Recent studies have demonstrated that organic matter released by hermatypic corals can play an important role as carrier of energy, thereby initiating element cycles in coral reef systems. However, ...although another commonly occurring cnidarian, the scyphozoan upside-down jellyfish
Cassiopea sp., can reach high abundances in such reef systems, its potential contribution to cycles of matter remains unresolved. Therefore this study aimed to quantify organic matter release by
Cassiopea from the Northern Red Sea and evaluate whether this material is transferred to planktonic microbes and zooplankton. Mean mucoid particulate organic matter release was 21.2
±
9.4
mg POC and 2.3
±
1.1 PN m
−
2
jellyfish surface area h
−
1
, which exceeds release rates reported for hermatypic corals by factors of 2 to 15. Labelling experiments using stable N isotopes demonstrated uptake of
Cassiopea-derived organic matter by the jellyfish-associated zooplanktonic mysids
Idiomysis tsurnamali. Incubation experiments revealed that O
2 consumptions by microbes and zooplankton were 5.9- and 3.8-fold higher compared to seawater controls, respectively, when
Cassiopea-derived organic matter was present. Total organic carbon (TOC) degradation rates increased 5.0-fold (0.27% h
−
1
versus 1.38% h
−
1
), thereby indicating fast mineralization of
Cassiopea-derived organic matter. These findings suggest that
Cassiopea-derived organic matter may function as a newly discovered trophic pathway for organic matter from the benthic environment to pelagic food chains in coral reefs and other marine ecosystems.
Organic matter release by scleractinian corals fulfils an important ecological role as energy carrier and particle trap in reef ecosystems, but the hypothetically stimulating impact of water ...currents, an essential and ubiquitous environmental factor in coral reefs, on this process has not been investigated yet. This study therefore quantifies organic matter release by two species of scleractinian corals subjected to ambient water current velocities ranging from 4 to 16 cm s
−1
using closed-system flow-through chambers. Findings revealed that particulate organic matter (POM) concentration was significantly increased in the flow-through chambers in all investigated coral species compared to still water conditions, while no effect on dissolved organic carbon (DOC) concentration could be observed. These results suggest that POM release by corals may be controlled by hydro-mechanical impacts, while DOC fluxes are rather influenced by the physiological condition of the corals. Hence, this study indicates that previous POM release quantification results are conservative estimates and may have underestimated in situ POM release through corals in reef environments. The contribution of coral-derived POM to biogeochemical cycles in reef ecosystems, therefore, may be more pronounced than already assumed.
The 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 μmol l(-1)), phosphate (P; 2.0 μmol l(-1)) and combined inorganic nutrient enrichment treatment (N+P). Corals maintained without nutrient enrichment served as non-treated controls and revealed constant uptake rates for particulate organic carbon (POC) (-0.315±0.161 mg POC m(-2) coral surface area h(-1)), particulate nitrogen (PN) (-0.053±0.018 mg PN m(-2) h(-1)) and dissolved organic carbon (DOC) (-4.8±2.1 mg DOC m(-2) h(-1)). 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.
The zooxanthellate mangrove jellyfish Cassiopea sp. represents a prominent invasive species and a potential bioindicator for nutrient monitoring in coral reefs. However, information about its spatial ...distribution in combination with abundance, habitat specificity and life cycle elements is barely available. This study, therefore, presents the results of field surveys conducted within four different benthic habitat types (coral reef, seagrass meadow, reef-sand transition and sand flat) in the Northern Red Sea. Cassiopea sp. exhibited a highly patchy distribution within the entire study area with mean abundance of 1.6 ± 0.3 animals m⁻² and benthic coverage of 3.2%. Within coral reef habitats, maximum abundance of up to 31 animals m⁻² and benthic coverage of up to 20% were detected. Additionally, this study revealed that 65% of all observed Cassiopea specimens were associated with the commensalistic crustacean mysid Idiomysis tsurnamali. Cassiopea abundance and size as well as association patterns with mysids differed between most of the surveyed habitats. In summary, the findings of the present study (1) characterize Cassiopea as one of the key organisms in investigated benthic habitats, (2) indicate active habitat selection by the jellyfish and (3) may hint to an unexplored life cycle of Cassiopea with central role of seagrass meadows providing cues for larval settlement and metamorphosis in the absence of mangroves.
Many coral reef ecosystems experience shifts in benthic community composition from scleractinian corals to algae. However, consequences of such phase shifts on O₂ availability, important for many ...reef organisms, are unresolved. This study therefore comparatively investigated potential in situ effects of different benthic cover by reef macroalgae and scleractinian corals on water column O₂ concentrations in a Northern Red Sea fringing reef. Findings revealed that mean daily O₂ concentrations at algae-dominated sites were significantly lower compared to coral-dominated sites. Minimum O₂ concentrations were significantly negatively correlated, while diurnal variability in O₂ concentration was significantly positively correlated, with increasing benthic cover by algae. In contrast, no correlation with coral cover was found. These results indicate that shifts from corals to benthic algae may likely affect both in situ O₂ availability and variability. This may be particularly pronounced in reef systems with low water exchange (e.g. closed lagoons) or under calm weather conditions and suggests potential O₂-mediated effects on reef organisms.
Coral reef ecosystems fringing the coastline of Dahab (South Sinai, Egypt) have experienced increasing anthropogenic disturbance as an emergent international tourism destination. Previous reports ...covering tourism-related impacts on coastal environments, particularly mechanical damage and destructive fishing, have highlighted the vital necessity for regular ecosystem monitoring of coral reefs near Dahab. However, a continuous scientific monitoring programme of permanent survey sites has not been established to date. Thus, this study conducted in situ monitoring surveys to investigate spatio-temporal variability of benthic reef communities and selected reef-associated herbivores along with reef health indicator organisms by revisiting three of the locally most frequented dive sites during expeditions in March 2010, September 2011 and February 2013. In addition, inorganic nutrient concentrations in reef-surrounding waters were determined to evaluate bottom-up effects of key environmental parameters on benthic reef community shifts in relation to grazer-induced top-down control. Findings revealed that from 2010 to 2013, live hard coral cover declined significantly by 12 % at the current-sheltered site Three Pools (TP), while showing negative trends for the Blue Hole (BH) and Lighthouse (LH) sites. Hard coral cover decline was significantly and highly correlated to a substantial increase in turf algae cover (up to 57 % at TP) at all sites, replacing hard corals as dominant benthic space occupiers in 2013. These changes were correlated to ambient phosphate and ammonium concentrations that exhibited highest values (0.64 ± 0.07 μmol PO
4
3−
l
−1
, 1.05 ± 0.07 μmol NH
4
+
l
−1
) at the degraded site TP. While macroalgae appeared to respond to both bottom-up and top-down factors, change in turf algae was consistent with expected indications for bottom-up control. Temporal variability measured in herbivorous reef fish stocks reflected seasonal impacts by local fisheries, with concomitant changes in macroalgal cover. These findings represent the first record of rapid, localised change in benthic reef communities near Dahab, consistent with indications for bottom-up controlled early-stage phase shifts, underlining the necessity for efficient regional wastewater management for coastal facilities.
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.
Many coral reef ecosystems experience shifts in benthic community composition from scleractinian corals to algae. However, consequences of such phase shifts on O sub(2) availability, important for ...many reef organisms, are unresolved. This study therefore comparatively investigated potential in situ effects of different benthic cover by reef macroalgae and scleractinian corals on water column O sub(2) concentrations in a Northern Red Sea fringing reef. Findings revealed that mean daily O sub(2) concentrations at algae-dominated sites were significantly lower compared to coral-dominated sites. Minimum O sub(2) concentrations were significantly negatively correlated, while diurnal variability in O sub(2) concentration was significantly positively correlated, with increasing benthic cover by algae. In contrast, no correlation with coral cover was found. These results indicate that shifts from corals to benthic algae may likely affect both in situ O sub(2) availability and variability. This may be particularly pronounced in reef systems with low water exchange (e.g. closed lagoons) or under calm weather conditions and suggests potential O sub(2)-mediated effects on reef organisms.
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 situO₂ concentration measurements within reef environments that were dominated by corals or algae. Dissolved organic carbon (DOC) release was 14.5 ± 2.3 mg m–2surface area h–1for 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–2h–1and 0.35 ± 0.03 mg PON m–2h–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 minimumin situO₂ concentrations in the water directly above the reef (≤10 cm) were significantly higher in coral dominated than in algae dominated sites, confirming thein siturelevance of results of previous laboratory studies. Findings also suggest that benthic reef algae decrease O₂ availability in waters close to reef environments via the release of labile OM and its subsequent fast microbial degradation.
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