% of the variation. The unexplained variation was high (about 75%) at all three sites, indicating that other factors were influencing variation in community composition at the scale of the patches, or that there was a large amount of stochastic variation. Landscape and wave exposure variables explained 62.5% of the variation in the species abundance data, and the unexplained variation at the landscape level was correspondingly low (12%). Canonical correspondence analysis produced an ordination that suggests that, while mean wind velocity and exceedance were important in explaining the differences between the communities in the two harbours, spatial patterning of the habitat, primarily fractal dimension, and secondarily patch isolation (or some factors that were similarly correlated), were important in contributing to variability in community composition at the two sites in Manukau Harbour. This study suggests that spatial patterning of seagrass habitat at landscape scales, independent of the patch scale characteristics of the seagrass beds, can affect benthic community composition. Community composition inside and outside seagrass habitats involves responses to seagrass bed structure at a series of hierarchical levels, and we need to consider more than one spatial scale if we are to understand community dynamics in seagrass habitats.     

Evidence for Declines in the Native Leukoma staminea as a Result of the Intentional Introduction of the Non-native Venerupis philippinarum in Coastal British Columbia,Canada

On the west coast of British Columbia (BC), Canada, the intertidal regions are under ever increasing pressure to be used primarily for near-bottom mariculture practices. These include seeding the foreshore with the nonindigenous Venerupis philippinarum (Manila clam) followed by the application of antipredator netting. The Manila is confamilial with the indigenous Leukoma staminea (littleneck clam), and seeding could possibly provide a competitive advantage for the Manila leading to the extirpation of the littleneck within coastal BC. Over two survey years, nine and seven farm-reference paired beaches (18 and 14 beaches) from three geographically distinct regions of BC were sampled for abundances and size class structure of the Manila and littleneck clam. Several lines of evidence suggest that the Manila is replacing the native littleneck; (1) comparison of average abundances of the littleneck versus Manila showed a significantly greater number of Manila on both farmed and reference sites across all three regions (p?<?0.05; years I and II); (2) as distance between farmed and reference sites increased, numbers of littlenecks on reference sites also increased suggesting that close proximity to farmed sites increases the effect of seeding on numbers of the native species; (3) comparison of percent similarity of the population structure as determined by size class distribution for the Manila versus the littleneck clam indicated that intertidal reference sites in close proximity to farmed sites tended to be more similar to each other with respect to similar Manila population structure versus that of the littleneck (r?=?0.4; p?=?0.08); (4) within the region where active farming is the most aggressive (Baynes Sound), Manila clams are the dominant bivalve on all sampled intertidal regions; and (5) where the dispersal of “wild” (not-seeded) Manila clam is prevented because of thermal tolerance limits, the littleneck is the dominant bivalve. Ecological consequences of such species replacement on intertidal function are as yet known.     

The six capacities of community resilience: evidence from three small Texas communities impacted by Hurricane Harvey

This article builds upon disaster scholarship that suggests community resilience is driven by six capacities: social, economic, physical, human, institutional, and environmental. Together, these capacities constitute a conceptual framework that can be used to investigate and assess community resilience. While recent scholarship has provided insights into how resilience operates in large communities, there remain questions about whether this conceptual framework is appropriate for the study of resilience in small communities. To narrow this knowledge gap, we conducted interviews with twenty-six subjects from three small Texas communities affected by Hurricane Harvey: City of Dickinson; City of Port Aransas; and Town of Refugio. Analysis of the interview data confirms that the six capacities of resilience provide an appropriate framework for the investigation of resilience in small communities. Given the complex and dynamic nature of community resilience, the findings also suggest that it is unlikely policymakers will be able to develop a unified policy solution for hazard events that is appropriate for all communities. Rather, policymakers need to consider community-based resilience solutions, driven by local strengths and weaknesses, that facilitate the reduction of risks associated with hazard events.

     

Landslide disaster risk awareness in Mexico: community access to mapping at local scale

Recent investigations have sought to understand the spatial-temporal distribution of landslides in Teziutlán, Puebla, a municipality historically affected by landslides. The latest initiative, under the umbrella of the ICL-IPL Project “Landslide disaster risk communication in mountain areas,” was the publication of a book of Atlas type comprising a collection of 142 maps and their corresponding explanatory texts that included a context analysis of landslide disaster risk drivers at various scales, from regional to local. This paper aims to recognise and address the necessity to further enhance the guiding principle of the Sendai Framework for Disaster Risk Reduction to focus on the understanding of disaster risk drivers at local level, for the determination of measures to reduce disaster risk. We present an initial contribution to promote landslide disaster risk awareness in the urban area of Teziutlán by providing to the community direct access to maps of landslide disaster risk at local scale; this is a first step towards the establishment of a robust strategy to communicate landslide risk in the long term. Effective implementation calls for decreasing vulnerability and exposure. Beyond contexts of vulnerability reflected by social, economic, cultural, political, and institutional conditions, it may be difficult to picture the spatial interactions of exposure of communities, assets, and the environment because the means of analysing spatial relationships between society and nature are not commonly available in mountain areas. Therefore, for people to better understand risk, maps of landslide susceptibility and risk exposure present a good way for the inhabitants to familiarise themselves with the spatial context of the dynamics in which they are immersed.     

Relationships between microbial communities and environmental parameters at sites impacted by mining of volcanogenic massive sulfide deposits,Prince William Sound,Alaska

The relations among geochemical parameters and sediment microbial communities were examined at three shoreline sites in the Prince William Sound, Alaska, which display varying degrees of impact by acid-rock drainage (ARD) associated with historic mining of volcanogenic massive sulfide deposits. Microbial communities were examined using total fatty acid methyl esters (FAMEs), a class of compounds derived from lipids produced by eukaryotes and prokaryotes (bacteria and Archaea); standard extraction techniques detect FAMEs from both living (viable) and dead (non-viable) biomass, but do not detect Archaeal FAMEs. Biomass and diversity (as estimated by FAMEs) varied strongly as a function of position in the tidal zone, not by study site; subtidal muds, Fe oxyhydroxide undergoing biogenic reductive dissolution, and peat-rich intertidal sediment had the highest values. These estimates were lowest in acid-generating, intertidal zone sediment; if valid, the estimates suggest that only one or two bacterial species predominate in these communities, and/or that Archeal species are important members of the microbial community in this sediment.     

Responses of estuarine phytoplankton communities to nitrogen form and mixing using microcosm bioassays

We examined the effects of different forms of nitrogen and mixed versus static conditions on the structure and function of natural Neuse River estuary phytoplankton communities incubated in 66-liter microcosms in March, May, August, and November 1999. Significant differences were found between effects of mixed versus static treatments in three of four experiments, but no differences were observed between effects of different forms of nitrogen. Mixed incubations resulted in higher contributions of diatoms to total community biomass (measured as chlorophylla) than in static tanks in May. Significantly higher rates of carbon fixation were also observed, likely due to increased suspension of diatoms in surface (illuminated) layers of the tanks. In August, we found significantly higher abundances of cyanobacteria, total community biomass, and rates of carbon fixation in static tanks than in tanks that were mixed. In November, static incubations showed significantly higher abundances of cryptophytes resulting in higher total community biomass and rates of carbon fixation in static tanks than in mixed tanks. Nitrogen additions significantly increased total community biomass relative to controls in May and August, indicating that the communities were nitrogen-limited at these times. We conclude that while nitrogen additions may result in increases in phytoplankton biomass when nitrogen is limiting, phytoplankton community structure in the Neuse River Estuary may be determined more by the hydrodynamics of the system (mixing versus stratification) than by the form of nitrogen available for growth.     

Ecotones as Indicators of Changing Environmental Conditions: Rapid Migration of Salt Marsh–Upland Boundaries

Ecotones, the narrow transition zones between extensive ecological systems, may serve as sensitive indicators of climate change because they harbor species that are often near the limit of their physical and competitive tolerances. We investigated the ecotone between salt marsh and adjacent upland at Elkhorn Slough, an estuary in California, USA. Over a period of 10 years, we monitored movement of the ecotone–upland boundary, plant community structure, and physical factors likely to drive ecotone response. At three undiked sites, the ecotone boundary migrated about 1 m landward, representing a substantial shift for a transition zone that is only a few meters wide. Analysis of potential correlates of this upward migration suggests that it was driven by increased tidal inundation. Mean sea level did not increase during our study, but inundation at high elevations did. While the ecotone boundary responded dynamically to interannual changes in inundation at these undiked sites, the plant community structure of the ecotone remained stable. At two diked sites, we observed contrasting patterns. At one site, the ecotone boundary migrated seaward, while at the other, it showed no consistent trend. Diking appears to eliminate natural sensitivity of the ecotone boundary to interannual variation in oceanic and atmospheric drivers, with local factors (management of water control structures) outweighing regional ones. Our study shows that the marsh–upland ecotone migrated rapidly in response to environmental change while maintaining stable plant community structure. Such resilience, stability, and rapid response time suggest that the marsh–upland ecotone can serve as a sensitive indicator of climate change.     

The Response of Macrobenthic Communities to Environmental Variability in Tropical Coastal Waters

The relative contributions of spatial and temporal fluctuations are different in shaping natural communities in a tropical coastal/estuarine system. Understanding how coastal communities respond to these fluctuations is still equivocal, and thus, available data are rare. Here, multiple analytical approaches were used to identify key spatial and temporal factors, and to quantify their relative roles in shaping a macrobenthic community through space (contamination degree, physical parameters, and sediment characteristics) and time (climatic factors, season, and year). A dataset of eight sampling times was analyzed over a period of 2 years, in which macrobenthic species abundances were sampled. A total of 33 species were identified, including 18 bivalves, 5 gastropods, and 4 crustaceans. The other taxa were less diverse. The results show that there were no significant temporal changes of macrobenthic community structure, but spatial changes were significant and synchronized with environmental factors (i.e., sediment characteristics, water depth, and the distance from anthropogenic sources). This study demonstrates that spatial factors played a primary role in structuring of macrobenthic assemblages, whereas the influence of temporal factors appeared less across geographically distinct sites. Thus, temporal variation of a coastal macrobenthic community appears to be controlled by partly different processes at different scales.     

Effects of Local Shoreline and Subestuary Watershed Condition on Waterbird Community Integrity: Influences of Geospatial Scale and Season in the Chesapeake Bay

In many coastal regions throughout the world, there is increasing pressure to harden shorelines to protect human infrastructures against sea level rise, storm surge, and erosion. This study examines waterbird community integrity in relation to shoreline hardening and land use characteristics at three geospatial scales: (1) the shoreline scale characterized by seven shoreline types: bulkhead, riprap, developed, natural marsh, Phragmites-dominated marsh, sandy beach, and forest; (2) the local subestuary landscape scale including land up to 500 m inland of the shoreline; and (3) the watershed scale >500 m from the shoreline. From 2010 to 2014, we conducted waterbird surveys along the shoreline and open water within 21 subestuaries throughout the Chesapeake Bay during two seasons to encompass post-breeding shorebirds and colonial waterbirds in late summer and migrating and wintering waterfowl in late fall. We employed an Index of Waterbird Community Integrity (IWCI) derived from mean abundance of individual waterbird species and scores of six key species attributes describing each species’ sensitivity to human disturbance, and then used this index to characterize communities in each subestuary and season. IWCI scores ranged from 14.3 to 19.7. Multivariate regression model selection showed that the local shoreline scale had the strongest influence on IWCI scores. At this scale, percent coverage of bulkhead and Phragmites along shorelines were the strongest predictors of IWCI, both with negative relationships. Recursive partitioning revealed that when subestuary shoreline coverage exceeded thresholds of approximately 5% Phragmites or 8% bulkhead, IWCI scores decreased. Our results indicate that development at the shoreline scale has an important effect on waterbird community integrity, and that shoreline hardening and invasive Phragmites each have a negative effect on waterbirds using subestuarine systems.     

Participation in payments for ecosystem services: Case studies from the Lacandon rainforest, Mexico

Understanding people’s willingness to participate in projects and programmes of payments for ecosystem services (PES) has not been a key analytical concern of the scholarly literature around this new field of environmental policy and practice. This paper analyses participation in four communities benefiting from payments for biodiversity and carbon fixation in Mexico, and contrasts the results for each case with neighbouring communities that do not receive payments. We take a holistic approach that accounts for procedural rules, actors’ interactions, institutions and values, and individuals’ characteristics. We show that the nature of PES rules and the effectiveness of communication with government officers and NGOs influence resource managers’ ability and willingness to participate. We highlight community size, resource managers’ ability to diversify livelihood activities and local perspectives on the conservation of common forests, particularly sacred values and intergenerational concerns on forest conservation, as critical participation drivers. This analysis provides insights on why and how these new institutions may be attractive for some resource managers and permits to draw some recommendations for the future design of PES projects and programmes.     

Do Spartina maritima Plantations Enhance the Macroinvertebrate Community in European Salt Marshes?

Ecological restoration of salt marshes using plantations may enhance the macroinvertebrate community, but little is known about the development of benthic macroinvertebrates after ecological engineering projects in European salt marshes. This study analyzed the environment and the macroinvertebrate community in European salt marshes 3 years after restoration using Spartina maritima plantations in comparison with non-restored and preserved marshes in Odiel Marshes (Southwest Iberian Peninsula). We hypothesized that planting Spartina maritima on intertidal mudflats would increase species richness and diversity (Shannon–Weaver index) of the benthic macroinvertebrate community by increasing environmental heterogeneity, providing feeding resources and improving sediments characteristics. Benthic macrofauna samples (composed mainly of annelids, crustaceans, and mollusks) were sampled in plots of 20 cm?×?25 cm to 5 cm depth between +1.8 and +3.0 m above Spanish Hydrographic Zero. Sediment organic matter content, bulk density, pH, and redox potential were the variables that best explained macroinvertebrate distribution. Restored marshes achieved similar diversity and even higher specific richness than preserved marshes, although with differences in species composition. Non-restored marshes showed the lowest diversity. Restored and preserved marshes did not differ in total abundance or biomass of macroinvertebrates, both being higher than in non-restored marshes. The macroinvertebrate communities in preserved and non-restored marshes showed the largest difference in taxa composition, with restored marshes occupying an intermediate position. Salt marsh restoration using S. maritima increased the complexity (ecological diversity and species richness) and abundance of the benthic macroinvertebrate community. Our study offers new information about the role of salt marsh plants in mediating faunal communities via ecological engineering projects.     

Comparative Phylogeography of North American Atlantic Salt Marsh Communities

Identifying differential population structure within metacommunities is key toward describing the mechanisms that maintain biodiversity in natural systems. At both local and regional scales on the North American Atlantic coast, we assessed phylogeographic and genetic diversity patterns of six common salt marsh invertebrates using equivalent sampling schemes and sequence data from the same mitochondrial locus. In general, our results suggest little genetic structure across four previously sampled biogeographic regions and a slight increase in genetic diversity from northern to southern areas; however, two of the species (Geukensia demissa and Uca pugilator) exhibited significant differentiation between the northernmost populations and other regions, consistent with a number of previous studies. Although the minimal genetic structure recovered in this community is consistent with expectations based on the larval life history of the species examined, confirmation of this result suggests that latitudinal shifts in ecological interactions in salt marsh systems are environmentally driven, rather than due to heritable adaptation.     

Biological Assessment of Eastern Oysters (Crassostrea virginica) Inhabiting Reef,Mangrove, Seawall,and Restoration Substrates

The eastern oyster, Crassostrea virginica, plays an essential functional role in many estuarine ecosystems on the east and Gulf coasts of the USA. Oysters form biogenic reefs but also live on alternative intertidal substrates such as artificial surfaces and mangrove prop roots. The hypothesis tested in this study was that non-reef-dwelling oysters (i.e., those inhabiting mangrove, seawall, or restoration substrates) were similar to their reef-dwelling counterparts based upon a suite of biological parameters. The study was carried out at six sites in three zones in Tampa Bay on the west coast of Florida using monthly samples collected from October 2008–September 2009. The timing of gametogenesis and spawning, fecundity, and juvenile recruitment were the same for oysters in all four habitats. Oyster size (measured as shell height), density, and Perkinsus marinus infection intensity and prevalence varied among habitats. This study indicates that oysters on mangroves, seawalls, and oyster restoration substrates contribute larvae, habitats for other species, and likely other ecosystem benefits similar to those of intertidal oyster reefs in Tampa Bay. Oysters from alternative intertidal substrates should be included in any system wide studies of oyster abundance, clearance rates, and the provision of alternate habitats, especially in highly developed estuaries.