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We used a 12-yr data set of benthic cover (2005–2017), spanning two bleaching events, to assess changes in benthic cover and coral community composition along 21 islands within Gulf of Mannar (GoM), southeast India. Overall, between 2005 and 2017 reefs had a simultaneous decrease in relative coral cover (avg. = − 36%) and increase in algal cover (avg. = + 45%). Changes in benthic cover were not consistent among islands, ranging from − 34 to + 5% for coral cover and from − 0.3 to + 50% for algae. There was a spatial gradient in coral mortality, which increased among islands from west to east. However, there was a disconnect between coral loss and subsequent increases in algae. Algal cover increased more on islands in west GoM where coral loss was minimal. Environmental co-factors (coral cover, percent bleaching, degree heating weeks, fish densities, Chl-a, pollution) explained > 50% of the benthic cover responses to successive bleaching. Coral survival was favored on islands with higher fish densities and chlorophyll-a levels, and increases in algal cover were associated with higher measures of pollution from terrestrial runoff. Coral morphotypes differed in their response following successive bleaching resulting in changes in the relative abundance of different coral morphotypes. Existing climate projections (RCP8.5) indicate a 22-yr gap in the onset of annual severe bleaching (ASB) for reefs in the east versus west GoM, and ASB was ameliorated for all reefs under the RCP4.5 projections. There is limited knowledge of the resilience of GoM reefs, and this study identifies coral morphotypes and reefs that are most likely to recover or decline from successive bleaching, in the context of forecasts of the frequency of future bleaching events in GoM. [ABSTRACT FROM AUTHOR]

The study reports the colonization and ecological succession of epibenthic communities on perforated trapezoidal Artificial Reef (AR) modules deployed in Vaan Island of Gulf of Mannar, southeast India. These AR communities assist in building climate resilience among the coastal ecosystems, which have faced severe climate change impacts during the last decade. Based on wave dynamics modeling studies, 10,600 modules were deployed in two layers to protect the Island from beach erosion and to enhance biodiversity. Randomly selected modules were subject to continuous monitoring from 2015 to 2020 to understand the ecological succession of the epibenthic communities. Hard corals turned out to be the dominant epibenthic category with 76.01 no.module−1(SE ± 2.16) by 2020. A total of 37 coral species belonging to 16 genera were found inhabiting the modules at the end of five years. The other major epibenthic categories were molluscs, hydroids, sponges, ascidians, octocorals and echinoderms with a total density of 40.44 no.module−1(SE ± 1.41) by 2020. A couple of years after the deployment, when hard corals started to flourish on the AR modules, the density of other epibenthic categories began to decline. A comparison of the numbers of epibenthic organisms on the inner and outer layers of AR modules reveals that the inner layer has a larger epibenthic community. After five years, the AR modules have started to act as coral refugia and are expected to create reef ecosystem analogous to natural reefs. The modules also provide the much needed topographic complexity for the fish to move in. This planned deployment not only helped in reef recovery and enhancement of associated biodiversity in Gulf of Mannar, which is severely impacted by global climate change, but also would serve to enhance the climate resilience of the coral ecosystems by increasing the coral biomass and thereby restoring the ecological services, which help to sustain the livelihood of the dependent small-scale fisher folk. [Display omitted] • Perforated trapezoidal Artificial Reef (AR) modules attract an abundance of epibenthic communities and the model used in this study can be replicated in areas where substrate availability is less for the benthic communities. • By acting as ideal substrates and providing suitable surface for juvenile corals to attach themselves and grow, the AR modules would aid in reef recovery and biodiversity enhancement in degraded reef areas • By restoring the ecological services through biodiversity enhancement, they help to sustain the livelihood of the dependent small-scale fisher folk [ABSTRACT FROM AUTHOR]

Underwater survey was conducted to assess the accumulation and impact of marine debris in the reef areas of Gulf of Mannar in southeast India. A combination of roving diver technique and belt transect method was applied for the assessment, which was conducted during the period between February 2018 and March 2019. An estimated total reef area of 1152 m2 has been affected by marine debris. Abandoned fishing nets were found to constitute the major portion of 43.17 ± 5.48% of the marine debris. Live corals were found to be dominant substrates for marine debris with 39.11%. The average prevalence of coral colonies in contact with marine debris was 3.28 ± 0.27%. Prevalence of corals in contact with debris was very high in genus Acropora with 8.23 ± 1.29% followed by Montipora with 4.63 ± 1.29% due to their complex growth form. Of the corals in contact with debris, 47.56% were fragmented and 34% were found with tissue loss. Unlabelled Image • Focusing on the underwater accumulation of marine debris in the reef areas of GOM. • Debris composed of nets, ropes, lines and traps made of non-biodegradable plastics. • Live corals have been found to be the dominant substrate for marine debris. • Reef area of 1,152 m2 has been affected by marine debris • Acropora and Montipora are the common coral genera most affected by marine debris. [ABSTRACT FROM AUTHOR]

Malvan Marine Sanctuary (MMS), Maharashtra, India is rich in coral reefs and the associated resources, which provide livelihood for the people involved in fishing and tourism. The elevated seasurface temperature triggered by climate change had caused the coral reefs around the world to undergo severe bleaching during 2014-2016. Scientists have declared this as the third global coral bleaching event. Two underwater surveys during December 2015 and May 2016 were conducted in MMS to assess the intensity and trend of coral bleaching. A high prevalence of coral bleaching, i.e. 70.93% (SD = 4.53) was recorded inside MMS during December 2015, with a mortality of about 8.38% (SD = 0.91). After a lapse of six months, corals were found to recover. This is borne out by the reduction in the bleaching prevalence to 6.77 ± 0.12% during May 2016. Climate change being a global issue, reduction in the local stressors such as fishing and tourism is highly recommended in order to allow the corals to recover and enable sustainable utilization of coral reef resources around MMS. [ABSTRACT FROM AUTHOR]

Coral reefs around the world are undergoing severe decline in the past few decades. Mass coral mortalities have predominantly been reported to be caused by coral bleaching or disease outbreaks. Temporary hypoxic conditions caused by algal blooms can trigger mass coral mortalities though are reported rarely. In this study in Gulf of Mannar (GoM), southeast India, we report a significant coral mortality caused by a bloom of the ciguatoxic dinoflagellate Noctiluca scintillans during September-October 2019. Dissolved oxygen levels declined below 2 mg l -1 during the bloom causing temporary hypoxia and mortality (up to 71.23%) in the fast growing coral genera Acropora, Montipora and Pocillopora. Due to global climate change, more frequent and larger algal blooms are likely in the future. Hence, it is likely that shallow water coral reefs will be affected more frequently by episodic hypoxic conditions driven by algal blooms. More studies are, however, required to understand the mechanism of coral mortality due to algal blooms, impacts on community composition and the potential for subsequent recovery.