Transformation of dissolved organic matter by two Indo‐Pacific sponges

Abstract

Dissolved organic matter (DOM) is the largest organic carbon reservoir in the ocean and an integral component of biogeochemical cycles. The role of free-living microbes in DOM transformation has been studied thoroughly, whereas little attention has been directed towards the influence of benthic organisms. Sponges are efficient filter feeders and common inhabitants of many benthic communities circumglobally. Here, we investigated how two tropical coral reef sponges shape marine DOM. We compared bacterial abundance, inorganic and organic nutrients in off reef, sponge inhalant, and sponge exhalant water of Melophlus sarasinorum and Rhabdastrella globostellata. DOM and bacterial cells were taken up, and dissolved inorganic nitrogen was released by the two Indo-Pacific sponges. Both sponge species utilized a common set of 142 of a total of 3040 compounds detected in DOM on a molecular formula level via ultrahigh-resolution mass spectrometry. In addition, species-specific uptake was observed, likely due to differences in their associated microbial communities. Overall, the sponges removed presumably semi-labile and semi-refractory compounds from the water column, thereby competing with pelagic bacteria. Within minutes, sponge holobionts altered the molecular composition of surface water DOM (inhalant) into a composition similar to deep-sea DOM (exhalent). The apparent radiocarbon age of DOM increased consistently from off reef and inhalant to exhalant by about 900 14 C years for M. sarasinorum. In the pelagic, similar transformations require decades to centuries. Our results stress the dependence of DOM lability definition on the respective environment and illustrate that sponges are hotspots of DOM transformation in the ocean.

Nutrient fluxes, oxygen consumption and fatty acid composition from deep-water demo- and hexactinellid sponges from New Zealand

“…This corresponds to 10 to 18% of the recycled N in the oligotrophic west Australian continental shelf (Keesing et al, 2013). Sponges are also a major transformer of dissolved organic matter (DOM) (Hildebrand et al, 2022).…”

“…This corresponds to 10 to 18% of the recycled N in the oligotrophic west Australian continental shelf (Keesing et al, 2013). Sponges are also a major transformer of dissolved organic matter (DOM) (Hildebrand et al, 2022). Sponges are holobionts (Webster and Taylor, 2012) consisting of the sponge itself and a microbial community that can contribute up to 38% to the overall sponge holobiont volume (Vacelet, 1975).…”

Terrestrial and Biological Activities Shaped the Fate of Dissolved Organic Nitrogen in a Subtropical River‐Dominated Estuary and Adjacent Coastal Area

“…The composition and structure of DON differ among variable sources (Y. Li et al., 2019; Petrone et al., 2008). As a major fraction of dissolved organic matter (DOM), DON is in line with dissolved organic carbon (DOC) in coastal waters (Hildebrand et al., 2022; Lee et al., 2020). This synergistic change enables the characterization of DON using similar techniques, such as ultraviolet‐visible (UV‐vis) adsorption spectroscopy and the emission‐excitation matrix combined with parallel factor analysis (EEM‐PARAFAC), to explore its composition and distinguish its sources (Osburn et al., 2016; L. Wang et al., 2021).…”

Sponge Organic Matter Recycling: Reduced Detritus Production Under Extreme Environmental Conditions

“…Among sponges, the massive Rhabdastrella globostellata (Carter, 1883) is the most abundant species at Bouraké, reaching up to 40 % cover (Maggioni et al, 2021). This Indo-Pacific high microbial abundance (HMA) species (Moitinho-Silva et al, 2017a) has been demonstrated to efficiently filter bacteria cells and remove DOM from surrounding seawater (Hildebrand et al, 2022), fundamentally altering its composition.…”