As one of the most diverse and productive ecosystems known, and one of the first ecosystems to exhibit major climate-warming impacts (coral bleaching), coral reefs have drawn much scientific attention to what may prove to be their Achilles heel, the thermal sensitivity of reef-building corals. Here we show that climate change-driven loss of live coral, and ultimately structural complexity, in the Seychelles results in local extinctions, substantial reductions in species richness, reduced taxonomic distinctness, and a loss of species within key functional groups of reef fish. The importance of deteriorating physical structure to these patterns demonstrates the longer-term impacts of bleaching on reefs and raises questions over the potential for recovery. We suggest that isolated reef systems may be more susceptible to climate change, despite escaping many of the stressors impacting continental reefs.biodiversity ͉ climate change ͉ coral bleaching ͉ resilience ͉ reef fish G lobal warming is causing reef corals around the world to expel their photosynthetic symbionts, resulting in ''bleaching'' and extensive coral mortality (1-3). Widespread impacts of bleaching are predicted (4), although empirical data on the long-term effects on other components of the ecosystem are lacking. Of particular interest are reef fish, which support local fisheries and tourism (5), and are crucial for the resilience of coral reefs (6-8). Existing studies of the indirect effects of bleaching mediated coral mortality on reef fish assemblages have been short-term and indicated limited change (9-11); however, the longer-term implications of coral loss may be much more substantial (12). Long-term responses may result from changes in the physiological condition of species following coral loss (13) or through processes such as the breakdown of the physical matrix of the remaining reef structure.The global mass bleaching event of 1998 was devastating in the western Indian Ocean, where the El Niño event interacted with the Indian Ocean dipole (14), resulting in 75-99% loss of live coral (15). The Seychelles suffered particularly badly; live coral was reduced by Ͼ90% across the entire range of the inner islands (2, 16), with no apparent depth refuge. With widely accepted predictions of all reef regions of the world suffering similar large-scale degradation through bleaching in coming decades (1, 2), the study of such locations provides a unique opportunity to understand longer-term impacts on other components of the ecosystem, with implications for resilience and the persistence of vulnerable species.We surveyed coral and fish communities at 21 sites across the inner islands of the Seychelles in 1994 (17) and 2005. Over 50,000 m 2 of three distinct coral reef habitats were surveyed: fringing reefs with carbonate framework, coral growth on a granitic substrate, and patch reefs on a sand, rock, or rubble base (17). The study specifically aimed to assess changes in benthic variables after the 1998 bleaching event and relate these to changes in the ...

The increased frequency and intensity of bleaching episodes has led to wide-scale loss of reef corals and raised concerns over the effectiveness of existing conservation and management efforts. The 1998 bleaching event was most severe in the western Indian Ocean where coral declined by up to 90% in some locations. Using fisheries independent data, we assess the long-term impacts of this event in the Seychelles on fishery target species, the overall size structure of the fish assemblage and assess the effectiveness of two marine protected areas (MPAs) in offering resilience. Fishery target species above size at first capture showed little change in biomass between 1994 and 2005, corroborating studies that suggest fisheries yields are currently not affected. Biomass remained higher in protected areas, indicating they are still effective in protecting fish stocks. However, the size structure of the fish communities, as described with size-spectra, changed in both fished and protected areas, with a decline in smaller fish (<30 cm) and an increase in larger fish (>45 cm). This is likely to represent a time lag response; with the larger fish that are lost to natural mortality and fishing no longer being replaced by juveniles. This effect is expected to be even greater in terms of productivity, affect fisheries and, as congruent patterns are observed for herbivores, suggests no long term resilience in the MPAs.Corallivores and planktivores demonstrate striking declines in numerical abundance which are greatest in MPAs, and associated with a similar pattern of decline in their preferred corals. There is an urgent need for climate mediated disturbance to be at the fore of conservation and management planning for coral reefs, which should include MPAs placed in areas of resistance and resilience to bleaching, and a greater emphasis on reducing other stressors to the system as a whole.3

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SUMMARYFisheries scientists and managers are increasingly engaging with fishers' knowledge (FK) to provide novel information and improve the legitimacy of fisheries governance. Disputes between the perceptions of fishers and scientists can generate conflicts for governance, but can also be a source of new perspectives or understandings. This paper compares artisanal trap fishers' reported current catch rates with landings data and underwater visual census (UVC). Fishers' reports of contemporary 'normal' catch per day tended to be higher than recent median landings records. However, fishers' reports of 'normal' catch per trap were not significantly different from the median CPUE calculated from landings data, and reports of 'good' and 'poor' catch rates were indicative of variability observed in landings data. FK, landings and UVC data all gave different perspectives of trends over a ten-year period. Fishers' perceptions indicated greater declines than statistical models fitted to landings data, while UVC evidence for trends varied between sites and according to the fish assemblage considered. Divergence in trend perceptions may have resulted from differences in the spatial, temporal or taxonomic focus of each dataset. Fishers may have experienced and understood behavioural changes and increased fishing power, which may have obscured declines from landings data. Various psychological factors affect memory and recall, and may have affected these memory-based estimates of trends, while different assumptions underlying the analysis of both interview data and conventional scientific data could also have led to qualitatively different trend perceptions. Differing perspectives from these three data sources illustrate both the potential for 'cognitive conflicts' between stakeholders who do not rely on the same data sources, as well as the importance of multiple information sources to understand dynamics of fisheries. Collaborative investigation of such divergence may facilitate learning and improve fisheries governance.

Disturbance plays an important role in structuring marine ecosystems, and there is a need to understand how conservation practices, such as the designation of Marine Protected Areas (MPAs), facilitate postdisturbance recovery. We evaluated the association of MPAs, herbivorous fish biomass, substrate type, postdisturbance coral cover, and change in macroalgal cover with coral recovery on the fringing reefs of the inner Seychelle islands, where coral mortality after a 1998 bleaching event was extensive. We visually estimated benthic cover and fish biomass at 9 sites in MPAs where fishing is banned and at 12 sites where fishing is permitted in 1994, 2005, 2008, and 2011. We used analysis of variance to examine spatial and temporal variations in coral cover and generalized additive models to identify relations between coral recovery and the aforementioned factors that may promote recovery. Coral recovery occurred on all substrate types, but it was highly variable among sites and times. Between 2005 and 2011 the increase in coral cover averaged 1%/year across 21 sites, and the maximum increase was 4%/year. However, mean coral cover across the study area (14%) remained at half of 1994 levels (28%). Sites within MPAs had faster rates of coral recovery than sites in fished areas only where cover of macroalgae was low and had not increased over time. In MPAs where macroalgae cover expanded since 1998 there was no recovery. Where coral was recovering on granite reefs there was a shift in relative prevalence of colony life-form from branching to encrusting species. This simplification of reef structure may affect associated reef fauna even if predisturbance levels of coral cover are attained.

Repeated bouts of coral bleaching threaten the long-term persistence of coral reefs and associated communities. Here we document the short-and long-term impacts of heatwave events on coral and fish assemblages, based on regular surveys of 18 reefs of the granitic islands of Seychelles over 23 years. Extreme heat events in 1998 and 2016 led to bleaching associated declines in coral cover, whilst between these years there was an interim period of coral recovery on some reefs. Coral decline and recovery were primarily due to changes in the cover of branching coral, particularly those from the families Acroporidae and Pocilloporidae. Surveys during the 2016 bleaching, found that 95% of the 484 Acropora and Pocillopora colonies observed were either bleached or recently dead. The extent of bleaching and subsequent mortality were best explained by a priori assessments of community susceptibility to heat stress. One year later (2017) coral cover had fallen by 70% and average coverage across the 18 reefs was at 6%, similar to levels recorded in 2005, seven years after the 1998 bleaching. Decline in coral following the 2016 bleaching coincided with reduced abundance of fish <11cm TL, particularly corallivores, invertivores and mixed diet feeders. These changes are likely to foreshadow more widespread loss once the habitat structure erodes. Accordingly, seven years after the 1998 bleaching, when coral skeletons and reef structure had collapsed on some reefs, abundance of both large and small bodied fish had declined. We show that fluctuation in the cover of branching coral is positively associated with changes in the abundance of small-bodied fish which contribute to ecological processes and high diversity, suggesting branching corals are a keystone structure. Increased frequency of bleaching threatens the capacity of branching corals to fully recover after disturbances, reducing the amplitude of boom bust cycles of these corals and the keystone habitat structure they provide reef fish.

There is a global trend in the depletion of transient reef fish spawning aggregations (“FSAs”), making them a primary target for management with marine protected areas (MPAs). Here, we review the observed and likely effectiveness of FSA MPAs, discuss how future studies could fill knowledge gaps, and provide recommendations for MPA design based on species' life history and behaviour, enforcement potential, and management goals. Modelling studies indicate that FSA MPAs can increase spawning-stock biomass and normalize sex ratio in protogynous fish populations, unless fishing mortality remains high outside protected FSA sites and spawning times. In the field, observations of no change or continued decline in spawning biomass are more common than population recovery. When empirical studies suggest that FSA MPAs may not benefit fish productivity or recovery, extenuating factors such as insufficient time since MPA creation, poor or lack of enforcement, inadequate design, and poorly defined management objectives are generally blamed rather than failure of the MPA concept. Results from both the empirical and modelling literature indicate that FSA MPAs may not improve exploitable biomass and fisheries yields; however, investigations are currently too limited to draw conclusions on this point. To implement effective FSA MPAs, additional modelling work, long-term monitoring programmes at FSA sites, and collections of fisheries-dependent data are required, with greater attention paid to the design and enforcement of area closures. We recommend a harmonized, adaptive approach that combines FSA MPA design with additional management measures to achieve explicitly stated objectives. Conservation objectives and, therefore, an overall reduction in mortality rates should be targeted first. Fisheries objectives build on conservation objectives, in that they require an overall reduction in mortality rates while maintaining sufficient access to exploitable biomass. Communication among researchers, regulatory agencies, park authorities, and fishers will be paramount for effective action, along with significant funds for implementation and enforcement.

Artificial ocean iron fertilization (OIF) enhances phytoplankton productivity and is being explored as a means of sequestering anthropogenic carbon within the deep ocean. To be considered successful, carbon should be exported from the surface ocean and isolated from the atmosphere for an extended period (e.g., the Intergovernmental Panel on Climate Change's standard 100 year time horizon). This study assesses the impact of deep circulation on carbon sequestered by OIF in the Southern Ocean, a high‐nutrient low‐chlorophyll region known to be iron stressed. A Lagrangian particle‐tracking approach is employed to analyze water mass trajectories over a 100 year simulation. By the end of the experiment, for a sequestration depth of 1000 m, 66% of the carbon had been reexposed to the atmosphere, taking an average of 37.8 years. Upwelling occurs predominately within the Antarctic Circumpolar Current due to Ekman suction and topography. These results emphasize that successful OIF is dependent on the physical circulation, as well as the biogeochemistry.