Factors affecting the cycling of dimethylsulfide and dimethylsulfoniopropionate in coral reef waters of the Great Barrier Reef

Abstract

Environmental context. Levels of atmospheric dimethylsulfide (DMS) and its oxidation products are reputed to affect the microphysics of clouds and the amount of incoming solar radiation to the ocean. Studies of DMS and its precursor compound dimethylsulfoniopropionate (DMSP) at two inshore fringing coral reefs in the Great Barrier Reef highlight pronounced seasonal, diurnal and tidal variation of these compounds, with dissolved DMS and DMSP significantly correlated with sea surface temperatures (SSTs) up to 30°C. During a coral bleaching episode at one of the reef sites, dissolved DMS concentrations decreased when SSTs exceeded 30°C, a result replicated in chamber experiments with staghorn coral. The results raise interesting questions on the role of these organosulfur substances in corals and whether DMS emissions from coral reefs could have an effect on regional climate in the Great Barrier Reef. Abstract. A study of dissolved dimethylsulfide (DMSw), dissolved and particulate dimethylsulfoniopropionate (DMSPd, DMSPp), and atmospheric dimethylsulfide (DMSa) was carried out at two inshore fringing coral reefs (Orpheus Island and Magnetic Island) in the Great Barrier Reef (GBR) to investigate the variation of these organosulfur substances with season, sea surface temperature, tides, and time of day. Highest concentrations of these organosulfur substances occurred in the summer months at both reefs, with lowest concentrations occurring during winter, suggesting a biological source of these compounds from the reef flats. At the Orpheus Island reef, where more measurements were made, DMSw and DMSPd were significantly correlated with tidal height during the flooding tide over the reef (r = 0.37, P < 0.05; r = 0.58, P < 0.01 respectively), and elevated DMSw and DMSa concentrations generally occurred in the daylight hours, possibly reflecting photosynthetic production of DMSw from the reef flats. Chamber experiments with the staghorn coral Acropora formosa confirmed that corals produce DMSw in the day. DMSw (r = 0.43, P < 0.001) and DMSPd (r = 0.59, P < 0.001) were significantly positively correlated with sea surface temperatures (SST) at the Orpheus Island reef. During severe coral bleaching at the eutrophic Magnetic Island reef in the summer, DMSw concentrations decreased at SSTs greater than 30°C, suggesting that reef production of DMSw decreases during elevated SSTs. This was later confirmed in chamber experiments with Acropora formosa, which showed that when this coral was exposed to temperatures at its bleaching threshold (31°C), decreased production of DMSw occurred. These results suggest that DMS and DMSP in coral zooxanthellae may be functioning as antioxidants, but further experiments are needed to substantiate this.

The effect of coral bleaching on the cellular concentration of dimethylsulphoniopropionate in reef corals

“…However, the coral only releases a fraction of this as we have estimated that the % of S (DMS + DMSP) expelled from Acropora spp. each day is 0.2-0.4% of the total available pool (Jones et al, 2007). This is in agreement with estimates of zooxanthellae released from A. formosa (Hoegh-Guldberg and Smith, 1989;Jones, 1995) and strongly suggests that monitoring organosulphur production from corals in chamber experiments is a good indicator of zooxanthellae expulsion and coral stress (Jones et al, 2007).…”

“…DMSP contributions from the coral host are also possible . However, in our view the major fraction of DMSP released into the chamber is from expelled zooxanthellae (Jones et al, 2007). For example, A. intermedia in this study contained 1.2 × 10 6 cells per cm 2 of coral surface area and the cellular concentration of unbleached A. intermedia contained~147 fmol cell −1 .…”

“…Coral reefs are significant sources of DMSP and DMS to reef waters (Broadbent andJones, 2004, 2006;Fischer and Jones, 2012;Jones et al, 2007) and contribute significantly to regional biogeochemical sulphur cycles (Andreae, 1990;Andreae et al, 1983). The expulsion of coral symbionts and coral mucous to reef waters raises DMS and DMSP concentrations (Broadbent and Jones, 2004) making coral reefs potential "hotspots" of atmospheric DMS production .…”

“…Corals contain relatively high concentrations of dimethylsulphoniopropionate (DMSP), an organic sulphur substance that seems to have many biological roles such as osmoregulation in various species of phytoplankton (Stefels, 2000;Vairavamurthy et al, 1985), an antioxidant response in phytoplankton and coral (Deschaseaux et al, 2014a;Jones et al, 2007;Sunda et al, 2002), anti-predation (Otte and Morris, 1994;Van Alstyne and Houser, 2003;Van Alstyne et al, 2001;Wolfe et al, 1997), anti-bacterial activity (Sieburth, 1960(Sieburth, , 1961, and as a methyl donor in the synthesis of nitrogen based metabolites (Chillemi et al, 1990). It also functions as a chemo-attractant for a whole range of marine species (DeBose et al, 2008;Knight, 2012;Savoca and Nevitt, 2014;Seymour et al, 2010), and as a chemical cue for bacteria (Garren et al, 2013;Seymour et al, 2010) including coral-associated bacterial communities, with important consequences for coral health and the resilience of coral reefs (Raina et al, 2009(Raina et al, , 2010.…”

Quantification of total and particulate dimethylsulfoniopropionate (DMSP) in five Bermudian coral species across a depth gradient

“…In corals, bleached colonies of Acropora formosa show significantly greater DMSP concentrations per zooxanthellae (436 fmol cell -1 ) than in unbleached colonies (171 fmol cell -1 ) (Broadbent et al 2002). Jones et al (2007) also reported significant DMS and DMSP correlations with sea surface temperatures up to 30°C. While the above-mentioned observations suggest a potential link between DMSP production and photophysiological stress, there have, however, been no studies characterizing how DMSP in corals might vary along a photosynthetic (light) gradient that exposes corals to varying amounts of solar radiation and cellular oxidative stress.…”