Based on current greenhouse gas emission trajectories, Malaysian coral reefs are predicted to experience severe annual coral bleaching events by 2043, imminently threatening the survival of Malaysian coral reefs within this century. However, there is no field data on how Malaysian coral reefs respond to successive sequences of coral bleaching. Numerous scleractinian taxa have shown the ability to acclimatize to thermal stress events after previous exposure to heat disturbances. Nonetheless, thermal tolerance and acclimatization potentials might corroborate with accelerating warming rates and increasing frequencies of thermal stress anomalies, necessitating repeated field studies at reef scale to investigate thermal tolerance and acclimatization of scleractinian taxa. Here, we studied two successive thermal stress events during the 2019 El Niño Southern Oscillation (ENSO) and during the onset of the La Niña Oscillation in 2020. We recorded the bleaching susceptibility of scleractinian taxa to document bleaching trajectories across fine temporal and environmental gradients in Northeast Peninsular Malaysia. In addition, we analyzed historic temperature trends to demonstrate rapid warming rates (0.17°C per decade) and high return frequencies of thermal stress anomalies. Despite high maximum temperatures in both years (31.07°C and 31.74°C, respectively), accumulated thermal stress was relatively low during the bleaching episodes (Degree Heating Weeks 1.05°C-weeks and 0.61°C-weeks, respectively) and marginally varied across reef scales (0.94°C-weeks, 0.76°C-weeks, 0.48°C-weeks in 2020), suggesting a widespread thermal sensitivity of most scleractinian taxa (55.21% and 26.63% bleaching incidence in 2019 and 2020, respectively). However, significant discrepancies between satellite and in-situ temperature data were found (0.63°C; SD±0.26). Bleaching susceptibility was highly taxon-specific and contrasted historical bleaching patterns (e.g., Acropora and Montipora showed high thermal tolerance). In 2020, successive heat disturbance moderately increased bleaching susceptibility of three taxa (Galaxea, Leptastrea and Platygyra) despite lower heat stress, while Heliopora was highly susceptible in both years. Bleaching analysis of taxa on biophysical reef scales revealed significant difference across depth, wind sites (e.g., leeward and windward), and the combined interactions of wind and depth (e.g., leeward shallow) on bleaching response were significant for numerous taxa. Findings suggest thermal acclimatization of fast-growing taxa, whereby successive bleaching events and accelerating warming rates selectively pressure scleractinian assemblages.

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Coral reefs globally are experiencing chronic stress leading to the deterioration of health and functionality. Analysis of size frequency distribution (SFD) of hard corals enables post hoc assessments of major demographic events (e.g., recruitment and mortality) that follow ecological disturbances. Here, we present an evaluation of current reef health, SFD and recruitment of 37 morpho-taxa in Northeast Peninsular Malaysia. Results highlight stress viable demographic structure of massive taxa (e.g., massive Porites) and significant differences of SFD across gradients of reef health, whereby degraded sites were predominantly characterized by negatively skewed (e.g., large colonies) and leptokurtic (e.g., high population turnover) distribution of dominant hard coral taxa. Ultimately, results suggest that locally coral reef degradation can exceed tipping points, after which annual monsoon conditions and degraded reef substrates interact to reinforce and manifest negative feedback loops, thereby impeding demographic recovery, and altering coral SFD and population assemblage.

Coral reefs in Malaysia have been degraded by environmental and anthropogenic stressors, and enthusiasm for coral propagation aimed at site restoration is rapidly growing as a local management tool. However, coral propagation activities in the region are in their infancy and little data currently exists to guide and inform effective practices. We therefore established the first multi‐taxa coral tree nursery (6 species and 300 fragments) in Malaysia and tracked survival and growth to determine the relative return‐on‐effort (RRE) over an approximately 14‐month monitoring period. We observed differences in growth and survival among six coral species and were successful at benchmarking results against coral restoration operations globally and in the East Asian Seas region. Major findings include (1) overall ranges in species level survivorship of 34–94% and specific growth rate of 0.14–0.29%/day, leading to variable RRE scores among species, (2) variable growth rates among coral species based on seasonal changes in environmental conditions, (3) similar RRE scores to other nursery locations worldwide, which suggests effective practice, and (4) calculation of RRE scores for species not previously reported in nursery culture (Acropora florida, A. hoeksemai, and Echinopora horrida). Ultimately, our study supports previous findings that RRE is an effective technique for comparing coral nursery performance and offers valuable insight to guide future restoration activities in Malaysia.