Amidst global environmental changes, predicting species' responses to future environments is a critical challenge for preserving biodiversity and associated human benefits. We explored the original ...idea that coral competitive performances, the ability of corals to preempt ecological space on the reef through territorial warfare, serve as indicators of species' ecological niches and environmental windows, and therefore, responses to future environments. Our surveys indicated that coral performances varied with taxonomic identity, size and position along environmental gradients, highlighting complex interplays between life-history, warfare-strategy and niche segregation. Our results forewarn that growing alterations of coastal environments may trigger shifts in coral dominance, with the decline of major reef-building taxa like acroporids, and emphasize the importance of limiting human impacts for coastal resilience. Our empirical approach untangles the complexity of species' battle-like interactions and can help identify winners and losers in various communities caught in the interplay between ecological niches, environmental windows and global changes.
A single ecosystem can exhibit great biogeographic and environmental variability. While a given ecological driver might have a strong impact in one region, it does not necessarily hold that its ...importance will extend elsewhere. Coral reefs provide a striking example in that coral communities have low resilience in the Atlantic and remarkable resilience in parts of the species‐rich Pacific. Recent experimental evidence from the Atlantic finds that fishing of large herbivorous fish can be a strong driver of coral resilience. Here, we repeat the Atlantic experiment in the highly resilient forereef of Moorea (French Polynesia), which has repeatedly recovered from disturbances. A combination of cages, fish deterrents (FDs), and controls allowed us to simulate the consequences of fishing large herbivores on algal assemblages, coral recruitment, and the demographic rates of coral juveniles. We find that the impacts of removing large herbivorous reef fish vary with early coral ontogeny. Reduced herbivore access led to a modest macroalgal bloom and reduction in coral recruitment. However, larger juvenile corals (> 1 cm diameter) survived better and grew faster under these conditions because of a reduction in corallivory. To determine the net impact of losing larger herbivorous fish, we combined experimental results with estimated demographic parameters in an individual‐based model. Simulating coral recovery trajectories for five years, we find that protecting larger reef fish led to better recovery in 66–99% of simulations, depending on underlying assumptions (with the more credible assumptions being associated with greater likelihood of net positive impacts). While we find that fishing effects are detrimental to corals in both the Atlantic and Pacific systems studied, the nature of the interactions varied markedly. In the identical previously‐published study in the Atlantic, macroalgae exhibited a rapid bloom and caused a sufficiently large reduction in coral recruitment to force a predicted ecosystem shift to an alternative attractor. The commensurate macroalgal bloom in Moorea was weak yet the corals were two orders of magnitude more sensitive to its presence. We do not suggest that a reduction in recruitment in Moorea will lead to alternative attractors but the long‐term risks of a reduction in recovery rate are cause for concern as rates of coral mortality are projected to increase. The emerging picture is that Pacific reefs are less likely to experience macroalgal blooms but are surprisingly sensitive to such blooms if they occur.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Understanding colonization of new habitats and ecological successions is key to ecosystem conservation. However, studies on primary successions are scarce for reef-building corals, due to the rarity ...of newly formed substratum and the long-term monitoring efforts required for their long life cycle and slow growth rate. We analysed data describing the diversity, structure and demography of coral assemblages on lava flows of different ages and coral reefs at Reunion Island, to evaluate the strength and mechanisms of succession, and its agreement to the theoretical models. No significant differences were observed between the two habitats for most structure and demographic descriptors. In contrast, species richness and composition differentiated coral reefs from lava flows, but were not related to the age of the lava flow. We observed a strong dominance of Pocillopora colonies, which underline the opportunistic nature of this taxa, with life-history traits advantageous to dominance on primary and secondary successional stages. Although some results argue in favor of the tolerance model of succession, the sequences of primary successions as theorized in other ecosystems were difficult to observe, which is likely due to the high frequency and intensity of disturbances at Reunion, that likely distort or set back the expected successional sequences.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Coral recruitment refers to the processes allowing maintenance and renewal of coral communities. Recruitment success is therefore indispensable for coral reef recovery after disturbances. Recruitment ...processes are governed by a variety of factors occurring at all spatial and temporal scales, from centimetres to hundreds of kilometres. In the present context of rising disturbances, it is thus of major importance to better understand the relative importance of different scales in this variation, and when possible, the factors associated with these scales. Multiscale spatio-temporal variability of scleractinian coral recruitment was investigated at two of the Mascarene Islands: Reunion and Rodrigues. Recruitment rates and taxonomic composition were examined during three consecutive six-month periods from regional to micro-local scales (i.e. from hundreds of kilometres to few centimetres) and between two protection levels (no-take zones and general protection zones). Very low recruitment rates were observed. Rodrigues displayed lower recruitment rates than Reunion. Recruit assemblage was dominated by Pocilloporidae (77.9%), followed by Acroporidae (9.9%) and Poritidae (5.2%). No protection effect was identified on coral recruitment, despite differences in recruitment rates among sites within islands. Recruits were patchily distributed within sites but no aggregative effect was detected, i.e. the preferentially colonised tiles were not spatially grouped. Recruits settled mainly on the sides of the tiles, especially at Rodrigues, which could be attributed to the high concentration of suspended matter. The variability of recruitment patterns at various spatial scales emphasises the importance of micro- to macro-local variations of the environment in the dynamics and maintenance of coral populations. High temporal variability was also detected, between seasons and years, which may be related to the early 2016 bleaching event at Rodrigues. The low recruitment rates and the absence of protection effect raise questions about the potential for recovery from disturbances of coral reefs in the Mascarene Islands.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The functioning of tropical coral reefs is imperilled by climate change, overfishing, and decreasing water quality. Maintaining their capacity to provide goods and services will critically depend on ...our ability to monitor their functioning at appropriate spatial and temporal scales. Given the constraints of traditional methods to respond to those needs, the potential of complementary tools such as Passive Acoustic Monitoring (PAM) is emerging. Coral reef soundscapes (i.e. ambient sound) encompass sounds produced by numerous organisms. Soundscape characteristics quantified by ecoacoustic indices have been found to reflect general ecosystem properties, such as diversity and abundance of fishes, and coral cover. The present study tested, on the virtually pristine coral reefs around Europa Island, South-West Indian Ocean, the capacity of acoustic indices to assess key ecosystem functions. Soundscapes were recorded during 2 h, and ecosystem functions were evaluated using video footage of the fish assemblages and underwater photogrammetry of the benthic landscapes. We found significant and strong correlations between six ecoacoustic indices and six key ecosystem functions, including habitat features and fish assemblage characteristics. The six ecoacoustic indices were representative of several combinations of frequency, amplitude and time analysis domains, highlighting the diversity of the functional information conveyed by soundscapes. Our findings reveal that a 2 h daytime recording on a coral reef could provide sufficient acoustic information to characterise major ecosystem functions of a site. This should facilitate the detection of functional disturbances at temporal and spatial scales adapted to the rapidity of upcoming climate changes. Our results also highlight the potential of ecoacoustics to bring novel and relevant insights in the functioning of ecosystems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Madagascar is a major hotspot of biodiversity in the Western Indian Ocean, but, as in many other regions, coral reefs surrounding the island confront large-scale disturbances and human-induced local ...stressors. Conservation actions have been implemented with encouraging results for fisheries, though their benefit on coral assemblages has never been rigorously addressed. In this context, we analyzed the multiscale spatial variation of the composition, generic richness, abundance, life history strategies, and cover of coral assemblages among 18 stations placed at three regions around the island. The potential influences of marine protected areas (MPAs), algal cover, substrate rugosity, herbivorous fish biomass, and geographic location were also analyzed. Our results highlight the marked spatial variability, with variation at either or both regional and local scales for all coral descriptors. The northeast coastal region of Masoala was characterized by the high abundance of coral colonies, most notably of the competitive Acropora and Pocillopora genera and stress-tolerant taxa at several stations. The southwest station of Salary Nord was distinguished by lower abundances, with depauperate populations of competitive taxa. On the northwest coast, Nosy-Be was characterized by higher diversity and abundance as well as by high coral cover (~42–70%) recorded at unfished stations. Results clearly underline the positive effects of MPAs on all but one of the coral descriptors, particularly at Nosy-Be where the highest contrast between fished and unfished stations was observed. Biomass of herbivorous fishes, crustose coralline algae cover, and substrate rugosity were also positively related to several coral descriptors. The occurrence of reefs with high diversity, abundance, and cover of corals, including the competitive Acropora, is a major finding of this study. Our results strongly support the implementation of locally managed marine areas with strong involvement by primary users, particularly to assist in management in countries with reduced logistic and human resources such as Madagascar.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Planar area and diameter of coral colonies are good proxies of shelter volume.•Shelter sizes can be inferred from the surface complexity of colonies.•Within reefscapes, abundance and size of ...colonies determine shelter distribution.•Quantifying shelter can enhance assessment of reefs’ capacity to support biodiversity.
Structural complexity plays a key role in the functioning of coral reef ecosystems. Reef-building corals are major contributors to this complexity, providing shelter and food for numerous invertebrates and fish species. Both structural complexity and shelter capacity of reefscapes are determined by several components such as spurs and grooves, slope, caves and holes, vegetation and coral colonies. Quantifying the shelter capacity from coral colonies to reefscapes is a fundamental step to estimating ecosystem potential to support biodiversity. Here, we applied underwater photogrammetry to quantify shelter volumes provided by individual coral colonies. Overall, 120 3D models of coral colonies from branching, massive, columnar and tabular growth forms were studied. Three reefscapes were also 3D modeled. The study encompasses three Indo-Pacific Islands: Reunion, Europa and New Caledonia. At the colony level, measurements of diameter, planar area, surface and shelter volume were computed. At the reefscape, the diameter and planar area of each colony were extracted from orthomosaics and then used to estimate shelter capacity. Linear models had high accuracy for predicting shelter volume (a 3D metric) from 2D metrics: the diameter= 83.1%, R2= 0.95; the planar area= 87.5%, R2= 0.95 and the colony surface= 87.3%, R2= 0.96. The surface complexity and the shelter volume of the colonies allowed inferring the size of shelters provided by coral growth forms. Quantitative descriptors (i.e. relative percentage of shelter by growth form, the abundance of coral colonies, “Shannon-Shelter Index”) revealed reefscape-scale shelter differences.
Our major finding is that planar area and diameter of coral colonies are satisfactory proxies for estimating shelter volume. These new proxies allow 2D metrics to quantify 3D shelter provision, which can support scientists and managers in conservation actions since such metrics are widely used in monitoring programs. Future investigations on the relationships between shelter provision and reef biodiversity will improve the understanding of these complex ecosystems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Coral reefs offer natural coastal protection by attenuating incoming waves. Here we combine unique coral disturbance-recovery observations with hydrodynamic models to quantify how structural ...complexity dissipates incoming wave energy. We find that if the structural complexity of healthy coral reefs conditions is halved, extreme wave run-up heights that occur once in a 100-years will become 50 times more frequent, threatening reef-backed coastal communities with increased waves, erosion, and flooding.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Madagascar is a major hotspot of biodiversity in the Western Indian Ocean, but, as in many other regions, coral reefs surrounding the island confront large-scale disturbances and human-induced local ...stressors. Conservation actions have been implemented with encouraging results for fisheries, though their benefit on coral assemblages has never been rigorously addressed. In this context, we analyzed the multiscale spatial variation of the composition, generic richness, abundance, life history strategies, and cover of coral assemblages among 18 stations placed at three regions around the island. The potential influences of marine protected areas (MPAs), algal cover, substrate rugosity, herbivorous fish biomass, and geographic location were also analyzed. Our results highlight the marked spatial variability, with variation at either or both regional and local scales for all coral descriptors. The northeast coastal region of Masoala was characterized by the high abundance of coral colonies, most notably of the competitive Acropora and Pocillopora genera and stress-tolerant taxa at several stations. The southwest station of Salary Nord was distinguished by lower abundances, with depauperate populations of competitive taxa. On the northwest coast, Nosy-Be was characterized by higher diversity and abundance as well as by high coral cover (~42-70%) recorded at unfished stations. Results clearly underline the positive effects of MPAs on all but one of the coral descriptors, particularly at Nosy-Be where the highest contrast between fished and unfished stations was observed. Biomass of herbivorous fishes, crustose coralline algae cover, and substrate rugosity were also positively related to several coral descriptors. The occurrence of reefs with high diversity, abundance, and cover of corals, including the competitive Acropora, is a major finding of this study. Our results strongly support the implementation of locally managed marine areas with strong involvement by primary users, particularly to assist in management in countries with reduced logistic and human resources such as Madagascar.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Sea‐level rise is predicted to cause major damage to tropical coastlines. While coral reefs can act as natural barriers for ocean waves, their protection hinges on the ability of scleractinian corals ...to produce enough calcium carbonate (CaCO3) to keep up with rising sea levels. As a consequence of intensifying disturbances, coral communities are changing rapidly, potentially reducing community‐level CaCO3 production. By combining colony‐level physiology and long‐term monitoring data, we show that reefs recovering from major disturbances can produce 40% more CaCO3 than currently estimated due to the disproportionate contribution of juvenile corals. However, the buffering effect of highly productive juvenile corals is compromised by recruitment failures, which have been more frequently observed after large‐scale, repeated bleaching events. While the size structure of corals can bolster a critical ecological function on reefs, climate change impacts on recruitment may undermine this buffering effect, thus further compromising the persistence of reefs and their provision of important ecosystem services.
While coral reefs can act as natural barriers for ocean waves, their protection hinges on the ability of scleractinian corals to produce enough calcium carbonate (CaCO3) to keep up with rising sea levels. As a consequence of intensifying disturbances, coral communities are changing rapidly, potentially reducing community‐level CaCO3 production. By combining colony‐level physiology and long‐term monitoring data, we show that reefs recovering from major disturbances can produce 40% more CaCO3 than currently estimated due to the disproportionate contribution of juvenile corals.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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