Budget of Primary Production and Dinitrogen Fixation in a Highly Seasonal Red Sea Coral Reef

Cardini, Ulisse; Bednarz, Vanessa N.; Hoytema, Nanne van; Rovere, Alessio; Naumann, Malik S.; Al-Rshaidat, Mamoon M. D.; Wild, Christian

doi:10.1007/s10021-016-9966-1

Cited by 48 publications

(58 citation statements)

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“…This is due to the fact that corals form specific associations with diazotrophs (see Section Diversity of Diazotrophs in Tropical Corals), and they also release large amounts of mucus that constitutes an energetic substrate enhancing the growth of diazotrophs and N 2 fixation rates. High rates of organic matter release by corals can also explain the higher rates of N 2 fixation measured in the reef waters of Aqaba in summer as compared to winter (Larkum et al, 1988;Rahav et al, 2013;Bednarz et al, 2015a;Cardini et al, 2016a). In this area, high light and temperature in summer enhance coral photosynthesis and thereby the release of organic matter in addition to the fact that high temperature per se enhances pelagic N 2 fixation too (Böttjer et al, 2016).…”

Section: N 2 Fixation In Coral Reef Ecosystems Description Of N 2 Fixmentioning

confidence: 99%

“…The primary limitation to estimate reef-wide N 2 fixation is its spatial and temporal variability. N 2 fixation largely varies depending on the diazotroph community composition, itself varying within and between reefs, or according to seasons and nutrient concentrations in seawater (O'Neil and Capone, 2008;Cardini et al, 2014Cardini et al, , 2016a.…”

Section: N 2 Fixation In Coral Reef Ecosystems Description Of N 2 Fixmentioning

confidence: 99%

“…Capone and Carpenter (1982) provided the first estimates of the importance of N 2 fixation for the net and gross primary productivity of reefs. However, recent studies (Charpy-Roubaud et al, 2001;Charpy et al, 2007;Casareto et al, 2008;Cardini et al, 2016a) have performed more comprehensive analyses on both seasonal and annual bases regarding the relative contributions of key individual benthic and pelagic categories to N 2 fixation and overall reef primary productivity. Bednarz et al (2015b) considered processes occurring in different reef sediments and estimated that DDN would supply 8.4, 8.1, and 13.3% of the total nitrogen needs for microphytoplanktonic productivity in carbonate sand, silicate sand and microbial mats, respectively.…”

Section: Contribution Of N 2 Fixation To Primary Productivitymentioning

confidence: 99%

“…At the reef scale, DDN can sustain ∼10% of the total net primary production on an annual basis and up to 20% in summer, when inorganic nitrogen availability limits such primary production (Cardini et al, 2016a). Therefore, there is a positive correlation between the oligotrophic state of the reef and its reliance on DDN as a nitrogen source for primary productivity.…”

Section: Contribution Of N 2 Fixation To Primary Productivitymentioning

confidence: 99%

“…On the coral reef ecosystem scale, the contribution of coralassociated N 2 fixation to reef-wide benthic N 2 fixation is low compared to other benthic reef compartments such as turf algae, microbial mats, coral rock or reef sands, but occasionally relevant (∼18%) during certain periods of the year (Cardini et al, 2016a). This suggests that DDN input from coral-associated diazotrophs is mostly of lower importance for the nitrogen budget of the entire coral reef, but it may facilitate coral reef ecosystem functioning indirectly by fueling the high productivity of corals and coral mucus production.…”

Section: Contribution To Nitrogen Nutritionmentioning

confidence: 99%

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Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

2017

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Coral reefs are highly productive ecosystems thriving in nutrient-poor waters. Their productivity depends largely on the availability of nitrogen, the proximate limiting nutrient for primary production. In reefs, the major nitrogen pathways include regeneration, nitrification, ammonification and dinitrogen (N 2 ) fixation. N 2 fixation is performed by prokaryotes called "diazotrophs" that abound in coral rubbles, sandy bottoms, microbial mats, or seagrass meadows. Corals, which are the main reef builders, have developed a partnership with dinoflagellates which transform dissolved inorganic nitrogen into amino acids and protein, and with diazotrophs to gain diazotrophically-derived nitrogen (DDN). Pioneering studies found active diazotrophic cyanobacteria in the corals' mucus and/or tissue, and later high throughput sequencing efforts have described diverse communities of non-cyanobacterial diazotrophs associated with scleractinian corals. Yet, the metabolic processes behind these associations and how they benefit corals are currently not well understood. While genomic studies describe the diversity of diazotrophs and isotopic tracer experiments quantify N 2 fixation rates, combined advanced methods are needed to elucidate the mechanisms behind the transfer of DDN to the coral holobiont and whether these mechanisms change according to the identity of the diazotrophs or coral species. Here we review our current knowledge on N 2 fixation in corals: the diversity and localization of diazotrophs in the coral holobiont, the environmental factors controlling N 2 fixation, the fate of DDN within the coral symbiosis as well as its potential role in coral resilience. We finally summarize the unknowns: are the diversity, abundance and localization of diazotrophs within the holobiont species-and/or site-specific? Do they have an impact on DDN production? What are the metabolic mechanisms implicated? Do they change spatially, temporally or according to environmental factors? We encourage scientists to undertake research efforts to tackle these questions in order to shed light on nitrogen cycling in reef ecosystems and to understand if coral-associated N 2 fixation can improve coral's resilience in the face of climate change.

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