Dataset: Carbon flux for Caribbean coral reef sponges

At each location, a total of 2-7 individuals of sponge species common throughout the Caribbean were haphazardly selected for study between 15 and 20 meter depths. Sponge species were chosen that exhibit morphologies that distinctly separate incurrent from excurrent flow; these include barrel, vase and tube-forming species. Of the species investigated, Agelas tubulata (cf. conifera), Verongula gigantea, V. reiswigi, and Xestospongia muta are considered HMA species (high icrobial abundance) and Callyspongia plicifera, C. vaginalis, Mycale laxissima, and Niphates digitalis are considered LMA species (low microbial abundance). An additional species, the HMA sponge Ircinia strobilina, was selected for study on Conch Reef only. With the exception of A. tubulata, only individuals with a single osculum were studied for each species. Additionally, only sponges with no obvious signs of disease or tissue damage and not fouled with algae or colonized by epibionts (e.g. zoanthids) were included.

Paired 1.5 liter incurrent (ambient) and excurrent seawater samples were collected from each sponge with 100 milliliter syringes, 5 millimeter diameter tip opening, as previously described (McMurray et al. 2016) for measurements of live particulate organic carbon (LPOC), total particulate organic carbon (POC), and dissolved organic carbon (DOC). Incurrent seawater samples were collected adjacent to the ostia that lines the external sponge surface and excurrent samples were slowly collected from approximately 5 centimeters below the osculum within the atrium (inner empty space) of each sponge and at a rate lower than the excurrent water velocity to avoid contamination from ambient seawater. Samples thus represent an integration of approximately 10 to 20 minutes of sponge feeding. Following seawater collection, the velocity of excurrent seawater at the centerline of the osculum of each sponge was measured using a Sontek Micro acoustic Doppler velocimeter mounted on a tripod for 3 minutes at 2 hertz (Hz). The dimensions of each sponge were subsequently measured using a flexible measuring tape.  Sponge volume, excluding the spongocoel, was calculated by approximating the morphology of each individual as a geometric solid.

To quantify the flux of LPOC in the form of picoplankton, 5 milliliters of both incurrent and excurrent seawater samples were preserved in electron microscopy grade glutaraldehyde at a final concentration of 0.1% in cryovials for 10 minutes in the dark and subsequently frozen in liquid nitrogen and stored at -80°C until flow cytometry analysis. Phytoplankton (Prochlorococcus (Pro), Synechococcus (Syn), and photosynthetic pico- and nanoeukaryotes (Euk)) and bacterioplankton (high nucleic acid bacteria (HNA) and low nucleic acid bacteria (LNA)) in seawater samples were enumerated using a BD FACSCelesta Flow Cytometer and populations characterized as previously described (McMurray et al. 2016). Briefly, cells were excited with a 488 nanometer laser and forward scatter, side scatter, green fluorescence (530 ± 30 nm), orange fluorescence (575 ± 26 nm), and red fluorescence (695 ± 40 nm) emissions were measured. Phytoplankton were analyzed for 10 minutes at high flow rate and heterotrophic bacteria were stained with SYBR Green-I as previously described (Marie et al. 1997) and analyzed at low flow rate for 5 minutes. Picoplankton were classified based on their characteristic flow cytometric signatures relative to standard fluorescent microspheres following standard population gating schemes. Carbon (C) content of each type of picoplankton was estimated using standard cell conversions used in previous studies of sponge feeding: 53 femtogram (fg) of carbon per cell for Pro, 470 femtogram of carbon per cell for Syn, 1496 femtogram of carbon per cell for Euk, and 20 femtogram of carbon per cell for HNA and LNA bacteria.  

To quantify sponge-mediated flux of particulate organic carbon (POC) and dissolved organic carbon (DOC), the remaining seawater from each sample was filtered through a 100 micron (μm) mesh that excluded particles greater than the size of incurrent ostia and subsequently through a precombusted GF/F glass fiber filter under low pressure. Filters were individually wrapped in aluminum foil and frozen until analysis of POC.  Twenty milliliters (20 mL) of the filtrate from each sample was transferred to an EPA precleaned glass vial, acidified with 100 microliter (μL) of 50% phosphoric acid, and stored at 4°C until analysis of DOC. Particulate organic carbon was measured using a CE Elantech NC2100 combustion elemental analyzer after filters were dried at 50°C and subsequently exposed to hydrochloric acid fumes for 24 hours. DOC was measured using high temperature catalytic oxidation with a Shimadzu TOC 5050 analyzer. Calibration was achieved with standards diluted from a stock solution of potassium hydrogen phthalate and both standards and deep seawater consensus reference material (Batch 9, lot #09-09, Hansell Laboratory, University of Miami, RSMAS) were interspersed with samples for quality assurance and control. Each seawater sample was run in duplicate and each analysis tube was injected three to five times for a coefficient of variance < 1.5%. The approximate analytical precision of the instrument was 2 micromoles of carbon per liter of seawater (2 umols C/ L seawater). All plastic used for sample collection was soaked in a 0.5 molar HCl bath for at least 24 hours and then thoroughly rinsed in ultrapure water before use and all glassware and aluminum foil used to process samples were combusted at 450° for > 4 hours prior to use. We note that some samples were discarded due to potential contamination while processing in the field; therefore, a small number of individuals are lacking flux estimates for one or two of the three carbon pools investigated.

Detrital carbon in incurrent and excurrent seawater samples was estimated as the portion of total POC not accounted for by LPOC (i.e. Detritus = POC – LPOC). Sponge specific filtration rates, or carbon flux (carbon per second per liter of sponge), of DOC, LPOC, and detritus were calculated as: where Cin and Cex are the incurrent and excurrent concentrations of each carbon pool (carbon per milliliter), Vsponge is sponge tissue volume (L), and Q is the volume flow or pumping rate for each sponge (milliliter per second). Positive and negative flux estimates therefore represent consumption and production of a particular carbon pool, respectively. For Q, we assumed that the mean excurrent velocity for each sponge was equivalent to the velocity of seawater measured at the osculum centerline with an Acoustic Doppler Velocimeter (i.e. plug flow), and volume flow was calculated as the product of the centerline excurrent velocity and the osculum area; for X. muta, the mean excurrent seawater velocity for each sponge was corrected for the uneven velocity distribution across the osculum due to the morphology of the spongocoel (Eq. 3, McMurray et al. 2014).