Calcification, Storm Damage and Population Resilience of Tabular Corals under Climate Change

Joshua S Madin,Sean R Connolly,Terry P Hughes,Mónica Medina

doi:10.1371/journal.pone.0046637

Joshua S Madin, Sean R Connolly + Show 2 more

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https://doi.org/10.1371/journal.pone.0046637

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Abstract

Two facets of climate change–increased tropical storm intensity and ocean acidification–are expected to detrimentally affect reef-building organisms by increasing their mortality rates and decreasing their calcification rates. Our current understanding of these effects is largely based on individual organisms’ short-term responses to experimental manipulations. However, predicting the ecologically-relevant effects of climate change requires understanding the long-term demographic implications of these organism-level responses. In this study, we investigate how storm intensity and calcification rate interact to affect population dynamics of the table coral Acropora hyacinthus, a dominant and geographically widespread ecosystem engineer on wave-exposed Indo-Pacific reefs. We develop a mechanistic framework based on the responses of individual-level demographic rates to changes in the physical and chemical environment, using a size-structured population model that enables us to rigorously incorporate uncertainty. We find that table coral populations are vulnerable to future collapse, placing in jeopardy many other reef organisms that are dependent upon them for shelter and food. Resistance to collapse is largely insensitive to predicted changes in storm intensity, but is highly dependent on the extent to which calcification influences both the mechanical properties of reef substrate and the colony-level trade-off between growth rate and skeletal strength. This study provides the first rigorous quantitative accounting of the demographic implications of the effects of ocean acidification and changes in storm intensity, and provides a template for further studies of climate-induced shifts in ecosystems, including coral reefs.

Highlights

Widespread changes in marine ecosystem function, species abundances and geographic ranges are all a likely consequence of environmental trends associated with ongoing anthropogenic effects on ocean pH [1], sea temperatures [2], and storm intensity [3]
For scenarios in which substrate strength is unaffected by future pCO2 levels and coral colonies sacrifice colony growth in order to maintain skeletal strength, decreases in Dislodgement Mechanical Thresholds (DMTs) are driven only by storm intensity
Our study focuses on two environmental changes likely to be associated with anthropogenic effects on climate, and it explores their demographic effects on adult coral growth and mortality from storms

Summary

Introduction

Widespread changes in marine ecosystem function, species abundances and geographic ranges are all a likely consequence of environmental trends associated with ongoing anthropogenic effects on ocean pH [1], sea temperatures [2], and storm intensity [3]. Predicting the large-scale, long-term effects of climate change requires a better understanding of how climate change will alter demography and population dynamics over decadal timespans [6], [7]. Mortality rates of coral colonies are elevated by severe summer storms and cyclones, which dislodge colonies from the substrate, in wave-exposed, highly productive habitats like reef crests [12], [15]. Such mechanical disturbances limit the dominance of fast-growing, mechanically unstable coral growth forms, and facilitates the maintenance of high local diversity in coral assemblages [16]. If manifested as slower colony growth rates [18], may have implications for lifetime reproductive output, which is strongly related to colony size and longevity [19]

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