Thermal stress restructures volatile gas emissions from the model cnidarian Aiptasia

Abstract

Coral bleaching events, in which symbionts are lost from host tissues, have become more frequent and severe because of climate change—specifically, elevated temperatures. How such events impact biogenic volatile organic compound (BVOC) emissions, compounds that can function as metabolic signalling elements, remains underexplored. Here we used gas chromatography coupled with mass spectrometry (GC–MS) to characterise the suite of BVOCs (collectively the ‘volatilome’) from the model sea anemone Exaiptasia diaphana (‘Aiptasia’) under three temperatures (control: 25 °C; sub-bleaching: 30 °C; and bleaching: 33.5 °C), both without symbionts (aposymbiotic) and when populated by its native dinoflagellate symbiont, Breviolum minutum . The volatilome of symbiotic anemones during bleaching at an elevated temperature was distinct from that at lower temperatures, with high dimethyl sulphide (DMS), eucalyptol, and 1-iodododecane levels at the higher temperature. In comparison, the volatilome of aposymbiotic anemones at sub-bleaching temperature produced the most differentially abundant BVOCs, including 2-phenyl-3-methyl-pyrrolo(2,3-b)pyrazine, acetone, and naphthalene. Symbiotic anemones had 12-fold more ‘core volatiles’ (BVOCs in all biological replicates across all temperature treatments) than aposymbiotic anemones (48 vs . 4 BVOCs); during thermal stress, the symbiotic anemone volatilomes retained their compound richness, whereas the richness of aposymbiotic anemone volatilomes decreased. These observations suggest that symbiotic dinoflagellates enhance BVOC diversity and abundance and may confer a degree of metabolic stability to the intact symbiosis (i.e. ‘holobiont'). Such changes in metabolic outputs can inform our understanding of how coral holobionts respond to increasing seawater temperatures, enable targeted studies of BVOC function, and facilitate the development of biomarkers indicative of coral reef health.

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