Coral reefs worldwide face unprecedented cumulative anthropogenic effects of interacting local human pressures, global climate change and distal social processes. Reefs are also bound by the natural ...biophysical environment within which they exist. In this context, a key challenge for effective management is understanding how anthropogenic and biophysical conditions interact to drive distinct coral reef configurations. Here, we use machine learning to conduct explanatory predictions on reef ecosystems defined by both fish and benthic communities. Drawing on the most spatially extensive dataset available across the Hawaiian archipelago-20 anthropogenic and biophysical predictors over 620 survey sites-we model the occurrence of four distinct reef regimes and provide a novel approach to quantify the relative influence of human and environmental variables in shaping reef ecosystems. Our findings highlight the nuances of what underpins different coral reef regimes, the overwhelming importance of biophysical predictors and how a reef's natural setting may either expand or narrow the opportunity space for management interventions. The methods developed through this study can help inform reef practitioners and hold promises for replication across a broad range of ecosystems.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The global impacts of climate change are evident in every marine ecosystem. On coral reefs, mass coral bleaching and mortality have emerged as ubiquitous responses to ocean warming, yet one of the ...greatest challenges of this epiphenomenon is linking information across scientific disciplines and spatial and temporal scales. Here we review some of the seminal and recent coral‐bleaching discoveries from an ecological, physiological, and molecular perspective. We also evaluate which data and processes can improve predictive models and provide a conceptual framework that integrates measurements across biological scales. Taking an integrative approach across biological and spatial scales, using for example hierarchical models to estimate major coral‐reef processes, will not only rapidly advance coral‐reef science but will also provide necessary information to guide decision‐making and conservation efforts. To conserve reefs, we encourage implementing mesoscale sanctuaries (thousands of km2) that transcend national boundaries. Such networks of protected reefs will provide reef connectivity, through larval dispersal that transverse thermal environments, and genotypic repositories that may become essential units of selection for environmentally diverse locations. Together, multinational networks may be the best chance corals have to persist through climate change, while humanity struggles to reduce emissions of greenhouse gases to net zero.
With the growing severity of marine heatwaves, mass coral bleaching and mortality has become widespread. Yet, our understanding of coral bleaching and its cascading consequences is incomplete. One of the greatest challenges of this epiphenomenon is integrating findings from different disciplines and across biological and spatial scales. Here, we synthesize seminal and recent coral‐bleaching discoveries, evaluate which data and processes can improve predictive models, and provide a conceptual framework that integrates studies across scales. An integrative approach across biological and spatial scales will not only advance coral‐reef science but will also provide necessary information to guide conservation efforts.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Dramatic coral loss has significantly altered many Caribbean reefs, with potentially important consequences for the ecological functions and ecosystem services provided by reef systems. Many studies ...examine coral loss and its causes—and often presume a universal decline of ecosystem services with coral loss—rather than evaluating the range of possible outcomes for a diversity of ecosystem functions and services at reefs varying in coral cover. We evaluate 10 key ecosystem metrics, relating to a variety of different reef ecosystem functions and services, on 328 Caribbean reefs varying in coral cover. We focus on the range and variability of these metrics rather than on mean responses. In contrast to a prevailing paradigm, we document high variability for a variety of metrics, and for many the range of outcomes is not related to coral cover. We find numerous “bright spots,” where herbivorous fish biomass, density of large fishes, fishery value, and/or fish species richness are high, despite low coral cover. Although it remains critical to protect and restore corals, understanding variability in ecosystem metrics among low‐coral reefs can facilitate the maintenance of reefs with sustained functions and services as we work to restore degraded systems. This framework can be applied to other ecosystems in the Anthropocene to better understand variance in ecosystem service outcomes and identify where and why bright spots exist.
Dramatic coral loss has significantly altered Caribbean reefs, and coral loss is predicted to result in broad declines in ecosystem services. We evaluate 10 key ecosystem metrics, relating to a variety of different reef services and functions, using data from 328 Caribbean reefs varying in coral cover. Our results document high variability for a variety of metrics and suggest that “bright spots”—sites where these metrics are comparatively high (i.e., 90th percentile)—can occur where coral cover is low. Notably, bright spots for many metrics related to fish communities are more likely at medium than high coral cover sites.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Conservation of ecological communities requires deepening our understanding of genetic diversity patterns and drivers at community-wide scales. Here, we use seascape genetic analysis of a diversity ...metric, allelic richness (AR), for 47 reef species sampled across 13 Hawaiian Islands to empirically demonstrate that large reefs high in coral cover harbour the greatest genetic diversity on average. We found that a species's life history (e.g. depth range and herbivory) mediates response of genetic diversity to seascape drivers in logical ways. Furthermore, a metric of combined multi-species AR showed strong coupling to species richness and habitat area, quality and stability that few species showed individually. We hypothesize that macro-ecological forces and species interactions, by mediating species turnover and occupancy (and thus a site's mean effective population size), influence the aggregate genetic diversity of a site, potentially allowing it to behave as an apparent emergent trait that is shaped by the dominant seascape drivers. The results highlight inherent feedbacks between ecology and genetics, raise concern that genetic resilience of entire reef communities is compromised by factors that reduce coral cover or available habitat, including thermal stress, and provide a foundation for new strategies for monitoring and preserving biodiversity of entire reef ecosystems.
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Aim
Species ranges provide a valuable foundation for resolving biogeographical regions, evolutionary processes and extinction risks. To inform conservation priorities, here we develop the first ...bioregionalization based on reef fish abundance of the Hawaiian Archipelago, which spans nearly 10° of latitude across 2,400 km, including 8 high volcanic islands in the populated main Hawaiian Islands (MHI), and 10 low islands (atolls, shoals and islets) in the remote northwestern Hawaiian Islands (NWHI).
Location
The Hawaiian Archipelago.
Taxon
Fishes (276 taxa).
Methods
We compiled 5,316 visual fish surveys at depths of 1–30 m from throughout the Hawaiian Archipelago. Geographical range (km2) for each species was measured as extent of occurrence (EOO) and area of occurrence (AOO). PERMANOVA and PCO were used to investigate drivers of fish assemblage structure. Distance‐based multivariate analyses were used to evaluate the relationship between fish assemblage structure and predictor variables including latitude, reef area, temperature, chlorophyll‐a, wave energy and human population density.
Results
Distinct fish assemblages exist in the MHI and NWHI, with two additional faunal breaks driven primarily by endemic species abundance. Latitude explained 37% of the variability in fish assemblages, with reef area accounting for an additional 9%. EOO showed a significant correlation with latitude. Endemics comprised 52%–55% of the numerical abundance at the northern end of the archipelago but only 17% on Hawai‘i Island in the extreme south. Maximum size and activity regime (day vs. night) explained the most variation in the abundance of endemics.
Main conclusions
The Hawaiian fish assemblages are strongly influenced by endemic species, affirming the archipelago as a biodiversity hotspot of high conservation value. The higher abundance of endemics in the NWHI may represent preadaptation to oceanic (oligotrophic) conditions. Resolution of distinct bioregions across the archipelago provides a better understanding of reef fish macroecology, with implications for management at the archipelago scale.
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Ancient Hawaiians developed sophisticated natural resource management systems that included various forms of spatial management.
The state of Hawaiʻi established its first legislated marine protected ...area (MPA) in 1953, and today there exists a patchwork of spatial marine management strategies along a range of sizes, with varying levels of governance, enforcement, and effectiveness.
Approximately 12% of waters within the 50 m depth contour and 5% of waters within state jurisdiction (≤3 nmi) have some form of marine management. No‐take areas make up <0.5% of nearshore waters, and combined with highly protected areas account for 3.4% of this habitat. Most of the existing MPAs are small, with a median area of 1.2 km2 (confidence interval 0.2–8.1).
Twenty‐five datasets, representing 1,031 individual surveys conducted throughout Hawaiʻi since 2000, were used to compare fish assemblage characteristics amongst a subset of MPAs using a regulation‐based protection classification scheme.
Fully and highly protected areas had significantly greater resource fish biomass than areas with intermediate or low protection did. High human population density adjacent to MPAs had a negative influence on fish trophic structure within MPAs, whereas remote MPAs harboured higher fish biomass. Complex and heterogeneous habitats were important contributors to MPA effectiveness.
Long‐term monitoring of select MPAs showed mixed and complex trajectories. Resource fish biomass increased after the establishment of the Hanauma Bay Marine Life Conservation District in 1967 but plateaued after ~15 years, followed by changes in assemblage structure from fish feeding and invasive species. The Pūpūkea Marine Life Conservation District, established in 1983, was expanded sevenfold in 2003 and showed dramatic increases in resource fish biomass following increased protection.
This information is critical to improving effectiveness of existing MPAs, helping inform ongoing efforts to implement a network of MPAs statewide, and aiding in the development of comprehensive statewide marine spatial planning.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Building trust in science and evidence-based decision-making depends heavily on the credibility of studies and their findings. Researchers employ many different study designs that vary in their risk ...of bias to evaluate the true effect of interventions or impacts. Here, we empirically quantify, on a large scale, the prevalence of different study designs and the magnitude of bias in their estimates. Randomised designs and controlled observational designs with pre-intervention sampling were used by just 23% of intervention studies in biodiversity conservation, and 36% of intervention studies in social science. We demonstrate, through pairwise within-study comparisons across 49 environmental datasets, that these types of designs usually give less biased estimates than simpler observational designs. We propose a model-based approach to combine study estimates that may suffer from different levels of study design bias, discuss the implications for evidence synthesis, and how to facilitate the use of more credible study designs.
Comparison across terrestrial and aquatic ecosystems facilitates a broader understanding of ecological patterns. Although meta-analyses are important for quantitative synthesis across ecosystems, ...detailed comparisons of natural history and species interactions also illuminate convergence among systems. We compare the ecology of superficially dissimilar African savannas and coral reefs via shared characteristics including: (1) hyperdiverse guilds of large vertebrate herbivores and predators, (2) similar mechanisms driving positive feedback loops between herbivory and primary production, (3) similar roles of disturbance and herbivory in mediating ecosystem state, and (4) numerous smaller vertebrate and invertebrate species that underpin diversity and ecosystem processes. Our goal in comparing the natural history and ecology of these ecosystems is to facilitate others in finding their own comparative systems. We encourage scientists, especially early-career scientists, to explore ecosystems other than their primary focus. Whatever your ecosystem of study, examining the ecology of its analog in another environment may enliven your career.
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To design effective marine reserves and support fisheries, more information on fishing patterns and impacts for targeted species is needed, as well as better understanding of their key habitats. ...However, fishing impacts vary geographically and are difficult to disentangle from other factors that influence targeted fish distributions. We developed a set of fishing effort and habitat layers at high resolution and employed machine learning techniques to create regional-scale seascape models and predictive maps of biomass and body length of targeted reef fishes for the main Hawaiian Islands. Spatial patterns of fishing effort were shown to be highly variable and seascape models indicated a low threshold beyond which targeted fish assemblages were severely impacted. Topographic complexity, exposure, depth, and wave power were identified as key habitat variables that influenced targeted fish distributions and defined productive habitats for reef fisheries. High targeted reef fish biomass and body length were found in areas not easily accessed by humans, while model predictions when fishing effort was set to zero showed these high values to be more widely dispersed among suitable habitats. By comparing current targeted fish distributions with those predicted when fishing effort was removed, areas with high recovery potential on each island were revealed, with average biomass recovery of 517% and mean body length increases of 59% on Oahu, the most heavily fished island. Spatial protection of these areas would aid recovery of nearshore coral reef fisheries.
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BFBNIB, FZAB, GIS, IJS, INZLJ, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZRSKP
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