In situ eutrophication stimulates dinitrogen fixation, denitrification, and productivity in Red Sea coral reefs

2020 ◽  
Vol 645 ◽  
pp. 55-66
Author(s):  
YC El-Khaled ◽  
F Roth ◽  
A Tilstra ◽  
N Rädecker ◽  
DB Karcher ◽  
...  
Keyword(s):  
Coral Reefs ◽  
Functional Groups ◽  
Red Sea ◽  
Nutrient Enrichment ◽  
N Cycling ◽  
Turf Algae ◽  
Incubation Experiments ◽  
Ambient Concentrations ◽  
Microbial N

Eutrophication (i.e. the increase of [in-]organic nutrients) may affect the functioning of coral reefs, but knowledge about the effects on nitrogen (N) cycling and its relationship to productivity within benthic reef communities is scarce. Thus, we investigated how in situ manipulated eutrophication impacted productivity along with 2 counteracting N-cycling pathways (dinitrogen [N2]-fixation, denitrification), using a combined acetylene assay. We hypothesised that N2-fixation would decrease and denitrification increase in response to eutrophication. N fluxes and productivity (measured as dark and light oxygen fluxes assessed in incubation experiments) were determined for 3 dominant coral reef functional groups (reef sediments, turf algae, and the scleractinian coral Pocillopora verrucosa) after 8 wk of in situ nutrient enrichment in the central Red Sea. Using slow-release fertiliser, we increased the dissolved inorganic N concentration by up to 7-fold compared to ambient concentrations. Experimental nutrient enrichment stimulated both N2-fixation and denitrification across all functional groups 2- to 7-fold and 2- to 4-fold, respectively. Productivity doubled in reef sediments and remained stable for turf algae and P. verrucosa. Our data therefore suggest that (1) turf algae are major N2-fixers in coral reefs, while denitrification is widespread among all investigated groups; (2) surprisingly, and contrary to our hypothesis, both N2-fixation and denitrification are involved in the response to moderate N eutrophication, and (3) stimulated N2-fixation and denitrification are not directly influenced by productivity. Our findings underline the importance and ubiquity of microbial N cycling in (Red Sea) coral reefs along with its sensitivity to eutrophication.

Nutrient enrichment caused by in situ fish farms at Eilat, Red Sea is detrimental to coral reproduction

2004 ◽  
Vol 49 (4) ◽  
pp. 344-353 ◽  
Author(s):  
Y. Loya ◽  
H. Lubinevsky ◽  
M. Rosenfeld ◽  
E. Kramarsky-Winter
Keyword(s):  
Red Sea ◽  
Nutrient Enrichment ◽  
Fish Farms ◽  
Coral Reproduction

Porifera, one new species Suberea purpureaflava n. sp. (Demospongiae, Verongida, Aplysinellidae) from northern Red Sea coral reefs, with short descriptions of Red Sea Verongida and known Suberea species

Zootaxa ◽  
2011 ◽  
Vol 2994 (1) ◽  
pp. 60 ◽  
Author(s):  
JOCHEN GUGEL ◽  
MARIT WAGLER ◽  
FRANZ Brümmer
Keyword(s):  
New Species ◽  
Coral Reefs ◽  
Red Sea ◽  
Colour Change ◽  
Gulf Of Aqaba ◽  
Light Yellow ◽  
Dark Violet ◽  
One New Species ◽  
Northern Red Sea

A new verongid sponge (Suberea purpureaflava n. sp.) is described from Dahab, Gulf of Aqaba, in the northern Red Sea. It has a pronounced colour change (a dark red ectosome with whitish pore sieves and a light yellow choanosome in the living specimen changes to a uniform dark violet in the fixed state) and rather rare dendritic fibres with pith and bark and a diameter of about 110–165µm, with the pith occupying 80–90 % of the fibre. Especially the pore sieves were very striking in situ. The new species is compared to all verongid sponges so far recorded from the Red Sea and to all known and accepted Suberea species worldwide. An identification key to all known Suberea species is given. This new species record brings the number of Suberea species described to a total of 11.

scholarly journals Nitrogen fixation and denitrification activity differ between coral- and algae-dominated Red Sea reefs

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yusuf C. El-Khaled ◽  
Florian Roth ◽  
Nils Rädecker ◽  
Arjen Tilstra ◽  
Denis B. Karcher ◽  
...  
Keyword(s):  
Coral Reefs ◽  
Red Sea ◽  
Nitrogen Availability ◽  
Benthic Communities ◽  
Phase Shifts ◽  
Coral Rubble ◽  
Total N ◽  
Net Productivity ◽  
Turf Algae ◽  
Denitrification Activity

AbstractCoral reefs experience phase shifts from coral- to algae-dominated benthic communities, which could affect the interplay between processes introducing and removing bioavailable nitrogen. However, the magnitude of such processes, i.e., dinitrogen (N2) fixation and denitrification levels, and their responses to phase shifts remain unknown in coral reefs. We assessed both processes for the dominant species of six benthic categories (hard corals, soft corals, turf algae, coral rubble, biogenic rock, and reef sands) accounting for > 98% of the benthic cover of a central Red Sea coral reef. Rates were extrapolated to the relative benthic cover of the studied organisms in co-occurring coral- and algae-dominated areas of the same reef. In general, benthic categories with high N2 fixation exhibited low denitrification activity. Extrapolated to the respective reef area, turf algae and coral rubble accounted for > 90% of overall N2 fixation, whereas corals contributed to more than half of reef denitrification. Total N2 fixation was twice as high in algae- compared to coral-dominated areas, whereas denitrification levels were similar. We conclude that algae-dominated reefs promote new nitrogen input through enhanced N2 fixation and comparatively low denitrification. The subsequent increased nitrogen availability could support net productivity, resulting in a positive feedback loop that increases the competitive advantage of algae over corals in reefs that experienced a phase shift.

scholarly journals A doubling of stony coral cover on shallow forereefs at Carrie Bow Cay, Belize from 2014 to 2019

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Luis X. de Pablo ◽  
Jonathan S. Lefcheck ◽  
Leah Harper ◽  
Valerie J. Paul ◽  
Scott Jones ◽  
...  
Keyword(s):  
Coral Reefs ◽  
Coral Cover ◽  
Monitoring Program ◽  
Significant Shift ◽  
Learning Tools ◽  
Turf Algae ◽  
Coral Communities ◽  
The Face ◽  
Time Required

AbstractTo better understand the decline of one of earth’s most biodiverse habitats, coral reefs, many survey programs employ regular photographs of the benthos. An emerging challenge is the time required to annotate the large volume of digital imagery generated by these surveys. Here, we leverage existing machine-learning tools (CoralNet) and develop new fit-to-purpose programs to process and score benthic photoquadrats using five years of data from the Smithsonian MarineGEO Network’s biodiversity monitoring program at Carrie Bow Cay, Belize. Our analysis shows that scleractinian coral cover on forereef sites (at depths of 3–10 m) along our surveyed transects increased significantly from 6 to 13% during this period. More modest changes in macroalgae, turf algae, and sponge cover were also observed. Community-wide analysis confirmed a significant shift in benthic structure, and follow-up in situ surveys of coral demographics in 2019 revealed that the emerging coral communities are dominated by fast-recruiting and growing coral species belonging to the genera Agaricia and Porites. While the positive trajectory reported here is promising, Belizean reefs face persistent challenges related to overfishing and climate change. Open-source computational toolkits offer promise for increasing the efficiency of reef monitoring, and therefore our ability to assess the future of coral reefs in the face of rapid environmental change.

scholarly journals Response of Growth and Grazing Rate of Nanoflagellates on Synechococcus spp. to Experimental Nutrient Enrichment

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2686
Author(s):  
An-Yi Tsai ◽  
Vladimir Mukhanov
Keyword(s):  
Nutrient Enrichment ◽  
Grazing Rate ◽  
Grazing Impact ◽  
Nutrient Additions ◽  
Planktonic Food ◽  
Incubation Experiments ◽  
In Situ Conditions ◽  
Marked Decline ◽  
Enrichment Experiments

As important bacterivores in planktonic food webs, mixotrophic nanoflagellates cancause mortality in marine Synechococcus spp. Our previous study found that the pigmented nanoflagellate (PNF) has a significant grazing impact on Synechococcus spp. In the current study, we applied the dilution approach to test the growth and grazing rates of nanoflagellates on Synechococcus spp. We then compared the differences between experimental nutrient additions and in situ conditions in the coastal waters of the East China Sea during the summer season from July to September. The growth rates of Synechococcus spp. in the ambient environment were between 0.54 and 0.62 day−1, which were slightly higher than the 0.56 and 0.66 day−1 with nutrient enrichment in summer. In contrast, our nutrient enrichment experiments produced a marked decline approximately from 21% to 58%in the nanoflagellate grazing rate on Synechococcus spp. The reason was that the mixotrophic PNFs directly used the added nutrients and reduced their supply of nutrients from prey during the incubation experiments.

scholarly journals In situ effects of simulated overfishing and eutrophication on settlement of benthic coral reef invertebrates in the Central Red Sea

2014 ◽  
Author(s):  
Christian Jessen ◽  
Christian R. Voolstra ◽  
Christian Wild
Keyword(s):  
Coral Reef ◽  
Coral Reefs ◽  
Red Sea ◽  
Combined Treatment ◽  
Coastal Development ◽  
Combined Effects ◽  
Hard Coral ◽  
Coral Settlement ◽  
In Situ Study

In the Central Red Sea, relatively pristine coral reefs meet intense coastal development, but data on the effects of related stressors for reef functioning are lacking. This in situ study therefore investigated the independent and combined effects of simulated overfishing and eutrophication on settlement of reef associated invertebrates on light-exposed and -shaded tiles over 4 months. Findings revealed that at the end of the study period invertebrates had almost exclusively colonized shaded tiles, indicating that algae were superior settling competitors on light-exposed tiles. On the shaded tiles, simulated overfishing prevented settlement of hard corals, but significantly increased settlement of polychaetes, while simulated eutrophication only significantly decreased hard coral settlement relative to controls. The combined treatment significantly increased settlement of bryozoans and bivalves compared to controls and individual manipulations, but significantly decreased polychaetes compared to simulated overfishing. These results suggest settlement of polychaetes and hard corals as potential bioindicators for overfishing and eutrophication, respectively, and settlement of bivalves and bryozoans for a combination of both. Therefore, if investigated stressors are not controlled, phase shifts from dominance by hard corals to that by other invertebrates may occur at shaded reef locations in the Central Red Sea.

scholarly journals In situ effects of simulated overfishing and eutrophication on settlement of benthic coral reef invertebrates in the Central Red Sea

2014 ◽  
Author(s):  
Christian Jessen ◽  
Christian R. Voolstra ◽  
Christian Wild
Keyword(s):  
Coral Reef ◽  
Coral Reefs ◽  
Red Sea ◽  
Combined Treatment ◽  
Coastal Development ◽  
Combined Effects ◽  
Hard Coral ◽  
Coral Settlement ◽  
In Situ Study

In the Central Red Sea, relatively pristine coral reefs meet intense coastal development, but data on the effects of related stressors for reef functioning are lacking. This in situ study therefore investigated the independent and combined effects of simulated overfishing and eutrophication on settlement of reef associated invertebrates on light-exposed and -shaded tiles over 4 months. Findings revealed that at the end of the study period invertebrates had almost exclusively colonized shaded tiles, indicating that algae were superior settling competitors on light-exposed tiles. On the shaded tiles, simulated overfishing prevented settlement of hard corals, but significantly increased settlement of polychaetes, while simulated eutrophication only significantly decreased hard coral settlement relative to controls. The combined treatment significantly increased settlement of bryozoans and bivalves compared to controls and individual manipulations, but significantly decreased polychaetes compared to simulated overfishing. These results suggest settlement of polychaetes and hard corals as potential bioindicators for overfishing and eutrophication, respectively, and settlement of bivalves and bryozoans for a combination of both. Therefore, if investigated stressors are not controlled, phase shifts from dominance by hard corals to that by other invertebrates may occur at shaded reef locations in the Central Red Sea.

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