Bottom-up effects and thermal stress drive growth in four Caribbean coral reef sponge species regardless of distance to anthropogenic influence

Sponges (Porifera) are integral members of coral reef ecosystems and many sponge species are experiencing long-term declines on Caribbean reefs under changing ocean conditions. This multi-year study uses observational and experimental data on four sponge species, in two locations with distinct coral reef ecosystems, to elucidate the responses of these species to distance to anthropogenic influence and correlated water quality parameters. At reefs at varying distances from anthropogenic influence, inorganic nutrient concentration, picoplankton abundance, light availability, temperature, and the volume of living sponges for two high microbial abundance (HMA) species ( Aplysina cauliformis and Aplysina fulva ) and two low microbial abundance (LMA) species ( Amphimedon compressa and Iotrochota birotulata ) were quantified annually. Reciprocal transplant experiments were then used to test the effects of inorganic nutrient concentration, picoplankton abundance, light, and temperature on HMA and LMA sponge survival and growth. In transplant experiments, specific growth across species was positively correlated with picoplankton abundance and negatively correlated with temperature on reefs in both Florida, USA and Bocas del Toro, Panama. Sponge growth did not show a consistent relationship with nutrient concentration or light availability between these two study locations. Transplants originating from lower picoplankton, higher temperature sites exhibited superior growth across all reef sites, and all transplants, regardless of collection site, exhibited greater growth at sites with higher picoplankton abundance and lower temperature. However, these short-term trends in growth rate were not reflected in long-term, standing volume of these species, which was greater further from anthropogenic influence regardless of temperature or food availability.