Climate change scenarios of increased CO₂ and temperature affect a coral reef peracarid (Crustacea) community

The effects of applying scenarios of increasing CO₂ and temperature, using a mesocosm experiment, on the structure of a macrofaunal coral reef peracarid community were investigated for the first time. Samples were taken from artificial substrate units (ASUs), colonized by macrofauna from the coral reef subtidal zone of Serrambi beach (Brazil). In the laboratory, the ASUs were exposed to a Control (Ctrl) treatment and three climate change Scenarios (Sc) (increase of T° of 0.6, 2, and 3 °C, and pH drop of 0.1, 0.3, and 0.7 units for Sc I, II and III respectively), and were collected after 15 and 29 days of exposure. Our results showed that the effect of different temperature and acidity levels under experimental climate change scenarios significantly impacted density, diversity and community structure. Major differences were observed when applying Sc II and III. Peracarida also showed a reduction in specimen number when comparing both exposure times. Overall, Amphipoda, Tanaidacea and Isopoda communities all displayed a reduction in the number of individuals for both scenarios and exposure time factors, while Cumacea responded negatively in all scenarios, suggesting that these individuals were more sensitive to the experimental conditions. Dissimilarities were greatest between the Ctrl and Sc III, particularly after 29 days. Two species, Elasmopus longipropodus (Amphipoda) and Chondrochelia dubia (Tanaidacea), greatly contributed to these dissimilarities. This study demonstrates that even an intermediate level of increasing ocean temperature and acidification will negatively impact the structure of the Peracarida macrofaunal community on coral reefs. Also demonstrates that different species of Peracarida exhibit divergent response patterns, highlighting the specific responses of these taxa to the impacts of environmental stressors. These outcomes highlight the importance of studying the effects of climate change on benthic peracarids, especially because they incubate their eggs. This characteristic can reduce migration potential and thereby reduces the individual's ability to disperse in response to a changing environment.