Invasive sun corals and warming pose independent threats to the brain coral Mussismilia hispida in the Southwestern Atlantic

Abstract

Sun corals Tubastraea tagusensis have invaded reef habitats along the tropical-subtropical Western Atlantic, negatively impacting native habitat-forming species, including the most abundant scleractinian in Southeastern Brazil, the brain coral Mussismilia hispida. We combined field and laboratory experiments to closely evaluate temperature effects on the interaction between these corals. Field experiments undertaken during winter and late summer-fall aimed to test species interactions under current temperature regimes. When in contact with sun corals, all brain corals necrosed (8 to 12% colony surface mo −1 ). Their growth rates were also lower compared to stand-alone control colonies (−0.17 vs. 1.23 cm 2 mo −1 ). Necrosis was never observed in sun corals, and average growth rates (0.36 cm 2 mo −1 ) did not differ between interacting and isolated colonies. No season effects were detected for any of the coral traits examined. Negative effects of sun corals were further investigated in the laboratory both at current winter (23°C) and summer average temperatures (26°C), as well as extreme low (20°C) and high (29°C) temperature conditions that might persist under a climate-change scenario. Results suggest that species interactions may remain unaffected by climate change. Temperature effects were important but independent of whether brain corals were held isolated or in contact with sun corals. Interestingly, brain corals performed better at 20°C, with most colonies remaining undamaged over 95 d. Seatemperature increase and the sun coral invasion may thus be viewed as independent drivers potentially impacting brain coral populations and their associated assemblages.