Heterotrophy mitigates the response of the temperate coral Oculina arbuscula to temperature stress.

Hannah E Aichelman,Justin H Baumann,Karl D Castillo,Sarah W Davies,Travis A Courtney,Joseph E Townsend

doi:10.1002/ece3.2399

Hannah E Aichelman, Justin H Baumann + Show 4 more

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https://doi.org/10.1002/ece3.2399

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Abstract

Anthropogenic increases in atmospheric carbon dioxide concentration have caused global average sea surface temperature (SST) to increase by approximately 0.11°C per decade between 1971 and 2010 – a trend that is projected to continue through the 21st century. A multitude of research studies have demonstrated that increased SSTs compromise the coral holobiont (cnidarian host and its symbiotic algae) by reducing both host calcification and symbiont density, among other variables. However, we still do not fully understand the role of heterotrophy in the response of the coral holobiont to elevated temperature, particularly for temperate corals. Here, we conducted a pair of independent experiments to investigate the influence of heterotrophy on the response of the temperate scleractinian coral Oculina arbuscula to thermal stress. Colonies of O. arbuscula from Radio Island, North Carolina, were exposed to four feeding treatments (zero, low, moderate, and high concentrations of newly hatched Artemia sp. nauplii) across two independent temperature experiments (average annual SST (20°C) and average summer temperature (28°C) for the interval 2005–2012) to quantify the effects of heterotrophy on coral skeletal growth and symbiont density. Results suggest that heterotrophy mitigated both reduced skeletal growth and decreased symbiont density observed for unfed corals reared at 28°C. This study highlights the importance of heterotrophy in maintaining coral holobiont fitness under thermal stress and has important implications for the interpretation of coral response to climate change.

Highlights

Anthropogenic activities have increased global atmospheric carbon dioxide from approximately 280 ppm during the Industrial Revolution to presentday values exceeding 400 ppm (Doney et al 2009)
Our experiments reveal that the temperate coral O. arbuscula can utilize heterotrophic carbon to minimize growth reductions and loss of symbionts associated with exposure to moderate thermal stress
Unfed O. arbuscula fragments under moderate thermal stress were not able to maintain growth and exhibited approximately zero net calcification, an effect that was alleviated once corals were provided the opportunity for heterotrophy

Summary

Introduction

Anthropogenic activities have increased global atmospheric carbon dioxide (pCO2) from approximately 280 ppm during the Industrial Revolution to presentday values exceeding 400 ppm (Doney et al 2009) This increase in atmospheric pCO2 has resulted in global sea surface temperature (SST) increases of 0.11°C per decade between 1971 and 2010, and these trends are projected to continue into the 21st century (Rhein et al 2013). Over the last several decades, warming has been more prominent in the North Atlantic Ocean relative to other ocean basins with warming of up to 4°C predicted for temperate Atlantic waters by the end of this century (Rhein et al 2013) This ocean warming trend has affected the health of marine ecosystems, including thermally sensitive coral reef habitats worldwide (Hoegh-Guldberg 1999; Hoegh-Guldberg and Bruno 2010).

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