Effects of thermal conditioning on the performance of Pocillopora acuta adult coral colonies and their offspring

Crystal J Mcrae,Isabelle M Côté,Wen-Bin Huang,Tung-Yung Fan

doi:10.1007/s00338-021-02123-9

Abstract

Ocean warming induced by climate change is the greatest threat to the persistence of coral reefs globally. Given the current rate of ocean warming, there may not be sufficient time for natural acclimation or adaptation by corals. This urgency has led to the exploration of active management techniques aimed at enhancing thermal tolerance in corals. Here, we test the capacity for transgenerational acclimation in the reef-building coral Pocillopora acuta as a means of increasing offspring performance in warmer waters. We exposed coral colonies from a reef influenced by intermittent upwelling and constant warm-water effluent from a nuclear power plant to temperatures that matched (26 °C) or exceeded (29.5 °C) season-specific mean temperatures for three reproductive cycles; offspring were allowed to settle and grow at both temperatures. Heated colonies reproduced significantly earlier in the lunar cycle and produced fewer and smaller planulae. Recruitment was lower at the heated recruitment temperature regardless of parent treatment. Recruit survival did not differ based on parent or recruitment temperature. Recruits from heated parents were smaller and had lower maximum quantum yield (Fv/Fm), a measurement of symbiont photochemical performance. We found no direct evidence that thermal conditioning of adult P. acuta corals improves offspring performance in warmer water; however, chronic exposure of parent colonies to warmer temperatures at the source reef site may have limited transgenerational acclimation capacity. The extent to which coral response to this active management approach might vary across species and sites remains unclear and merits further investigation.

Highlights

Coral reefs have declined dramatically over the past several decades (Bellwood et al 2004; Bruno and Selig 2007; Hughes et al 2017a)
We found no direct evidence that thermal conditioning of adult P. acuta corals improves offspring performance in warmer water; chronic exposure of parent colonies to warmer temperatures at the source reef site may have limited transgenerational acclimation capacity
There was no difference in reproductive timing between temperature treatments in March; in April and May, colonies held at 29.5 °C released planulae significantly earlier in the lunar cycle (Watson’s tests, April: F = 0.63, p \ 0.001; May: F = 0.94, p \ 0.001) (Fig. 2a, Table 1)

Summary

Introduction

Coral reefs have declined dramatically over the past several decades (Bellwood et al 2004; Bruno and Selig 2007; Hughes et al 2017a). The many drivers of coral decline include a range of natural (e.g. disease, storms) and human-induced (e.g. pollution, fishing) local stressors (Nystrom et al 2000; Burke et al 2011). It is chronic ocean warming and acute thermal anomalies induced by climate change that pose the greatest threat to the persistence of corals (Hoegh-Guldberg et al 2007, 2017; Carpenter et al 2008; Hughes et al 2017b). Increased water temperature can alter reproductive timing (Crowder et al 2014; Fan et al 2017), fertilization/

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Conclusion