Abstract
BackgroundCoral reefs can experience salinity fluctuations due to rainfall and runoff; these events can have major impacts on the corals and lead to bleaching and mortality. On the Great Barrier Reef (GBR), low salinity events, which occur during summer seasons and can involve salinity dropping ~ 10 PSU correlate with declines in coral cover, and these events are predicted to increase in frequency and severity under future climate change scenarios. In other marine invertebrates, exposure to low salinity causes increased expression of genes involved in proteolysis, responses to oxidative stress, and membrane transport, but the effects that changes in salinity have on corals have so far received only limited attention. To better understand the coral response to hypo-osmotic stress, here we investigated the transcriptomic response of the coral Acropora millepora in both adult and juvenile life stages to acute (1 h) and more prolonged (24 h) exposure to low salinity.ResultsDifferential gene expression analysis revealed the involvement of both common and specific response mechanisms in Acropora. The general response to environmental stressors included up-regulation of genes involved in the mitigation of macromolecular and oxidative damage, while up-regulation of genes involved in amino acid metabolism and transport represent specific responses to salinity stress.ConclusionsThis study is the first comprehensive transcriptomic analysis of the coral response to low salinity stress and provides important insights into the likely consequences of heavy rainfall and runoff events on coral reefs.
Highlights
Coral reefs can experience salinity fluctuations due to rainfall and runoff; these events can have major impacts on the corals and lead to bleaching and mortality
Differential gene expression analyses Between 5.5–10.2 million RNAseq reads were obtained from each adult coral sample, while 3.4–8.8 million reads were recovered from each juvenile coral sample
principal component analysis (PCA) of the count matrix of the 26,622 A. millepora gene predictions revealed that the colony had a stronger effect on gene expression than the salinity treatment for the adult corals, while in the case of juveniles variation was primarily explained by treatment (Additional file 1: Figure S1)
Summary
Coral reefs can experience salinity fluctuations due to rainfall and runoff; these events can have major impacts on the corals and lead to bleaching and mortality. Our current understanding of osmoregulation processes in corals is largely derived from other marine invertebrates such as sea anemones and bivalves; in these organisms, small organic molecules and inorganic ions are used to prevent osmotic lysis [15, 16]. These molecules, known as osmolytes, include free amino acids (FAAs), FAA derivates (taurine, glycine betaine), floridoside and other compounds such as dimethylsulfoniopropionate (DMSP) [17, 18]. Several other environmental stressors, such as temperature and elevated CO2, cause changes in the expression of specific molecular chaperones in corals [21, 22] and these are likely to be components of a general stress response system
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