Two sun coral species, Tubastraea tagusensis and T. coccinea, have successfully colonized reef habitats along the Southwest Atlantic. However, their invasive biology has been largely addressed without considering species-specific distribution patterns. Here, we assessed the distribution and abundance of Tubastraea spp. at vertical rocky reef sites within a number of islands along 120 km of coastline off the northern coast of São Paulo State, Brazil, to (1) investigate possible mechanisms underlying the invasion dynamics in the region, (2) test species-specific distributions according to a key environmental filter (depth), and (3) examine within-patch patterns to assess whether competition, niche-based or neutral processes are best candidates to modulate local species coexistence. Sun corals were found in the great majority of the studied locations, and the probability of finding them at any given reef site was estimated to be 0.54. There was substantial species segregation across locations, consistent with primary priority effects. Within locations, results suggest environmental filtering, with T. coccinea apparently advantaged in more hydrodynamic environments just below the surf zone. At sun coral patches with extensive co-occurrence of T. tagusensis and T. coccinea, the presence of each species can be, remarkably, modeled as an independent event, suggesting neutral coexistence. The spread of sun corals is an ongoing and increasingly invasive process that may be explained by the enemy-release hypothesis and the lack of negative interactions between Tubastraea species. The stochastic nature of small-scale distributions sets an additional challenge to predict (and thus control) sun coral invasion.
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.
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