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

Fiorella Prada,Nicola Baraldi,Stefano Mengoli,Francesco Ricci,Loris Giorgini,Paola Fantazzini,Giuseppe Falini,Zvy Dubinsky,Katharina E. Fabricius,Leonardo Brizi,Iryna Polishchuk,Simona Fermani,Quinzia Palazzo,Stefano Goffredo,Silvia Franzellitti,Erik Caroselli,Boaz Pokroy

doi:10.1038/s41598-021-98976-9

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.

Highlights

This study investigates the effects of long-term exposure to ocean acidification (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 two control sites differed between the two locations (t = 2.112, P = 0.002), while seep sites were similar (t = 1.244, P = 0.154)
The BEST routine revealed that pCO2 and ΩAR were strongly autocorrelated with the other environmental parameters (Rho = 0.995, P = 0.001) and were excluded from the following PERMANOVA analysis

Summary

Introduction

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. 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. The discrepancy among responses could derive from different experimental designs and analytical methods (e.g., addition of acid vs CO2 bubbling to mimic OA), co-limiting environmental conditions (e.g., temperature, light intensity, flow, feeding, etc.), and exposure times (days to months or even life times)[5]

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Conclusion