The scaling of metabolic traits differs among larvae and juvenile colonies of scleractinian corals

Body size profoundly affects organism fitness and ecosystem dynamics through the scaling of physiological traits. This study tested for variation in metabolic scaling and its potential drivers among corals differing in life history strategies and taxonomic identity. Data were compiled from published sources and augmented with empirical measurements of corals in Moorea, French Polynesia. The data compilation revealed metabolic isometry in broadcasted larvae, but size-independent metabolism in brooded larvae; empirical measurements of Pocillopora acuta larvae also supported size-independent metabolism in brooded coral larvae. In contrast, for juvenile colonies (i.e. 1-4 cm diameter), metabolic scaling was isometric for Pocillopora spp., and negatively allometric for Porites spp. The scaling of biomass with surface area was isometric for Pocillopora spp., but positively allometric for Porites spp., suggesting the surface area to biomass ratio mediates metabolic scaling in these corals. The scaling of tissue biomass and metabolism were not affected by light treatment (i.e. either natural photoperiods or constant darkness) in either juvenile taxa. However, biomass was reduced by 9-15% in the juvenile corals from the light treatments and this coincided with higher metabolic scaling exponents, thus supporting the causal role of biomass in driving variation in scaling. This study shows that metabolic scaling is plastic in early life stages of corals, with intrinsic differences between life history strategy (i.e. brooded and broadcasted larvae) and taxa (i.e. Pocillopora spp. and Porites spp.), and acquired differences attributed to changes in area-normalized biomass.