Abstract
Abstract. Resolving the environmental drivers shaping planktonic communities is fundamental for understanding their variability, in the present and the future, across the ocean. More specifically, addressing the temperature-dependence response of planktonic communities is essential as temperature plays a key role in regulating metabolic rates and thus potentially defining the ecosystem functioning. Here we quantified plankton metabolic rates along the Red Sea, a uniquely oligotrophic and warm environment, and analysed the drivers that regulate gross primary production (GPP), community respiration (CR), and net community production (NCP). The study was conducted on six oceanographic surveys following a north–south transect along the Saudi Arabian coast. Our findings revealed that GPP and CR rates increased with increasing temperature (R2=0.41 and 0.19, respectively; p<0.001 in both cases), with a higher activation energy (Ea) for GPP (1.20±0.17 eV) than for CR (0.73±0.17 eV). The higher Ea for GPP than for CR resulted in a positive relationship between NCP and temperature. This unusual relationship is likely driven by the relatively higher nutrient availability found towards the warmer region (i.e. southern Red Sea), which favours GPP rates above the threshold that separates autotrophic from heterotrophic communities (1.7 mmol O2 m−3 d−1) in this region. Due to the arid nature, the basin lacks riverine and terrestrial inputs of organic carbon to subsidise a higher metabolic response of heterotrophic communities, thus constraining CR rates. Our study suggests that GPP increases steeply with increasing temperature in the warm ocean when relatively high nutrient inputs are present.
Highlights
The balance between gross primary production and community respiration, which involves both autotrophic and heterotrophic metabolic activity (Williams, 1993; Cullen, 2001; Ducklow and Doney, 2013), sets the metabolic status of an ecosystem by defining the carbon available to fuel pelagic food webs and determining whether plankton communities act as a source or sink of CO2 (Del Giorgio et al, 1997; Williams, 1998)
Due to the consistent relationship existing between plankton metabolism and temperature across diverse marine regions (Regaudie-de-Gioux and Duarte, 2012; García-Corral et al, 2014), we examined how plankton metabolic rates covariate with temperature in the Red Sea, a system whose temperature range is higher than previously encountered in marine planktonic metabolism research
Our results demonstrate that planktonic metabolic rates are markedly different between the southern and northern regimes of the Red Sea, with a northward increase in the overall mean gross primary production (GPP) and community respiration (CR) by factors of 5 and 4, respectively
Summary
The balance between gross primary production and community respiration, which involves both autotrophic and heterotrophic metabolic activity (Williams, 1993; Cullen, 2001; Ducklow and Doney, 2013), sets the metabolic status of an ecosystem by defining the carbon available to fuel pelagic food webs and determining whether plankton communities act as a source or sink of CO2 (Del Giorgio et al, 1997; Williams, 1998). In tropical and subtropical oligotrophic regions, the high temperatures may amplify the metabolic imbalances in plankton communities as CR tends to increase faster than GPP (Harris et al, 2006; Regaudie-de-Gioux and Duarte, 2012) if the allochthonous sources of organic carbon are enough to subsidise their carbon demand These allochthonous inputs may be delivered from land through riverine discharge, from the atmosphere through atmospheric deposition of dust and volatile organic carbon (Jurado et al, 2008), or are exported from productive coastal habitats (Duarte et al, 2013; Barrón and Duarte, 2015)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
