Colony-specific investigations reveal highly variable responses among individual corals to ocean acidification and warming

Abstract

As anthropogenic climate change is an ongoing concern, scientific investigations on its impacts on coral reefs are increasing. Although impacts of combined ocean acidification (OA) and temperature stress (T) on reef-building scleractinian corals have been studied at the genus, species and population levels, there are little data available on how individual corals respond to combined OA and anomalous temperatures. In this study, we exposed individual colonies of Acropora digitifera, Montipora digitata and Porites cylindrica to four pCO2-temperature treatments including 400 μatm-28 °C, 400 μatm-31 °C, 1000 μatm-28 °C and 1000 μatm-31 °C for 26 days. Physiological parameters including calcification, protein content, maximum photosynthetic efficiency, Symbiodinium density, and chlorophyll content along with Symbiodinium type of each colony were examined. Along with intercolonial responses, responses of individual colonies versus pooled data to the treatments were investigated. The main results were: 1) responses to either OA or T or their combination were different between individual colonies when considering physiological functions; 2) tolerance to either OA or T was not synonymous with tolerance to the other parameter; 3) tolerance to both OA and T did not necessarily lead to tolerance of OA and T combined (OAT) at the same time; 4) OAT had negative, positive or no impacts on physiological functions of coral colonies; and 5) pooled data were not representative of responses of all individual colonies. Indeed, the pooled data obscured actual responses of individual colonies or presented a response that was not observed in any individual. From the results of this study we recommend improving experimental designs of studies investigating physiological responses of corals to climate change by complementing them with colony-specific examinations.

Effects of seawater pCO2 and temperature on calcification and productivity in the coral genus Porites spp.: an exploration of potential interaction mechanisms

“…Responses of coral colonies to temperature and seawater pCO 2 are highly variable for a range of coral species (Kavousi et al 2015;Shaw et al 2016), and we measured the individual responses of colonies of a range of genotypes. We utilised seawater pCO 2 which were both lower and higher than the present day, and we measured the effect of environmental change on colony calcification, photosynthesis and respiration to explore how these physiological processes interact.…”

Light induced intraspecific variability in response to thermal stress in the hard coral Stylophora pistillata

“…Susceptibility of hard corals to thermal stress can vary significantly between species (interspecific; Baird et al, 2009 ; Kavousi et al, 2015 ), within species (intraspecific; Sotka & Thacker, 2005 ; Kavousi et al, 2015 ), and even within the same colony (intracolonial; Brown et al, 2002a , 2002b ). The present study tested thermal stress responses based on recent light history using three colonies of the scleractinian coral S. pistillata .…”

“…In general, analysis of pooled data is not reliably representative for all the individual colonies tested (sensu Kavousi et al, 2015 ). Most importantly, in some cases, the use of pooled data can reveal a completely opposite outcome from what is obtained for the individual colony analysis.…”

Perilous Consequences of Global Climatic Change: A Review

“…Under stressful abnormal conditions such as warmer sea temperatures, the corals expel their tiny photosynthetic algae, draining them of their colour. Prolonged bleaching often leads to death of corals (Kavousi et al, 2015). The 2300 km world heritage listed reef ,The Great Barrier Reef, suffered its most severe bleaching on record last year (2016).The loss of corals ecosystems would have severe economic repercussions in region that depend on reefs for food, tourism income and for the protection of coastal land from destructive waves.…”