Short-term responses of tropical lagoon sponges to elevated temperature and nitrate

Sponges are often important components of coastal lagoons, however their responses to anthropogenic stressors remain poorly understood. Here, we tested the responses of three lagoon sponges, Neopetrosia exigua, Amphimedon navalis and Spheciospongia vagabunda from Mauritius (Western Indian Ocean), to nine temperature and nitrate combinations for 14 days. We found that elevated seawater temperature resulted in significant physiological responses in all species, but there was generally little negative effect of elevated nitrate. At the end of the experiment, the buoyant weight of all three species were significantly reduced, while for the two chlorophyll a-containing species, N. exigua and S. vagabunda, effective quantum yield (ΔF/Fm') of photosystem (PS) II, photosynthetic pigment concentrations, gross photosynthetic rate and gross photosynthesis to respiration (P:R) ratio were also reduced. Dark respiration rates were higher in all three species at elevated temperature. While these lagoon sponges appeared to be impacted by elevated temperature, here, we demonstrate that these species are physiologically tolerant to excess nitrate concentrations.