Non-random orientation of Pocillopora colonies on forereefs of Moorea, French Polynesia

Abstract

Morphological variation in scleractinian corals has been variously ascribed to genetic differentiation and phenotypic plasticity, with a likely influence of both factors. Experimental approaches have dominated studies of phenotypic plasticity, for example with asymmetrical colony formation resulting from exposure to experimentally imposed unidirectional water flow. However, it has been difficult to disentangle the effects of competition for space between sessile organisms from the influence of physical forcing on coral morphologies in situ. To this end, we investigated morphological variation of coral colonies of the genus Pocillopora on reefs in Moorea, French Polynesia, where recovery (by 2018) after near complete loss of coral cover on the forereef in 2010 was driven predominantly by recruitment and growth of Pocillopora. We employed a large-area imaging approach at 8 study sites in the forereef of Moorea, constructing digital models of 100 m2 benthic plots to describe the orientation of ~400 individual colonies of Pocillopora. Results demonstrate that Pocillopora colonies on the forereef of Moorea exhibit non-random orientations, with a systematic orientation of the major axis that lies approximately perpendicular to the 20-30 m isobath.