Spatio-temporal variation in stable isotope signatures (δ<sup>13</sup>C and δ<sup>15</sup>N) of sponges on the Saba Bank
2018
Duyl, Van, Fleur C. | Mueller, Benjamin | Meesters, Erik H.
Sponges are ubiquitous on coral reefs, mostly long lived and therefore adaptive to changing environmental conditions. They feed on organic matter withdrawn from the passing water and they may harbor microorganisms (endosymbionts), which contribute to their nutrition. Their diets and stable isotope (SI) fractionation determine the SI signature of the sponge holobiont. Little is known of spatio- temporal variations in SI signatures of δ<sup>13</sup>C and δ<sup>15</sup>N in tropical sponges and whether they reflect variations in the environment. We investigated the SI signatures of seven common sponge species with different functional traits and their potential food sources between 15 and 32 m depth along the S-SE and E-NE side of the Saba Bank, Eastern Caribbean, in October 2011 and October 2013. SI signatures differed significantly between most sponge species, both in mean values and in variation, indicating different food preferences and/or fractionation, inferring sponge species-specific isotopic niche spaces. In 2011, all sponge species at the S-SE side were enriched in δ<sup>13</sup>C compared to the E-NE side. In 2013, SI signatures of sponges did not differ between the two sides and were overall lighter in δ<sup>13</sup>C and δ<sup>15</sup>N than in 2011. Observed spatio-temporal changes in SI in sponges could not be attributed to changes in the SI signatures of their potential food sources, which remained stable with different SI signatures of pelagic (particulate organic matter (POM): δ<sup>13</sup>C -24.9‰, δ<sup>15</sup>N +4.3‰) and benthic-derived food (macroalgae: δ<sup>13</sup>C -15.4‰, δ<sup>15</sup>N +0.8‰). Enriched δ
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