Tropical fishery nutrient production depends on biomass-based management.

The need to enhance nutrient production from tropical ecosystems to feed the poor could potentially create a new framework for fisheries science and management. Early recommendations have included targeting small fishes and increasing the species richness of fish catches, which could represent a departure from more traditional approaches such as biomass-based management. To test these recommendations, we compared the outcomes of biomass-based management with hypothesized factors influencing nutrient density in nearshore artisanal fish catches in the Western Indian Ocean. We found that enhancing nutrient production depends primarily on achieving biomass-based targets. Catches dominated by low- and mid-trophic level species with smaller body sizes and faster turnover were associated with modest increases in nutrient densities, but the variability in nutrient density was small relative to human nutritional requirements. Therefore, tropical fishery management should focus on restoring biomass to achieve maximum yields and sustainability, particularly for herbivorous fishes.

Macroalgae exhibit diverse responses to human disturbances on coral reefs.

Scientists and managers rely on indicator taxa such as coral and macroalgal cover to evaluate the effects of human disturbance on coral reefs, often assuming a universally positive relationship between local human disturbance and macroalgae. Despite evidence that macroalgae respond to local stressors in diverse ways, there have been few efforts to evaluate relationships between specific macroalgae taxa and local human-driven disturbance. Using genus-level monitoring data from 1205 sites in the Indian and Pacific Oceans, we assess whether macroalgae percent cover correlates with local human disturbance while accounting for factors that could obscure or confound relationships. Assessing macroalgae at genus level revealed that no genera were positively correlated with all human disturbance metrics. Instead, we found relationships between the division or genera of algae and specific human disturbances that were not detectable when pooling taxa into a single functional category, which is common to many analyses. The convention to use percent cover of macroalgae as an indication of local human disturbance therefore likely obscures signatures of local anthropogenic threats to reefs. Our limited understanding of relationships between human disturbance, macroalgae taxa, and their responses to human disturbances impedes the ability to diagnose and respond appropriately to these threats.

Water quality mediates resilience on the Great Barrier Reef.

Threats from climate change and other human pressures have led to widespread concern for the future of Australia's Great Barrier Reef (GBR). Resilience of GBR reefs will be determined by their ability to resist disturbances and to recover from coral loss, generating intense interest in management actions that can moderate these processes. Here we quantify the effect of environmental and human drivers on the resilience of southern and central GBR reefs over the past two decades. Using a composite water quality index, we find that while reefs exposed to poor water quality are more resistant to coral bleaching, they recover from disturbance more slowly and are more susceptible to outbreaks of crown-of-thorns starfish and coral disease-with a net negative impact on recovery and long-term hard coral cover. Given these conditions, we find that 6-17% improvement in water quality will be necessary to bring recovery rates in line with projected increases in coral bleaching among contemporary inshore and mid-shelf reefs. However, such reductions are unlikely to buffer projected bleaching effects among outer-shelf GBR reefs dominated by fast-growing, thermally sensitive corals, demonstrating practical limits to local management of the GBR against the effects of global warming.

Author Correction: High frequency temperature variability reduces the risk of coral bleaching.

The original version of the Article was missing an acknowledgement of a funding source. The authors acknowledge that A. Safaie and K.Davis were supported by National Science Foundation Award No. 1436254 and G. Pawlak was supported by Award No. 1436522. This omission has now been corrected in the PDF and HTML versions of the Article.

High frequency temperature variability reduces the risk of coral bleaching.

Coral bleaching is the detrimental expulsion of algal symbionts from their cnidarian hosts, and predominantly occurs when corals are exposed to thermal stress. The incidence and severity of bleaching is often spatially heterogeneous within reef-scales (<1 km), and is therefore not predictable using conventional remote sensing products. Here, we systematically assess the relationship between in situ measurements of 20 environmental variables, along with seven remotely sensed SST thermal stress metrics, and 81 observed bleaching events at coral reef locations spanning five major reef regions globally. We find that high-frequency temperature variability (i.e., daily temperature range) was the most influential factor in predicting bleaching prevalence and had a mitigating effect, such that a 1 °C increase in daily temperature range would reduce the odds of more severe bleaching by a factor of 33. Our findings suggest that reefs with greater high-frequency temperature variability may represent particularly important opportunities to conserve coral ecosystems against the major threat posed by warming ocean temperatures.

Community- and government-managed marine protected areas increase fish size, biomass and potential value.

Government-managed marine protected areas (MPAs) can restore small fish stocks, but have been heavily criticized for excluding resource users and creating conflicts. A promising but less studied alternative are community-managed MPAs, where resource users are more involved in MPA design, implementation and enforcement. Here we evaluated effects of government- and community-managed MPAs on the density, size and biomass of seagrass- and coral reef-associated fish, using field surveys in Kenyan coastal lagoons. We also assessed protection effects on the potential monetary value of fish; a variable that increases non-linearly with fish body mass and is particularly important from a fishery perspective. We found that two recently established community MPAs (< 1 km2 in size, ≤ 5 years of protection) harbored larger fish and greater total fish biomass than two fished (open access) areas, in both seagrass beds and coral reefs. As expected, protection effects were considerably stronger in the older and larger government MPAs. Importantly, across management and habitat types, the protection effect on the potential monetary value of the fish was much stronger than the effects on fish biomass and size (6.7 vs. 2.6 and 1.3 times higher value in community MPAs than in fished areas, respectively). This strong effect on potential value was partly explained by presence of larger (and therefore more valuable) individual fish, and partly by higher densities of high-value taxa (e.g. rabbitfish). In summary, we show that i) small and recently established community-managed MPAs can, just like larger and older government-managed MPAs, play an important role for local conservation of high-value fish, and that ii) these effects are equally strong in coral reefs as in seagrass beds; an important habitat too rarely included in formal management. Consequently, community-managed MPAs could benefit both coral reef and seagrass ecosystems and provide spillover of valuable fish to nearby fisheries.

Correction: To Fish or Not to Fish: Factors at Multiple Scales Affecting Artisanal Fishers' Readiness to Exit a Declining Fishery.

[This corrects the article DOI: 10.1371/journal.pone.0031460.].

Correction: Modeling Reef Fish Biomass, Recovery Potential, and Management Priorities in the Western Indian Ocean.

[This corrects the article DOI: 10.1371/journal.pone.0154585.].

Modeling Reef Fish Biomass, Recovery Potential, and Management Priorities in the Western Indian Ocean.

Fish biomass is a primary driver of coral reef ecosystem services and has high sensitivity to human disturbances, particularly fishing. Estimates of fish biomass, their spatial distribution, and recovery potential are important for evaluating reef status and crucial for setting management targets. Here we modeled fish biomass estimates across all reefs of the western Indian Ocean using key variables that predicted the empirical data collected from 337 sites. These variables were used to create biomass and recovery time maps to prioritize spatially explicit conservation actions. The resultant fish biomass map showed high variability ranging from ~15 to 2900 kg/ha, primarily driven by human populations, distance to markets, and fisheries management restrictions. Lastly, we assembled data based on the age of fisheries closures and showed that biomass takes ~ 25 years to recover to typical equilibrium values of ~1200 kg/ha. The recovery times to biomass levels for sustainable fishing yields, maximum diversity, and ecosystem stability or conservation targets once fishing is suspended was modeled to estimate temporal costs of restrictions. The mean time to recovery for the whole region to the conservation target was 8.1(± 3SD) years, while recovery to sustainable fishing thresholds was between 0.5 and 4 years, but with high spatial variation. Recovery prioritization scenario models included one where local governance prioritized recovery of degraded reefs and two that prioritized minimizing recovery time, where countries either operated independently or collaborated. The regional collaboration scenario selected remote areas for conservation with uneven national responsibilities and spatial coverage, which could undermine collaboration. There is the potential to achieve sustainable fisheries within a decade by promoting these pathways according to their social-ecological suitability.

What Happens after Conservation and Management Donors Leave? A Before and After Study of Coral Reef Ecology and Stakeholder Perceptions of Management Benefits.

The coral reefs of Tanga, Tanzania were recognized as a national conservation priority in the early 1970s, but the lack of a management response led to damage by dynamite, beach seines, and high numbers of fishers until the mid 1990s. Subsequently, an Irish Aid funded IUCN Eastern Africa program operated from 1994 to mid 2007 to implement increased management aimed at reducing these impacts. The main effects of this management were to establish collaborative management areas, reduce dynamite and seine net fishing, and establish small community fisheries closures beginning in 1996. The ecology of the coral reefs was studied just prior to the initiation of this management in 1996, during, 2004, and a few years after the project ended in 2010. The perceptions of resource users towards management options were evaluated in 2010. The ecological studies indicated that the biomass of fish rose continuously during this period from 260 to 770 kg/ha but the small closures were no different from the non-closure areas. The benthic community studies indicate stability in the coral cover and community composition and an increase in coralline algae and topographic complexity over time. The lack of change in the coral community suggests resilience to various disturbances including fisheries management and the warm temperature anomaly of 1998. These results indicate that some aspects of the management program had been ecologically successful even after the donor program ended. Moreover, the increased compliance with seine net use and dynamite restrictions were the most likely factors causing this increase in fish biomass and not the closures. Resource users interviewed in 2010 were supportive of gear restrictions but there was considerable between-community disagreement over the value of specific restrictions. The social-ecological results suggest that increased compliance with gear restrictions is largely responsible for the improvements in reef ecology and is a high priority for future management programs.

Biogeography and change among regional coral communities across the Western Indian Ocean.

Coral reefs are biodiverse ecosystems structured by abiotic and biotic factors operating across many spatial scales. Regional-scale interactions between climate change, biogeography and fisheries management remain poorly understood. Here, we evaluated large-scale patterns of coral communities in the western Indian Ocean after a major coral bleaching event in 1998. We surveyed 291 coral reef sites in 11 countries and over 30° of latitude between 2004 and 2011 to evaluate variations in coral communities post 1998 across gradients in latitude, mainland-island geography and fisheries management. We used linear mixed-effect hierarchical models to assess total coral cover, the abundance of four major coral families (acroporids, faviids, pocilloporids and poritiids), coral genus richness and diversity, and the bleaching susceptibility of the coral communities. We found strong latitudinal and geographic gradients in coral community structure and composition that supports the presence of a high coral cover and diversity area that harbours temperature-sensitive taxa in the northern Mozambique Channel between Tanzania, northern Mozambique and northern Madagascar. Coral communities in the more northern latitudes of Kenya, Seychelles and the Maldives were generally composed of fewer bleaching-tolerant coral taxa and with reduced richness and diversity. There was also evidence for continued declines in the abundance of temperature-sensitive taxa and community change after 2004. While there are limitations of our regional dataset in terms of spatial and temporal replication, these patterns suggest that large-scale interactions between biogeographic factors and strong temperature anomalies influence coral communities while smaller-scale factors, such as the effect of fisheries closures, were weak. The northern Mozambique Channel, while not immune to temperature disturbances, shows continued signs of resistance to climate disturbances and remains a priority for future regional conservation and management actions.

Life histories predict coral community disassembly under multiple stressors.

Climate change is reshaping biological communities against a background of existing human pressure. Evaluating the impacts of multiple stressors on community dynamics can be particularly challenging in species-rich ecosystems, such as coral reefs. Here, we investigate whether life-history strategies and cotolerance to different stressors can predict community responses to fishing and temperature-driven bleaching using a 20-year time series of coral assemblages in Kenya. We found that the initial life-history composition of coral taxa largely determined the impacts of bleaching and coral loss. Prior to the 1998 bleaching event, coral assemblages within no-take marine reserves were composed of three distinct life histories - competitive, stress-tolerant and weedy- and exhibited strong declines following bleaching with limited subsequent recovery. In contrast, fished reefs had lower coral cover, fewer genera and were composed of stress-tolerant and weedy corals that were less affected by bleaching over the long term. Despite these general patterns, we found limited evidence for cotolerance as coral genera and life histories were variable in their sensitivities to fishing and bleaching. Overall, fishing and bleaching have reduced coral diversity and led to altered coral communities of 'survivor' species with stress-tolerant and weedy life histories. Our findings are consistent with expectations that climate change interacting with existing human pressure will result in the loss of coral diversity and critical reef habitat.

Evaluating life-history strategies of reef corals from species traits.

Classifying the biological traits of organisms can test conceptual frameworks of life-history strategies and allow for predictions of how different species may respond to environmental disturbances. We apply a trait-based classification approach to a complex and threatened group of species, scleractinian corals. Using hierarchical clustering and random forests analyses, we identify up to four life-history strategies that appear globally consistent across 143 species of reef corals: competitive, weedy, stress-tolerant and generalist taxa, which are primarily separated by colony morphology, growth rate and reproductive mode. Documented shifts towards stress-tolerant, generalist and weedy species in coral reef communities are consistent with the expected responses of these life-history strategies. Our quantitative trait-based approach to classifying life-history strategies is objective, applicable to any taxa and a powerful tool that can be used to evaluate theories of community ecology and predict the impact of environmental and anthropogenic stressors on species assemblages.

Assessing gear modifications needed to optimize yields in a heavily exploited, multi-species, seagrass and coral reef fishery.

Effective management is necessary if small-scale fisheries, such as those found in mixed habitats including seagrass and coral reefs, are to continue providing food for many of the poorest communities of the world. Gear-based management, although under represented and under studied, has the potential to be adaptive, address multiple objectives, and be crafted to the socio-economic setting. Management effectiveness in seagrass and coral reef fisheries has generally been evaluated at the scale of the fish community. However, community level indicators can mask species-specific declines that provide significant portions of the fisheries yields and income. Using a unique dataset, containing ten years of species level length frequency catch data from a multi-gear, multi-species seagrass and coral reef fishery in Kenya, we evaluate species specific fishery statuses, compare gear use to gear regulations and estimate the potential needs for further gear restrictions. Despite the high diversity of the fishery, fifteen species represented over 90% of the catch, and only three species represented 60% of the catch. The three most abundant species in the catch, Lethrinus lentjan (Lacepède), Siganus sutor (Valenciennes) and Leptoscarus vaigiensis (Quoy & Gaimard) all showed evidence of growth overfishing. Lethrinus lentjan, with an exploitation rate of 0.82, also shows evidence of recruitment overfishing. Current legal but weakly enforced gear restrictions are capable of protecting a significant portion of the catch up to maturity but optimization of yield will require that the current mesh size be increased from 6.3 to 8.8 and 9.2 cm to increase yields of L. lentjan and S. sutor, respectively. Given the difficulties of enforcing mesh size, we recommend that the economic benefits of these larger mesh sizes be communicated and enforced through co-management. This abstract is also available in Kiswahili (Abstract S1).

Comparison of marine spatial planning methods in Madagascar demonstrates value of alternative approaches.

The Government of Madagascar plans to increase marine protected area coverage by over one million hectares. To assist this process, we compare four methods for marine spatial planning of Madagascar's west coast. Input data for each method was drawn from the same variables: fishing pressure, exposure to climate change, and biodiversity (habitats, species distributions, biological richness, and biodiversity value). The first method compares visual color classifications of primary variables, the second uses binary combinations of these variables to produce a categorical classification of management actions, the third is a target-based optimization using Marxan, and the fourth is conservation ranking with Zonation. We present results from each method, and compare the latter three approaches for spatial coverage, biodiversity representation, fishing cost and persistence probability. All results included large areas in the north, central, and southern parts of western Madagascar. Achieving 30% representation targets with Marxan required twice the fish catch loss than the categorical method. The categorical classification and Zonation do not consider targets for conservation features. However, when we reduced Marxan targets to 16.3%, matching the representation level of the "strict protection" class of the categorical result, the methods show similar catch losses. The management category portfolio has complete coverage, and presents several management recommendations including strict protection. Zonation produces rapid conservation rankings across large, diverse datasets. Marxan is useful for identifying strict protected areas that meet representation targets, and minimize exposure probabilities for conservation features at low economic cost. We show that methods based on Zonation and a simple combination of variables can produce results comparable to Marxan for species representation and catch losses, demonstrating the value of comparing alternative approaches during initial stages of the planning process. Choosing an appropriate approach ultimately depends on scientific and political factors including representation targets, likelihood of adoption, and persistence goals.

To fish or not to fish: factors at multiple scales affecting artisanal fishers' readiness to exit a declining fishery.

Globally, fisheries are challenged by the combined impacts of overfishing, degradation of ecosystems and impacts of climate change, while fisheries livelihoods are further pressured by conservation policy imperatives. Fishers' adaptive responses to these pressures, such as exiting from a fishery to pursue alternative livelihoods, determine their own vulnerability, as well as the potential for reducing fishing effort and sustaining fisheries. The willingness and ability to make particular adaptations in response to change, such as exiting from a declining fishery, is influenced by economic, cultural and institutional factors operating at scales from individual fishers to national economies. Previous studies of exit from fisheries at single or few sites, offer limited insight into the relative importance of individual and larger-scale social and economic factors. We asked 599 fishers how they would respond to hypothetical scenarios of catch declines in 28 sites in five western Indian Ocean countries. We investigated how socioeconomic variables at the individual-, household- and site-scale affected whether they would exit fisheries. Site-level factors had the greatest influence on readiness to exit, but these relationships were contrary to common predictions. Specifically, higher levels of infrastructure development and economic vitality - expected to promote exit from fisheries - were associated with less readiness to exit. This may be due to site level histories of exit from fisheries, greater specialisation of fishing households, or higher rewards from fishing in more economically developed sites due to technology, market access, catch value and government subsidies. At the individual and household scale, fishers from households with more livelihood activities, and fishers with lower catch value were more willing to exit. These results demonstrate empirically how adaptive responses to change are influenced by factors at multiple scales, and highlight the importance of understanding natural resource-based livelihoods in the context of the wider economy and society.

Comparison of modern and historical fish catches (AD 750-1400) to inform goals for marine protected areas and sustainable fisheries.

We tested the unsustainable fishing hypothesis that species in assemblages of fish differ in relative abundance as a function of their size, growth rates, vagility, trophic level, and diet by comparing species composition in historical bone middens, modern fisheries, and areas closed to fishing. Historical data came from one of the earliest and most enduring Swahili coastal settlements (approximately AD 750-1400). Modern data came from fisheries near the archeological site and intensively harvested fishing grounds in southern Kenya. The areas we sampled that were closed to fishing (closures) were small (<28 km(2) ) and permanent. The midden data indicated changes in the fish assemblage that are consistent with a weak expansion of fishing intensity and the unsustainable fishing hypothesis. Fishes represented in the early midden assemblages from AD 750 to 950 had longer life spans, older age at maturity, and longer generation times than fish assemblages after AD 950, when the abundance of species with longer maximum body lengths increased. Changes in fish life histories during the historical period were, however, one-third smaller than differences between the historical and modern assemblages. Fishes in the modern assemblage had smaller mean body sizes, higher growth and mortality rates, a higher proportion of microinvertivores, omnivores, and herbivores, and higher rates of food consumption, whereas the historical assemblage had a greater proportion of piscivores and macroinvertivores. Differences in fish life histories between modern closures and modern fishing grounds were also small, but the life histories of fishes in modern closures were more similar to those in the midden before AD 950 because they had longer life spans, older age at maturity, and a higher proportion of piscivores and macroinvertivores than the modern fisheries. Modern closures and historical fish assemblages were considerably different, although both contained species with longer life spans.

Effects of fisheries closures and gear restrictions on fishing income in a Kenyan coral reef.

The adoption of fisheries closures and gear restrictions in the conservation of coral reefs may be limited by poor understanding of the economic profitability of competing economic uses of marine resources. Over the past 12 years, I evaluated the effects of gear regulation and fisheries closures on per person and per area incomes from fishing in coral reefs of Kenya. In two of my study areas, the use of small-meshed beach seines was stopped after 6 years; one of these areas was next to a fishery closure. In my third study area, fishing was unregulated. Fishing yields on per capita daily wet weight basis were 20% higher after seine-net fishing was stopped. The per person daily fishing income adjacent to the closed areas was 14 and 22% higher than the fishing income at areas with only gear restrictions before and after the seine-net restriction, respectively. Incomes differed because larger fish were captured next to the closed area and the price per weight (kilograms) increased as fish size increased and because catches adjacent to the closure contained fish species of higher market value. Per capita incomes were 41 and 135% higher for those who fished in gear-restricted areas and near-closed areas, respectively, compared with those who fished areas with no restrictions. On a per unit area basis (square kilometers), differences in fishing income among the three areas were not large because fishing effort increased as the number of restrictions decreased. Changes in catch were, however, larger and often in the opposite direction expected from changes in effort alone. For example, effort declined 21% but nominal profits per square kilometer (not accounting for inflation) increased 29% near the area with gear restrictions. Gear restrictions also reduced the cost of fishing and increased the proportion of self-employed fishers.

Marine reserves as linked social-ecological systems.

Marine reserves are increasingly recognized as having linked social and ecological dynamics. This study investigates how the ecological performance of 56 marine reserves throughout the Philippines, Caribbean, and Western Indian Ocean (WIO) is related to both reserve design features and the socioeconomic characteristics in associated coastal communities. Ecological performance was measured as fish biomass in the reserve relative to nearby areas. Of the socioeconomic variables considered, human population density and compliance with reserve rules had the strongest effects on fish biomass, but the effects of these variables were region specific. Relationships between population density and the reserve effect on fish biomass were negative in the Caribbean, positive in the WIO, and not detectable in the Philippines. Differing associations between population density and reserve effectiveness defy simple explanation but may depend on human migration to effective reserves, depletion of fish stocks outside reserves, or other social factors that change with population density. Higher levels of compliance reported by resource users was related to higher fish biomass in reserves compared with outside, but this relationship was only statistically significant in the Caribbean. A heuristic model based on correlations between social, cultural, political, economic, and other contextual conditions in 127 marine reserves showed that high levels of compliance with reserve rules were related to complex social interactions rather than simply to enforcement of reserve rules. Comparative research of this type is important for uncovering the complexities surrounding human dimensions of marine reserves and improving reserve management.

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 Niño 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.