The Lakshadweep Islands, renowned for their highly biodiverse and pristine reef ecosystems, face increasing stress from climate change, notably rising sea surface temperatures (SST), leading to recurrent bleaching events. In 2024, the Lakshadweep Islands experienced mass coral bleaching when the SST peaked to 32.2°C and Degree Heating Weeks (DHW) reached an unprecedented 9.2°C-weeks, the highest ever recorded for the Lakshadweep Islands. Concurrently, several non-scleractinians, such as Radianthus magnifica (Ritteri anemone) and Tridacna maxima (Small giant clam), experienced complete bleaching, while Heliopora coerulea (Blue coral) and Anemonia cf. majano (Carpet anemone) exhibited 60% and 55% bleaching, respectively. In contrast, during another comparatively less intense bleaching event that occurred in 2025, characterised by SST above the bleaching threshold but DHW <4°C-weeks, bleaching was evident only in Heliopora coerulea. This study indicates that DHW >4°C-weeks can induce widespread bleaching in non-scleractinians similar to scleractinians, and the distinct responses and bleaching thresholds of the diverse non-scleractinians to varying bleaching intensities.

This study assessed the density and distribution of the sea anemone Radianthus magnifica and examined its bleaching responses around the east coast of Rodrigues Island, Republic of Mauritius, Western Indian Ocean. The abundance of anemone-associated fish and anemone body size along with the relationship between depth and R. magnifica bleaching were investigated. Surveys were conducted at depths from 2 to 23 m via belt transects of 30×1 m, in triplicates during April 2024. Radianthus magnifica bleaching was observed and a comparison of chlorophyll-a fluorometry between non-bleached and bleached anemones was done using a Junior Pulse-Amplitude-Modulated (J-PAM) fluorometer. Radianthus magnifica was reported at only two out of seven surveyed sites, and its density did not differ significantly (p>0.05, One-Way ANOVA). Significant negative correlations were obtained between R. magnifica bleached individuals and depth, possibly due to lower irradiance and thermal regimes at deeper areas. A damselfish species, Dascyllus trimaculatus, was more abundant than Amphiprion chrysogaster and the presence of D. trimaculatus was also negatively correlated with degree of R. magnifica bleaching. Bleached R. magnifica exhibited a significantly lower photosystem II (PSII) efficiency and slightly lower relative maximum electron transport rate (rETR_max), and a higher non-photochemical quenching (NPQ_max) than non-bleached individuals, indicating an affected photo-physiological state of the remaining Symbiodiniaceae symbionts. These findings suggest that the distribution of R. magnifica is limited and to a certain extent, vulnerable to thermally-induced bleaching around Rodrigues Island, and thus may require further attention in terms of adaptive management and conservation strategies.

Coral reefs support approximately 30% of all marine life, making them some of the most biodiverse ecosystems on Earth. However, due to global climate change and human activities, coral reef ecosystems are now facing devastation. Under these circumstances and to support future conservation efforts, it is crucial to document the current state of zooxanthellate scleractinians, primary architects of coral reefs, as accurately and comprehensively as possible. This study reports details genus-level diversity of scleractinian corals in western Miyako Island and Irabu Island in late 2023.

Reef-building corals form essential symbioses with Symbiodiniaceae, a diverse family of photosynthetic dinoflagellates. Characterizing this association is critical because it greatly influences the physiology of the host. To this end, we aimed to document the coral-algal associations on a high-latitude reef to detect potentially endemic or flexible associations. Using a gel-based genetic analysis, this study characterized the dominant Symbiodiniaceae genera in four coral species: Acropora lovelli, Isopora cuneata, Porites heronensis, and Seriatopora hystrix, at six sites around Lord Howe Island (LHI)—the world's southernmost coral reef. Genetic analysis revealed that symbiont identity varied among species more than sampling site. Seriatopora hystrix was consistently dominated by Durusdinium, a symbiont generally associated with stress tolerance, potentially reflecting differential survival following recent marine heatwaves. Porites heronensis hosted a potentially distinct Cladocopium lineage. Acropora lovelli and I. cuneata predominantly hosted Cladocopium goreaui or Cladocopium "C4". Our findings highlight the importance of characterizing coral-algal associations in multiple locations to better understand spatial variation in host-specificity.

Mass coral bleaching driven by global warming has caused severe declines in shallow reef communities worldwide. Following the 1998 bleaching event, shallow population of the genus Seriatopora were presumed locally extinct around Sesoko Island, Okinawa, Japan. Recently, small shallow populations were rediscovered in northern Okinawa Island; however, the severe thermal anomaly in summer 2024 again caused widespread bleaching, particularly in shallow habitats, raising concerns about the long-term persistence of the genus. In this study, we assessed changes in Seriatopora cover during and after the 2024 bleaching event to evaluate its short-term impact and potential for recovery. Photoquadrat surveys were conducted before and after the bleaching events at two sites on Okinawa Island, "Sate" and "Ryugu," where a shallow population occurred across depths of 5-10 m. Overall, Seriatopora cover declined markedly following bleaching, with near-complete loss at ≤ 5m depth both sites. At deeper depth (≥ 10 m), several healthy colonies were discovered at Sate, whereas only a few surviving colonies were observed at Ryugu. These results indicate that shallow Seriatopora populations are highly vulnerable to acute thermal stress, while deeper colonies may function as refugia following bleaching events. Understanding the connectivity and recovery dynamics of these populations will be crucial for evaluating the feasibility of conservation and restoration strategies for shallow Seriatopora populations under ongoing ocean warming.

Coral recruits of the reef-building coral genus Acropora acquire dinoflagellate symbionts, primarily Durusdinium and Symbiodinium, in early life stages. While the molecular responses of host corals to Symbiodinium are well documented, those to Durusdinium during early life stages remain poorly understood. In this study, we report the larval transcriptomic responses of Acropora tenuis to inoculation with three different Durusdinium strains. We found that few gene expression changes were elicited in planula larvae exposed to Durusdinium, while obvious gene expression changes were observed in planula larvae inoculated with Symbiodinium. These findings suggest that gene expression of host corals is flexibly controlled depending on the identity of the algal symbionts.