Trait-mediated ecosystem impacts: how morphology and size affect pumping rates of the Caribbean giant barrel sponge

Abstract

Sponges are a dominant component of Caribbean coral reef suspension-feeding communities. Understanding how pumping rates are affected by sponge size and morphology, as well as the environment, is fundamental to understanding the ecological interactions that are mediated by sponge filtration. In a comprehensive in situ investigation of sponge pumping, the excurrent seawater velocities of 274 specimens of the largest Caribbean species, the giant barrel sponge Xestospongia muta, were measured at sites in the Bahamas and Florida Keys to investigate (1) the relationship between excurrent velocity distributions and sponge morphology, (2) the scaling relationship between pumping and sponge size, and (3) temporal variation of pumping and sensitivity to environmental changes. Excurrent velocity distributions across the osculum showed peak velocities at the center and diminishing velocities near the edges of the osculum. The degree of center-weighting was explained by the distribution of sponge biomass relative to the spongocoel. Volumetric pumping rates scaled isometrically with sponge size and averaged 0.06 ± 0.04 l s-1 l-1 sponge tissue, but were reduced for extremely large sponges. Pumping activity was relatively constant over short temporal scales, but varied over longer scales; however, variations in pumping rates, including periods of cessation, were asynchronous across the population and uncorrelated with changes in environmental conditions. We estimate that populations of X. muta in the Florida Keys and Bahamas process a volume of water equivalent to a layer 1.7 to 12.9 m thick each day and overturn the water column every 2.3 to 18.0 d.