Organic matter release by Red Sea coral reef organisms—potential effects on microbial activity and in situ O2 availability

Abstract

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.

Assessing coral reef health in the North Ari Atoll (Maldives) using the FoRAM Index

“…All the means of the water parameters we measured fall within typical ranges for reef environments and within ranges previously recorded in the Maldives and, more widely, in the Indian Ocean and adjacent regions (e.g., Ramamirtham, 1968;Wild et al, 2010;Zweng et al, 2013;Lauvset et al, 2015. Thus, it is not surprising that the parameters we measured do not correlate strongly with the FI (Fig.…”

Autotrophic carbon budget in coral tissue: a new 13C-based model of photosynthate translocation

“…11, 16 and 28% after 4, 24 and 48h, respectively, or 4.3gCcm -2 h -1 after 48h. These values are in the range of estimates of total DOC release by some other scleractinian corals (Tanaka et al, 2009;Tanaka et al, 2010;Naumann et al, 2010;Wild et al, 2010), and within the range of 6-40% of total fixed carbon measured after a few hours and up to 24h (Crossland et al, 1980;Davies, 1984;Davies, 1991;Edmunds and Davies, 1986). Our results also indicate that in the branching species S. pistillata, a high amount of newly fixed carbon can be rapidly transferred (within 2days) to the surrounding medium.…”

Microbial to reef scale interactions between the reef-building coral Montastraea annularis and benthic algae

“…allelochemicals) from some algae have been shown to damage corals, these compounds are highly specific to the algal species and require direct contact for effect [36]. In contrast, DOC is a watersoluble product of photosynthesis that is potentially released by many algae [51,63] and does not require contact to affect the coral holobiont. Various forms of DOC released by algae have been shown to kill corals and increase microbial growth rates [40,41], while some algae cause coral death and hypoxia that is mediated by microbes [38].…”