Co-occurrence of a reef-building coral and canopy-forming macroalgae in the Mediterranean Sea

Canopy-forming macroalgae are among the main competitors of corals, affecting coral recruitment, growth of recruits and adults, fecundity, and in the worst-case scenario causing coral bleaching and necrosis. However, potentially reef-building coral Cladocora caespitosa (Linnaeus, 1767) and canopy-forming macroalgae of the order Fucales (Cystoseira sensu lato) are known to coexist at a few sites in the Mediterranean Sea. Here, we examine the small-scale relationships between Cladocora abundance and Cystoseira s. l. densities at three different sites where they coexist. We found that these relationships were both species-and site-specific, even though most were neutral, suggesting a predominant concurrence of corals and macroalgae at the small scale. These findings shed new light on the relationship between corals and fleshy macroalgae in a temperate environment and serve as a starting point for future studies addressing the interactions between C. caespitosa and Cystoseira s. l.