Microbial degradation of cold-water coral-derived organic matter: potential implication for organic C cycling in the water column above Tisler Reef

Abstract

Cold-water corals release organic matter, in particular mucus, but its role in the ecological functioning of reef ecosystems is still poorly understood. The present study investigates the planktonic microbial degradation of mucus released by Lophelia pertusa colonies from Tisler Reef, Skagerrak. Results are compared to the degradation of dissolved and particulate organic substrates, including the carbohydrates glucose and starch, as well as gum xanthan and the cyanobacterium Spirulina spp. as the model organism for phytoplankton. Resulting microbial organic C degradation rates for the dissolved fraction of L. pertusa-derived mucus showed nearly linear progression over time and revealed similar degradation rates compared to glucose and starch. Degradation of the particulate mucus fraction, in contrast, displayed exponential progression and was much faster than degradation of the dissolved fraction. In addition, particulate mucus degradation showed a 4-fold increase compared to that of the added Spirulina spp. suspension. Mucus-associated microbial communities apparently play a key role in organic matter recycling, as degradation rates more than doubled in untreated compared to sterile coral-derived mucus over 3 d of incubation. Quantification of O 2 consumption in the water column above Tisler Reef showed significantly increased values in the direct vicinity of the reef. C-stable isotope signatures of suspended particulate organic matter close to Tisler were close to those of L. pertusa-derived mucus, and high dissolved organic carbon (DOC) concentrations were detected above Tisler Reef. These findings demonstrate the stimulating effect of cold-water coral reefs on microbial activity in the adjacent water column and may indicate some control over organic C cycling.

Opportunistic feeding on various organic food sources by the cold-water coral <i>Lophelia pertusa</i>

“…The assimilation of external DOM and the re-assimilation of DOM from coral mucus release, responsible for high labile DOM concentrations above CWC reefs (van Duyl et al, 2008;Wild et al, 2009) might help the coral to withstand several months without POM supply.…”

“…This might be especially relevant since bacteria occur in high abundance around cold-water coral reefs and food uptake in L. pertusa is positively correlated with prey abundance (Purser et al, 2010). Additionally, bacteria are constantly available to the coral since they are fertilized by the coral itself via mucus production (Wild et al, 2009;Maier et al, 2011), while POM availability can vary spatially and temporally (Duineveld et al, 2007).…”

Calcification rates and the effect of ocean acidification on Mediterranean cold-water corals

“…The alkalinity anomaly technique used in this study has the advantage that it is sensitive enough to use for short-term incubations and that corals can be kept alive. However, it has been shown that L. pertusa and M. oculata excrete inorganic nutrients and that bacterial growth is stimulated during incubations owing to the release of organic matter [38,41,42]. This may also alter the T A during incubation.…”

Cold-water coral ecosystem (Tisler Reef, Norwegian Shelf) may be a hotspot for carbon cycling

“…live stands, dead coral and rubble) would likely alter oxygen uptake rates (e.g. Wild et al 2009, Wagner et al 2011), but the approach here was to assess a bulk respiration rate for the CWC ecosystem and provide a first order estimate. There was evidence for significant seasonal variability in oxygen uptake rates, as might be expected.…”