Mark A. Priest

The Ecological Role of Sharks on Coral Reefs.

Sharks are considered the apex predator of coral reefs, but the consequences of their global depletion are uncertain. Here we explore the ecological roles of sharks on coral reefs and, conversely, the importance of reefs for sharks. We find that most reef-associated shark species do not act as apex predators but instead function as mesopredators along with a diverse group of reef fish. While sharks perform important direct and indirect ecological roles, the evidence to support hypothesised shark-driven trophic cascades that benefit corals is weak and equivocal. Coral reefs provide some functional benefits to sharks, but sharks do not appear to favour healthier reef environments. Restoring populations of sharks is important and can yet deliver ecological surprise.

Integrating research using animal‐borne telemetry with the needs of conservation management

Animal-borne telemetry has revolutionized our ability to study animal movement, species physiology, demography and social structures, changing environments and the threats that animals are experiencing. While there will always be a need for basic ecological research and discovery, the current conservation crisis demands we look more pragmatically at the data required to make informed management decisions. Here, we define a framework that distinguishes how research using animal telemetry devices can influence conservation. We then discuss two critical questions which aim to directly connect telemetry-derived data to applied conservation decision-making: (i) Would my choice of action change if I had more data? (ii) Is the expected gain worth the money and time required to collect more data? Policy implications. To answer questions about integrating telemetry-derived data with applied conservation, we suggest the use of value of information analysis to quantitatively assess the return-on-investment of animal telemetry-derived data for conservation decision-making.

Larval fish dispersal in a coral-reef seascape

Larval dispersal is a critical yet enigmatic process in the persistence and productivity of marine metapopulations. Empirical data on larval dispersal remain scarce, hindering the use of spatial management tools in efforts to sustain ocean biodiversity and fisheries. Here we document dispersal among subpopulations of clownfish (Amphiprion percula) and butterflyfish (Chaetodon vagabundus) from eight sites across a large seascape (10,000 km2) in Papua New Guinea across 2 years. Dispersal of clownfish was consistent between years, with mean observed dispersal distances of 15 km and 10 km in 2009 and 2011, respectively. A Laplacian statistical distribution (the dispersal kernel) predicted a mean dispersal distance of 13–19 km, with 90% of settlement occurring within 31–43 km. Mean dispersal distances were considerably greater (43–64 km) for butterflyfish, with kernels declining only gradually from spawning locations. We demonstrate that dispersal can be measured on spatial scales sufficient to inform the design of and test the performance of marine reserve networks.

Restricted grouper reproductive migrations support community-based management

Conservation commonly requires trade-offs between social and ecological goals. For tropical small-scale fisheries, spatial scales of socially appropriate management are generally small—the median no-take locally managed marine area (LMMA) area throughout the Pacific is less than 1 km2. This is of particular concern for large coral reef fishes, such as many species of grouper, which migrate to aggregations to spawn. Current data suggest that the catchment areas (i.e. total area from which individuals are drawn) of such aggregations are at spatial scales that preclude effective community-based management with no-take LMMAs. We used acoustic telemetry and tag-returns to examine reproductive migrations and catchment areas of the grouper Epinephelus fuscoguttatus at a spawning aggregation in Papua New Guinea. Protection of the resultant catchment area of approximately 16 km2 using a no-take LMMA is socially untenable here and throughout much of the Pacific region. However, we found that spawning migrations were skewed towards shorter distances. Consequently, expanding the current 0.2 km2 no-take LMMA to 1–2 km2 would protect approximately 30–50% of the spawning population throughout the non-spawning season. Contrasting with current knowledge, our results demonstrate that species with moderate reproductive migrations can be managed at scales congruous with spatially restricted management tools.

Reassessing shark-driven trophic cascades on coral reefs: a reply to Ruppert et al

In our recent review of the ecological roles of sharks on coral reefs [1], we concluded that the evidence to support hypothesised shark-driven trophic cascades on coral reefs was weak and equivocal. In their response to our review, Ruppert et al. [2] assert that a major issue with our approach was that we primarily reviewed evidence from correlative observational studies to reach this conclusion. This is incorrect, because our conclusion is based upon multiple lines of evidence, including observational studies, food-web models, dietary and stable isotope analysis, trophic position, habitat use, and behavioural evidence [1].

Isolation and characterization of 29 microsatellite markers for the bumphead parrotfish, Bolbometopon muricatum, and cross amplification in 12 related species

We isolated and characterized 29 microsatellite loci for the bumphead parrotfish, Bolbometopon muricatum, a wide-ranging parrotfish listed as vulnerable by the International Union for Conservation of Nature (IUCN). The 29 loci were tested on 95 individuals sampled from the Solomon Islands. The number of alleles ranged from two to ten. Evidence of linkage disequilibrium was found for only one pair of loci (Bm54 and Bm112). Two loci (Bm20 and Bm119) showed significant departure from Hardy-Weinberg equilibrium. We also tested each locus for amplification and polymorphism on 11 other scarine labrid species and one labrid species. Amplification success ranged from zero to ten loci per species. These microsatellite loci are the first specific set for B. muricatum and will be a useful tool for assessing genetic population structure, genetic diversity, and parentage in future studies.

What a difference a bay makes: natural variation in dietary resources mediates growth in a recently settled herbivorous fish

Processes acting during the early stages of coral reef fish life cycles have a disproportionate influence on their adult abundance and community structure. Higher growth rates, for example, confer a major fitness advantage in larval and juvenile fishes, with larger fish undergoing significantly less mortality. The role of dietary resources in the size-structuring process has not been well validated, especially at the early post-settlement phase, where competition and predation are seen as preeminent drivers of juvenile fish assemblage structure. Here, we report on a size differential of 10–20% between recently settled Siganus spinus rabbitfish recruits from different bays around the Pacific island of Guam. This difference was maintained across multiple recruitment events within and between years. After confirming the validity of our observations through otolith increment analysis, subsequent investigation into the drivers of this variation revealed significant differences in the structure of algal assemblages between bays, congruent with the observed differences in size of the recently settled fish. Gut analyses showed a greater presence of algal types with higher levels of nitrogen and phosphorus in the stomachs of fish from Tanguisson, the bay with the largest observed recruits. To ensure this mechanism was one of causation and not correlation, we conducted a fully factorial experiment in which S. spinus recruits sampled from different bays were reared on all combinations of algal diets representative of the different bays. Recruits on the ‘Tanguisson’ diet grew faster than recruits on other diets, regardless of their origin. We propose that the greater availability of high-quality dietary resources at this location is likely conferring benefits that impact on the population-level dynamics of this species. The spatial and temporal extent of this process clearly implicates food as a limiting resource, capable of mediating fish population dynamics at multiple spatial scales and ontogenetic phases.