Influence of thermal stress and bleaching on heterotrophic feeding of two scleractinian corals on pico-nanoplankton

Abstract The feeding strategies of Montipora digitata and Porites lutea, two dominant corals in the Okinawan reefs, were investigated. The focus was on pico- and nanoplankton feeding efficiencies, using 6-h incubations. Although healthy M. digitata consumed from 72% to 87% more pico-nanoplankton cells than P. lutea, feeding rates of bleached corals of both species were similarly low at heat stress (33 °C). Heterotrophic carbon acquisition with respect to dark respiration varied from 3% to 65% in M. digitata and from 7% to 68% in P. lutea. A decrease in the feeding efficiency of bleached M. digitata under heat stress shows its vulnerability to water heating events. Feeding rates of P. lutea were low under all conditions and treatments; therefore, this species is less vulnerable to heat stress due to the strategy of meeting metabolic costs by using translocated organic matter from endoliths and selecting pico-nanoplankton cells with a high C/N ratio.