Seasonality affects dinitrogen fixation associated with two common macroalgae from a coral reef in the northern Red Sea

Tilstra, Arjen; Bednarz, Vanessa N.; Cardini, Ulisse; Hoytema, Nanne van; Al-Rshaidat, Mamoon M. D.; Wild, Christian

doi:10.3354/meps12206

Cited by 13 publications

(14 citation statements)

References 73 publications

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“…In the present study, relative nifH gene copy numbers decreased with decreasing PAR despite a lack of correlation with cell densities of their photosynthetic algal symbiont. PAR positively correlates with N 2 fixation activity in benthic coral reef organisms (Bednarz et al, 2015;Tilstra et al, 2017), while increased O 2 may negatively affect the nitrogenase enzyme complex (Compaoré and Stal, 2010). While the latter may in part explain the pattern observed in Podabacia sp.…”

Section: Discussionmentioning

confidence: 94%

Relative Diazotroph Abundance in Symbiotic Red Sea Corals Decreases With Water Depth

et al. 2019

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Microbial dinitrogen (N 2) fixation (diazotrophy) is a trait critical for coral holobiont functioning. The contribution of N 2 fixation to holobiont nitrogen (N) supply likely depends on the ecological niche of the coral holobiont. Consequently, coral-associated diazotroph communities may exhibit distinct activity patterns across a water depth gradient. We thus compared relative abundances of diazotrophs in the tissues of two common hard coral species, Podabacia sp. and Pachyseris speciosa, along their water depth distribution (10-30 m and 30-50 m, respectively) in the Central Red Sea. The relative gene copy numbers of the nifH gene (i.e., referenced against the eubacterial 16S rRNA gene), as a proxy for N 2 fixation potential, were assessed via quantitative PCR. We hypothesized that relative nifH gene copy numbers would decrease with water depth, assuming a related shift from autotrophy to heterotrophy. Findings confirmed this hypothesis and revealed that nifH gene abundances for both corals decreased by ∼97% and ∼90% from the shallowest to the deepest collection site. However, this result was not significant for Pachyseris speciosa due to high biological variability. The observed decrease in nifH gene abundances may be explained by the relative increase in heterotrophy of the coral animal at increasing water depths. Our results underline the importance of interpreting microbial functions and associated nutrient cycling processes within the holobiont in relation to water depth range reflecting steep environmental gradients.

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Section: Discussionmentioning

confidence: 94%

Relative Diazotroph Abundance in Symbiotic Red Sea Corals Decreases With Water Depth

et al. 2019

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“…Ayla's UL experiences more widely varying temperatures (16.2-28.8 • C), as shown in Supplementary Files S1 and S2 and discussed by Manasrah [29], than the ambient conditions in the GoA water (22.7-27.7 • C) [18,27,29,[33][34][35][36]. In particular, the UL has much lower winter temperatures (16.2-21.8 • C) than the ambient GoA water conditions (21.9-23.8 • C); this is due to the UL's shallow depth (~2 m) and high surface area, which makes it more vulnerable to losing heat due to surface wind effects, therefore decreasing its temperature during the winter.…”

Section: Discussionmentioning

confidence: 96%

Chlorophyll–Nutrient Relationships of an Artificial Inland Lagoon Equipped with Seawater Replenishment System in the Northern Red Sea (Gulf of Aqaba)

Al-Rshaidat

Segonds‐Pichon

Salem³

2020

JMSE

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Data are reported for an inland artificial lagoon (Ayla) to evaluate the impact of the lagoon’s modeled design and water replenishment system on its water quality and the coastal ecosystem. This study focused on Ayla’s upper lagoon (UL) only, due to its isolation from the two other lagoons and the ambient seawater in the Gulf of Aqaba (GoA). Nutrient measurements (nitrite, nitrate, ammonium, phosphate, and silicate) in addition to Chlorophyll a (Chl a) data were collected between July 2012 and June 2013. Chl a values in the UL were not significantly different from ambient seawater in the GoA, and the UL did not show seasonal differences (p = 0.456). Significant variability for nitrite was observed in the UL between spring and summer (p < 0.0001) and between fall and winter (p < 0.0001). Nitrite showed a stronger seasonal effect in the GoA seawater than in the UL (p = 0.056). Phosphorus showed a seasonal effect and remained similar between the UL and GoA. Nutrient stoichiometry showed a Redfield-like nitrogen-to-phosphorus (N:P) ratio for the ambient GoA seawater around the inlet pumping source and an increased N:P ratio inside the UL. This study emphasizes the importance of modeled lagoon design and seawater replenishment system in preventing and inhibiting eutrophication of the lagoon and therefore minimizing contamination in the coastal ecosystem.

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“…In-situ N enrichment resulted in an uptake of N in the tissues of turf algae, soft corals and hard corals, but not in sediments and hard coral zooxanthellae. The fact that turf algae exhibited the lowest δ 15 N at the start of our experiment suggests considerable assimilation of N from N 2 fixation (Yamamuro, Kayanne & Minagawao, 1995;Rix et al, 2015;Tilstra et al, 2017;Y El-Khaled et al, in review). Biological fixation of atmospheric N 2 leads to a depletion in 15 N in the N compounds of the fixer (Carpenter et al, 1997;Karl et al, 2002).…”

Section: Uptake Of Excess N By Major Benthic Functional Groupsmentioning

confidence: 57%

Peer Review #1 of "Nitrogen eutrophication particularly promotes turf algae in coral reefs of the central Red Sea (v0.1)"

2020

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While various sources increasingly release nutrients to the Red Sea, knowledge about their effects on benthic coral reef communities is scarce. Here, we provide the first comparative assessment of the response of all major benthic groups (hard and soft corals, turf algae, and reef sands-together accounting for 80 % of the benthic reef community) to in-situ eutrophication in a central Red Sea coral reef. For eight weeks, dissolved inorganic nitrogen (DIN) concentrations were experimentally increased 3-fold above environmental background concentrations around natural benthic reef communities using a slow release fertilizer with 15 % total nitrogen (N) content. We investigated which major functional groups took up the available N, and how this changed organic carbon (C org) and N contents using elemental and stable isotope measurements. Findings revealed that hard corals (in their tissue), soft corals, and turf algae incorporated fertilizer N as indicated by significant increases in δ 15 N by 8 %, 27 % and 28 %, respectively. Among the investigated groups, C org content significantly increased in sediments (+24 %) and in turf algae (+33 %). Altogether, this suggests that among the benthic organisms only turf algae were limited by N availability and thus benefited most from N addition. Thereby, based on higher C org content, turf algae potentially gained competitive advantage over e.g. hard corals. Local management should, thus, particularly address DIN eutrophication by coastal development and consider the role of turf algae as potential bioindicator for eutrophication.

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Seasonality affects dinitrogen fixation associated with two common macroalgae from a coral reef in the northern Red Sea

Cited by 13 publications

References 73 publications

Relative Diazotroph Abundance in Symbiotic Red Sea Corals Decreases With Water Depth

Relative Diazotroph Abundance in Symbiotic Red Sea Corals Decreases With Water Depth

Chlorophyll–Nutrient Relationships of an Artificial Inland Lagoon Equipped with Seawater Replenishment System in the Northern Red Sea (Gulf of Aqaba)

Peer Review #1 of "Nitrogen eutrophication particularly promotes turf algae in coral reefs of the central Red Sea (v0.1)"

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