Coral micro- and macro-morphological skeletal properties in response to life-long acclimatization at CO2 vents in Papua New Guinea

Abstract

This study investigates the effects of long-term exposure to OA on skeletal parameters of four tropical zooxanthellate corals naturally living at CO2 seeps and adjacent control sites from two locations (Dobu and Upa Upasina) in the Papua New Guinea underwater volcanic vent system. The seeps are characterized by seawater pH values ranging from 8.0 to about 7.7. The skeletal porosity of Galaxea fascicularis, Acropora millepora, massive Porites, and Pocillopora damicornis was higher (up to ~ 40%, depending on the species) at the seep sites compared to the control sites. Pocillopora damicornis also showed a decrease of micro-density (up to ~ 7%). Thus, further investigations conducted on this species showed an increase of the volume fraction of the larger pores (up to ~ 7%), a decrease of the intraskeletal organic matrix content (up to ~ 15%), and an increase of the intraskeletal water content (up to ~ 59%) at the seep sites. The organic matrix related strain and crystallite size did not vary between seep and control sites. This multi-species study showed a common phenotypic response among different zooxanthellate corals subjected to the same environmental pressures, leading to the development of a more porous skeletal phenotype under OA.

Host Traits and Phylogeny Contribute to Shaping Coral-Bacterial Symbioses

“…Several coral traits can more directly affect the microbiome. Coral skeletal architecture differs among species ( 22 ), affecting the physicochemical properties of the colony ( 23 ) and the microbial biomass ( 7 ). For instance, light scattering is a function of skeletal density ( 8 ), resulting in different spatial gradients of light intensity and spectral composition that affect the microbiome ( 8 , 24 – 26 ).…”

pH variability at volcanic CO2 seeps regulates coral calcifying fluid chemistry

“…Periods of extremely low pH could cause physiological stress and even dissolution of resident organisms, especially for any individuals where skeletal CaCO 3 material becomes exposed. For example, the low pH values found in Upa-Upasina reef (Normanby Island) could also explain the deleterious effects of seawater pH on coral skeletal characteristics reported at this site (Prada et al, 2021). In this scenario, dissolution-resistant species would be favoured at Normanby.…”

Complex dynamics of coral gene expression responses to low pH across species

“…Differential gene expression related to calcium ion activity and calcification in host P. astreoides is consistent with reduced calcification in low pH relative to ambient pH sites (driven by a decrease in skeletal density; Crook et al, 2013). In reefs across the Pacific, Porites skeletal density but not extension was also negatively affected by low pH (Mollica et al, 2018); likewise, skeletal porosity of massive Porites was higher in low pH sites (Prada et al, 2021).…”