Larval dispersal reveals regional sources and sinks in the Great Barrier Reef

We analysed simulated connectivity patterns for reef fish larvae in the Cairns section of the Great Barrier Reef, and identified 2 key subregions that exhibit regional scale source–sink dynamics. The source and sink were separated latitudinally by a boundary at 16.1°S, with the source subregion lying to the north. Larval transport between the 2 subregions was predominantly unidirectional, from north to south. Only a few local populations, described here as ‘gateway reefs’, were able to transport larvae from the sink subregion to the source subregion and thus maintain the connectedness of the metapopulation. The northern subregion was able to persist without external larval supply, but when conditions were recruitment limited, the southern subregion depended on larval supply from the north to persist. The relative autonomy of the northern subregion, and its importance in sustaining the southern subregion, will influence the effectiveness of conservation efforts

Evaluation of a nonlinear reef parametrisation for steady flows

Modelling ocean circulation in regions of high topographic complexity, notably around groups of reefs and islands, makes large demands on spatial resolution. This problem has largely been overcome by a parametrisation scheme in which the dynamics associated with flow around unresolved reefs and islands are represented by modified momentum equations on a relatively coarse grid. However, the performance of this scheme deteriorates at high velocities, due to the increasing importance of flow separation and eddy formation, processes that are excluded in the original scheme. We extend the earlier model to include a parametrisation of the nonlinear advective terms, and test the performance of the modified scheme in the case of steady flow

Evaluation of a nonlinear reef parametrisation for steady flows

Modelling ocean circulation in regions of high topographic complexity, notably around groups of reefs and islands, makes large demands on spatial resolution. This problem has largely been overcome by a parametrisation scheme in which the dynamics associated with flow around unresolved reefs and islands are represented by modified momentum equations on a relatively coarse grid. However, the performance of this scheme deteriorates at high velocities, due to the increasing importance of flow separation and eddy formation, processes that are excluded in the original scheme. We extend the earlier model to include a parametrisation of the nonlinear advective terms, and test the performance of the modified scheme in the case of steady flow

Surrogates for reef fish connectivity when designing marine protected area networks

Reef fishes and other marine species occur in patchily distributed benthic populations that are interlinked by a larval stage where individuals disperse throughout the pelagic environment. This larval connectivity will play a critical role in determining whether marine protected area (MPA) networks can effectively promote the persistence of increasingly exploited reef fish populations. However, the amount, direction and variation of this connectivity are unknown for most species in most reef ecosystems of conservation concern. Furthermore, connectivity data are difficult to obtain and expensive to measure. Here, we demonstrate that if MPA locations are chosen according to certain easily measurable reef characteristics-'connectivity surrogates'-the resulting MPA networks can maintain reef fish populations and allow fishery harvests superior to random expectation. Surrogates offer managers an opportunity to cheaply consider connectivity into MPA network design while data collection on connectivity is ongoing. We use a high-resolution biophysical model of reef fish larval connectivity on the Great Barrier Reef (GBR) to assess the effectiveness of 5 connectivity surrogates: 2 based on the reef's physical dimensions, 2 based on spawning biomass and 1 based on the efficient representation of conservation features. Biomass attributes generally perform best; however, the appropriate choice depends on the size of the proposed MPA network and the relative value placed on conservation outcomes and fisheries performance. Our results are relatively insensitive to the parameters used in the model and the morphology of the reef system. This robustness suggests that insights from the GBR could provide useful guidance to the management of other reef systems

The economic optimality of learning from marine protected areas

Marine Protected Areas (MPAs) are an emerging tool for managing marine resources. Many of the benefits associated with MPAs have been widely investigated and the field is an active area of research in theoretical ecology. One benefit of MPAs that has remained largely overlooked is their value as a tool for learning about the population dynamics of a fishery. We investigate the economic optimality of implementing an MPA, purely for the purpose of obtaining more informative data about a fish population, thereby allowing a better management strategy. A stochastic dynamic programming framework for finding optimal management strategies in this scenario is developed. A simple example is investigated using this framework, with the results illustrating that in some situations the knowledge gained from MPAs can be sufficient to make their creation economically optimal. This establishes an additional benefit of MPAs that should be considered further by fishery managers

The economic optimality of learning from marine protected areas

Marine Protected Areas (MPAs) are an emerging tool for managing marine resources. Many of the benefits associated with MPAs have been widely investigated and the field is an active area of research in theoretical ecology. One benefit of MPAs that has remained largely overlooked is their value as a tool for learning about the population dynamics of a fishery. We investigate the economic optimality of implementing an MPA, purely for the purpose of obtaining more informative data about a fish population, thereby allowing a better management strategy. A stochastic dynamic programming framework for finding optimal management strategies in this scenario is developed. A simple example is investigated using this framework, with the results illustrating that in some situations the knowledge gained from MPAs can be sufficient to make their creation economically optimal. This establishes an additional benefit of MPAs that should be considered further by fishery managers

Resilient reefs may exist, but can larval dispersal models find them?

<p>Resilient reefs may exist, but can larval dispersal models find them?</p

Modeling suspended sediment during construction in Great Barrier Reef world heritage area

A marina was constructed in the Great Barrier Reef World Heritage Area in close proximity to coral reefs that could be damaged by excess turbidity generated during construction. Since there was uncertainty about both the fate of suspended sediments and their effect on corals, initial water quality constraints were set very conservatively. In order to better understand the movement of suspended sediment during construction, a numerical model study was commissioned using three-dimensional, numerical, hydrodynamic, and Lagrangian particle tracking models. The study was successful in: (1) increasing the understanding of and reducing the uncertainty of sediment dispersal patterns under a range of common forcing conditions; (2) testing the variation in suspended sediment concentrations over sensitive areas for two different outfall locations; (3) offering evidence that a good choice in outfall locations will reduce the threat to corals; and importantly (4) presenting the results in a way that enhanced understanding by nontechnical reef managers. This final result was achieved by creating movies of sediment movement that clearly demonstrated the complex hydrodynamic processes involved with near-coastal water currents. Specific model results showed: (1) that a more seaward outfall increases effluent dispersal away from sensitive areas; (2) the highest concentrations of effluent over sensitive sites occur during no wind and neap tide conditions; and (3) prevailing southeast winds advect effluent offshore, away from sensitive sites

When to press on or turn back: dispersal strategies for reef fish larvae

Events that occur during the pelagic larval stage are thought to be important determinants of reef fish population dynamics. Recent research contradicts the early paradigm of larvae being advected as passive propagules and indicates that many late stage larvae have well-developed sensory and locomotory capabilities. Whether and how larvae use these capabilities to influence their dispersal is unknown. We compare alternative hypotheses regarding larval behavior. Contrary to the trend in dispersal modeling, we focus on larval biology rather than physical oceanographic considerations. Specifically, we present two streams of models: one that describes a return-based strategy and one in which dispersal is a central component. The models depend on different sets of behavioral assumptions for a pomacentrid species and for acanthurids, two groups with contrasting early life histories. Whether dispersal or return‐based strategies are favored depends on the efficiency and sustainability of larval swimming methods and the environmental conditions experienced during dispersal. We argue that dispersal models should consider a variety of behavioral hypotheses and that the sensitivity of results to the behavioral assumptions made should be quantified