Respiratory electron transport system activity in symbiotic corals and its link to calcification

Abstract

Scleractinian corals host photosynthetic endosymbionts, making direct measurement of the host respiration rate via incubation methods based on O 2 consumption impossible. We tested the use of the respiratory electron transport system activity (ETSA) for measuring host potential respiration. The applied method, modified from a previous study, is based on the reduction of (4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride (INT) to formazan. After the development of a protocol suitable for corals, the method was tested on 5 different species. Metabolism, including photosynthesis, dark respiration and light and dark calcification, was measured through incubation. Host and zooxanthellae fractions were separated and their ETSAs, protein contents and zooxanthellae densities were measured. Mean ETSA/dark respiration (ETSA/R) ratios for host corals ranged from 1.7 ± 0.2 to 3.5 ± 0.6, while ratios for zooxanthellae ranged from 3.7 to 7.8. The high ratios observed for zooxanthellae indicate that their respiration may be 5 times higher under light conditions than in the dark. Considering the obtained ratios, host respiration in light could increase at most by a factor of 3.5 compared with dark respiration rates. Ratios close to 1 were found for some specimens, which suggests that higher respiration rates under light compared with dark conditions are not possible. Therefore, increased respiration in light cannot explain the observed enhancement of calcification under light conditions. ETSA was correlated with zooxanthellae density, suggesting adaptation of the levels of host ETS enzymes to the amount of translocated photosynthetates under optimal conditions. Estimated dark host respiration was correlated with photosynthesis, which suggests that it is determined mainly by the amount of energy available but also the amount of electron transport system enzymes. This constrains the amount of ATP available for calcification. Hence, we propose a mechanism by which respiration limits the calcification rate. KEY WORDS: Electron transport system · ETS · Respiration · Calcification · Symbiotic coralsResale or republication not permitted without written consent of the publisher Aquat Biol 18: 125-139, 2013 host photosymbionts known as zooxanthellae, which is the name given to a wide array of different algae of the genus Symbiodinium.The biochemical methods proposed for conducting respiratory measurements include the quantification of respiratory electron transport system activity (ETSA) (Packard 1971), which was later modified by Owens & King (1975). This method measures the activities of the enzymes that constitute the electron transport system (ETS) at saturated substrate concentrations. Therefore, ETSA represents the potential respiratory rate and has been used to estimate oxygen consumption in various environments and community assemblages, including sediment meiofauna (Olanczukneyman & Vosjan 1977, Broberg 1985, Relexans 1996a, plankton (Kenner & Ahmed 1975a, Owens & King 1975, Packard et al. 1975, Bams...

The northern limit of corals of the genus Acropora in temperate zones is determined by their resilience to cold bleaching

“…Values of respiratory ETSA suggested that potential respiration of host coral decreases under cold stress. We performed all ETSA measurements at 25 °C to compare the state of the enzymatic system under analogous conditions; the actual ETSA at 13 °C would have been even lower, due to its positive correlation with temperature 27 . The decrease in potential respiration rates, as measured by ETSA, and in actual respiration rates could be due to a continuous decrease in the amount of substrate available for respiration, potentially contributing to the decreased calcification rates by limiting the energy available for the calcification process.…”

“…After sonication, the suspension was centrifuged at 14,000 × g for 10 min and used as the zooxanthella fraction for protein and enzyme assays. The ETSA assay 27 of host extract was conducted after 5 min of sonication (VP-050, TAITEC) at 25% power on ice. The SOD activities of host and zoox fractions were assayed spectrophotometrically 36 37 .…”

Warm-preconditioning protects against acute heat-induced respiratory dysfunction and delays bleaching in a symbiotic sea anemone

“…These changes could reflect the availability of translocated carbon-rich material from the symbionts, as nutritional input directly affects respiration (Båmstedt, 1980;Clarke and Walsh, 1993;Holcomb et al, 2014). Indeed, host CS and CCO activities in the reef coral Stylophora pistillata decreased with reduced irradiance (Gattuso et al, 1993), and Symbiodinium density and host mitochondrial electron transport rates or CS activities were positively correlated in six coral species (Agostini et al, 2013) and E. pallida (Hawkins et al, 2016a).…”

Peer Review #2 of "Light enhanced calcification in Stylophora pistillata: effects of glucose, glycerol and oxygen (v0.1)"

“…Even greater enhancements have been reported for short-term respiration measurements made immediately after light incubations (Edmunds and Davies 1988;Colombo-Pallotta et al, 2010). However, much of this enhancement of respiration may be due to respiration by the zooxanthellae, with a relatively small enhancement in the animal host (Agostini et al, 2013).…”