Nutrient and temperature constraints on primary production and net phytoplankton growth in a tropical ecosystem
KAUST DepartmentRed Sea Research Center King Abdullah University of Science and Technology (KAUST) Thuwal-Jeddah Saudi Arabia
Biological and Environmental Sciences and Engineering (BESE) Division
Marine Science Program
Red Sea Research Center (RSRC)
Embargo End Date2022-06-12
Permanent link to this recordhttp://hdl.handle.net/10754/669572
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AbstractThe Red Sea depicts a north–south gradient of positively correlated temperature and nutrient concentration. Despite its overall oligotrophic characteristics, primary production rates in the Red Sea vary considerably. In this study, based on five cruises and a 2-year time series (2016–2018) sampling in the Central Red Sea, we determined phytoplankton photosynthetic rates (PP) by using 13C as a tracer and derived phytoplankton net growth rates (μ) and chlorophyll a (Chl a)-normalized photosynthesis (PB). Our results indicate a ninefold variation (14–125 mgC m−2 h−1) in depth-integrated primary production and reveal a marked seasonality in PP, PB, and μ. Depth-integrated PP remained <30 mg C m−2 h−1 during spring and summer, and peaked in autumn–winter, particularly in the southernmost stations (~17°N). In surface waters, phytoplankton grew at a slow rate (0.2 ± 0.02 d−1), with the population doubling every 3.5 days, on average. However, during the autumn–winter period, when Chl a concentrations peaked in the central and southern regions, μ increased to values between 0.60 and 0.84 d−1, while PB reached its maximum rate (7.8 mgC [mg Chl a]−1 h−1). We used path analysis to resolve direct vs. indirect components between correlations. Our results show that nutrient availability modulates the photosynthetic performance and growth of phytoplankton communities and that PB and μ fluctuations are not directly associated with temperature changes. Our study suggests that similarly to other oligotrophic warm seas, phosphorus concentration exerts a key role in defining photosynthetic rates and the biomass levels of phytoplankton communities in the region.
CitationLópez-Sandoval, D. C., Duarte, C. M., & Agustí, S. (2021). Nutrient and temperature constraints on primary production and net phytoplankton growth in a tropical ecosystem. Limnology and Oceanography. doi:10.1002/lno.11849
SponsorsThe authors thank Sebastian Overmans, Alexa Coello Camba, Sreejith Kottuparambil, Juan M. Ayala, and Gala González González for their field support during the Threats and DUST Cruise, and during the sampling at the time-series station. We also would like to thank CMOR personal and the crew of the R/V Thuwal and Al Azizi. This research has been funded by the King Abdullah University of Science and Technology (grant nos. BAS/1/1072-01-01 assigned to SA, BAS/1/1071-01-01 assigned to C.M.D., and CCF/1/1973-21-01 assigned to RSRC).
JournalLimnology and Oceanography