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Coral calcification mechanisms facilitate adaptive responses to ocean acidification.

ABSTRACT: Ocean acidification (OA) is a pressing threat to reef-building corals, but it remains poorly understood how coral calcification is inhibited by OA and whether corals could acclimatize and/or adapt to OA. Using a novel geochemical approach, we reconstructed the carbonate chemistry of the calcifying fluid in two coral species using both a pH and dissolved inorganic carbon (DIC) proxy (?11B and B/Ca, respectively). To address the potential for adaptive responses, both species were collected from two sites spanning a natural gradient in seawater pH and temperature, and then subjected to three pHT levels (8.04, 7.88, 7.71) crossed by two temperatures (control, +1.5°C) for 14 weeks. Corals from the site with naturally lower seawater pH calcified faster and maintained growth better under simulated OA than corals from the higher-pH site. This ability was consistently linked to higher pH yet lower DIC values in the calcifying fluid, suggesting that these differences are the result of long-term acclimatization and/or local adaptation to naturally lower seawater pH. Nevertheless, all corals elevated both pH and DIC significantly over seawater values, even under OA. This implies that high pH upregulation combined with moderate levels of DIC upregulation promote resistance and adaptive responses of coral calcification to OA.

SUBMITTER: Schoepf V

PROVIDER: S-EPMC5740286 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Coral calcification mechanisms facilitate adaptive responses to ocean acidification.

Schoepf Verena V Jury Christopher P CP Toonen Robert J RJ McCulloch Malcolm T MT

Proceedings. Biological sciences 20171201 1868

Ocean acidification (OA) is a pressing threat to reef-building corals, but it remains poorly understood how coral calcification is inhibited by OA and whether corals could acclimatize and/or adapt to OA. Using a novel geochemical approach, we reconstructed the carbonate chemistry of the calcifying fluid in two coral species using both a pH and dissolved inorganic carbon (DIC) proxy (δ<sup>11</sup>B and B/Ca, respectively). To address the potential for adaptive responses, both species were collec ...[more]

PMID: 29212728

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Project description:Ocean acidification (OA) threatens the growth and function of coral reef ecosystems. A key component to coral health is the microbiome, but little is known about the impact of OA on coral microbiomes. A submarine CO2 vent at Maug Island in the Northern Mariana Islands provides a natural pH gradient to investigate coral responses to long-term OA conditions. Three coral species (Pocillopora eydouxi, Porites lobata, and Porites rus) were sampled from three sites where the mean seawater pH is 8.04, 7.98, and 7.94. We characterized coral bacterial communities (using 16S rRNA gene sequencing) and determined pH of the extracellular calcifying fluid (ECF) (using skeletal boron isotopes) across the seawater pH gradient. Bacterial communities of both Porites species stabilized (decreases in community dispersion) with decreased seawater pH, coupled with large increases in the abundance of Endozoicomonas, an endosymbiont. P. lobata experienced a significant decrease in ECF pH near the vent, whereas P. rus experienced a trending decrease in ECF pH near the vent. In contrast, Pocillopora exhibited bacterial community destabilization (increases in community dispersion), with significant decreases in Endozoicomonas abundance, while its ECF pH remained unchanged across the pH gradient. Our study shows that OA has multiple consequences on Endozoicomonas abundance and suggests that Endozoicomonas abundance may be an indicator of coral response to OA. We reveal an interesting dichotomy between two facets of coral physiology (regulation of bacterial communities and regulation of calcification), highlighting the importance of multidisciplinary approaches to understanding coral health and function in a changing ocean.IMPORTANCE Ocean acidification (OA) is a consequence of anthropogenic CO2 emissions that is negatively impacting marine ecosystems such as coral reefs. OA affects many aspects of coral physiology, including growth (i.e., calcification) and disrupting associated bacterial communities. Coral-associated bacteria are important for host health, but it remains unclear how coral-associated bacterial communities will respond to future OA conditions. We document changes in coral-associated bacterial communities and changes to calcification physiology with long-term exposure to decreases in seawater pH that are environmentally relevant under midrange IPCC emission scenarios (0.1 pH units). We also find species-specific responses that may reflect different responses to long-term OA. In Pocillopora, calcification physiology was highly regulated despite changing seawater conditions. In Porites spp., changes in bacterial communities do not reflect a breakdown of coral-bacterial symbiosis. Insights into calcification and host-microbe interactions are critical to predicting the health and function of different coral taxa to future OA conditions.

Dataset Information

Coral calcification mechanisms facilitate adaptive responses to ocean acidification.

Publications

Coral calcification mechanisms facilitate adaptive responses to ocean acidification.

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