The Extent and spatial scale of connectivity among reef fish populations: implications for marine protected areas designated for fisheries enhancement

Enthusiasm for the use of no-take marine protected areas (MPAs) as management tools for the protection and enhancement of coral reef fishes is widespread. However, evidence that such marine reserves actually enhance fishery yields is limited, primarily because of difficulties in quantifying the exchange of individuals—especially larvae—between local populations within and outside the protected area. Knowledge of the extent and spatial scale of this connectivity is of vital importance for the effective design and implementation of marine reserves intended as fishery management tools. We review our current understanding of connectivity among coral reef populations, including the role of important determining factors such as pelagic larval duration, larval behavior, and hydrodynamics. We also discuss artificial and natural tagging methods that potentially can be used to track movements of larvae between marine reserves and surrounding waters. To illustrate the application of such methods, we discuss ECONAR (Ecological CONnections Among Reefs), a new, regional-scale research project designed to measure the extent of connectivity among populations of coral reef fishes in the Mesoamerican Barrier Reef System

Serum magnesium and calcium levels in relation to ischemic stroke : Mendelian randomization study

ObjectiveTo determine whether serum magnesium and calcium concentrations are causally associated with ischemic stroke or any of its subtypes using the mendelian randomization approach.MethodsAnalyses were conducted using summary statistics data for 13 single-nucleotide polymorphisms robustly associated with serum magnesium (n = 6) or serum calcium (n = 7) concentrations. The corresponding data for ischemic stroke were obtained from the MEGASTROKE consortium (34,217 cases and 404,630 noncases).ResultsIn standard mendelian randomization analysis, the odds ratios for each 0.1 mmol/L (about 1 SD) increase in genetically predicted serum magnesium concentrations were 0.78 (95% confidence interval [CI] 0.69-0.89; p = 1.3 7 10-4) for all ischemic stroke, 0.63 (95% CI 0.50-0.80; p = 1.6 7 10-4) for cardioembolic stroke, and 0.60 (95% CI 0.44-0.82; p = 0.001) for large artery stroke; there was no association with small vessel stroke (odds ratio 0.90, 95% CI 0.67-1.20; p = 0.46). Only the association with cardioembolic stroke was robust in sensitivity analyses. There was no association of genetically predicted serum calcium concentrations with all ischemic stroke (per 0.5 mg/dL [about 1 SD] increase in serum calcium: odds ratio 1.03, 95% CI 0.88-1.21) or with any subtype.ConclusionsThis study found that genetically higher serum magnesium concentrations are associated with a reduced risk of cardioembolic stroke but found no significant association of genetically higher serum calcium concentrations with any ischemic stroke subtype

Stability of coral reef fish assemblages impacted by nuclear tests

Investigating the resilience of fish assemblages requires large-scale experiments, but large-scale manipulations are rarely possible, and "natural experiments" frequently must take their place. Here we report a unique opportunity to explore the resilience of reef fish assemblages. The underground nuclear testing program conducted by the French Armed Forces at Mururoa Atoll, while not intended as an ecological experiment, caused multiple instantaneous removals of fish over areas of approximately 12.5 km2, without otherwise affecting their environment or the opportunity for recolonization. We show that fish assemblages responded rapidly to these intense, large-scale perturbations, restoring assemblage structure within 1-5 yr. Reef fishery conservation efforts must emphasize protection of habitat, because reef fish assemblages are resilient even to intensive, localized harvesting so long as the structural and biotic integrity of their habitat is maintained and neighboring sites are able to supply recruits. © 2005 by the Ecological Society of America

Larval retention and connectivity among populations of corals and reef fishes: history, advances and challenges

The extent of larval dispersal on coral reefs has\ud important implications for the persistence of coral reef\ud metapopulations, their resilience and recovery from an\ud increasing array of threats, and the success of protective\ud measures. This article highlights a recent dramatic increase\ud in research effort and a growing diversity of approaches to\ud the study of larval retention within (self-recruitment) and\ud dispersal among (connectivity) isolated coral reef populations. Historically, researchers were motivated by\ud alternative hypotheses concerning the processes limiting\ud populations and structuring coral reef assemblages,\ud whereas the recent impetus has come largely from the need\ud to incorporate dispersal information into the design of no-take marine protected area (MPA) networks. Although the\ud majority of studies continue to rely on population genetic\ud approaches to make inferences about dispersal, a wide\ud range of techniques are now being employed, from smallscale\ud larval tagging and paternity analyses, to large-scale\ud biophysical circulation models. Multiple approaches are\ud increasingly being applied to cross-validate and provide\ud more realistic estimates of larval dispersal. The vast\ud majority of empirical studies have focused on corals and\ud fishes, where evidence for both extremely local scale patterns of self-recruitment and ecologically significant\ud connectivity among reefs at scales of tens of kilometers\ud (and in some cases hundreds of kilometers) is accumulating.\ud Levels of larval retention and the spatial extent of\ud connectivity in both corals and fishes appear to be largely\ud independent of larval duration or reef size, but may be\ud strongly influenced by geographic setting. It is argued that\ud high levels of both self-recruitment and larval import can\ud contribute to the resilience of reef populations and MPA\ud networks, but these benefits will erode in degrading reef\ud environments

Thinking and managing outside the box: coalescing connectivity networks to build region-wide resilience in coral reef ecosystems

As the science of connectivity evolves, so too must the management of coral reefs. It is now clear that the spatial scale of disturbances to coral reef ecosystems is larger and the scale of larval connectivity is smaller than previously thought. This poses a challenge to the current focus of coral reef management, which often centers on the establishment of no-take reserves (NTRs) that in practice are often too small, scattered, or have low stakeholder compliance. Fished species are generally larger and more abundant in protected reserves, where their reproductive potential is often greater, yet documented demographic benefits of these reproductive gains outside reserves are modest at best. Small reproductive populations and limited dispersal of larvae play a role, as does the diminished receptivity to settling larvae of degraded habitats that can limit recruitment by more than 50%. For “demographic connectivity” to contribute to the resilience of coral reefs, it must function beyond the box of no-take reserves. Specifically, it must improve nursery habitats on or near reefs and enhance the reproductive output of ecologically important species throughout coral reef ecosystems. Special protection of ecologically important species (e.g., some herbivores in the Caribbean) and size-regulated fisheries that capitalize on the benefits of NTRs and maintain critical ecological functions are examples of measures that coalesce marine reserve effects and improve the resilience of coral reef ecosystems. Important too is the necessity of local involvement in the management process so that social costs and benefits are properly assessed, compliance increased and success stories accrued