EFFECTS OF PREDATOR FORAGING BEHAVIOR ON PATTERNS OF PREY MORTALITY IN MARINE SOFT BOTTOMS

This study links spatial and seasonal patterns of mortality of the hard clam, Mercenaria mercenaria (L.), in marine soft bottoms with the predation rates and habitat use of its main predator, the blue crab, Callinectes sapidus Rathbun. Patterns of predation on tethered juvenile clams exposed to the natural assemblage of predators were compared among different habitat types in fall and summer. Between-habitat patterns of predation on clams varied with season. In fall, predation on tethered clams was greater in subtidal sand bottoms and just inside the edge of intertidal salt marshes than in intertidal sand flats. In summer, predation on clams was similar in all habitats. Experiments conducted in field enclosures showed that: (a) individual crabs spent more time in the salt marsh habitat than in intertidal sand flats; (b) crab individuals placed in a sand bottom habitat had greater predation rates in high-density prey patches than in low-density patches; (c) individuals had greater predation rates in prey patches located just inside the edge of salt marshes than in intertidal sand flats, when prey density was held constant between the two habitats; (d) at intermediate and high crab densities predation mortality of clams was similar between vegetated and unvegetated habitats; (e) both individual crabs and groups of crabs consumed similar numbers of clams in the two habitat types when large predatory birds (mainly various species of terns, Sterna spp., herring gulls, Larus argentatus Coues, and ring-billed gulls, L. delawarensis Ord) were excluded from enclosures, but the crabs consumed more clams in the salt marsh than in the sand flat habitat in control enclosures where birds were not excluded. In the fall, when Herring and Ring-billed Gulls were abundant in the study area, preference by blue crabs for safer and more profitable habitats may explain the greater predation on clams in salt marshes than in intertidal sand flats. In the summer, when Herring and Ring-billed Gulls were rare and crab densities are 1.5-3 times greater than in the fall, competition with conspecifics may have caused crabs to disperse and feed in intertidal flats and may explain the general lack of differences in predation intensity among habitat types observed in the summer. Thus, patterns of predation and habitat use by blue crabs appeared to explain between-habitat and seasonal differences in predation mortality of clams. Focusing on the variation in the feeding rates of individual predators in response to external conditions can produce the mechanistic understanding of spatial and seasonal patterns of predation needed to understand and better predict the processes that structure benthic marine communities

Achieving Success under Pressure in the Conservation of Intensely Used Coastal Areas

2siUnderstanding how conservation and socioeconomic development can be harmonized in organizational and social- ecological systems is at the core of sustainability science. We present the case of an organization that manage a Mediterranean marine protected area (MPA), the Tavolara-Punta Coda Cavallo MPA, that exhibits high ecological performance under intense pressure from fishing, tourism, and coastal development. This case study illustrates how socioeconomic development and significant conservation benefits can coexist, even in a challenging context. Based on this case study, we present a framework for what elements and interactions have determined the high ecological performance of this MPA, and highlight the key organizational leverages that have enabled ecosystem recovery. In particular, the most critical elements underlying high performance were sufficient leadership and knowledge to identify a conservation vision and to catalyze some key actors in the implementation of this vision. Thus, success was ultimately determined by the ability of the leadership of the MPA to devise and implement an effective strategy, with the support and participation of key actors that were external to the MPA organization. The insights from this case study may be applicable to improving MPA management in other systems with similar characteristics, including high human pressures and the presence of an MPA authority.openMICHELI F.; NICCOLINI F.Micheli, F.; Niccolini, Federic

Gribov ambiguity and degenerate systems

The relation between Gribov ambiguity and degeneracies in the symplectic structure of physical systems is analyzed. It is shown that, in finite-dimensional systems, the presence of Gribov ambiguities in regular constrained systems (those where the constraints are functionally independent) always leads to a degenerate symplectic structure upon Dirac reduction. The implications for the Gribov-Zwanziger approach to QCD are discussed.Comment: 26 pages, 6 figures. Comments and references adde

Predation intensity in estuarine soft bottoms: between-habitat comparisons and experimental artifacts

The aim of this study was to determine whether experimental artifacts have the potential to bias comparisons of relative predation intensity among different soft-sediment estuarine habitats. A field experiment was used to test (1) whether predation intensity on the infaunal clam Mercenaria mercenaria (L.) differed between shallow-subtidal and intertidal sand flats, (2) whether predation on clams differed between intertidal sand flats and vegetated habitats [the edge of Spartina alterniflora (Loisel) salt marshes] of similar elevation, and (3) whether the outcome of these comparisons was influenced by the experimental method used. For mobile prey, some restraint on prey movement is typically required to compare predation intensity among different habitats. This is most often achieved by tethering prey. Tethering and other experimental interventions may induce different experimental artifacts in estimates of predation intensity in different habitats, which would invalidate between-habitat comparisons (Peterson & Black 1994: Mar Ecol Frog Ser 111:289-297). I used combinations of 2 types of prey restraint, tethers and buried fences, to test for possible interactive effects of habitat and prey restraint on prey mortality. Tethered or untethered clams were deployed within fenced or unfenced field plots within each habitat type, in a factorial design, and were exposed to the natural assemblage of predators for 1 wk. Within each habitat type, both tethering and fencing increased the proportion of clams recovered Live after 1 wk compared to the treatment in which no prey restraints were used. Significantly more Live clams were recovered in the intertidal sand flats than in the subtidal sand bottoms within field plots enclosed with buried fences, suggesting lower predation intensity in the intertidal than in subtidal sand fiats. In contrast, there was no significant difference in proportions of live clams between subtidal sand bottoms and intertidal sand flats within unfenced plots. These results were obtained with both tethered and untethered clams. Significantly more clams were recovered live in intertidal sand flats than in intertidal salt marshes of similar elevation in all treatment combinations, suggesting lower predation intensity in unvegetated than in vegetated habitats. This result was unexpected because habitat structural complexity is known to decrease predation rates in other shallow marine habitats, such as rocky intertidal habitats and seagrass beds. Results of this field experiment indicate that prey restraints can bias not only estimates of predation intensity within a single habitat type but can also bias between-habitat comparisons of predation intensity, probably by causing experimental artifacts of different magnitudes in each habitat. The actual magnitude of experimental artifacts in each habitat type can only be estimated with direct observations of predator-prey interactions in the field

PRINCIPLES FOR THE DESIGN OF MARINE RESERVES

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Quantum Degenerate Systems

Degenerate dynamical systems are characterized by symplectic structures whose rank is not constant throughout phase space. Their phase spaces are divided into causally disconnected, nonoverlapping regions such that there are no classical orbits connecting two different regions. Here the question of whether this classical disconnectedness survives quantization is addressed. Our conclusion is that in irreducible degenerate systems --in which the degeneracy cannot be eliminated by redefining variables in the action--, the disconnectedness is maintained in the quantum theory: there is no quantum tunnelling across degeneracy surfaces. This shows that the degeneracy surfaces are boundaries separating distinct physical systems, not only classically, but in the quantum realm as well. The relevance of this feature for gravitation and Chern-Simons theories in higher dimensions cannot be overstated.Comment: 18 pages, no figure

Recent pace of change in human impact on the world's ocean.

Humans interact with the oceans in diverse and profound ways. The scope, magnitude, footprint and ultimate cumulative impacts of human activities can threaten ocean ecosystems and have changed over time, resulting in new challenges and threats to marine ecosystems. A fundamental gap in understanding how humanity is affecting the oceans is our limited knowledge about the pace of change in cumulative impact on ocean ecosystems from expanding human activities - and the patterns, locations and drivers of most significant change. To help address this, we combined high resolution, annual data on the intensity of 14 human stressors and their impact on 21 marine ecosystems over 11 years (2003-2013) to assess pace of change in cumulative impacts on global oceans, where and how much that pace differs across the ocean, and which stressors and their impacts contribute most to those changes. We found that most of the ocean (59%) is experiencing significantly increasing cumulative impact, in particular due to climate change but also from fishing, land-based pollution and shipping. Nearly all countries saw increases in cumulative impacts in their coastal waters, as did all ecosystems, with coral reefs, seagrasses and mangroves at most risk. Mitigation of stressors most contributing to increases in overall cumulative impacts is urgently needed to sustain healthy oceans

Disentangling trophic interactions inside a Caribbean marine reserve

Author Posting. © Ecological Society of America, 2010. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 20 (2010): 1979–1992, doi:10.1890/09-1217.1.Recent empirical studies have demonstrated that human activities such as fishing can strongly affect the natural capital and services provided by tropical seascapes. However, policies to mitigate anthropogenic impacts can also alter food web structure and interactions, regardless of whether the regulations are aimed at single or multiple species, with possible unexpected consequences for the ecosystems and their associated services. Complex community response to management interventions have been highlighted in the Caribbean, where, contrary to predictions from linear food chain models, a reduction in fishing intensity through the establishment of a marine reserve has led to greater biomass of herbivorous fish inside the reserve, despite an increased abundance of large predatory piscivores. This positive multi-trophic response, where both predators and prey benefit from protection, highlights the need to take an integrated approach that considers how numerous factors control species coexistence in both fished and unfished systems. In order to understand these complex relationships, we developed a general model to examine the trade-offs between fishing pressure and trophic control on reef fish communities, including an exploration of top-down and bottom-up effects. We then validated the general model predictions by parameterizing the model for a reef system in the Bahamas in order to tease apart the wide range of species responses to reserves in the Caribbean. Combining the development of general theory and site-specific models parameterized with field data reveals the underlying driving forces in these communities and enables us to make better predictions about possible population and community responses to different management schemes.This work was supported by funding from the Bahamas Biocomplexity Project (U.S. NSF Biocomplexity grant OCE-0119976) and U.S. EPA Science to Achieve Results (R832223)

Fish assemblages across the Mediterranean Sea and the effects of protection from fishing = I Popolamenti ittici nel Mediterraneo e gli effetti della protezione dall’impatto della pesca

Several studies have assessed the effectiveness of individual marine protected areas (MPAs) in protecting fish assemblages, but regional assessments of multiple parks are scarce. Here fish surveys using visual census were done in marine parks and fished areas at 31 locations across the Mediterranean Sea. Fish species richness, diversity and biomass (especially of top predators) were higher in MPAs compared to fished areas, and community structure differed significantly between MPAs and fished areas. Results suggest that MPAs are generally effective means to protect and recover fish populations and assemblages

Comparing spatial patterns of marine vessels between vessel-tracking data and satellite imagery

Monitoring marine use is essential to effective management but is extremely challenging, particularly where capacity and resources are limited. To overcome these limitations, satellite imagery has emerged as a promising tool for monitoring marine vessel activities that are difficult to observe through publicly available vessel-tracking data. However, the broader use of satellite imagery is hindered by the lack of a clear understanding of where and when it would bring novel information to existing vessel-tracking data. Here, we outline an analytical framework to (1) automatically detect marine vessels in optical satellite imagery using deep learning and (2) statistically contrast geospatial distributions of vessels with the vessel-tracking data. As a proof of concept, we applied our framework to the coastal regions of Peru, where vessels without the Automatic Information System (AIS) are prevalent. Quantifying differences in spatial information between disparate datasets—satellite imagery and vessel-tracking data—offers insight into the biases of each dataset and the potential for additional knowledge through data integration. Our study lays the foundation for understanding how satellite imagery can complement existing vessel-tracking data to improve marine oversight and due diligence