Trophic ecology of sponges from shallow to mesophotic depths (3 to 150 m): Comment on Pawlik et al. (2015)

Pawlik et al. (2015; Mar Ecol Prog Ser 519: 265-283) proposed 4 hypotheses regarding the influence of food limitation on growth and distribution of Caribbean sponges: (1) increasing sponge cover as particulate organic carbon increases with depth, (2) replacement of high microbial abundance sponges with low microbial abundance sponges at depth, (3) dominance of sponges with photosymbionts above the photosynthetic compensation point, and (4) sponge morphologies that reflect adaptations to feeding. Pawlik et al. (2015) concluded that there is no evidence of food limitation (i.e. bottom-up control), and that predation is the primary process that determines the growth, biomass and biodiversity of sponges on Caribbean coral reefs. Here, we address the conclusions of Pawlik et al. (2015) in the context of the observational, correlational, and manipulative studies they utilized in their analysis. We argue that both top-down (predation pressure) and bottom- up (food limitation) processes influence the distribution of sponges on coral reefs, that these factors vary in time and space, and that only when multifactorial manipulative experiments are undertaken will the magnitude of the roles of predation and food limitation be understood.