Regulation of isoprene production by coastal benthic communities

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Isporene (2-methyl-1,3-butadiene) is one of several volatile organic compounds produced by micro-organisms but is of particular interest since it is one of the most highly reactive hydrocarbons emitted that can alter the our climate. Isoprene rapidly oxidises when released to the atmosphere, which in turn lengthens the residence times of gases that contribute to the 'greenhouse' affect, and induces formation of ozone (in presence of nitric oxides) and cloud-condensing nuclei. To date, international attention of global isoprene fluxes has focused primarily on terrestrial systems whilst aquatic systems have been largely ignored. Estimates for global isoprene emissions from marine systems are thought to be substantially lower than those from terrestrial systems. However, these estimates from marine systems have been constructed from few laboratory-based studies upon microalgae. Recent research conducted in the field suggests that isoprene emissions from marine waters may be higher than previously estimated, in particular during microalgal blooms. Nevertheless, the focus of the limited previous research investigating isoprene emissions from marine systems has neglected two key factors that likely determine its global importance: (1) production by highly productive coastal marine communities and (2) the dynamics underlying both isoprene synthesis and degradation. Isoprene is synthesised by plants, algae and bacteria, all of which are abundant across the fringing, and permanently submerged habitats of coastal waters. Coastal marine systems cover a relatively small fraction of the earth's surface yet are highly productive (accounting 25% of all aquatic production). Simultaneously, these systems subject their inhabitants to continuously (and often extreme) fluctuating environmental conditions, such as light and temperature; such a highly variable growth environment is known to induce elevated isoprene synthesis in terrestrial systems. Both tropical and temperate marine coastal systems are characterised by analogous functional groups that likely synthesis substantial concentrations of isoprene, for example saltmarshes, macroalgae and microalgae (temperate) and mangroves, corals and seagrasses (tropical). However, not all isoprene that is synthesised is thought to reach the atmosphere. Degradation of isoprene by heterotrophic bacteria in soils has also been identified as an important component contributing to net isoprene emissions from terrestrial systems. Recent microcosm experiments at the University of Essex have demonstrated substantial isoprene degradation along an estuarine gradient and thus the occurrence of a marine sink for gross isoprene production. Here, we propose a curiosity-driven but proof-of-concept investigation to address this unknown importance of isoprene synthesis and degradation within coastal marine systems. Data collected here will directly form the basis of a future full proposal that will examine the mechanistics and biological interactions if net isoprene production and emission by marine systems. Within the context of this study, we have proposed the purchase of a commercially available field-operable Fast Isoprene Sensor (FIS, Hill Scientific, USA) and use this instrument for the first time for assaying marine communities in both laboratory and field settings. Therefore, this proposal will also determine the capabilities of the FIS for assaying aquatic organisms and for generating rapid field-based measurements. Experiments are described that will employ short- and long- term incubation experiments for a wide range of aquatic organisms that are commonly found within temperate and tropical coastal marine systems.