Competition drives the dispersal dynamics of two cup coral morphs in populations on the Powell Basin slopes, Weddell Sea, Antarctica.

Coexistence of ecologically similar taxa can contribute considerably to local biodiversity patterns. Deep water Southern Ocean benthic communities provide a unique setting to investigate coexistence mechanisms due to the relatively pristine nature of Antarctic ecosystems and a lack of disturbances like ice scour or top-down predator control. Here, we examine cup coral populations on the deep (~ 2000 m) rocky slopes of Powell Basin, Weddell Sea-an ecosystem with dense and speciose epibenthic communities. We investigate the spatial ecology of two coral morphotypes-"orange" and "pink" cup corals (likely Caryophyllia or Flabellum) using high-resolution seabed images from the RV Polarstern cruise PS118. Across 36 sites, we recorded 3431 pink and 1545 orange corals, which formed both mixed and single-population dominant (where either morph was near absent) communities. Spatial point process analysis revealed that reproductive processes drive their spatial patterns, with orange corals showing consistent dispersal behaviour regardless of community type. In contrast, pink corals exhibited greater dispersal plasticity in mixed populations, significantly increasing dispersal distances, suggesting that they are the weaker competitors. Our results suggest that in these deep water hard substrate Antarctic communities, dispersal plasticity has the ability to enable coexistence of ecologically similar morphs, thereby increasing alpha diversity.