The 27–year decline of coral cover on the Great Barrier Reef and its causes

This study investigates the spatial and temporal dynamics of coral cover, identifies the main drivers of coral mortality, and quantifies the rates of potential recovery of the Great Barrier Reef.The world’s coral reefs are being degraded, and the need to reduce local pressures to offset the effects of increasing global pressures is now widely recognized. This study investigates the spatial and temporal dynamics of coral cover, identifies the main drivers of coral mortality, and quantifies the rates of potential recovery of the Great Barrier Reef. Based on the world’s most extensive time series data on reef condition (2,258 surveys of 214 reefs over 1985–2012), we show amajor decline in coral cover from 28.0%to 13.8% (0.53%y−1), a loss of 50.7% of initial coral cover. Tropical cyclones, coral predation by crown-of-thorns starfish (COTS), and coral bleaching accounted for 48%, 42%,and 10%of the respective estimated losses,amounting to 3.38% y−1 mortality rate. Importantly, the relatively pristine northern region showed no overall decline. The estimated rate of increase in coral cover in the absence of cyclones, COTS, and bleaching was 2.85%y−1, demonstrating substantial capacity for recovery of reefs. In the absence of COTS, coral cover would increase at 0.89% y−1, despite ongoing losses due to cyclones and bleaching. Thus, reducing COTS populations, by improvingwater quality and developing alternative control measures, could prevent further coral decline and improve the outlook for the Great Barrier Reef. Such strategies can, however, only be successful if climatic conditions are stabilized, as losses due to bleaching and cyclones will otherwise increase. Image: Wibble_Roisin / flick

Ocean acidification: summary for policymakers

This paper presents a summary of the state of knowledge on ocean acidification.Summary of outcomes:The ocean continues to acidify at an unprecedented rate in Earth’s history. Latest research indicates the rate of change may be faster than at any time in the last 300 million years.As ocean acidity increases, its capacity to absorb CO2 from the atmosphere decreases. This decreases the ocean’s role in moderating climate change. Species-specific impacts of ocean acidification have been seen in laboratory and field studies on organisms from the poles to the tropics. Many organisms show adverse effects, such as reduced ability to form and maintain shells and skeletons, as well as reduced survival, growth, abundance and larval development. Conversely, evidence indicates that some organisms tolerate ocean acidification and that others, such as some seagrasses, may even thrive. Within decades, large parts of the polar oceans will become corrosive to the unprotected shells of calcareous marine organisms. Changes in carbonate chemistry of the tropical ocean may hamper or prevent coral reef growth within decades.The far-reaching effects of ocean acidification are predicted to impact food webs, biodiversity, aquaculture and hence societies. Species differ in their potential to adapt to new environments. Ocean chemistry may be changing too rapidly for many species or populations to adapt through evolution.Multiple stressors – ocean acidification, warming, decreases in oceanic oxygen concentrations (deoxygenation), increasing UV-B irradiance due to stratospheric ozone depletion, overfishing, pollution and eutrophication – and their interactions are creating significant challenges for ocean ecosystems. We do not fully understand the biogeochemical feedbacks to the climate system that may arise from ocean acidification. Predicting how whole ecosystems will change in response to rising CO2 levels remains challenging. While we know enough to expect changes in marine ecosystems and biodiversity within our lifetimes, we are unable to make reliable, quantitative predictions of socio-economic impacts. People who rely on the ocean’s ecosystem services are especially vulnerable and may need to adapt or cope with ocean acidification impacts within decades. Shellfish fisheries and aquaculture in some areas may be able to cope by adjusting their management practices to avoid ocean acidification impacts. Tropical coral reef loss will affect tourism, food security and Katharina Fabricius shoreline protection for many of the world’s poorest people.Authors: Wendy Broadgate, IGBP; Ulf Riebesell, GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany; Claire Armstrong, University of Tromsø, Norway; Peter Brewer, Monterey Bay Aquarium Research Institute, USA; Ken Denman, University of Victoria, Canada; Richard Feely, Pacific Marine Environmental Laboratory, NOAA, USA; Kunshan Gao, Xiamen University, China; Jean-Pierre Gattuso, CNRS-UPMC, Laboratoire d’Océanographie, France; Kirsten Isensee, IOC-UNESCO; Joan Kleypas, National Center for Atmospheric Research (Climate and Global Dynamics), USA; Dan Laffoley, International Union for Conservation of Nature, Switzerland; James Orr, Laboratoire des Sciences du Climat et l’Environnement, France; Hans-Otto Pörtner, Alfred Wegener Institute, Germany; Carlos Eduardo de Rezende, Universidade Estadual do Norte Fluminese, Brazil; Daniela Schmidt, University of Bristol, UK; Ed Urban, SCOR; Anya Waite, University of Western Australia; Luis Valdés, IOC-UNESCO

SPATIAL ANALYSIS AS TOOL FOR SENSITIVITY ASSESSMENT OF SEA LEVEL RISE IMPACTS ON MARTINIQUE

Sea level in the Caribbean region is expected to rise approximately10-20 cm by 2025. In some areas of Martinique coastal erosion and saltwater intrusion are already a severe problem. Because the island has a mountainous character, the majority of its settlements are situated along the coast almost at sea level. Considerations and strategies for dealing with potential sea level rise and its consequences for Martinique do not exist. This part of a detailed case study concentrates on the evaluation of sea level rise impacts on Martinique. It is going to test the suitability of spatial data for impact scenarios at a regional scale. Also, it conceptualises the possible effects of sea level rise on the island for future regional planning purposes. An elevation model is created that visualises the low-lying coastal areas and a second model evaluates the sensitivity of each coastal segment to erosion, flooding and inundation. The resulting map distinguishes between coastal parts at high, medium, or low risk to sea level rise impacts. Results show that nearly three quarters of the Martinique coast are highly sensitive to flooding and erosion.Caribbean, Lesser Antilles, Regional Planning, GIS, Climate Change, Coastal Change, Erosion, Inundation

Caribbean Corals in Crisis: Record Thermal Stress, Bleaching, and Mortality in 2005

BACKGROUND The rising temperature of the world's oceans has become a major threat to coral reefs globally as the severity and frequency of mass coral bleaching and mortality events increase. In 2005, high ocean temperatures in the tropical Atlantic and Caribbean resulted in the most severe bleaching event ever recorded in the basin. METHODOLOGY/PRINCIPAL FINDINGS Satellite-based tools provided warnings for coral reef managers and scientists, guiding both the timing and location of researchers' field observations as anomalously warm conditions developed and spread across the greater Caribbean region from June to October 2005. Field surveys of bleaching and mortality exceeded prior efforts in detail and extent, and provided a new standard for documenting the effects of bleaching and for testing nowcast and forecast products. Collaborators from 22 countries undertook the most comprehensive documentation of basin-scale bleaching to date and found that over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles. CONCLUSIONS/SIGNIFICANCE Thermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years. Comparison of satellite data against field surveys demonstrated a significant predictive relationship between accumulated heat stress (measured using NOAA Coral Reef Watch's Degree Heating Weeks) and bleaching intensity. This severe, widespread bleaching and mortality will undoubtedly have long-term consequences for reef ecosystems and suggests a troubled future for tropical marine ecosystems under a warming climate.This work was partially supported by salaries from the NOAA Coral Reef Conservation Program to the NOAA Coral Reef Conservation Program authors. NOAA provided funding to Caribbean ReefCheck investigators to undertake surveys of bleaching and mortality. Otherwise, no funding from outside authors' institutions was necessary for the undertaking of this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Benthic community structure and sea urchin distribution : the bay of Diego-Suarez / Mrowicki, R.J., & Fanning, E. (eds)

The Bay of Diego-Suarez, considered to be one of the finest and largest natural harbours in the world, is located towards the northernmost tip of Madagascar in the Antsiranana province. Despite its historical and current use as a port, much of its convoluted perimeter is still somewhat untouched, harbouring pristine shorelines and subtidal coral reefs. The position of the bay between other regions in which high marine biodiversity has already been revealed suggests that it may also harbour high biodiversity. However, the relatively long coastline and limited connectivity of the bay with the Indian Ocean, in combination with existing anthropogenic activities, potentially make its marine environments susceptible to a range of environmental impacts including sedimentation, nutrification and pollution. The Frontier-Madagascar Marine Research Programme (FMMRP) became involved in conducting marine ecological survey work in the Bay of Diego-Suarez, north Madagascar, in April 2005, having relocated from its previous base at Anakao in southwest Madagascar. The rationale for the survey programme stemmed from the affiliation of the FMMRP with the Malagasy organisations Association Nationale pour la Gestion des Aires Protégées (ANGAP) and Service d’Appui a la Gestion de l’Environnement (SAGE), who were interested in identifying areas of the bay with particularly healthy coral reef systems. Additional environmental interest in the bay has arisen as a result of its proximity to surrounding terrestrial protected areas such as the newly managed Ramena complex, incorporating Orangea and Montagne des Français, and also Montagne d’Ambre. Since its relocation to the Diego-Suarez area, the FMMRP has compiled over two years’ worth of marine ecological data relating to benthic community composition, fish species abundance and population size structure, frequency of algae and invertebrate indicator species, and physical environmental parameters. Thus there exists an extensive dataset for the Bay of Diego-Suarez, from which details of the current condition of its marine habitats can be investigated and a baseline for temporal monitoring can be established. The primary purpose of this report is to signify the initial detailed dissection of the dataset and demonstrate the conclusions that can be made regarding the ecological status of coral reef systems within the bay. This has mostly involved the examination of benthic data, focusing upon variations in percentage cover of substrata and coral community characteristics as useful structural indicators of reef condition. Additionally, the report includes an assessment of the abundance and distribution of sea urchins and their relation to benthic community patterns, as a demonstration of the ability to interrelate different aspect of the FMMRP dataset to enhance the conclusions that can be drawn. Benthic community data were obtained from 380 line intercept transects conducted in different sectors of the Bay of Diego-Suarez between October 2005 and December 2007, representing a combined distance of 7,600 m. Sediment occupied the greatest overall proportion of the benthos (around 38%), especially in the western areas of the bay. Overall mean hard coral cover was around 15%, and tended to co-vary with other ‘hard’ substrata such as rock and rubble. In total, 38 scleractinian coral genera were recorded during survey work, in addition to a number of unidentified genera. The coral communities of the bay were dominated by Acropora and Porites spp., which comprised around 33% and 20% of total recorded hard coral cover, respectively. Hard coral cover and generic diversity appeared to be positively related. These indicators were greatest in the northeast area opposite the mouth of the bay, reaching mean values of around 37% and 6.8 genera, respectively. Here, the hard coral community was dominated by Acropora spp. and comprised a relatively high proportional cover of Galaxea spp. In the northwest of the bay, coral cover was approximately half as great and consisted primarily of species belonging to the genera Porites and Millepora. Habitats in this area were highly similar in terms of their overall coral community composition. Hard coral cover and diversity were generally lower in the southern portion of the bay, especially in more immediate proximity to the population centre of Diego-Suarez (around 2% and 1.5- 5.5 genera, respectively). Coral community composition was considerably more variable than in the northern portion of the bay. v After sediment and ‘hard’ substrata, seagrass formed the next major interplaying component of the benthic environment (around 10% overall proportional cover). The easternmost areas adjacent to the mouth of the bay were characterised by high seagrass cover, whic h reached around 48%. Little or no seagrass was encountered elsewhere, except at one locality in the northwest (around 13% cover). Macroalgae cover was low and less variable, reaching a maximum value of around 10% adjacent to Diego-Suarez. There were no differences between island and mainland sites in terms of overall benthic substratum characteristics, yet soft coral cover was significantly greater amongst island sectors. Sea urchin abundance data were obtained from 498 belt transects conducted between April 2006 and December 2007, representing a total area of 49,800 m2. A total of 6 species were recorded, of which Diadema setosum comprised by far the greatest relative abundance (96%) and observation frequency (55%). The greatest population densities of this species were encountered in the more exposed areas in the west and northwest, reaching around 1.5 m-2, and very few individuals were recorded in the eastern reaches. Data suggest a possible seasonal increase in D. setosum densities, corresponding with an increase in water temperature towards the end of the year. No significant correlation existed between D. setosum population density and coral cover, although these seemed to be inversely related in the central northern area of the bay. There was also no significant correlation with macroalgae cover. However, D. setosum density was positively and negatively associated with rubble and seagrass cover, respectively. There was a lack of a clear pattern amongst sectors with respect to overall benthic community characteristics, let alone between the density of D. setosum and benthic substratum composition. In conclusion, a relatively detailed map of benthic community composition has been produced for the Bay of Diego-Suarez, which shall be useful in elucidating the primary factors determining the condition of marine environments within the bay and developing effective sustainable management strategies. Further analysis, incorporating additional components of the FMMRP dataset, is required in order to further clarify our understanding of the key issues surrounding the current status of these coral reef systems. It is hoped that continued survey work will enable important long-term ecological monitoring of the marine environment of the bay and assessment of the effectiveness of any management initiatives that may be implemented

Geospatial analysis of the effects of tsunami on coral and mangrove ecosystems of Mayabunder in Andaman Islands, India

Mangroves and coral reefs are among the major ecosystems of tropical and subtropical coastlines. The Andaman group of islands, situated at the juncture of Bay of Bengal and Indian Ocean, are one of the richest coastal ecosystems of India in terms of biodiversity. Since the tsunami waves of 2004 affected this region severely, the outer fringes as well as inland areas of these islands faced extensive ecological degradation. Mayabunder is one such place of this region, where corals and mangroves had experienced both natural and anthropogenic threat. Considering the notable vulnerability of this coastal environment, the present study aimed to assess the transformations of the coral and mangrove ecosystems at Mayabunder both in pre-tsunami and post-tsunami periods till the present year using multi-temporal satellite imageries and geospatial techniques. Results showed that the areal coverage of healthy living coral reefs was reduced by 466.56 ha (10.42 %) from 1990 to 2000. Afterwards, the coupled ecosystem had experienced serious degradation again during the 2000−2010 phase. The areal coverage of dense mangroves decreased by 47.37%, whereas the area of dead coral covers showed a significant rise of 55.52%. However, partial restoration of both mangroves as well as healthy corals had also been observed here in recent years. It was raised from the extensive field visits and feedbacks from local inhabitants that this restoration initiative could become more effective if a participatory mode of management is adopted

Climate change promotes parasitism in a coral symbiosis.

Coastal oceans are increasingly eutrophic, warm and acidic through the addition of anthropogenic nitrogen and carbon, respectively. Among the most sensitive taxa to these changes are scleractinian corals, which engineer the most biodiverse ecosystems on Earth. Corals' sensitivity is a consequence of their evolutionary investment in symbiosis with the dinoflagellate alga, Symbiodinium. Together, the coral holobiont has dominated oligotrophic tropical marine habitats. However, warming destabilizes this association and reduces coral fitness. It has been theorized that, when reefs become warm and eutrophic, mutualistic Symbiodinium sequester more resources for their own growth, thus parasitizing their hosts of nutrition. Here, we tested the hypothesis that sub-bleaching temperature and excess nitrogen promotes symbiont parasitism by measuring respiration (costs) and the assimilation and translocation of both carbon (energy) and nitrogen (growth; both benefits) within Orbicella faveolata hosting one of two Symbiodinium phylotypes using a dual stable isotope tracer incubation at ambient (26 °C) and sub-bleaching (31 °C) temperatures under elevated nitrate. Warming to 31 °C reduced holobiont net primary productivity (NPP) by 60% due to increased respiration which decreased host %carbon by 15% with no apparent cost to the symbiont. Concurrently, Symbiodinium carbon and nitrogen assimilation increased by 14 and 32%, respectively while increasing their mitotic index by 15%, whereas hosts did not gain a proportional increase in translocated photosynthates. We conclude that the disparity in benefits and costs to both partners is evidence of symbiont parasitism in the coral symbiosis and has major implications for the resilience of coral reefs under threat of global change

Exhibition of Bleaching Resistance Via Adaptive Bleaching Pattern by Coral Reefs of the Gulf of Mannar during Massive Bleaching Event 2019

Coral reefs in the Gulf of Mannar (GoM) and Palk Bay regions are facing potential threats from climate change, sedimentation and anthropogenic activities. Considerably, coral reefs in these two regions are highly damaged due to frequent bleaching events caused by increased sea surface temperature (SST) recorded over the past two decades. Recently, during February to May 2019, mass bleaching event of corals was documented again in GoM and Palk Bay regions due to increased sea surface temperatures ranged between 32°C to 36°C. Despite of completely bleached corals, some coral colonies of the same bleached coral species have displayed adaptive bleaching pattern (ABP) for survival. This incidence is displayed by the symbiotic zooxanthellae to protect coral polyps from environmental stress such as elevated temperatures. These observations infer that coral colonies with preferential bleaching pattern ability would serve as environmental stress resisting coral colonies which can be used for restoration activities and cryopreservation. Further studies are needed to explain the potential mechanisms or specific environmental drivers responsible for ABP.