Differential responses to ocean acidification between populations ofBalanophyllia eleganscorals from high and low upwelling environments

Abstract

Ocean acidification (OA), the global decrease in surface water pH from absorption of anthropogenic CO2, may put many marine taxa at risk. However, populations that experience extreme localized conditions, and are adapted to these conditions predicted in the global ocean in 2,100, may be more tolerant to future OA. By identifying locally adapted populations, researchers can examine the mechanisms used to cope with decreasing pH. One oceanographic process that influences pH is wind‐driven upwelling. Here we compare two Californian populations of the coral Balanophyllia elegans from distinct upwelling regimes, and test their physiological and transcriptomic responses to experimental seawater acidification. We measured respiration rates, protein and lipid content, and gene expression in corals from both populations exposed to pH levels of 7.8 and 7.4 for 29 days. Corals from the population that experiences lower pH due to high upwelling maintained the same respiration rate throughout the exposure. In contrast, corals from the low upwelling site had reduced respiration rates, protein content and lipid–class content at low pH exposure, suggesting they have depleted their energy reserves. Using RNA‐Seq, we found that corals from the high upwelling site upregulated genes involved in calcium ion binding and ion transport, most likely related to pH homeostasis and calcification. In contrast, corals from the low upwelling site downregulated stress response genes at low pH exposure. Divergent population responses to low pH observed in B. elegans highlight the importance of multi‐population studies for predicting a species' response to future OA.

Ocean acidification induces subtle shifts in gene expression and DNA methylation in mantle tissue of the Eastern oyster (Crassostrea virginica)

“…These results contrast a study by Li et al (2016) on P. fuctata mantle tissue, which found that approximately 10-11% of genes in their microarray were differentially expressed in response to moderate or severe OA, including a tendency for up-regulation of ion transport genes and down-regulation of biomineralization genes within the severe OA treatment. It is unlikely that the lack of differential gene expression observed in the present study was the result of low statistical power due to small number of biological replicates, as a number of similar studies on marine invertebrates have observed significant gene expression responses to OA with the same number of, or fewer biological replicates (Evans et al, 2013;Li et al, 2016;Johnson and Hofmann, 2017;Griffiths et al, 2019) .…”

“…A wide variety of marine calcifying organisms are known to mount significant transcriptomic responses to OA including; corals, urchins, pteropods and other species of oysters (Evans et al, 2013;Davies et al, 2016;Li et al, 2016;Johnson and Hofmann, 2017;Griffiths et al, 2019) . Studies of the pearl oyster Pinctada fuctata , the purple sea urchin Strongylocentrotus purpuratus , and the scleractinian coral Siderastrea siderea identified genes associated with ion transport, acid-base regulation, and biomineralization differentially expressed in response to OA (Evans et al, 2013;Evans and Watson-Wynn, 2014;Davies et al, 2016;Li et al, 2016) .…”

“…Transcriptomic studies have proven to be a powerful approach for identifying genes and understanding pathways that shape organismal response to OA, and have been used to help elucidate potential trade-offs that result from acclimatization (Evans and Hofmann, 2012) , including genes associated with biomineralization, acid-base regulation, and metabolic function (Evans et al, 2013;Davies et al, 2016;Li et al, 2016;Goncalves et al, 2017;Wong et al, 2018;Griffiths et al, 2019) . From this literature it has been hypothesized that there is a trade-off between maintaining calcification versus other core functions (Wood et al, 2008) , whereby increased or sustained calcification under continued exposure may become too costly over time.…”

Cold-water coral (Lophelia pertusa) response to multiple stressors: High temperature affects recovery from short-term pollution exposure

“…efforts indicate that corals collected in this manner represent distinct 'genets' with potentially different physiological adaptations 48,53 . There is evidence for genotypic variation in coral stress response, both at the phenotypic and molecular level 48,60,61 . When exposed to low pH (7.6) for short (2-week) or long (6-month) periods of time, some genets of L. pertusa were able to continue to calcify, while other genets experienced a net dissolution over the same timeframe 48 .…”

Characterizing the multivariate physiogenomic response to environmental change

“…As a reasonable starting point to quantify standing genetic variation to ocean acidification, Griffiths, Pan, and Kelley () use data on the pH seascape across the range of a temperate coral (Figure a) to identify two populations that have been exposed to different extremes of pH conditions. The first population comes from a location that experiences lower pH due to a high degree of upwelling.…”