Abstract
Coral reefs are biologically diverse ecosystems that provide numerous ecological services to our oceans, yet their survival is threatened by climate change and local disturbances. Reef-building corals depend upon photosynthetic partnerships for most of their carbon needs. During marine heatwaves, this energy source is lost in a phenomenon called coral bleaching. In these stressful conditions, corals increase their proportion of heterotrophic feeding to enhance their chances of survival. The present study investigates coral feeding mechanisms of two South Florida coral species, Montastraea cavernosa and Pseudodiploria clivosa. Using Particle Image Velocimetry (PIV), a fluid mechanics technique that optically measures fluid flows, the coral-generated flows are quantified. We hypothesize that corals actively generate flow fields around them to increase the efficiency of capture of zooplankton and mucus entrapment of particulate organic matter. Our results show a novel suction flow mechanism with strong vertical flows that pull particulate matter to the coral’s gastrovascular cavity at rates of around 500 μm/s. Mucus nets often accompanied the observed suction flow patterns, promoting optimized capture rates by immobilizing the particulate matter. The actively generated vertical flow-fields are likely integral to coral nutrition during coral bleaching and further studies on this phenomenon may help explain the differential survivorship of corals during episodic marine heatwaves.