Morphological and trophic coupling distinguishes coral clades along a light gradient

Abstract

Light availability is critical to the growth and survival of most scleractinian corals due to their endosymbiotic relationship with photosynthetic dinoflagellates. Natural light gradients are expected to be associated with shifts in coral physiology, morphology, and trophic strategy. However, few studies have assessed the interplay of these biological metrics simultaneously in multiple species. We collected three coral species from each of the two scleractinian clades along a light gradient in La Parguera, Puerto Rico, and quantified corallite morphology, symbiont physiology, tissue condition, and trophic strategy. All six species experienced significant morphological change and minimal physiological change along the light gradient. Stable isotope niche analyses indicated significant decoupling between coral host and symbiont isotopic niches, consistent with a high reliance on heterotrophy in most species. This pattern was not strongly modulated by light availability in any species. However, trophic strategy differed between clades and covaried with corallite size, offering novel insights into characteristics that may differentiate clades. Our results suggest that corals change their morphologies in response to light availability to maintain physiological and trophic performance.