Biodiversity drives stability in communities, allowing it to withstand environmental fluctuations without changes in aggregate properties like total abundance or biomass. We investigated biodiversity’s influence on two crucial population-level mechanisms governing abundance stability in mesopredatory coral reef fishes: ‘community asynchrony,’ where species populations fluctuate inversely over time, and ‘dominant stability,’ where highly abundant species with significant community contributions display minimal population fluctuations. Analyzing data from 83 reef fish communities across the Indian and Pacific Oceans over a decade, we found that community asynchrony, rather than dominant stability, primarily predicts community stability. Functional diversity, not taxonomic diversity, regulates this stability, emphasizing the role of niche differences in stabilizing communities. We highlight that community attributes that promote asynchronous population fluctuations, enhancing response diversity and tempering strong trophic interactions are vital for stabilizing mesopredatory reef fish communities in the face of global change.

A quarter century after the 1998 El Niño, it is still difficult to predict how individual reefs will respond to recurring disturbances. Reports differ on the relative importance of anthropogenic influences, local geography and bleaching recurrence in determining resistance and recovery. It is assumed that coral traits largely determine winners and losers, based on bleaching susceptibility, recruitment, survival and growth. Whether this translates to the long-term fates of corals on reefs is still debated. We tracked multi-decadal coral compositional changes in reefs across the densely populated Lakshadweep Archipelago to explore how global bleaching events and local geographical factors (depth and wave exposure) influenced responses to repeated mass bleaching. Coral resistance increased with recurrent bleaching, uninfluenced by local geography. However, wave exposure regimes positively influenced recovery rates, given sufficient time between mortality events (>7 years). The overall trajectory though, was of protracted decline interspersed with periods of halting recovery, with many losers, and few resistant genera that lose less. Based on these responses, we identified six community clusters that describe contrasting long-term responses to local and global factors. Interestingly, genera with different functional traits cluster together, sharing similar fates, as a result of complex interactions between bleaching susceptibility, local geography and inter-bleaching intervals. These clusters provide a clear site-specific predictive framework of long-term community change, indicating that geography, community and time largely determine local responses to climate disturbances.

As invasive species spread, the ability of local communities to resist invasion depends on the strength of biotic interactions. Evolutionarily unused to the invader, native predators or herbivores may be initially wary of consuming newcomers, allowing them to proliferate. However, these relationships may be highly dynamic, and novel consumer-resource interactions could form as familiarity grows. Here, we explore the development of effective biotic resistance towards a highly invasive alga using multiple space-for-time approaches. We show that the principal native Mediterranean herbivore learns to consume the invader within less than a decade. At recently invaded sites, the herbivore actively avoided the alga, shifting to distinct preference and high consumptions at older sites. This rapid strengthening of the interaction contributed to the eventual collapse of the alga after an initial dominance. Therefore, our results stress the importance of conserving key native populations to allow communities to develop effective resistance mechanisms against invaders.

Predictions for the future of coral reef are largely based on thermal exposure and poorly account for geographic variation in biological sensitivity and resistance to thermal stress. Based on the ratio of thermal exposure and sensitivity, geographic variability of coral resistance was estimated during the 2016 global-bleaching event. Exposure was estimated as historical cumulative excess summer heat (CTA) and a multivariate index of SST, light, and water flow (CE). Site sensitivity was estimated for 226 sites using coordinated bleaching observations. Site resistance was evaluated by 128 possible models for the influences of geography, historical SST variation, coral cover, and number of coral genera. Most factors were statistically significant but the strongest factor was geography - Coral Triangle having higher resistance than non-Coral Triangle sites. Consequently, future predictions of thermal stress will need to account for strong geographic differences in acclimation/adaptation.