Dynamics of nonphotochemical superoxide production in the Great Barrier Reef lagoon

Abstract

Superoxide (O 2 2 ) and hydrogen peroxide (H 2 O 2 ) concentrations ranging from 87 to 1120 pmol L 21 and 5 to 107 nmol L 21 , respectively, were measured in samples of surface water from the Great Barrier Reef (GBR) lagoon in the absence of photochemistry. Nonphotochemical, particle-associated net production rates of O 2 2 ranging from 1 to 16 pmol L 21 s 21 were also determined and calculated to be similar in magnitude to the likely abiotic photochemical O 2 2 production rates in GBR surface waters. Manipulative experiments using 0.22-mm filtration and addition of biological inhibitors demonstrated that the majority of this particle-associated production was biological and likely driven by photosynthetic organisms. Pseudo-first-order O

Species-specific control of external superoxide levels by the coral holobiont during a natural bleaching event

“…1). Background superoxide levels within the reef seawater located at the same depth as the corals but >10 cm from their surface ranged from 4 to 11 nM—values consistent with previously reported superoxide levels in productive marine waters but up to several orders of magnitude higher than in typical open ocean sites3536373839. Average superoxide concentrations measured only millimetres above coral surfaces ranged from levels below bulk seawater ( M. capitata ) to steady-state concentrations that were ∼120 nM higher than bulk seawater ( P. lobata ) (Fig.…”

“…To measure superoxide, both the analyte solution and the MCLA reagent are independently flushed through the FeLume system at an identical flow rate using a peristaltic pump. The MCLA reagent consisted of 4.0 μM MCLA (similar to concentrations used previously and by other investigators38397071) in 0.10 M MES with 50 μM DTPA adjusted to pH 6.0. The solutions converge in a spiral flow cell immediately adjacent to a photomultiplier tube, which continuously acquires data that is displayed in real time using a PC interface.…”

Photochemical production of superoxide and hydrogen peroxide from natural organic matter

“…Formation of ROS in sunlit waters has been attributed largely to the photochemical reactions of NOM (Cooper et al, 1989), though growing evidence suggests that microbial activity may also produce ROS at comparable or greater rates (Rose et al, 2010;Vermilyea et al, 2010). In the case of photochemical formation it has been assumed that photo-excited NOM reduces dioxygen to form O À 2 with subsequent reactions producing other ROS and ultimately water (Cooper et al, 1989).…”

Comment on “Application of a superoxide (O2−) thermal source (SOTS-1) for the determination and calibration of O2− fluxes in seawater” by Heller and Croot

“…However we strongly disagree with the authors' criticisms of a photochemical technique for generating O 2 − standards [2] that has now been quite widely used by a number of research groups [3][4][5][6][7][8][9] including our own. These criticisms are concerning because they cast unfair aspersions on the validity of work from these research groups.…”