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This study presents a comprehensive dataset (223 reef organisms that were separately incubated during 44 independent experiments during 4 seasonal expeditions) of dissolved and particulate organic matter (DOM and POM) release by dominant benthic organisms from the Northern Red Sea. Reef organisms studied were scleractinian and fire corals, the upside-down jellyfish and reef-associated algae. Subsequently, the effect of this organic matter (OM) release on microbial activity was determined. These studies were complemented by high resolution, in situ O 2 concentration measurements within reef environments that were dominated by corals or algae. Dissolved organic carbon (DOC) release was 14.5 ± 2.3 mg m -2 surface area h -1 for all 9 investigated reef algae, which was significantly higher than DOC release by scleractinian corals during all seasons except winter. POM release (particulate organic carbon and nitrogen, POC and PON, respectively) was observed for all investigated reef organisms. Benthic reef algae released 5.1 ± 0.5 mg POC m -2 h -1 and 0.35 ± 0.03 mg PON m -2 h -1 , which are significantly higher than POM release rates by scleractinian corals in spring and autumn. Algae-derived OM, presumably the DOC fraction, stimulated microbial activity in the adjacent water more significantly than OM released by the investigated scleractinian and fire corals. Consequently, the daily mean and minimum in situ O 2 concentrations in the water directly above the reef (≤10 cm) were significantly higher in coral dominated than in algae dominated sites, confirming the in situ relevance of results of previous laboratory studies. Findings also suggest that benthic reef algae decrease O 2 availability in waters close to reef environments via the release of labile OM and its subsequent fast microbial degradation.

Mucus, a complex composed primarily of carbohydrates, is released in similar quantities by scleractinian warm-and cold-water reef corals, and can function as an important carrier of organic material from corals to a range of consumers, microbes in particular. However, information about mucus chemical composition is rare for warm-water corals and non-existent for cold-water corals. This study therefore presents comparative carbohydrate composition analyses of mucus released by the dominant and cosmopolitan warm-and cold-water coral genera. Arabinose was the major mucus carbohydrate component for the genus Acropora, but was not found in cold-water coral mucus. Mucus derived from corals of the genus Fungia contained significantly more fucose than the mucus of all other coral genera. However, comparison of mucus carbohydrate composition for the warm-and cold-water corals in the present study and in the literature revealed no significant differences. This indicates use of similar carbohydrate components (with the exception of arabinose) during mucus synthesis by scleractinian corals, largely irrespective of zooxanthellate or azooxanthellate carbon supply mechanisms.KEY WORDS: Warm-water coral · Cold-water coral · Mucus · Chemical composition · Carbohydrate · Microbes · Degradability Resale or republication not permitted without written consent of the publisherAquat Biol 10: [41][42][43][44][45] 2010 revealed that the main component of mucus released by the staghorn coral Acropora formosa consisted of a proteoglycan (Richards et al. 1983). Wild et al. (2005a) further analysed the carbohydrate composition of mucus released by 6 different coral species within the genus Acropora and found arabinose, mannose, galactose, glucose and N-acetyl glucosamine present in all samples, whereas rhamnose, fucose and xylose were detected only in some samples. Such differences in mucus composition may control microbial community composition in WC (Allers et al. 2008) and CC reef habitats ), with ensuing effects on microbial activity.In comparison with zooxanthellate WC, azooxanthellate CC likely release mucus with a distinctly different carbohydrate composition, as they do not receive any photosynthetically produced transfer metabolites. Up to half of the carbon assimilated by the endosymbiotic algae can be released as mucus by WC (Crossland et al. 1980, Davies 1984, and chemical analyses showed that carbohydrate mucus components such as arabinose may be directly transferred from the algae to the coral host (Meikle et al. 1988).Substrate specificity in marine polysaccharide complexes is, however, critical for microbial degradation and concomitant organic matter recycling (Arnosti 2000). The present study therefore presents carbohydrate compositions of mucus released from dominant WC genera (Acropora, Stylophora, Pocillopora, Fungia and Ctenactis) in comparison to the 2 cosmopolitan CC genera Lophelia and Madrepora. In addition, all literature data available for carbohydrate composition of warm-water coral-derived mucus ...

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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.