Sustainably managing ecosystems is challenging, especially for complex systems such as coral reefs. This study develops critical reference points for sustainable management by using a large empirical dataset on the coral reefs of the western Indian Ocean to investigate associations between levels of target fish biomass (as an indicator of fishing intensity) and eight metrics of ecosystem state. These eight ecological metrics each exhibited specific thresholds along a continuum of fishable biomass ranging from heavily fished sites to old fisheries closures. Three thresholds lay above and five below a hypothesized window of fishable biomass expected to produce a maximum multispecies sustainable yield (B MMSY ). Evaluating three management systems in nine countries, we found that unregulated fisheries often operate below the B MMSY , whereas fisheries closures and, less frequently, gear-restricted fisheries were within or above this window. These findings provide tangible management targets for multispecies coral reef fisheries and highlight key tradeoffs required to achieve different fisheries and conservation goals.human-environment interactions | sustainable fisheries | marine protected areas | resilience | social-ecological systems C oral reefs have proven difficult to manage sustainably, in part because the multispecies nature of reef fisheries, the complexity of trophic interactions, and the times scales on which processes manifest may allow coral reefs to appear healthy long after serious degradation has occurred (1, 2). This also means that signs of degradation may not be readily apparent in the information that many managers use to evaluate the condition of reef systems [metrics such as catch data or coral cover (2)]. In addition, most reefs are located in developing countries (3) where food security concerns often take priority over conservation. In the absence of reference points that signal when further exploitation may have serious consequences for reef ecosystems, managers are often unlikely to make the socially and politically difficult decisions to restrict fishing activities. A question of critical relevance to scientists, managers, and resource users alike is whether meaningful limits or reference points can provide effective warning of conditions beyond which coral reef social-ecological systems incur a risk of serious degradation and lost value (4, 5).Here we examine where major changes in coral reef systems occur along a gradient of fishable biomass, a readily measured and managed variable, and explore how this can be used to define key reference points that can help inform management decisions (4, 6). We compiled information from more than 300 surveys of shallow coral reefs from nine countries across the Indian Ocean (Table S1 ). Survey sites spanned some 35°of latitude and 52°of longitude and were evenly distributed among unregulated, restricted, and fisheries closure management areas (details in SI Methods). We used a suite of four statistical models (null, linear, switch-point, and piecewis...

International audienceA field study of coral bleaching and coral communities was undertaken spanning 8 countries and ~35° of latitude in 2005. This was combined with studies in southern Kenya and northeast Madagascar in 1998 and Mauritius in 2004 to develop a synoptic analysis of coral community structure, bleaching response, susceptibility of the communities to bleaching, and the relative risk of extinctions in western Indian Ocean coral reefs. Cluster analysis identified 8 distinct coral communities among the 91 sites sampled, with 2 distinct communities in northern South Africa and central Mozambique, a third in the central atolls of the Maldives, and 5 less differentiated groups, in a swath from southern Kenya to Mauritius, including Tanzania, the granitic islands of the Seychelles, northeast Madagascar, and Réunion. Massive Porites, Pavona, and Pocillopora dominated the central and northern Indian Ocean sites and, from historical records, replaced dominance by Acropora and Montipora. From southern Kenya to Mauritius, coral communities were less disturbed, with Acropora and Montipora dominating, and a mix of subdominants including branching Porites, Fungia, Galaxea, massive Porites, Pocillopora, and Synarea. The survey identified an area from southernmost Kenya to Tanzania as having the least disturbed and highest diversity reefs, and as being a regional priority for management. Taxa vulnerable to future extinction based on their response to warm water, population density, and commonness include largely low-diversity genera with narrow environmental ranges, such as Gyrosmilia interrupta, Plesiastrea versipora, Plerogyra sinuosa, and Physogyra lichtensteini

Erosion rates and sources of sediment ingested were quantified for the 2 most abundant parrotfish species on a leeward fringing reef of Bonaire, Netherlands Antilles: Scarus vetula and Spansoma viride. Direct estimates of erosion by different size classes were obtained from daily feeding rates and grazing scar frequency, scar volume and substrate density. Foraging preference and distribution of fish on the reef were used to examine patterns of bioerosion at 2 spatial scales: reef zones and individual substrates used for grazing. Sediment mass ingested by fish provided an independent check on erosion rates, and was partitioned according to source. S. vetula, employing a scraping feeding mode, removed less material from grazed substrates than similar sized S. vjride, which forages by excavating the substrate. Eros~on rates increased strongly with fish size in both species. The (indigestible) carbonate derived from epilithic algae accounted for all sediment ingested by juvenile fish. In adult fish, the proportion of freshly eroded carbonate substrate ingested increased with fish size. The distribution of adults of these large scarids over different reef zones determines the rate of bioerosion on a large spatial scale. The highest bioerosional rates occur on the shallow reef (ca 7 kg m-2 y r ' ) , and they decrease with depth. Parrotfish foraging preferences, and the effects of food type and skeletal density of substrates on the size of the grazing scars, cause large differences in bioerosional rates on a small spatial scale. The highest rates of bioerosion occur on substrates infested with boring algae and of low skeletal density, while high-density substrates and substrates covered with crustose corallines undergo lower rates. Living coral is rarely eaten by scarids, and largely escapes erosion by grazing.

Food selection by the Canbbean stoplight parrotfish Spansoma vlrlde was lnvestlgated on a fnnging coral reef of Bonalre, Netherlands Antllles For different reef zones, the diet composition for each life phase was determined by descnption of randomly selected bites, and compared to the avallabllity of food resources, as determined w~t h the aid of chaln-llnk transects S viride employs an excavating grazing mode and feeds almost exclus~vely on algae associated with dead coral substrates Preferred food types are large and sparse turfs growlng on carbonate substrates inhabited by endohthic algae Crustose corallines, with or without algal turfs are not preferred Feeding forays were longer on the preferred food types Foraging preferences are related to nutntlonal quahty of the food types and their yleld, i e the amounts of blomass, proteln and energy that can be Ingested per bite, as calculated from the size of grazing scars and the biochemical composition of the algae In spite of selective foragIng, a large proportion of b~t e s is taken on infenor food types Endolithic algae constitute an Important food resource for scraping herbivores, such as S vlnde These algae have relatively hlgh energetic value, and allow a high yield as a result of weakening the carbonate matrix by thelr boring filaments The yield of algal resources also depends on the skeletal density of the limestone substrates On deeper reef parts ( > 3 5 m depth), low-density substrates predomnate, resulting in higher y~e l d s of algae per bite than are attalned from high-denslty substrates that predominate on shallower reef parts The increased availablllty of hlgh-yleld food and substrate types coinc~des w~t h the occurrence of harermc terrltorlal behavlour m S v i r~d e males on the deeper reef parts Terntones are defended agalnst conspeclflcs and have a n Important function as spawning sites It 1s argued that the access to supenor food resources on the deeper reef makes terntonal defence feaslble for S viride

A corollary of island biogeographical theory is that islands are largely colonized from their nearest mainland source. Despite MadagascarÕs extreme isolation from India and proximity to Africa, a high proportion of the biota of the Madagascar region has Asian affinities. This pattern has rarely been viewed as surprising, as it is consistent with Gondwanan vicariance. Molecular phylogenetic data provide strong support for such Asian affinities, but often not for their vicariant origin; most divergences between lineages in Asia and the Madagascar region post-date the separation of India and Madagascar considerably (up to 87 Myr), implying a high frequency of dispersal that mirrors colonization of the Hawaiian archipelago in distance. Indian Ocean bathymetry and the magnitude of recent sea-level lowstands support the repeated existence of sizeable islands across the western Indian Ocean, greatly reducing the isolation of Madagascar from Asia. We put forward predictions to test the role of this historical factor in the assembly of the regional biota.