Impact of the 3rd global coral bleaching event on the Western Indian Ocean (2025)

Coral reef degradation in the Indian Ocean. Status reports and project presentation 2000

2000

The temperatures of the world's oceans are increasing at an accelerating rate. Recent estimates indicate that the magnitude of these increases might be as much as several degrees over the next century and undoubtedly, the impacts of these changes on the Earth's ecosystems are likely to become increasingly obvious. Coral reefs have already shown dramatic responses to the increasing ocean temperatures.

Post-bleaching mortality of a remote coral reef community in Seychelles, Western Indian Ocean

Western Indian Ocean Journal of Marine Science

Aims and scope: The Western Indian Ocean Journal of Marine Science provides an avenue for the wide dissemination of high quality research generated in the Western Indian Ocean (WIO) region, in particular on the sustainable use of coastal and marine resources. This is central to the goal of supporting and promoting sustainable coastal development in the region, as well as contributing to the global base of marine science. The journal publishes original research articles dealing with all aspects of marine science and coastal management. Topics include, but are not limited to: theoretical studies, oceanography, marine biology and ecology, fisheries, recovery and restoration processes, legal and institutional frameworks, and interactions/relationships between humans and the coastal and marine environment. In addition, Western Indian Ocean Journal of Marine Science features state-of-the-art review articles and short communications. The journal will, from time to time, consist of special issues on major events or important thematic issues.

Episodic heterogeneous decline and recovery of coral cover in the Indian Ocean

2011

Long term changes in coral cover for the Caribbean and the Pacific/Southeast Asia regions (PSEA) have proven extremely useful in assessing the main drivers, magnitude and time scales of change. The one major coral reef region where such assessments have not been made is the Indian Ocean (IO). Here we compiled coral cover survey data from across the IO into a database of~2000 surveys from 366 coral reef sites collected between 1977 and 2005. The compilation shows that the 1998 mass coral bleaching event was the single most important and widespread factor influencing the change in coral cover across the region. The trend in coral cover followed a step-type function driven by the 1998 period, which differs from findings in the Caribbean and the PSEA regions where declines have been more continuous and mostly began in the 1980s. Significant regional variation was observed, with most heterogeneity occurring during and after 1998. There was a significant relationship between cover and longitude for all periods, but the relationship became stronger in the period immediately after 1998. Before 1998, highest coral cover was observed in the central IO region, while this changed to the eastern region after 1998. Coral cover and latitude displayed a significant U-shaped relationship immediately after 1998, due to a large decrease in cover in the northern-central regions. Post-1998 coral cover was directly correlated to the impact of the disturbance; areas with the lowest mortality having the highest cover with India-Sri Lanka being an outlier due to its exceptionally high recovery. In 1998, reefs within Marine Protected Areas (MPAs) were more heavily impacted than unmanaged reefs, losing significantly greater total cover. MPA recovery was greater so that no differences were observed by 2001-2005. This study indicates that the regional patterns in coral cover distribution in the IO is driven mainly by episodic and acute environmental stress. Keywords: ENSO, climatic disturbance, climate change impact, coral bleaching, coral reef management, ecological vulnerability, marine protected areas (MPAs), marine reserves, recovery, regional variation al. 2008). While we recognize there are limitations, such as unmeasured changes in species composition, changes in provision of 3dimensional space with increasing cover, and changes in ecological processes (Hughes et al. 2010), coral cover can be a useful indicator of responses to large-scale disturbances, often linked to multiple stress factors that are not taxa specific (Gardner et al. 2003; Bruno and Selig 2007). Corals are major contributors to calcification and play an important role as ecological facilitators, and declines in coral cover will have significant ecological implications (Graham et al. 2006; Idjadi and Edmunds 2006). Coral cover is therefore commonly used to describe the overall health and general status of a reef in relation to shifting dominance, ecological processes, and economic services provided to human communities. Recent studies in the Caribbean, Pacific/Southeast Asia (PSEA) regions have compiled coral cover data since the 1970s and found significant long-term, region-wide declines in coral cover along with shifts in benthic cover dominance (Gardner et al. 2003; Bruno and Selig 2007). The Caribbean study (Gardner et al. 2003) showed a region-wide steady decline due to the combined effect of multiple stressors, which included overfishing, eutrophication, coastal development, coral diseases and coral bleaching. Later studies of Caribbean coral cover data have suggested that white-band disease in the early 1980s may have been one of the strongest sources of coral mortality (Aronson and Precht 2006; Schutte et al. 2010), however hurricane activity has also been implicated (Gardner et al. 2005). Bruno and Selig (2007) studied changes in cover in the PSEA region which also indicated a steady and uniform decline, irrespective of management, that is most likely associated with a steady increase in chronic stresses and bleaching disturbance (Bruno

Coral reefs of the Indian Ocean: their ecology and conservation

Oxford University Press eBooks, 2000

Status of the coral reefs of the South West Indian ocean islands states: Comoros, Madagascar, Mauritius, Réunion, Seychelles

Many reefs are recovering well from 1998 mass coral bleaching damage with all countries having some areas with good coral cover, and other areas with slow or little coral recovery; Mean live coral cover has continued to increase on some reefs of the Seychelles and Comoros, but has decreased on some reefs in Mauritius and La Réunion; The stresses causing low coral cover are mostly from human activities, such as trampling, pollution, chronic sedimentation and over-fishing; Cyclones and coral bleaching are the most important natural stresses damaging the reefs, with some bleaching recorded annually since 2000 in parts of the region; There is little information on the status of seagrass and mangrove areas in many countries, due to poor or no monitoring programs; Most countries have no active socio-economic monitoring, and ecological and socio- economic monitoring results are not reported regularly to reef managers; Recommendations include increasing efforts to reduce human impacts and i...

Coral Bleaching and Associated Mortality at Mayotte, Western Indian Ocean

2016

Abstract—Bleaching and associated coral mortality were assessed on fringing and barrier reefs on the north and east coasts of Mayotte from 1-24 May 2010. Major bleaching was encountered; nearly 80 % of the corals were bleached or dead (covered with thin algal overgrowth) on fringing reefs along the north coast, and 50 % and 35 % of the corals were bleached or dead at two sites on the east coast. The observations revealed spatial and temporal heterogeneity in the extent of the bleaching and mortality. The genera that appeared most susceptible to bleaching were Pocillopora and tabular Acropora, while Porites seemed to have suffered the least. Observations on the bleached genera were consistent with those made during the 1997-1998 bleaching event.

Coral bleaching impacts from back-to-back 2015–2016 thermal anomalies in the remote central Indian Ocean

Coral Reefs

Studying scleractinian coral bleaching and recovery dynamics in remote, isolated reef systems offers an opportunity to examine impacts of global reef stressors in the absence of local human threats. Reefs in the Chagos Archipelago, central Indian Ocean, suffered severe bleaching and mortality in 2015 following a 7.5 maximum degree heating weeks (DHWs) thermal anomaly, causing a 60% coral cover decrease from 30% cover in 2012 to 12% in April 2016. Mortality was taxon specific, with Porites becoming the dominant coral genus post-bleaching because of an 86% decline in Acropora from 14 to 2% cover. Spatial heterogeneity in Acropora mortality across the Archipelago was significantly negatively correlated with variation in DHWs and with chlorophyll-a concentrations. In 2016, a 17.6 maximum DHWs thermal anomaly caused further damage, with 68% of remaining corals bleaching in May 2016, and coral cover further declining by 29% at Peros Banhos Atoll (northern Chagos Archipelago) from 14% in March 2016 to 10% in April 2017. We therefore document back-to-back coral bleaching and mortality events for two successive years in the remote central Indian Ocean. Our results indicate lower coral mortality in 2016 than 2015 despite a more severe thermal anomaly event in 2016. This could be caused by increased thermal resistance and resilience within corals surviving the 2015 thermal anomaly; however, high bleaching prevalence in 2016 suggests there remained a high sensitivity to bleaching. Similar coral mortality and community change were seen in the Chagos Archipelago following the 1998 global bleaching event, from which recovery took 10 yr. This relatively rapid recovery suggests high reef resiliency and indicates that the Archipelago's lack of local disturbances will increase the probability that the reefs will again recover over time. However, as the return time between thermal anomaly events becomes shorter, this ability to recover will become increasingly compromised.

Coral bleaching in the Indian Ocean islands: Ecological consequences and recovery in Madagascar, Comoros, Mayotte and Reunion

Grande Comore is characterised essentially by fringing reefs. The results of the survey in NorthWest Mitsamiouli Reef suggests that 10% bleaching had occurred by November 1999. The cover of live corals was 40%, recently dead coral 15%, and hard substrates with algae, 32%. Itsamia, located in Mohéli island displayed a simi

Indian Coral reefs:Diversity,Anthropogenic influences and conservation measures

India is a country well known for its Biodiversity rich ecosystems. The coral reef ecosystems are indeed very unique and are home to a multitude of organisms. Currently there are 5 major reefs in India that include Gulf of Kutchch, Gulf of Mannar, Palk Bay, Lakshadweep Islands and Andaman and Nicobar islands and minor reefs are distributed along the intertidal regions of Ratnagiri, Malvan and Redi, South of Bombay, west of Mangalore and the Hermatypic corals along the shore are reported from Quilon in the Kerala Coast to Enayem in Tamil Nadu. But these rich abodes are facing a number of anthropogenic threats and the current status of the Indian reefs is also discussed in this review. BEST Journals 26 V. Jayaprakas & Ranju Radhakrishnan

The Diversity and Biogeography of Western Indian Ocean Reef-Building Corals

This study assesses the biogeographic classification of the Western Indian Ocean (WIO) on the basis of the species diversity and distribution of reef-building corals. Twenty one locations were sampled between 2002 and 2011. Presence/absence of scleractinian corals was noted on SCUBA, with the aid of underwater digital photographs and reference publications for species identification. Sampling effort varied from 7 to 37 samples per location, with 15 to 45 minutes per dive allocated to species observations, depending on the logistics on each trip. Species presence/absence was analyzed using the Bray-Curtis similarity coefficient, followed by cluster analysis and multi-dimensional scaling. Total (asymptotic) species number per location was estimated using the Michaelis-Menten equation. Three hundred and sixty nine coral species were named with stable identifications and used for analysis. At the location level, estimated maximum species richness ranged from 297 (Nacala, Mozambique) to 174 (Farquhar, Seychelles). Locations in the northern Mozambique Channel had the highest diversity and similarity, forming a core region defined by its unique oceanography of variable meso-scale eddies that confer high connectivity within this region. A distinction between mainland and island fauna was not found; instead, diversity decreased radially from the northern Mozambique Channel. The Chagos archipelago was closely related to the northern Mozambique Channel region, and analysis of hard coral data in the IUCN Red List found Chagos to be more closely related to the WIO than to the Maldives, India and Sri Lanka. Diversity patterns were consistent with primary oceanographic drivers in the WIO, reflecting inflow of the South Equatorial Current, maintenance of high diversity in the northern Mozambique Channel, and export from this central region to the north and south, and to the Seychelles and Mascarene islands