The impact of exploiting grazers (Scaridae) on the dynamics of Caribbean coral reefs.

Coral reefs provide a number of ecosystem services including coastal defense from storms, the generation of building materials, and fisheries. It is increasingly clear that the management of reef resources requires an ecosystem approach in which extractive activities are weighed against the needs of the ecosystem and its functions rather than solely those of the fishery. Here, I use a spatially explicit simulation model of a Caribbean coral reef to examine the ecosystem requirements for grazing which is primarily conducted by parrotfishes (Scaridae). The model allows the impact of fishing grazers to be assessed in the wider context of other ecosystem processes including coral-algal competition, hurricanes, and mass extinction of the herbivorous urchin Diadema antillarum. Using a new analytical model of scarid grazing, it is estimated that parrotfishes can only maintain between 10% and 30% of a structurally complex forereef in a grazed state. Predictions from this grazing model were then incorporated into a broader simulation model of the ecosystem. Simulations predict that scarid grazing is unable to maintain high levels of coral cover (> or = 30%) when severe hurricanes occur on a decadal basis, such as occurs in parts of the northern Caribbean. However, reefs can withstand such intense disturbance when grazing is undertaken by both scarids and the urchin Diadema. Scarid grazing is predicted to allow recovery from hurricanes when their incidence falls to 20 years or less (e.g., most of Central and South America). Sensitivity analyses revealed that scarid grazing had the most acute impact on model behavior, and depletion led to the emergence of a stable, algal-dominated community state. Under conditions of heavy grazer depletion, coral cover was predicted to decline rapidly from an initial level of 30% to less than 1% within 40 years, even when hurricane frequency was low at 60 years. Depleted grazers caused a population bottleneck in juvenile corals in which algal overgrowth caused elevated levels of postsettlement mortality and resulted in a bimodal distribution of coral sizes. Several new hypotheses were generated including a region-wide change in the spatial heterogeneity of coral reefs following extinction of Diadema. The management of parrotfishes on Caribbean reefs is usually approached implicitly through no-take marine reserves. The model predicts that depletion of grazers in nonreserve areas can severely limit coral accretion. Other studies have shown that low coral accretion can reduce the structural complexity and therefore quality of the reef habitat for many organisms. A speculative yet rational inference from the model is that failure to manage scarid populations outside reserves will have a profoundly negative impact on the functioning of the reserve system and status of non-reserve reefs.     

Effects of Fishing on the Ecosystem Structure of Coral Reefs

Overfishing is considered one of the three most significant threats to coral reef ecosystems. Exponentially increasing human populations in the tropics have placed enormous demands upon reefs as a food source. At high intensities, termed ecosystem or Malthusian overfishing, fishing causes major direct and indirect effects on the community structure of fishes and other organisms. It reduces species diversity and leads to local extinctions not only of target species but also of other species not fished directly. Conceivably it could also lead to global extinctions. Loss of keystone species, such as predators of echinoderms, through fishing, can lead to major effects on reef processes, such as accretion of calcium carbonate. Ultimately, sustained heavy fishing may lead to loss of entire functional groups of species, resulting in impairment of the potentially important ecosystem functions provided by those groups. Overfishing has been shown to interact with other agents of disturbance to reduce the ability of reefs to recover from natural occurrences such as hurricanes. Effective management of fishing will require a deeper understanding of the effects of exploitation than we now possess. Research initiatives are underway to examine the responses of fish populations to fishing, generally responses to protection from fishing. There is, however, an urgent need to look beyond fish communities and to consider the entire reef ecosystem. Studies that integrate population and community biology with ecosystem processes will provide a much better understanding of the effects of biodiversity loss on reef function and will improve our ability to manage these complex systems.     

Trophic cascades result in large-scale coralline algae loss through differential grazer effects

Removal of predators can have strong indirect effects on primary producers through trophic cascades. Crustose coralline algae (CCA) are major primary producers worldwide that may be influenced by predator removal through changes in grazer composition and biomass. CCA have been most widely studied in Caribbean and temperate reefs, where cover increases with increasing grazer biomass due to removal of competitive fleshy algae. However, each of these systems has one dominant grazer type, herbivorous fishes or sea urchins, which may not be functionally equivalent. Where fishes and sea urchins co-occur, fishing can result in a phase shift in the grazing community with subsequent effects on CCA and other substrata. Kenyan reefs have herbivorous fishes and sea urchins, providing an opportunity to determine the relative impacts of each grazer type and evaluate potential human-induced trophic cascades. We hypothesized that fish benefit CCA, abundant sea urchins erode CCA, and that fishing indirectly reduces CCA cover by removing sea urchin predators. We used closures and fished reefs as a large-scale, long-term natural experiment to assess how fishing and resultant changes in communities affect CCA abundance. We used a short-term caging experiment to directly test the effects of grazing on CCA. CCA cover declined with increasing fish and sea urchin abundance, but the negative impact of sea urchin grazing was much stronger than that of fishes. Abundant sea urchins reduced the CCA growth rate to almost zero and prevented CCA accumulation. A warming event (El Ni?o Southern Oscillation, ENSO) occurred during the 18-year study and had a strong but short-term positive effect on CCA cover. However, the effect of the ENSO on CCA was lower in magnitude than the effect of sea urchin grazing. We compare our results with worldwide literature on bioerosion by fishes and sea urchins. Grazer influence depends on whether benefits of fleshy algae removal outweigh costs of grazer-induced bioerosion. However, the cost-benefit ratio for CCA appears to change with grazer type, grazer abundance, and environment. In Kenya, predator removal leads to a trophic cascade that is expected to reduce net calcification of reefs and therefore reduce reef stability, growth, and resilience.     

Implications of Urbanization for Artisanal Parrotfish Fisheries in the Western Solomon Islands

Abstract: Increasing migration into urbanized centers in the Solomon Islands poses a great threat to adjacent coral reef fisheries because of negative effects on the fisheries and because it further erodes customary management systems. Parrotfish fisheries are of particular importance because the feeding habits of parrotfish (scrape and excavate coral) are thought to be critical to the resilience of coral reefs and to maintaining coral reef health within marine protected areas. We investigated the ecological impact of localized subsistence and artisanal fishing pressure on parrotfish fisheries in Gizo Town, Western Solomon Islands, by analyzing the density and size distribution of parrotfish with an underwater visual census (UVC), recall diary (i.e., interviews with fishers), and creel surveys to independently assess changes in abundance and catch‐per‐unit‐effort (CPUE) over 2 years. We then compared parrotfish data from Gizo Town with equivalent data from sites open to and closed to fishing in Kida and Nusa Hope villages, which have different customary management regimes. Results indicated a gradient of customary management effectiveness. Parrotfish abundance was greater in customary management areas closed to fishing, especially with regard to larger fish sizes, than in areas open to fishing. The decline in parrotfish abundance from 2004 to 2005 in Gizo was roughly the same magnitude as the difference in abundance decline between inside and outside customary management marine reserves. Our results highlight how weak forms of customary management can result in the rapid decline of vulnerable fisheries around urbanized regions, and we present examples in which working customary management systems (Kinda and Nusa Hope) can positively affect the conservation of parrotfish—and reef fisheries in general—in the highly biodiverse Coral Triangle region.     

Making a Model Meaningful to Coral Reef Managers in a Developing Nation: a Case Study of Overfishing and Rock Anchoring in Indonesia

Abstract: Most of the world's coral reefs line the coasts of developing nations, where impacts from intense and destructive fishing practices form critical conservation issues for managers. Overfishing of herbivorous fishes can cause phase shifts to macroalgal dominance, and fishers’ use of rocks as anchors lowers coral cover, giving further competitive advantage to macroalgae. Overfishing and anchoring have been studied extensively, but the role of their interaction in lowering coral reef resilience has not been quantified formally. We analyzed the combined effects of overfishing and rock anchoring on a range of reef habitat types—varying from high coral and low macroalgae cover to low coral and high macroalgae cover—in a marine park in Indonesia. We parameterized a model of coral and algal dynamics with three intensities of anchoring and fishing pressure. Results of the model indicated that damage caused by rock anchoring was equal to or possibly more devastating to coral reefs in the area than the impact of overfishing. This is an important outcome for local managers, who usually have the funds to distribute less‐damaging anchors, but normally are unable to patrol regularly and effectively enough to reduce the impact of overfishing. We translated model results into an interactive visual tool that allows managers to explore the benefits of reducing anchoring frequency and fishing pressure. The potential consequences of inaction were made clear: the likelihood that any of the reef habitats will be dominated in the future by macroalgae rather than corals depends on reducing anchoring frequency, fishing pressure, or both. The tool provides a platform for strengthened relationships between managers and conservationists and can facilitate the uptake of recommendations regarding resource allocation and management actions. Conservation efforts for coral reefs in developing nations are likely to benefit from transforming model projections of habitat condition into tools local managers can understand and interact with.     

Identifying management opportunities to combat climate,land, and marine threats across less climate exposed coral reefs

Conserving coral reefs is critical for maintaining marine biodiversity, protecting coastlines, and supporting livelihoods in many coastal communities. Climate change threatens coral reefs globally, but researchers have identified a portfolio of coral reefs (bioclimatic units [BCUs]) that are relatively less exposed to climate impacts and strongly connected to other coral reef systems. These reefs provide a proactive opportunity to secure a long-term future for coral reefs under climate change. To help guide local management efforts, we quantified marine cumulative human impact (CHI) from climate, marine, and land pressures (2013 and from 2008 to 2013) in BCUs and across countries tasked with BCU management. Additionally, we created a management index based on common management measures and policies for each pressure source (climate, marine, and land) to identify a country's intent and commitment to effectively manage these pressures. Twenty-two countries (79%) had increases in CHI from 2008 to 2013. Climate change pressures had the highest proportional contribution to CHI across all reefs and in all but one country (Singapore), but 18 BCUs (35%) and nine countries containing BCUs (32%) had relatively high land and marine impacts. There was a significant positive relationship between climate impact and the climate management index across countries (R² = 0.43, p = 0.02), potentially signifying that countries with greater climate impacts are more committed to managing them. However, this trend was driven by climate management intent in Fiji and Bangladesh. Our results can be used to guide future fine-scale analyses, national policies, and local management decisions, and our management indices reveal areas where management components can be improved. Cost-effectively managing local pressures (e.g., fishing and nutrients) in BCUs is essential for building a climate-ready future that benefits coral reefs and people.     

Alternative stable states and phase shifts in coral reefs under anthropogenic stress

Ecosystems with alternative stable states (ASS) may shift discontinuously from one stable state to another as environmental parameters cross a threshold. Reversal can then be difficult due to hysteresis effects. This contrasts with continuous state changes in response to changing environmental parameters, which are less difficult to reverse. Worldwide degradation of coral reefs, involving "phase shifts" from coral to algal dominance, highlights the pressing need to determine the likelihood of discontinuous phase shifts in coral reefs, in contrast to continuous shifts with no ASS. However, there is little evidence either for or against the existence of ASS for coral reefs. We use dynamic models to investigate the likelihood of continuous and discontinuous phase shifts in coral reefs subject to sustained environmental perturbation by fishing, nutrification, and sedimentation. Our modeling results suggest that coral reefs with or without anthropogenic stress can exhibit ASS, such that discontinuous phase shifts can occur. We also find evidence to support the view that high macroalgal growth rates and low grazing rates on macroalgae favor ASS in coral reefs. Further, our results suggest that the three stressors studied, either alone or in combination, can increase the likelihood of both continuous and discontinuous phase shifts by altering the competitive balance between corals and algae. However, in contrast to continuous phase shifts, we find that discontinuous shifts occur only in model coral reefs with parameter values near the extremes of their empirically determined ranges. This suggests that continuous shifts are more likely than discontinuous shifts in coral reefs. Our results also suggest that, for ecosystems in general, tackling multiple human stressors simultaneously maximizes resilience to phase shifts, ASS, and hysteresis, leading to improvements in ecosystem health and functioning.     

Effects of Artisanal Fishing on Caribbean Coral Reefs

Abstract:  Although the impacts of industrial fishing are widely recognized, marine ecosystems are generally considered less threatened by artisanal fisheries. To determine how coral reef fish assemblages and benthic communities are affected by artisanal fishing, we studied six Caribbean islands on which fishing pressure ranged from virtually none in Bonaire, increasing through Saba, Puerto Rico, St Lucia, and Dominica, and reaching very high intensities in Jamaica. Using stationary-point fish counts at 5 m and 15 m depth, we counted and estimated the lengths of all noncryptic, diurnal fish species within replicate 10-m-diameter areas. We estimated percent cover of coral and algae and determined reef structural complexity. From fish numbers and lengths we calculated mean fish biomass per count for the five most commercially important families. Groupers (Serranidae), snappers (Lutjanidae), parrotfish (Scaridae), and surgeonfish (Acanthuridae) showed order-of-magnitude differences in biomass among islands. Biomass fell as fishing pressure increased. Only grunts (Haemulidae) did not follow this pattern. Within families, larger-bodied species decreased as fishing intensified. Coral cover and structural complexity were highest on little-fished islands and lowest on those most fished. By contrast, algal cover was an order of magnitude higher in Jamaica than in Bonaire. These results suggest that following the Caribbean-wide mass mortality of herbivorous sea urchins in 1983–1984 and consequent declines in grazing pressure on reefs, herbivorous fishes have not controlled algae overgrowing corals in heavily fished areas but have restricted growth in lightly fished areas. In summary, differences among islands in the structure of fish and benthic assemblages suggest that intensive artisanal fishing has transformed Caribbean reefs.     

Exploited species impacts on trophic linkages along reef-seagrass interfaces in the Florida Keys

The removal of fish biomass by extensive commercial and recreational fishing has been hypothesized to drastically alter the strength of trophic linkages among adjacent habitats. We evaluated the effects of removing predatory fishes on trophic transfers between coral reefs and adjacent seagrass meadows by comparing fish community structure, grazing intensity, and invertebrate predation potential in predator-rich no-take sites and nearby predator-poor fished sites in the Florida Keys (USA). Exploited fishes were more abundant at the no-take sites than at the fished sites. Most of the exploited fishes were either omnivores or invertivores. More piscivores were recorded at no-take sites, but most (approximately 95%) were moderately fished and unexploited species (barracuda and bar jacks, respectively). Impacts of these consumers on lower trophic levels were modest. Herbivorous and smaller prey fish (< 10 cm total length) densities and seagrass grazing diminished with distance from reefs and were not negatively impacted by the elevated densities of exploited fishes at no-take sites. Predation by reef fishes on most tethered invertebrates was high, but exploited species impacts varied with prey type. The results of the study show that, even though abundances of reef-associated fishes have been reduced at fished sites, there is little evidence that this has produced cascading trophic effects or interrupted cross-habitat energy exchanges between coral reefs and seagrasses.     

Predators selectively graze reproductive structures in a clonal marine organism

Although the fitness consequences of herbivory on terrestrial plants have been extensively studied, considerably less is known about how partial predation impacts the fitness of clonal marine organisms. The trophic role of Caribbean parrotfish on coral reefs is complex: while these fish are important herbivores, as corallivores (consumers of live coral tissue), they selectively graze specific species and colonies of reef-building corals. Though the benefits of parrotfish herbivory for reef resilience and conservation are well documented, the negative consequences of parrotfish grazing for coral reproductive fitness have not been previously determined. We examined recently grazed colonies of Montastraea annularis corals to determine whether grazing was positively associated with coral reproductive effort. We measured gonad number, egg number and size, and proportional reproductive allocation for grazed and intact coral colonies 2–5 days prior to their annual spawning time. We found that parrotfish selectively grazed coral polyps with high total reproductive effort (number of gonads), providing the first evidence that parrotfish selectively target specific tissue areas within a single coral colony. The removal of polyps with high reproductive effort has direct adverse affects on coral fitness, with additional indirect implications for colony growth and survival. We conclude that chronic grazing by parrotfishes has negative fitness consequences for reef-building corals, and by extension, reef ecosystems.     

The Wicked Problem of China's Disappearing Coral Reefs

We examined the development of coral reef science and the policies, institutions, and governance frameworks for management of coral reefs in China in order to highlight the wicked problem of preserving reefs while simultaneously promoting human development and nation building. China and other sovereign states in the region are experiencing unprecedented economic expansion, rapid population growth, mass migration, widespread coastal development, and loss of habitat. We analyzed a large, fragmented literature on the condition of coral reefs in China and the disputed territories of the South China Sea. We found that coral abundance has declined by at least 80% over the past 30 years on coastal fringing reefs along the Chinese mainland and adjoining Hainan Island. On offshore atolls and archipelagos claimed by 6 countries in the South China Sea, coral cover has declined from an average of >60% to around 20% within the past 10–15 years. Climate change has affected these reefs far less than coastal development, pollution, overfishing, and destructive fishing practices. Ironically, these widespread declines in the condition of reefs are unfolding as China's research and reef‐management capacity are rapidly expanding. Before the loss of corals becomes irreversible, governance of China's coastal reefs could be improved by increasing public awareness of declining ecosystem services, by providing financial support for training of reef scientists and managers, by improving monitoring of coral reef dynamics and condition to better inform policy development, and by enforcing existing regulations that could protect coral reefs. In the South China Sea, changes in policy and legal frameworks, refinement of governance structures, and cooperation among neighboring countries are urgently needed to develop cooperative management of contested offshore reefs. El Problema Malvado de la Desaparición de los Arrecifes de Coral en China     

Trait groups as management entities in a complex,multispecies reef fishery

Localized stressors compound the ongoing climate-driven decline of coral reefs, requiring natural resource managers to work with rapidly shifting paradigms. Trait-based adaptive management (TBAM) is a new framework to help address changing conditions by choosing and implementing management actions specific to species groups that share key traits, vulnerabilities, and management responses. In TBAM maintenance of functioning ecosystems is balanced with provisioning for human subsistence and livelihoods. We first identified trait-based groups of food fish in a Pacific coral reef with hierarchical clustering. Positing that trait-based groups performing comparable functions respond similarly to both stressors and management actions, we ascertained biophysical and socioeconomic drivers of trait-group biomass and evaluated their vulnerabilities with generalized additive models. Clustering identified 7 trait groups from 131 species. Groups responded to different drivers and displayed divergent vulnerabilities; human activities emerged as important predictors of community structuring. Biomass of small, solitary reef-associated species increased with distance from key fishing ports, and large, solitary piscivores exhibited a decline in biomass with distance from a port. Group biomass also varied in response to different habitat types, the presence or absence of reported dynamite fishing activity, and exposure to wave energy. The differential vulnerabilities of trait groups revealed how the community structure of food fishes is driven by different aspects of resource use and habitat. This inherent variability in the responses of trait-based groups presents opportunities to apply selective TBAM strategies for complex, multispecies fisheries. This approach can be widely adjusted to suit local contexts and priorities.     

Tracking the response of industrial fishing fleets to large marine protected areas in the Pacific Ocean

Large marine protected areas (MPAs) of unprecedented size have recently been established across the global oceans, yet their ability to meet conservation objectives is debated. Key areas of debate include uncertainty over nations’ abilities to enforce fishing bans across vast, remote regions and the intensity of human impacts before and after MPA implementation. We used a recently developed vessel tracking data set (produced using Automatic Identification System detections) to quantify the response of industrial fishing fleets to 5 of the largest MPAs established in the Pacific Ocean since 2013. After their implementation, all 5 MPAs successfully kept industrial fishing effort exceptionally low. Detected fishing effort was already low in 4 of the 5 large MPAs prior to MPA implementation, particularly relative to nearby regions that did not receive formal protection. Our results suggest that these large MPAs may present major conservation opportunities in relatively intact ecosystems with low immediate impact to industrial fisheries, but the large MPAs we considered often did not significantly reduce fishing effort because baseline fishing was typically low. It is yet to be determined how large MPAs may shape global ocean conservation in the future if the footprint of human influence continues to expand. Continued improvement in understanding of how large MPAs interact with industrial fisheries is a crucial step toward defining their role in global ocean management.     

Marine reserves reduce risk of climate-driven phase shift by reinstating size- and habitat-specific trophic interactions

Spatial closures in the marine environment are widely accepted as effective conservation and fisheries management tools. Given increasing human-derived stressors acting on marine ecosystems, the need for such effective action is urgently clear. Here we explore mechanisms underlying the utility of marine reserves to reinstate trophic dynamics and to increase resilience of kelp beds against climate-driven phase shift to sea urchin barrens on the rapidly warming Tasmanian east coast. Tethering and tagging experiments were used to examine size- and shelter-specific survival of the range-extending sea urchin Centrostephanus rodgersii (Diadematidae) translocated to reefs inside and outside no-take Tasmanian marine reserves. Results show that survival rates of C. rodgersii exposed on flat reef substratum by tethering were approximately seven times (small urchins 10.1 times; large urchins 6.1 times) lower on protected reef within marine reserve boundaries (high abundance of large predatory-capable lobsters) compared to fished reef (large predatory lobsters absent). When able to seek crevice shelter, tag-resighting models estimated that mortality rates of C. rodgersii were lower overall but remained 3.3 times (small urchins 2.1 times; large urchins 6.4 times) higher in the presence of large lobsters inside marine reserves, with higher survival of small urchins owing to greater access to crevices relative to large urchins. Indeed, shelter was 6.3 times and 3.1 times more important to survival of small and large urchins, respectively, on reserved relative to fished reef. Experimental results corroborate with surveys throughout the range extension region, showing greater occurrence of overgrazing on high-relief rocky habitats where shelter for C. rodgersii is readily available. This shows that ecosystem impacts mediated by range extension of such habitat-modifying organisms will be heterogeneous in space, and that marine systems with a more natural complement of large and thus functional predators, as achievable within no-take reserves, will minimize local risk of phase shifts by reinstating size and habitat-specific predator-prey dynamics eroded by fishing. Importantly, our findings also highlight the crucial need to account for the influence of size dynamics and habitat complexity on rates of key predator-prey interactions when managing expectations of ecosystem-level responses within marine reserve boundaries.     

Biomass‐based targets and the management of multispecies coral reef fisheries

The failure of fisheries management among multispecies coral reef fisheries is well documented and has dire implications for the 100 million people engaged in these small‐scale operations. Weak or missing management institutions, a lack of research capacity, and the complex nature of these ecosystems have heralded a call for ecosystem‐based management approaches. However, ecosystem‐based management of coral reef fisheries has proved challenging due to the multispecies nature of catches and the diversity of fish functional roles. We used data on fish communities collected from 233 individual sites in 9 western Indian Ocean countries to evaluate changes in the site's functional composition and associated life‐history characteristics along a large range of fish biomass. As biomass increased along this range, fish were larger and grew and matured more slowly while the abundance of scraping and predatory species increased. The greatest changes in functional composition occurred below relatively low standing stock biomass (<600 kg/ha); abundances of piscivores, apex predators, and scraping herbivores were low at very light levels of fishing. This suggests potential trade‐offs in ecosystem function and estimated yields for different management systems. Current fishing gear and area restrictions are not achieving conservation targets (proposed here as standing stock biomass of 1150 kg/ha) and result in losses of life history and ecological functions. Fish in reefs where destructive gears were restricted typically had very similar biomass and functions to young and low compliance closures. This indicates the potentially important role of fisheries restrictions in providing some gains in biomass and associated ecological functions when fully protected area enforcement potential is limited and likely to fail. Our results indicate that biomass alone can provide broad ecosystem‐based fisheries management targets that can be easily applied even where research capacity and information is limited. Of particular value, is our finding that current management tools may be used to reach key ecosystem‐based management targets, enabling ecosystem‐based management in many socioeconomic contexts.     

Forest conservation delivers highly variable coral reef conservation outcomes

Coral reefs are threatened by human activities on both the land (e.g., deforestation) and the sea (e.g., overfishing). Most conservation planning for coral reefs focuses on removing threats in the sea, neglecting management actions on the land. A more integrated approach to coral reef conservation, inclusive of land-sea connections, requires an understanding of how and where terrestrial conservation actions influence reefs. We address this by developing a land-sea planning approach to inform fine-scale spatial management decisions and test it in Fiji. Our aim is to determine where the protection of forest can deliver the greatest return on investment for coral reef ecosystems. To assess the benefits of conservation to coral reefs, we estimate their relative condition as influenced by watershed-based pollution and fishing. We calculate the cost-effectiveness of protecting forest and find that investments deliver rapidly diminishing returns for improvements to relative reef condition. For example, protecting 2% of forest in one area is almost 500 times more beneficial than protecting 2% in another area, making prioritization essential. For the scenarios evaluated, relative coral reef condition could be improved by 8-58% if all remnant forest in Fiji were protected rather than deforested. Finally, we determine the priority of each coral reef for implementing a marine protected area when all remnant forest is protected for conservation. The general results will support decisions made by the Fiji Protected Area Committee as they establish a national protected area network that aims to protect 20% of the land and 30% of the inshore waters by 2020. Although challenges remain, we can inform conservation decisions around the globe by tackling the complex issues relevant to integrated land-sea planning.     

Coral Bleaching and Global Climate Change: Scientific Findings and Policy Recommendations

Abstract: In 1998, tropical sea surface temperatures were the highest on record, topping off a 50-year trend for some tropical oceans. In the same year, coral reefs around the world suffered the most extensive and severe bleaching ( loss of symbiotic algae) and subsequent mortality on record. These events may not be attributable to local stressors or natural variability alone but were likely induced by an underlying global phenomenon. It is probable that anthropogenic global warming has contributed to the extensive coral bleaching that has occurred simultaneously throughout the reef regions of the world. The geographic extent, increasing frequency, and regional severity of mass bleaching events are an apparent result of a steadily rising baseline of marine temperatures, combined with regionally specific El Niño and La Niña events. The repercussions of the 1998 mass bleaching and mortality events will be far-reaching. Human populations dependent on reef services face losses of marine biodiversity, fisheries, and shoreline protection. Coral bleaching events may become more frequent and severe as the climate continues to warm, exposing coral reefs to an increasingly hostile environment. This global threat to corals compounds the effects of more localized anthropogenic factors that already place reefs at risk. Significant attention needs to be given to the monitoring of coral reef ecosystems, research on the projected and realized effects of global climate change, and measures to curtail greenhouse gas emissions. Even those reefs with well-enforced legal protection as marine sanctuaries, or those managed for sustainable use, are threatened by global climate change.     

Slow Growth and Lack of Recovery in Overfished Holothurians on the Great Barrier Reef: Evidence from DNA Fingerprints and Repeated Large-Scale Surveys

Abstract:  Commercially fished holothurians have important functions in nutrient recycling, which increases the benthic productivity of coral reef ecosystems. Thus, removal of these animals through fishing may reduce the overall productivity of affected coral reefs. To investigate the potential for recovery of overfished holothurian (  Holothuria nobilis ) stocks on the Great Barrier Reef (GBR), we (1) conducted field surveys on 23 reefs after fishery closure, (2) modeled total virgin biomass and compared it with the total amount fished, and (3) estimated individual growth rates with a DNA fingerprinting technique. Two years after fishery closure, no recovery of H. nobilis stocks on reefs previously open to fishing was observed. Densities on reefs protected from fishing since the onset of the fishery in the mid 1980s remained about four times higher than on fished reefs. Based on density estimates and geographic information system data on the habitat area of each reef, we calculated that the virgin biomass (in the main fished area between 12° and 19°S) was about 5500 t and is now about 2500 t. The reduction is on the same order of magnitude as the total amount fished until 1999 (approximately 2500 t). The DNA analysis of repeated samples on three locations indicated high recapture rates of fingerprinted and released individuals of H. nobilis . Fitting growth curves with Francis's growth function indicated that medium-sized individuals (1 kg) grew 35–533 g /year, whereas large animals (2.5 kg) consistently shrank. Small animals (<500 g) were rarely observed. In combination, these data indicate that production of H. nobilis stocks is very low, presumably with low mortality, low recruitment, and slow individual growth rates. Consistent with anecdotal evidence, recovery of H. nobilis stocks on the GBR may take several decades, and we suggest a highly conservative management plan to protect both the stocks and the ecosystem.     

Practical management of cumulative anthropogenic impacts with working marine examples

Human pressure on the environment is expanding and intensifying, especially in coastal and offshore areas. Major contributors to this are the current push for offshore renewable energy sources, which are thought of as environmentally friendly sources of power, as well as the continued demand for petroleum. Human disturbances, including the noise almost ubiquitously associated with human activity, are likely to increase the incidence, magnitude, and duration of adverse effects on marine life, including stress responses. Stress responses have the potential to induce fitness consequences for individuals, which add to more obvious directed takes (e.g., hunting or fishing) to increase the overall population‐level impact. To meet the requirements of marine spatial planning and ecosystem‐based management, many efforts are ongoing to quantify the cumulative impacts of all human actions on marine species or populations. Meanwhile, regulators face the challenge of managing these accumulating and interacting impacts with limited scientific guidance. We believe there is scientific support for capping the level of impact for (at a minimum) populations in decline or with unknown statuses. This cap on impact can be facilitated through implementation of regular application cycles for project authorization or improved programmatic and aggregated impact assessments that simultaneously consider multiple projects. Cross‐company collaborations and a better incorporation of uncertainty into decision making could also help limit, if not reduce, cumulative impacts of multiple human activities. These simple management steps may also form the basis of a rudimentary form of marine spatial planning and could be used in support of future ecosystem‐based management efforts.     

A novel method for mapping reefs and subtidal rocky habitats using artificial neural networks

Reefs and subtidal rocky habitats are sites of high biodiversity and productivity which harbour commercially important species of fish and invertebrates. Although the conservation management of reef associated species has been informed using species distribution models (SDM) and community based approaches, to date their use has been constrained to specific regions where the locality and spatial extent of reefs is well known. Much of the world's subtidal habitats remain either undiscovered or unmapped, including coasts of intense human use. Consequently, to facilitate a stronger understanding of species-environmental relationships there is an urgent need for a cost and time effective standard method to map reefs at fine spatial resolutions across broad geographical extents. We used bathymetric data (∼250 m resolution) to calculate the local slope and curvature of the seabed. We then constructed artificial neural networks (ANNs) to forecast the probability of reef occurrence within grid cells as a function of bathymetric and slope variables. Testing over an independent data set not used in training showed that ANNs were able to accurately predict the location of reefs for 86% of all grid cells (Kappa = 0.63) without over fitting. The ANN with greatest support, combining bathymetric values of the target grid cell with the slope of adjacent grid cells, was used to map inshore reef locations around the Southern Australian coastline (∼250 m resolution). Broadly, our results show that reefs are identifiable from coarse-scale bathymetry data of the seabed. We anticipate that our research technique will strengthen systematic conservation planning tools in many regions of the world, by enabling the identification of rocky substratum and mapping in localities that remain poorly surveyed due to logistics or monetary constraints.