Detecting the coral bleaching at the coral reefs of Son Tra peninsula and Cu Lao Cham Island in the South central coast region of Vietnam

Coral bleaching events are of concern globally because of their adverse effect on the coral reef ecosystem. However, there is a lack of observed bleaching in many coral reefs in Vietnam, leading to difficulty in implementing the suitable management and protection solutions. The study aims to provide general information about coral bleaching in ST and CLC basing on bleaching alerts of NOAA Coral Reef Watch in 2019. Field data was collected by a photographic method for analyzing and classifying bleached coral. The results showed that coral reefs experienced low bleaching by an average of 8.86% and 9.09% in ST and CLC, respectively. In addition, the study broadly identified the relationship of sea surface temperature and Degree Heating Weeks to coral bleaching in the study area.

Analysis of composition and abundance of viral communities associated with coral \(\textit{Acropora formosa}\)

Coral reefs harbor the extraordinary biodiversity and not only provide livelihoods for coastal communities but also play a crucial role in economic development generally. Unfortunately, they are in decline in Vietnam and around the world because mass coral bleaching events have become more common worldwide. However, little is discovered, about viruses that infect corals and their symbionts. Herein, we present metagenomic analyses of the viral communities in coral mucus associated with healthy and bleached coral Acropora formosa which was collected at Con Dao Island, Vietnam. Interestingly, the number of viral species in bleached specimens are higher than those in healthy status. Viruses similar to those that infect humans and some marine animals also appeared in the coral viral assemblage. The results indicated that the proportion of shared viruses were quite small, and represented extremely abundance. Among the phage identified, vibriophage and cyanophage were only presented in healthy and bleached coral, respectively. Therefore, coral-associated viruses could prospectively infect all constituents of the holobiont - coral, microalgal and microbial. Thus, we expect viruses to be illustrated prominently in the preservation and breakdown of coral health.

Will community calcification reflect reef accretion on future, degraded coral reefs?

Coral bleaching events continue to drive the degradation of coral reefs worldwide, causing a shift in the benthic community from coral to algae dominated ecosystems. Critically, this shift may decrease the capacity of degraded coral reef communities to maintain net positive accretion during warming-driven stress events (e.g., reef-wide coral bleaching). Here we measured rates of net ecosystem calcification (NEC) and net ecosystem production (NEP) on a degraded coral reef lagoon community (coral cover 20 %) during a reef-wide bleaching event in February of 2020 at Heron Island on the Great Barrier Reef. We found that during this bleaching event, rates of community NEP and NEC across replicate transects remained positive and did not change in response to bleaching. Repeated benthic surveys over a period of 20 d indicated an increase in the percent area of bleached coral tissue, corroborated by relatively low Symbiodiniaceae densities (~0.6 × 106 cm−2) and dark-adapted photosynthetic yields in photosystem II of corals (~0.5) sampled along each transect over this period. Given that a clear decline in coral health was not reflected in the overall community NEC estimates, it is possible that elevated temperatures in the water column that compromise coral health enhanced the thermodynamic favourability for calcification in other, ahermatypic benthic calcifiers. These data suggest that positive NEC on degraded reefs may not equate to the net positive accretion of reef structure in a future, warmer ocean. Critically, our study highlights that if coral cover continues to decline as predicted, NEC may no longer be an appropriate proxy for reef growth as the proportion of the community NEC signal owed to ahermatypic calcification increases and coral dominance on the reef decreases.

Coral bleaching variability during the 2017 global bleaching event on a remote, uninhabited island in the western Pacific: Farallon de Medinilla, Commonwealth of the Northern Mariana Islands

A survey conducted in Fall 2017 by US Navy scientists around the small, uninhabited island of Farallon de Medinilla (FDM) documented severe bleaching related to extended regional heat stress. Three of the dominant scleractinian genera at FDM, Pocillopora, Leptastrea, and Astreopora, were severely impacted, with more than 90% of colonies from many species exhibiting bleaching. In contrast, several species of Porites corals, another dominant genus at FDM, fared better, with less bleaching (7%–68% by species) than the island average (78%). Bleaching was somewhat higher at shallower depths (<10 m depth stratum, compared to 10–20 m depth stratum) and on the leeward of the island. Surveying FDM presented logistical challenges including a compressed time window for survey execution, periods of strong currents >1 knot that precluded diving, rare but potentially hazardous ordnance items, survey requirements for georeferenced imagery, and quantitative data collection. The survey protocol designed to accommodate these challenges is presented here, as are lessons from an unsuccessful attempt to delineate bleached coral colonies in photographs using automated object-based image analysis.

Functional diversity of microboring Ostreobium algae isolated from corals

The filamentous chlorophyte Ostreobium sp. dominates shallow marine carbonate microboring communities, and is one of the major agents of reef bioerosion. While its large genetic diversity has emerged, its physiology remains little known, with unexplored relationship between genotypes and phenotypes (endolithic versus free-living growth forms). Here, we isolated 9 strains affiliated to 2 lineages of Ostreobium (>8% sequence divergence of the plastid gene rbcL), one of which was assigned to the family Odoaceae, from the fast-growing coral host Pocillopora acuta Lamarck 1816. Free-living isolates maintained their bioerosive potential, colonizing pre-bleached coral carbonate skeletons. We compared phenotypes, highlighting shifts in pigment and fatty acid compositions, carbon to nitrogen ratios and stable isotope compositions (δ13C and δ15N). Our data show a pattern of higher chlorophyll b and lower arachidonic acid (20:4ω6) content in endolithic versus free-living Ostreobium. Photosynthetic carbon fixation and nitrate uptake, quantified via 8h pulse-labeling with 13C-bicarbonate and 15N-nitrate, showed lower isotopic enrichment in endolithic compared to free-living filaments. Our results highlight the functional plasticity of Ostreobium phenotypes. The isotope tracer approach opens the way to further study the biogeochemical cycling and trophic ecology of these cryptic algae at coral holobiont and reef scales.

Inferences on the role of coral bleaching or seasonality on cross-habitat movement of nekton assemblages in adjacent coral reef, seagrass, and mangrove habitats

We investigated shifts in nekton assemblages in coral reef, seagrass, and mangrove habitats that coincided with a coral bleaching event in June 2016. The study was conducted in May 2016 (prebleaching), July 2016 (bleaching), October 2016 (4-mo postbleaching), and February 2017 (7-mo postbleaching) in relatively undisturbed coastal areas in Busuanga, Palawan, western Philippines. We used triangular trap nets to capture nekton samples from each habitat. In coral reef and mangrove habitats, there were increases in nekton abundance and biomass from the prebleaching to the bleaching period. After the bleaching event, however, there were reductions in nekton abundance and biomass at the coral reefs until 7-mo postbleaching. Species composition changed at all sites where shifts in dominant species, habitat affinity, and trophic category were observed. The postbleaching increase in nekton abundance in mangroves coincided with the decreased nekton abundance in the coral reef, suggesting a cross-habitat movement, likely due to the reduced suitability and/or food in the bleached coral reef. The changes in the nekton assemblage may also have been due to seasonal fluctuations in environmental parameters, especially salinity. Our study presents evidence of the possible role of coral bleaching or seasonal changes on cross-habitat movements of nekton assemblages, which can be inferred as an indicator of disturbance. The presence of adjacent vegetated habitats may provide refuge for the affected nekton assemblage of the coral reef.

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.

Dampak Pemutihan Karang Keras pada Komunitas Ikan Karang dan Makrozoobenthos di Wilayah Perairan Tejakula, Buleleng, Bali

<p>ABSTRAK<br />Pemutihan karang merupakan salah satu dampak dari perubahan iklim global, kenaikan suhu tersebut memberikan dampak negatif bagi keseimbangan ekosistem terumbu karang. ­Terumbu karang yang memutih dan kehilangan zooxanthella nya akan rentan terkena infeksi dan penyakit. Populasi komunitas ikan karang pemakan hewan karang dan makrozoobenthos juga akan menurun. Tujuan dari penelitian ini adalah untuk mengetahui besar dampak kerusa­kan terumbu karang dan dampaknya bagi populasi ikan dan makrozoobenthos. Survey dilakukan pada 3 titik di wilayah perairan Tejakula dengan metode reefcheck. Hasil penelitian menunjukkan kematian terumbu karang sebesar 5-7.5%, jumlah alga yang menutupi 3.125%. Kondisi ikan kepe-kepe yang merupakan pemakan hewan karang juga sudah ditemukan dalam jumlah cukup banyak. Keberadaan ikan herbivora dan makrozoobenthos herbivore membantu mengurangi jumlah alga yang menutupi. Sedangkan keberadaan ikan pemakan terumbu karang dan ikan predator memperlihatkan bahwa sistem ekologi yang ada di terumbu karang tersebut hampir kembali normal. <br />Kata Kunci: terumbu karang, komunitas ikan karang, makrozoobenthos.</p><p><strong>The Impact of Hard Coral Bleaching in Coral and Macrozoobenthos Fish Communities in Tejakula, Buleleng, Bali Water Areas</strong></p><p>ABSTRACT<br />Coral bleaching is one of the consequences of global climate change, as the rise of temperature negatively impacts the ecological balance of reef ecosystems. Bleached coral reefs lose their zooxanthellae, increasing vulnerability to infection and disease and consequently, causing population decline of macrozoobenthos and reef fish communities which prey on coral-consuming organisms. This research aims to determine the degree of coral reef damage and its impact on fish and macrozoobenthos population. The survey was conducted on 3 stations in Tejakula waters with the reef check method. Results show that coral reef death reaches 5-7.5%, with algal coverage of 3.125%. Kepe-kepe fish which prey on coral-consuming animals were also found in relatively high abundance. The presence of herbivore fish and macrozoobenthos help reduce algal cover. Meanwhile, the presence of coral-consuming and predator fish indicate that the coral reef ecological system has mostly returned to normal. <br />Keywords: coral reef, reef fish community, macrozoobenthos</p>