High temperature and crab density reduce atmospheric nitrogen fixation in Red Sea mangrove sediments
Booth, Jenny Marie
Duarte, Carlos M.
KAUST DepartmentBioscience Program
Red Sea Research Center (RSRC)
Biological and Environmental Sciences and Engineering (BESE) Division
Marine Science Program
KAUST Grant NumberOSR-2018-CARF-1973
Online Publication Date2019-11-20
Print Publication Date2020-01
Embargo End Date2021-11-20
Permanent link to this recordhttp://hdl.handle.net/10754/660511
MetadataShow full item record
AbstractMangrove ecosystems are highly productive and provide important ecosystem services. However, in the Red Sea mangroves are under severe nutrient-limiting conditions, reflected in dwarf plants. The nutrient limitation is especially acute for iron, as verified experimentally, although the low carbon-to-nutrient stoichiometric ratios reported for Red Sea mangrove leaves are indicative of general nutrient depletion. Therefore, atmospheric nitrogen (N2) fixation in mangrove sediments might be particularly important considering the minimal nitrogen inputs from land. Here, we tested the effect of temperature and crab density on sediment N2 fixation rates in mature and juvenile mangrove (Avicennia marina) stands in the central Red Sea. The average N2 fixation rates (from 0.002 ± 0.002 to 0.46 ± 0.12 mg N m−2 d−1) fall in the low range of N2 fixation rates reported in mangroves elsewhere, which is in agreement with the small size of the mangrove plants. Mature mangrove sediments hold higher N2 fixation rates than the juvenile mangrove sediment, related to a higher sediment organic matter and carbon content. We found a detrimental effect of temperature and crab density on sediment N2 fixation rates. Maximum N2 fixation rates were detected at 28 °C with a sharp decrease at 35 °C. Similarly, high crab-density reduced N2 fixation, likely due to the sediment oxygenation or the grazing of cyanobacteria by crabs. This is supported by i) previously reported higher oxygen concentration and redox around burrows compared to undisturbed sediment and ii) lighter sediment carbon isotopic composition in high crab-density than in low crab-density sediments, indicating a higher contribution of microphytobenthos in the mature sediments supporting low crab-density. Our data document temperature and crab density as factors affecting N2 fixation in the Red Sea mangrove sediments.
CitationQashqari, M. S., Garcias-Bonet, N., Fusi, M., Booth, J. M., Daffonchio, D., & Duarte, C. M. (2020). High temperature and crab density reduce atmospheric nitrogen fixation in Red Sea mangrove sediments. Estuarine, Coastal and Shelf Science, 232, 106487. doi:10.1016/j.ecss.2019.106487
SponsorsThis research was funded by King Abdullah University of Science and Technology (KAUST) through Baseline funding to C.M.D and D.D. D.D. acknowledges KAUST for financial support by the Office of Sponsored Research (OSR) under Award No. OSR-2018-CARF-1973 to the Red Sea Research Center. We thank Vincent Saderne for his help in salinity data acquisition.