Deposition of invasive sun-coral colonies (Tubastraea spp.) on a near-reef unconsolidated substrate triggers alternative macrofauna dynamics

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Abstract In the mid-1980s, sun-corals Tubastraea spp. were accidentally introduced to the Brazilian coast as oil and gas platform biofouling. Today, sun-corals are widespread along the Brazilian coastline, including several marine protected areas where dense populations are established. Recent observations in southeastern Brazil suggested that, in saturated localities, sun-coral adult colonies frequently detach from the rocky reef and accumulate on the unconsolidated substrate. Here, we conducted an in situ experiment of approximately 70 days to evaluate the effects of sun-coral deposition on macrofaunal assemblages across four cover levels (0, 33, 66, and 100%). Significant shifts in community structure and overall richness occurred at a threshold of 66% coral cover or higher. Polychaetes, ophiuroids, brachyurans, hermit crabs, caridean shrimps, tanaidaceans and amphipods were more abundant in high-coral cover plots (66% or 100%) compared to plots where sun-coral covered 33% or less. In contrast, abundances of cephalochordates, bivalves, and gastropods decreased from low-coral cover to high-cover plots. Overall, our findings demonstrate that the ecological influence of invasive sun-corals in the Southwest Atlantic extends far beyond the vertical reef surfaces, impacting directly the macrofaunal assemblages from the unconsolidated substrate. Initial attraction by mobile fauna followed by short-range spillover may profoundly affect food webs at the benthopelagic interface, potentially reshaping ecosystem functions along the depth gradient.

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