Inorganic nutrient availability affects organic matter fluxes and metabolic activity in the soft coral genus Xenia

Abstract

SUMMARYThe release of organic matter (OM) by scleractinian corals represents a key physiological process that importantly contributes to coral reef ecosystem functioning, and is affected by inorganic nutrient availability. Although OM fluxes have been studied for several dominant reef taxa, no information is available for soft corals, one of the major benthic groups in tropical reef environments. Thus, this study investigates OM fluxes along with other key physiological parameters (i.e. photosynthesis, respiration and chlorophyll a tissue content) in the common soft coral genus Xenia after a 4-week exposure period to elevated ammonium (N; 20.0mmoll ). Although DOC uptake significantly increased in the N treatment, POC flux was not affected. The P treatment significantly enhanced PN release as well as photosynthesis and respiration rates, suggesting that autotrophic carbon acquisition of zooxanthellae endosymbionts influences OM fluxes by the coral host. Our physiological findings confirm the significant effect of inorganic nutrient availability on OM fluxes and key metabolic processes for the soft coral Xenia, and provide the first clues on OM cycles initiated by soft corals in reef environments exposed to ambient and elevated inorganic nutrient concentrations.

Phosphorus metabolism of reef organisms with algal symbionts

“…, Bednarz et al. ). The symbiotic dinoflagellates, as photoautotrophs, depend on the uptake of nitrogen and phosphorus in dissolved inorganic forms (Grover et al.…”

“…Symbiotic species include, among others, several cnidarian orders (Scleractinia, Actinaria, Gorgonacea, Zoanthidea, Corallimorpharia, Rhizostomae, and Milleporina), molluscan species, and protozoa. In these symbiotic associations, the animal host acquires nutrients through heterotrophic feeding (Fabricius et al 1995, Sebens et al 1997, Lai et al 2013, Leal et al 2013, or uptake of dissolved organic nutrients (Grover et al 2008, Bednarz et al 2012. The symbiotic dinoflagellates, as photoautotrophs, depend on the uptake of nitrogen and phosphorus in dissolved inorganic forms (Grover et al 2002, Atkinson 2011.…”

Effects of temperature and UVR on organic matter fluxes and the metabolic activity ofAcropora muricata

“…Coral mucus (i.e. dissolved and particulate organic carbon and nitrogen) has several functions, both for corals (defense against external stressors and food source (Brown and Bythell, 2005; Levas et al, 2016) and for the reef organisms (energy carrier and particle trap) (Wild et al, 2004); however, changes in mucus quality and quantity under different environmental conditions are still poorly understood (Niggl et al, 2008; Tremblay et al, 2012), because few studies have investigated both carbon and nitrogen fluxes, in dissolved or particulate forms, in healthy and stressed coral species (Bednarz et al, 2012; Naumann et al, 2010), preventing a comprehensive overview of OM fluxes in corals. Our results first show constant release rates of total organic carbon (TOC) and total organic nitrogen (TON) by A. muricata , irrespective of the stress state.…”

Effect of active water movement on energy and nutrient acquisition in coral reef-associated benthic organisms

“…In hard corals, this organic carbon source is constantly released as mucus or dissolved organic carbon into reef-surrounding waters, where it acts as an energy carrier and particle trap, thereby controlling coral reef biogeochemical element cycling (15,16). On the contrary, xeniid soft corals do obviously not release substantial amounts of organic matter into their environment (17) and, thus likewise, do not provide this important ecosystem engineering function. As a consequence, available excess photosynthetic carbon may rather be channeled into growth and reproduction of Xeniids, which are fast-growing and often considered invasive, rapidly colonizing stressed or damaged reef areas (18).…”

“…As a consequence, available excess photosynthetic carbon may rather be channeled into growth and reproduction of Xeniids, which are fast-growing and often considered invasive, rapidly colonizing stressed or damaged reef areas (18). This behavior may additionally be supported by their pronounced physiological capacity to feed on ambient DOM (17,19), a trophic strategy likely enhanced by polyp pulsation. Conclusively, benthic community phase shifts to dominance by pulsating xeniid soft corals, as observed currently in many coral reefs (20), may result in the loss of essential ecosystem engineer organisms (i.e., hard corals) and a decline in fundamental aspects of coral reef functioning.…”