We investigated which microbial taxa in coastal Red Sea water were stimulated by addition of mucus from the coral Fungia sp. Decreases in the concentration and C/N ratio of particulate organic material during short-term incubations (50 h) were paralleled by a steep rise in the number of Gammaproteobacteria, particularly Alteromonadaceae, followed by Vibrionaceae. Two almost identical genotypes affiliated with Alteromonas macleodii accounted for up to >85% of all Alteromonadaceae (45% of the total cells) in the mucus-amended enrichments but were rare in unamended control incubations and in ambient seawater. A. macleodii-like bacteria might thus be important in the transfer of organic carbon from coral mucus to the pelagic microbial food webs of coral reefs.Coral reefs are located in some of the most nutrient-depleted marine areas but are nevertheless ecosystems with high primary production (20). Some corals secrete mucopolysaccharide material in such quantities that it can dominate the suspended matter in reefs (38). Mucus plays an important role as a carrier of energy and nutrients to a range of planktonic and benthic consumers (36). Moreover, it represents an important resource for microbial growth in reef ecosystems (reference 10 and references therein).We therefore, investigated which bacteria in seawater are favored by the release of freshly detached mucus material into seawater. Short-term changes in organic C and N and microbial community composition were simultaneously analyzed in enrichment cultures of coastal seawater amended with mucus from one of the most common Red Sea scleractinian corals (Fungia sp.).Coral mucus and seawater were collected from the lagoon of Dahab in the southern part of the Gulf of Aqaba, northern Red Sea, in May 2004. Polyps of Fungia sp. (diameter, 5 to 10 cm) were collected from water depths of 3 to 8 m using SCUBA and exposed to air for 3 min to trigger mucus production. Mucus released during the first 1 min was discarded to reduce contamination with bacteria from the coral surface. The mucus produced during the following 2 min was aseptically collected and placed into sterile glass bottles. The coral mucus was homogenized, mixed 1:10 (vol/vol) with seawater obtained from the same site within 60 min after collection, and placed in triplicate sterile 1-liter glass bottles. Triplicate bottles of unamended seawater served as controls. All bottles were incubated for 50 h at the in situ temperature (24°C) and light conditions (500 to 800 mol quanta m Ϫ2 day Ϫ1 at a water depth of 1 m [C. Jantzen, personal communication]).Substrate consumption and microbial growth. Portions (50 ml) from all bottles were filtered onto precombusted GF/F filters (diameter, 25 mm; Whatman) at 0, 26, and 50 h. The concentrations of particulate organic C (POC) and particulate N (PN) and stable isotope ratios of C to N were determined using dried filters (48 h at 40°C) with a THERMO NA 2500 elemental analyzer coupled to a THERMO/Finnigan MAT Delta plus isotope ratio mass spectrometer at GeoBio Center (Muni...
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