Introduction to the Proceedings of the Blue Crab Recruitment Symposium

The blue crab, Callinectes sapidus Rathbun, is found in all major coastal habitats along the mid-Atlantic, South Atlantic and Gulf of Mexico coasts of the United States, including large embayments, barrier island-lagoonal systems, and coastal marsh, mangrove and seagrass systems. Ecologically important, blue crabs may control abundances of other estuarine benthic species (Hines et aI., 1990). The blue crab also supports valuable commercial and recreational fisheries from New Jersey to Texas; commercial landings of 249.3 million pounds of hard blue crabs in 1993 had a dockside value of 126.6 million dollars (NMFS, 1994). Blue crab stocks vary interannually within and between regions as reflected in fishery catch records, which have been compiled since the early 1900s, and in fisheryindependent data sets. This variability apparently is unrelated to fishing pressure and has been attributed to environmental influences on blue crab recruitment. Published studies of blue crab biology date back to the turn of the century (Hay, 1905), but our understanding of the early life history of the species has been markedly refined over the past 3 decades. The complete larval development (7 zoea and I megalopa) of the blue crab was not described until 1959 (Costlow and Bookhout, 1959), and early accounts of blue crab life history suggested that the larval stages were retained within estuaries (Churchill, 1919; Van Engel, 1958). During the 1960s and early 1970s, however, studies of larval/postlarval distributions indicated that blue crab larvae might not be retained in estuaries but instead are exported to coastal waters with subsequent return by postlarvae (megalopae) or juveniles (Nichols and Keney, 1963; Tagatz, 1968; Dudley and Judy, 1971; King, 1971; Williams, 1971; Sandifer, 1975)

A Systematic Review of How Multiple Stressors From an Extreme Event Drove Ecosystem-Wide Loss of Resilience in an Iconic Seagrass Community

A central question in contemporary ecology is how climate change will alter ecosystem structure and function across scales of space and time. Climate change has been shown to alter ecological patterns from individuals to ecosystems, often with negative implications for ecosystem functions and services. Furthermore, as climate change fuels more frequent and severe extreme climate events (ECEs) like marine heatwaves (MHWs), such acute events become increasingly important drivers of rapid ecosystem change. However, our understanding of ECE impacts is hampered by limited collection of broad scale in situ data where such events occur. In 2011, a MHW known as the Ningaloo Niño bathed the west coast of Australia in waters up to 4°C warmer than normal summer temperatures for almost 2 months over 1000s of kilometers of coastline. We revisit published and unpublished data on the effects of the Ningaloo Niño in the seagrass ecosystem of Shark Bay, Western Australia (24.6–26.6° S), at the transition zone between temperate and tropical seagrasses. Therein we focus on resilience, including resistance to and recovery from disturbance across local, regional and ecosystem-wide spatial scales and over the past 8 years. Thermal effects on temperate seagrass health were severe and exacerbated by simultaneous reduced light conditions associated with sediment inputs from record floods in the south-eastern embayment and from increased detrital loads and sediment destabilization. Initial extensive defoliation of Amphibolis antarctica, the dominant seagrass, was followed by rhizome death that occurred in 60–80% of the bay\u27s meadows, equating to decline of over 1,000 km2 of meadows. This loss, driven by direct abiotic forcing, has persisted, while indirect biotic effects (e.g., dominant seagrass loss) have allowed colonization of some areas by small fast-growing tropical species (e.g., Halodule uninervis). Those biotic effects also impacted multiple consumer populations including turtles and dugongs, with implications for species dynamics, food web structure, and ecosystem recovery. We show multiple stressors can combine to evoke extreme ecological responses by pushing ecosystems beyond their tolerance. Finally, both direct abiotic and indirect biotic effects need to be explicitly considered when attempting to understand and predict how ECEs will alter marine ecosystem dynamics

Utilization Of A Seagrass Meadow And Tidal Marsh Creek By Blue Crabs Callinectes-sapidus II. Spatial And Temporal Patterns Of Molting

Blue crabs were collected weekly from a lower Chesapeake Bay seagrass meadow and adjacent tidal marsh creek over 2 months (July-August 1987) and molt staged. Molting activity, determined from a total of I ,220 crabs, was greater in the grassbed than in the marsh creek, and greater for small crabs and females. The difference between the two habitats in molting activity decreased from the first to the second month of sampling, possibly in response to seasonal decline in seagrass biomass. The proportion of small (\u3c70 mm) females in both habitats was greatest on full moons. There was a lunar rhythm of molting activity by large crabs (2:70 mm), with peak molting activity on fuIl moons. SmaIl crabs demonstrated a similar, but nonsignificant rhythm of molting. We suggest that blue crabs approaching ecdysis aggregate in seagrass meadows, taking advantage of the refuge from predation that this structurally complex habitat affords. Lunar rhythmicity of molting activity may further reduce predation mortality through a dilution effect

Linking water quality to living resources in a mid-Atlantic lagoon system, USA

The mid-Atlantic coastal bays are shallow coastal lagoons, separated from the Atlantic Ocean by barrier sand islands with oceanic exchanges restricted to narrow inlets. The relatively poor flushing of these lagoon systems makes them susceptible to eutrophication resulting from anthropogenic nutrient loadings. An intensive water quality and seagrass monitoring program was initiated to track ecological changes in the Maryland and Virginia coastal bays. The purpose of this study was to analyze existing monitoring data to determine status and trends in eutrophication and to determine any associations between water quality and living resources. Analysis of monitoring program data revealed several trends: (1) decadal decreases in nutrient and chlorophyll concentrations, followed by recently increasing trends; (2) decadal increases in seagrass coverage, followed by a recent period of no change; (3) blooms of macroalgae and brown tide microalgae; and (4) exceedance of water quality thresholds: chlorophyll a (15 mu g/L), total nitrogen (0.65 mg/L or 46 mu mol/L), total phosphorus (0.037 mg/L or 1.2 mu mol/L), and dissolved oxygen (5 mg/L) in many areas within the Maryland coastal bays. The water quality thresholds were based on habitat requirements for living resources (seagrass and fish) and used to calculate a water quality index, which was used to compare the bay segments. Strong gradients in water quality were correlated to changes in seagrass coverage between segments. These factors indicate that these coastal bays are in a state of transition, with a suite of metrics indicating degrading conditions. Continued monitoring and intensified management will be required to avert exacerbation of the observed eutrophication trends. Coastal lagoons worldwide are experiencing similar degrading trends due to increasing human pressures, and assessing status and trends relative to biologically relevant thresholds can assist in determining monitoring and management priorities and goals

Species-wide distribution of highly polymorphic minisatellite markers suggests past and present genetic exchanges among house mouse subspecies

Global analysis of four minisatellite loci in House Mouse reveals unexpected long-range gene flow between populations and subspecies

Restoring Coastal Plants to Improve Global Carbon Storage: Reaping What We Sow

Long-term carbon capture and storage (CCS) is currently considered a viable strategy for mitigating rising levels of atmospheric CO2 and associated impacts of global climate change. Until recently, the significant below-ground CCS capacity of coastal vegetation such as seagrasses, salt marshes, and mangroves has largely gone unrecognized in models of global carbon transfer. However, this reservoir of natural, free, and sustainable carbon storage potential is increasingly jeopardized by alarming trends in coastal habitat loss, totalling 30–50% of global abundance over the last century alone. Human intervention to restore lost habitats is a potentially powerful solution to improve natural rates of global CCS, but data suggest this approach is unlikely to substantially improve long-term CCS unless current restoration efforts are increased to an industrial scale. Failure to do so raises the question of whether resources currently used for expensive and time-consuming restoration projects would be more wisely invested in arresting further habitat loss and encouraging natural recovery

Wanted dead or alive : high diversity of macroinvertebrates associated with living and ’dead’ Posidonia oceanica matte

The Mediterranean endemic seagrass Posidonia oceanica forms beds characterised by a dense leaf canopy and a thick root-rhizome ‘matte’. Death of P. oceanica shoots leads to exposure of the underlying matte, which can persist for many years, and is termed ‘dead’ matte. Traditionally, dead matte has been regarded as a degraded habitat. To test whether this assumption was true, the motile macroinvertebrates of adjacent living (with shoots) and dead (without shoots) matte of P. oceanica were sampled in four different plots located at the same depth (5–6 m) in Mellieha Bay, Malta (central Mediterranean). The total number of species and abundance were significantly higher (ANOVA; P<0.05 and P<0.01, respectively) in the dead matte than in living P. oceanica matte, despite the presence of the foliar canopy in the latter. Multivariate analysis (MDS) clearly showed two main groups of assemblages, corresponding to the two matte types. The amphipods Leptocheirus guttatus and Maera grossimana, and the polychaete Nereis rava contributed most to the dissimilarity between the two different matte types. Several unique properties of the dead matte contributing to the unexpected higher number of species and abundance of motile macroinvertebrates associated with this habitat are discussed. The findings have important implications for the conservation of bare P. oceanica matte, which has been generally viewed as a habitat of low ecological value.peer-reviewe

Seagrass Canopy Photosynthetic Response Is a Function of Canopy Density and Light Environment: A Model for Amphibolis griffithii

A three-dimensional computer model of canopies of the seagrass Amphibolis griffithii was used to investigate the consequences of variations in canopy structure and benthic light environment on leaf-level photosynthetic saturation state. The model was constructed using empirical data of plant morphometrics from a previously conducted shading experiment and validated well to in-situ data on light attenuation in canopies of different densities. Using published values of the leaf-level saturating irradiance for photosynthesis, results show that the interaction of canopy density and canopy-scale photosynthetic response is complex and non-linear, due to the combination of self-shading and the non-linearity of photosynthesis versus irradiance (P-I) curves near saturating irradiance. Therefore studies of light limitation in seagrasses should consider variation in canopy structure and density. Based on empirical work, we propose a number of possible measures for canopy scale photosynthetic response that can be plotted to yield isoclines in the space of canopy density and light environment. These plots can be used to interpret the significance of canopy changes induced as a response to decreases in the benthic light environment: in some cases canopy thinning can lead to an equivalent leaf level light environment, in others physiological changes may also be required but these alone may be inadequate for canopy survival. By providing insight to these processes the methods developed here could be a valuable management tool for seagrass conservation during dredging or other coastal developments