Resistance of Two Mediterranean Cold-Water Coral Species to Low-pH Conditions

Juancho Movilla,Carlos Domínguez-Carrió,Covadonga Orejas,Carles Pelejero,Àngel López-Sanz,Jordi Grinyó,Andrea Gori,Eva Calvo

doi:10.3390/w6010059

Abstract

Deep-water ecosystems are characterized by relatively low carbonate concentration values and, due to ocean acidification (OA), these habitats might be among the first to be exposed to undersaturated conditions in the forthcoming years. However, until now, very few studies have been conducted to test how cold-water coral (CWC) species react to such changes in the seawater chemistry. The present work aims to investigate the mid-term effect of decreased pH on calcification of the two branching CWC species most widely distributed in the Mediterranean, Lophelia pertusa and Madrepora oculata. No significant effects were observed in the skeletal growth rate, microdensity and porosity of both species after 6 months of exposure. However, while the calcification rate of M. oculata was similar for all colony fragments, a heterogeneous skeletal growth pattern was observed in L. pertusa, the younger nubbins showing higher growth rates than the older ones. A higher energy demand is expected in these young, fast-growing fragments and, therefore, a reduction in calcification might be noticed earlier during long-term exposure to acidified conditions.

Highlights

Due to the absorption by the ocean of a major part of the anthropogenic CO2 emitted to the atmosphere, the pH of global surface waters has already dropped by 0.1 units since the pre-industrial era [1,2,3]
This would be the case of cold-water coral (CWC) communities, which are found in areas characterised by very low aragonite saturation state values (ΩA) [12,13]
The first short-term studies based on short incubations conducted on specimens of Lophelia pertusa and Madrepora oculata, found a reduction in the calcification rate ranging from 30% to 56% when the pH was dropped between 0.1 and 0.3 units [13,19,20]

Summary

Introduction

Due to the absorption by the ocean of a major part of the anthropogenic CO2 emitted to the atmosphere, the pH of global surface waters has already dropped by 0.1 units since the pre-industrial era [1,2,3]. It is expected that zones characterized by naturally low carbonate concentration values such as high-latitude and deep-water ecosystems will be amongst the first to experience undersaturated conditions [9,10,11]. This would be the case of cold-water coral (CWC) communities, which are found in areas characterised by very low aragonite saturation state values (ΩA) [12,13]. It is important to remark that, in these previous studies on possible effects of OA in the development of CWC, coral growth was exclusively assessed through measurements of calcification, with no studies so far reporting on possible effects on coral skeletal microdensity or porosity

Methods

Results

Conclusion