Larval fish dispersal in a coral-reef seascape

Free to read at publisher's site. 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 km(2)) 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 butterfly-fish, 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

Interactive effects of interspecifc competition and microhabitat on early post-settlement survival in a coral reef fish

Microhabitat type and the competition for microhabitats can each influence patterns of abundance and mortality in coral reef fish communities; however, the effect of microhabitat on the intensity and outcome of competition is not well understood. In Kimbe Bay, Papua New Guinea, surveys were used to quantify microhabitat use and selectivity in two live-coral specialist damselfishes (Pomacentridae), Chrysiptera parasema, and Dascyllus melanurus. A patch reef experiment was then conducted to test how intra- and interspecific competition interacts with two types of microhabitat to influence survival of recently settled C. parasema. Surveys demonstrated that C. parasema and D. melanurus recruits utilized similar coral microhabitats; 72% of C. parasema and 85% of D. melanurus used corymbose and bottlebrush growth forms of Acropora. One microhabitat type, Pocillopora sp. coral, was commonly used by D. melanurus but rarely by C. parasema. The patch reef experiment revealed that both microhabitat and interspecific competition influence abundance of recently settled C. parasema. Microhabitat had the strongest influence on survival of C. parasema. In the absence of interspecific competitors, »85% of C. parasema survived for 5 days after transplantation to high-complexity bottlebrush Acropora reefs when compared to only 25% survival of Pocillopora reefs. In both microhabitats, interspecific competition with D. melanurus, but not intraspecific competition, significantly decreased the survival of C. parasema. Taken together, these results suggest that the observed distribution of C. parasema results from specialized microhabitat requirements and competition for space in those microhabitats. This study demonstrates that interspecific competition and microhabitat type can interact to influence early post-settlement survival in coral reef fishes, though, whether and how these factors influence survival will depend on the behavioural attributes and strength of habitat associations among potential competitors

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

Reproductive biology of squaretail coralgrouper Plectropomus areolatus using age-based techniques

The squaretail coralgrouper Plectropomus areolatus was identified as a fast-growing, early maturing and relatively short-lived aggregation-spawning epinephelid. Examinations of sectioned otoliths found females and males first maturing at 2 and 3 years, respectively, suggesting protogynous hermaphroditism; however, no transitionals were observed in samples. Age distribution for the two sexes was similar and both were represented in the oldest age class; however, significant sex-specific differences in size-at-age were identified. Both sexes fully recruit into the fishery at age 4 years and reach 90% of asymptotic length by age 3 years. Underwater visual assessments, combined with the gonado-somatic indices, revealed a 5 month reproductive season, with interannual variability observed in the month of highest density within the spawning aggregation. Catch restrictions on adults during spawning times and at reproductive sites, combined with gear-based management and enhanced enforcement, are recommended to maintain spawning stocks. Based on the available evidence, the sexual pattern for this species is unresolved

Research partnerships with local communities: two case studies\ud from Papua New Guinea and Australia

Partnerships between scientists and local communities can increase research capacity and data delivery while improving management effectiveness through enhanced community participation. To encourage such collaboration, this study demonstrates how these partnerships can be formed, drawing on two case studies in coral reef ecosystems in very different social settings (Papua New Guinea and Australia). In each case, steps towards successfully engaging communities in research were similar. These included: (1) early engagement by collaborating organizations to build trust, (2) ensuring scientific questions have direct relevance to the community, (3) providing appropriate incentives for participation, and (4) clear and open communication. Community participants engaged in a variety of research activities, including locating and capturing fishes, collecting and recording data (weight, length and sex), applying external tags, and removing otoliths (ear bones) for ageing and elemental analysis. Research partnerships with communities enhanced research capacity, reduced costs and, perhaps more importantly, improved the likelihood of long-term community support for marine protected areas (MPAs)