Investigation of depth-dependence of pumping rates and filtration efficiencies in two Caribbean reef sponges
Suspension feeders perform a crucial role in uniting the benthic and pelagic environments in coral reef ecosystems. Of suspension feeders, sponges are one of the most highly abundant, widespread, and efficient filter-feeding organisms. However, suspension feeding in sponges is not completely understood. Previous studies have looked at the effect of temperature on pumping rate as well as the effect of particle size on retention rate. The purpose of this study was to investigate the depth-dependence of pumping rates and filtration efficiencies in two Caribbean reef sponges, Aplysina archeri and Aplysina lacunosa, at two depth profiles. Videos were taken of sponges pumping fluorescein dye to obtain pumping rates, and turbidity measurements were taken of both inhalant and exhalant water samples that were collected in situ via syringes in order to estimate filtration efficiency. The results revealed a species-specific interaction with depth for both pumping rate and filtration efficiency. Aplysina lacunosa was found to have both a faster pumping rate and increased filtration efficiency at the shallower depth, while no differences were observed across depths for A. archeri. Additionally, correlations were found between pumping rate and filtration efficiency for both species, suggesting the development of distinct filter-feeding strategies. Aplysina lacunosa had a positive correlation between pumping rate and filtration efficiency, while the correlation in A. archeri was found to be negative. Understanding the effect of depth on the filter-feeding mechanism of sponges is important to understanding the greater implications of the benthic-pelagic coupling process of sponges and suspension feeders in general.