Sponge Stable Isotope and Photosymbiont Analysis

At the Smithsonian Marine Station in Fort Pierce, Florida, USA, sponge samples were placed in a 60 °C oven to remove any residual moisture and ground to a fine powder using a mortar and pestle. Homogenized sponge tissue was acidified to remove carbonate and weighed into tared silver capsules for δ¹³C and δ¹⁵N as in Freeman & Thacker (2011) (link). Sponge and POM samples were analyzed in the Stable Isotope Ratio Mass Spectrometry laboratory (SIRMS) at the University of Hong Kong via combustion in a Eurovector EA3028 coupled to a Perspective IRMS (Nu Instruments). Analytical precision was determined by repeated analysis of an internal acetanilide standard (‘acet 6’; 70% C). Mean (±SE) precision during analysis was 0.2 ± 0.04 and 0.1 ± 0.01 for δ¹⁵N and δ¹³C, respectively. To assess photosymbiont abundance (chl a), analyses were carried out on dried tissue as in Freeman & Thacker (2011) (link) and Freeman et al. (2013) (link).