Predicting impact to assess the efficacy of community-based marine reserve design

During the planning phase the efficacy of different strategies to manage marine resources should ultimately be assessed by their potential impact, or ability to make a difference to ecological and social outcomes. While community-based and systematic approaches to establishing marine protected areas have their strengths and weaknesses, comparisons of their effectiveness often fail to explicitly address potential impact. Here, we predict conservation impact to compare recently implemented community-based marine reserves in Tonga to a systematic configuration specifically aimed at maximizing impact. Boosted regression tree outputs indicated that fishing pressure accounted for ∼24% of variation in target species biomass. We estimate that the community-based approach provides 84% of the recovery potential of the configuration with the greatest potential impact. This high potential impact results from community-based reserves being located close to villages, where fishing pressure is greatest. These results provide strong support for community-based marine management, with short-term benefits likely to accrue even where there is little scope for systematic reserve design

Life-history constraints, short adult life span and reproductive strategies in coral reef gobies of the genus Trimma

Body size influences many life-history traits, with small-bodied animals tending to have short life spans, high mortality and greater reproductive effort early in life. In this study, the authors investigated the life-history traits and reproductive strategies of three small-bodied coral reef gobies of the genus Trimma: Trimma benjamini, Trimma capostriatum and Trimma yanoi. The authors found all Trimma species studied attained a small body size of <25 mm, had a short life span of <140 days and experienced high estimated daily mortality of 3.0%–6.7%. Furthermore, the pelagic larval phase accounted for 25.3%–28.5% of the maximum life span, and maturation occurred between 74.1 and 82.1 days at 15.2–15.8 mm, leaving only 35%–43% of the total life span as a reproductively viable adult. All mature individuals had gonad structures consistent with bidirectional sex change, with bisexual gonads including both ovarian and testicular portions separated by a thin wall of connective tissue. In the female and male phases, only ovaries or testes were mature, whereas gonadal tissue of the non-active sex remained. One T. benjamini individual and one T. yanoi individual had ovarian and testicular tissue active simultaneously. The results of this study highlight the life-history challenges small CRFs face on their path to reproduction and reproductive strategies that could be beneficial in fishes with high and unpredictable mortality and short reproductive life spans

Incentivizing co-management for impact: mechanisms driving the successful national expansion of Tonga's Special Management Area program

The expansion of coastal marine protected areas can suffer from two key drawbacks: (a) the difficulty of incentivizing local communities to manage areas for conservation when their livelihoods also depend on resource use; and (b) that many protected areas get situated residually, or in locations with limited value for either biodiversity conservation or livelihoods. Here, we discuss and analyze key characteristics of Tonga's Special Management Area (SMA) program, including both the mechanisms that have motivated its successful national expansion and its ability to configure no-take reserves in areas that are considered to have high value to resource users. Granting communities exclusive access zones in exchange for implementing no-take reserves has encouraged conservation actions while fostering long-term relationships with resources. Ensuring no-take reserves occurred within the boundaries of exclusive access zones enabled communities to protect areas of greater extractive values than they would have otherwise. We conclude that the success of this program offers a way forward for achieving targets in the global expansion marine protected areas

Community management yields positive impacts for coastal fisheries resources and biodiversity conservation

Combining no-take marine reserves with exclusive access by communities to unreserved waters could provide the required incentives for community management to achieve positive impacts. However, few protected areas have been critically evaluated for their impact, which involves applying counterfactual thinking to predict conditions within protected areas if management had never occurred. Here, we use statistical matching to conduct a rigorous impact evaluation of dual management systems on coral reef fishes in Tonga, with communities having both full no-take areas and areas of exclusive fishing rights. No-take areas generally had positive impacts on the species richness, biomass, density, and size of target reef fish, while exclusive access areas were similar to predicted counterfactual conditions. The latter is likely because overall fishing pressure in exclusive access areas might not actually change, although more fish could be exploited by communities with access rights. Our findings suggest that dual management is effective at incentivizing effective community-based no-take areas for biodiversity conservation and resource management

Social–environmental drivers inform strategic management of coral reefs in the Anthropocene

Without drastic efforts to reduce carbon emissions and mitigate globalized stressors, tropical coral reefs are in jeopardy. Strategic conservation and management requires identification of the environmental and socioeconomic factors driving the persistence of scleractinian coral assemblages—the foundation species of coral reef ecosystems. Here, we compiled coral abundance data from 2,584 Indo-Pacific reefs to evaluate the influence of 21 climate, social and environmental drivers on the ecology of reef coral assemblages. Higher abundances of framework-building corals were typically associated with: weaker thermal disturbances and longer intervals for potential recovery; slower human population growth; reduced access by human settlements and markets; and less nearby agriculture. We therefore propose a framework of three management strategies (protect, recover or transform) by considering: (1) if reefs were above or below a proposed threshold of >10% cover of the coral taxa important for structural complexity and carbonate production; and (2) reef exposure to severe thermal stress during the 2014–2017 global coral bleaching event. Our findings can guide urgent management efforts for coral reefs, by identifying key threats across multiple scales and strategic policy priorities that might sustain a network of functioning reefs in the Indo-Pacific to avoid ecosystem collapse

Depth distribution and abundance of a coral-associated reef fish: roles of recruitment and post-recruitment processes

The abundance of many reef fish species varies with depth, but the demographic processes influencing this pattern remain unclear. Furthermore, while the distribution of highly specialized reef fish often closely matches that of their habitat, it is unclear whether changes in distribution patterns over depth are the result of changes in habitat availability or independent depth-related changes in population parameters such as recruitment and mortality. Here, we show that depth-related patterns in the distribution of the coral-associated goby, Paragobiodon xanthosoma, are strongly related to changes in recruitment and performance (growth and survival). Depth-stratified surveys showed that while the coral host, Seriatopora hystrix, extended into deeper water (> 20 m), habitat use by P. xanthosoma declined with depth and both adult and juvenile P. xanthosoma were absent below 20 m. Standardization of S. hystrix abundance at three depths (5, 15 and 30 m) demonstrated that recruitment of P. xanthosoma was not determined by the availability of its habitat. Reciprocal transplantation of P. xanthosoma to S. hystrix colonies among three depths (5, 15 and 30 m) then established that individual performance (survival and growth) was lowest in deeper water; mortality was three times higher and growth greatly reduced in individuals transplanted to 30 m. Individuals collected from 15 m also exhibited growth rates 50% lower than fish from shallow depths. These results indicate that the depth distribution of this species is limited not by the availability of its coral habitat, but by demographic costs associated with living in deeper water

Habitat morphology contrains the depth distribution and growth rate of a coral-associated reef fish

The distribution of coral reef fishes is often closely linked to the availability of preferred habitats. However, even in specialized gobies associated with a single coral species, their distribution does not always match that of the coral host. The coral goby Paragobiodon xanthosoma is primarily restricted to shallow water (30 m. Here, we use observational and experimental approaches to test whether depth-associated changes in morphology and partial mortality of the coral decrease habitat quality. Quantitative surveys from the surface to 30 m found pronounced changes in colony morphology over depth. S. hystrix colonies most likely to be occupied by P. xanthosoma were those with shallow-water characteristics, especially lower partial mortality and a more complex branching structure. In a binary choice experiment, P. xanthosoma individuals preferentially selected colonies from shallow water (5 m) over deep water (30 m) and with high complexity over low complexity when colonies were collected from a standardized depth (15 m). Finally, a transplant experiment examined the effect of depth-associated changes in the coral habitat on patterns of growth of P. xanthosoma. When the depth of placement was standardized, the growth of P. xantho soma was 8-fold lower on colonies collected from deep water (30 m) compared to colonies from shallower water (5 and 15 m). Together, these patterns suggest that depth-related changes in the morphology of the coral host are responsible for driving patterns of distribution over depth in their associated reef fish

Predicting impact to assess the efficacy of community‐based marine reserve design

During the planning phase the efficacy of different strategies to manage marine resources should ultimately be assessed by their potential impact, or ability to make a difference to ecological and social outcomes. While community‐based and systematic approaches to establishing marine protected areas have their strengths and weaknesses, comparisons of their effectiveness often fail to explicitly address potential impact. Here, we predict conservation impact to compare recently implemented community‐based marine reserves in Tonga to a systematic configuration specifically aimed at maximizing impact. Boosted regression tree outputs indicated that fishing pressure accounted for ∼24% of variation in target species biomass. We estimate that the community‐based approach provides 84% of the recovery potential of the configuration with the greatest potential impact. This high potential impact results from community‐based reserves being located close to villages, where fishing pressure is greatest. These results provide strong support for community‐based marine management, with short‐term benefits likely to accrue even where there is little scope for systematic reserve design

Incentivizing co‐management for impact: mechanisms driving the successful national expansion of Tonga's Special Management Area program

The expansion of coastal marine protected areas can suffer from two key drawbacks: (a) the difficulty of incentivizing local communities to manage areas for conservation when their livelihoods also depend on resource use; and (b) that many protected areas get situated residually, or in locations with limited value for either biodiversity conservation or livelihoods. Here, we discuss and analyze key characteristics of Tonga's Special Management Area (SMA) program, including both the mechanisms that have motivated its successful national expansion and its ability to configure no-take reserves in areas that are considered to have high value to resource users. Granting communities exclusive access zones in exchange for implementing no-take reserves has encouraged conservation actions while fostering long-term relationships with resources. Ensuring no-take reserves occurred within the boundaries of exclusive access zones enabled communities to protect areas of greater extractive values than they would have otherwise. We conclude that the success of this program offers a way forward for achieving targets in the global expansion marine protected areas

Tongan socio-environmental spatial layers for marine ecosystem management

Environmental conditions and anthropogenic impacts are key influences on ecological processes and associated ecosystem services. Effective management of Tonga's marine ecosystems therefore depends on accurate and up-to-date knowledge of environmental and anthropogenic variables. Although many types of environmental and anthropogenic data are now available in global layers, they are often inaccessible to end users, particularly in developing countries with limited accessibility and analytical training. Furthermore, the resolution of many global layers might not be sufficient to make informed local decisions. Although the near-shore marine ecosystem of Tonga is extensive, the resources available for its management are limited, and little is known about its current ecological state. Here we provide a marine socio-environmental dataset covering Tonga's near-shore marine ecosystem as compiled from various global layers, remote sensing projects, local ministries, and the 2016 national census. The dataset consists of 11 environmental and 6 anthropogenic variables summarised in ecologically relevant ways, spatially overlaid across the near-shore marine ecosystem of Tonga. The environmental variables selected include bathymetry, coral reef density, distance from deep water, distance from land, distance from major terrestrial inputs, habitat, land area, net primary productivity, salinity, sea surface temperature and wave energy. The anthropogenic variables selected include fishing pressure, management status, distance to fish markets, distance from villages, population pressure and a socioeconomic development index based on population density, growth, mean age, mean education level and unemployment. We hope this extensive and accessible dataset will be a useful tool for future assessment and management of marine ecosystems in Tonga