Effects of ocean warming and coral bleaching on aerosol emissions in the Great Barrier Reef, Australia

Climate Change Impacts on the Marine Cycling of Biogenic Sulfur: A Review

A key component of the marine sulfur cycle is the climate-active gas dimethylsulfide (DMS), which is synthesized by a range of organisms from phytoplankton to corals, and accounts for up to 80% of global biogenic sulfur emissions. The DMS cycle starts with the intracellular synthesis of the non-gaseous precursor dimethylsulfoniopropionate (DMSP), which is released to the water column by various food web processes such as zooplankton grazing. This dissolved DMSP pool is rapidly turned over by microbially mediated conversion using two known pathways: demethylation (releasing methanethiol) and cleavage (producing DMS). Some of the formed DMS is ventilated to the atmosphere, where it undergoes rapid oxidation and contributes to the formation of sulfate aerosols, with the potential to affect cloud microphysics, and thus the regional climate. The marine phase cycling of DMS is complex, however, as heterotrophs also contribute to the consumption of the newly formed dissolved DMS. Interestingly, due to microbial consumption and other water column sinks such as photolysis, the amount of DMS that enters the atmosphere is currently thought to be a relatively minor fraction of the total amount cycled through the marine food web—less than 10%. These microbial processes are mediated by water column temperature, but the response of marine microbial assemblages to ocean warming is poorly characterized, although bacterial degradation appears to increase with an increase in temperature. This review will focus on the potential impact of climate change on the key microbially mediated processes in the marine cycling of DMS. It is likely that the impact will vary across different biogeographical regions from polar to tropical. For example, in the rapidly warming polar oceans, microbial communities associated with the DMS cycle will likely change dramatically during the 21st century with the decline in sea ice. At lower latitudes, where corals form an important source of DMS (P), shifts in the microbiome composition have been observed during thermal stress with the potential to alter the DMS cycle.

Global Warming and Its Implications on Nature Tourism at Phinda Private Game Reserve, South Africa

The past decade recorded the highest number of high impact extreme weather events such as flooding, rainfall events, fires, droughts, and heatwaves amongst others. One of the key features and drivers of extreme weather events has been global warming, with record temperatures recorded globally. The World Meteorological Organization indicated that the 2010–2020 decade was one of the warmest on record. Continued global warming triggers a chain of positive feedback with far-reaching adverse implications on the environment and socio-economic activities. The tourism industry fears that increased global warming would result in severe challenges for the sector. The challenges include species extinction, disruption of tourism aviation, and several tourism activities. Given the extent of climate variability and change, this study examines the impacts of rising temperatures on tourism operations at Phinda Private Game Reserve in South Africa. The study adopts a mixed-method approach that uses secondary, archival, and primary data collected through interviews and field observations to investigate the impacts. Data analysis was done using XLSTAT and Mann–Kendall Trend Analysis to analyse climate trends, while content and thematic analyses were used to analyse primary data findings. The study found that increasing temperature is challenging for tourists and tourism employees as it affects productivity, sleeping patterns, tourism operations, and infrastructure. High temperatures are a considerable threat to water availability and animal sightings, adversely affecting the game drive experience. Increased heatwaves resulted in bird mortality and hatching mortality for turtles; this is a significant conservation challenge. The study recommends that heat stress be treated as a health and safety issue to protect tourists and employees.

Dimethylsulphoniopropionate as a water quality indicator of coral bleaching: Implications for monitoring studies on the Great Barrier Reef

Short term stress experiments with dissolved inorganic phosphorus (DIP) and tripolyphosphate (TPP) have been carried out on the staghorn coral Acropora intermedia, collected from Heron Island in the southern Great Barrier Reef, at low and elevated seawater temperatures. Zooxanthellae, chlorophyll a, intracellular and tissue dimethylsulfoniopropionate (DMSP), and extracellular DMSP production were measured to assess the level of stress on A. intermedia at different winter and summer seasons from 2001 to 2003. Whilst no significant changes were measured in these stress indicators in 2001 and 2003, significant changes occurred in winter 2002, reflecting natural stresses on A. intermedia in the field, and stress from added DIP and TPP at high seawater temperatures. These stresses caused corals to bleach, whilst extracellular DMSP, intracellular and tissue DMSP concentrations increased, reflecting the antioxidant role of DMSP in the coral zooxanthellae and coral host to combat stress. These results have important implications for future research in the GBR.

Coral reefs as a source of climate-active aerosols

We review the evidence for bio-regulation by coral reefs of local climate through stress-induced emissions of aerosol precursors, such as dimethylsulfide. This is an issue that goes to the core of the coral ecosystem’s ability to maintain homeostasis in the face of increasing climate change impacts and other anthropogenic pressures. We examine this through an analysis of data on aerosol emissions by corals of the Great Barrier Reef, Australia. We focus on the relationship with local stressors, such as surface irradiance levels and sea surface temperature, both before and after notable coral bleaching events. We conclude that coral reefs may be able to regulate their exposure to environmental stressors through modification of the optical properties of the atmosphere, however this ability may be impaired as climate change intensifies.

Coral endosymbionts (Symbiodiniaceae) emit species-specific volatilomes that shift when exposed to thermal stress

Biogenic volatile organic compounds (BVOCs) influence organism fitness by promoting stress resistance and regulating trophic interactions. Studies examining BVOC emissions have predominantly focussed on terrestrial ecosystems and atmospheric chemistry - surprisingly, highly productive marine ecosystems remain largely overlooked. Here we examined the volatilome (total BVOCs) of the microalgal endosymbionts of reef invertebrates, Symbiodiniaceae. We used GC-MS to characterise five species (Symbiodinium linucheae, Breviolum psygmophilum, Durusdinium trenchii, Effrenium voratum, Fugacium kawagutii) under steady-state growth. A diverse range of 32 BVOCs were detected (from 12 in D. trenchii to 27 in S. linucheae) with halogenated hydrocarbons, alkanes and esters the most common chemical functional groups. A thermal stress experiment on thermally-sensitive Cladocopium goreaui and thermally-tolerant D. trenchii significantly affected the volatilomes of both species. More BVOCs were detected in D. trenchii following thermal stress (32 °C), while fewer BVOCs were recorded in stressed C. goreaui. The onset of stress caused dramatic increases of dimethyl-disulfide (98.52%) in C. goreaui and nonanoic acid (99.85%) in D. trenchii. This first volatilome analysis of Symbiodiniaceae reveals that both species-specificity and environmental factors govern the composition of BVOC emissions among the Symbiodiniaceae, which potentially have, as yet unexplored, physiological and ecological importance in shaping coral reef community functioning.