Abstract
There is a paucity of information on the impacts of the 1997–8 El Niño event and subsequent climatic episodes on emergent intertidal coral reef assemblages. Given the environmental variability intertidal reefs experience, such reefs may potentially be more resilient to climatic events and provide important insights into the adaptation of reef fauna to future ocean warming. Here we report the results of a 17-year (1995–2011) biodiversity survey of four emergent coral reef ecosystems in Bahia, Brazil, to assess the impact of a major El Niño event on the reef fauna, and determine any subsequent recovery. The densities of two species of coral, Favia gravida and Siderastrea stellata, did not vary significantly across the survey period, indicating a high degree of tolerance to the El Niño associated stress. However, there were marked decreases in the diversity of other taxa. Molluscs, bryozoans and ascidians suffered severe declines in diversity and abundance and had not recovered to pre-El Niño levels by the end of the study. Echinoderms were reduced to a single species in 1999, Echinometra lucunter, although diversity levels had recovered by 2002. Sponge assemblages were not impacted by the 1997–8 event and their densities had increased by the study end. Multivariate analysis indicated that a stable invertebrate community had re-established on the reefs after the El Niño event, but it has a different overall composition to the pre-El Niño community. It is unclear if community recovery will continue given more time, but our study highlights that any increase in the frequency of large-scale climatic events to more than one a decade is likely to result in a persistent lower-diversity state. Our results also suggest some coral and sponge species are particularly resilient to the El Niño-associated stress and therefore represent suitable models to investigate temperature adaptation in reef organisms.
Highlights
Coral reefs around the world have already been degraded as a result human impacts from many local-scale and global scale impacts [1,2,3], and there is increasing interest in the resilience of reef species to such stressors [4]
Emergent intertidal coral reefs are common around the world [5], and organisms inhabiting these environments will be subject to much larger fluctuations in temperature and solar radiation stress compared to nearby subtidal organisms [6]
Despite some evidence to support the existence of other species of Siderastrea (S. radians, S. siderea and a third unidentified species) along the coast of Bahia, we are confident that only S. stellata occurs on the reefs we studied
Summary
Coral reefs around the world have already been degraded as a result human impacts from many local-scale and global scale impacts [1,2,3], and there is increasing interest in the resilience of reef species to such stressors [4]. There has been a recent focus on those organisms inhabiting marginal habitats as they often survive under sub-optimal conditions close to their physiological limits, and may be adapted to higher levels of physiological stress [5] Organisms inhabiting such environments have the potential to serve as models for understanding the impacts of global climate change and largescale climatic events. Emergent intertidal coral reefs are common around the world [5], and organisms inhabiting these environments will be subject to much larger fluctuations in temperature and solar radiation stress compared to nearby subtidal organisms [6] While this may mean such communities are more resilient to climatic related impacts than subtidal organisms, the reverse may be true, communities may be less resilient to stressors as they are living close to their physiological tolerance limits
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