Unraveling interactions: do temperature and competition with native species affect the performance of the non-indigenous sun coral Tubastraea coccinea?

The impact of invasive species has been increasing in recent decades due to globalization, threatening marine biodiversity. Tubastraea spp. (sun corals) have been spreading worldwide, showing rapid increases in abundance and/or spatial occupancy and adverse effects on recipient native ecosystems. In Brazil, they have become major invaders, extending discontinuously for more than 3000 km along the coast. Despite increased research efforts on sun coral ecology/biology over the last decade, information about the species’ environmental tolerance and interactions with native species is still scarce. In this context, temperature may be an important driver, as it affects species interactions, primarily through its influence on organismal physiology. Thus, in the present study we assessed the effects of temperature in the invasive T. coccinea and the native zoanthid Palythoa caribaeorum , as well as on their interactions, via a 3-week mesocosm experiment, exposing the species (individually and grafted together) to a temperature range of 16–31 °C. This was accompanied by measuring key physiological traits (metabolism, growth, feeding rates and competitive behavior) that underlie species performance, and hence, competitive strength. The results showed that at Arvoredo Island, Brazil, currently the southern distribution limit of both species, (1) T. coccinea exhibited limited capacity to adjust to sudden temperature changes, (2) T. coccinea ’s physical attacks did not affect P. caribaeorum, but induced increased metabolic costs in the former, while triggering increased growth in the latter, leading to eventual overgrowth of the sun coral and (3) that temperature interacted synergistically with the presence of the competitor in both species under high-temperature stress. These findings suggest that T. coccinea ’s successful invasion is mainly associated with r -selected life-history traits, rather than competitive strength or a high plasticity to temperature changes, and thus, communities with specific native competitors and/or a variable thermal regime may be more resistant to sun coral invasion.