Coral reefs typically occur in oligotrophic waters, where tight recycling of energy and nutrients is essential in order to support their high productivity. Sponges are efficient filter feeders that host diverse and abundant microbial communities that often contain members capable of carrying out complex nutrient transformations. Consequently, sponges often act as significant sources of bioavailable forms of nitrogen and phosphorus while acting as sinks for dissolved organic carbon (DOC). However, little attention has focused on variability of nutrient release by sponges and no studies have reported how abiotic conditions may impact sponge‐driven changes in nutrient concentrations. Here, we show that a common Caribbean sponge, Ircinia felix, is capable of being both a source and a sink for DOC, ammonium, nitrate/nitrite ( NOx−), and phosphate ( PO43−). Additionally, we show that abiotic conditions, particularly ambient nutrient availability, seem to explain a significant amount of the variability (R2 range from 0.40 to 0.65). Interestingly, as ambient nutrient concentrations increased, I. felix transitioned from acting as a source to serving as a sink for all nutrient forms measured. We also found I. felix‐associated bacteria exhibit a significantly higher abundance of predicted nitrogen metabolism, carbon fixation, and photosynthetic genes relative to ambient water and sediment. These results suggest that sponges play an important and dynamic role in biogeochemical cycling on reefs, particularly as human activities alter natural nutrient dynamics in coastal systems.

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S. (2015), Testing sample stability using four storage methods and the macroalgae Ulva and Gracilaria. Limnology and Oceanography: Methods,[13][14] carbon (δ 13 C) prompted an experiment to determine how important such factors were to 51 measured values in marine organisms. We stored the marine macroalgae Ulva and 52Gracilaria in four different ways and analyzed replicates every three months over the 53 course of a year to assess treatment effects on stability. Treatments consisted of algae 54 dried at 65°C, ground to a powder, and stored in a desiccator until analysis; algae left in a 55 drying oven or in a freezer and processed (dried and ground) just prior to analysis, as well 56 as some dried, ground samples kept out in the lab and re-analyzed quarterly for 12 57 months. Concurrently, to assess the ecological range in isotope values over the course of 58 a year, samples were freshly collected from the same location and analyzed along with 59 the other treatments at each time step. Neither storage technique nor time had an impact 60 on either δ 15 N or δ 13 C values or the %N and %C of the algae tissues. There were clear 61 and consistent differences between species and some large seasonal differences in the 62 freshly collected samples. The interspecies differences and seasonal ranges of values 63 underscore the stability associated with method and duration of sample storage. 64 65 66