Effects of future climate on coral-coral competition

RESEARCH ARTICLE Effects of future climate on coral-coral competition Nicole K. JohnstonID1*, Justin E. Campbell2,3, Valerie J. Paul3, Mark E. HayID1 1 School of Biological Sciences and Aquatic Chemical Ecology Center, Georgia Institute of Technology, Atlanta, GA, United States of America, 2 Department of Biological Sciences, Institute of Environment, Florida International University, North Miami, FL, United States of America, 3 Smithsonian Marine Station, Ft. Pierce, FL, United States of America * njohnston7@gatech.edu Abstract As carbon dioxide (CO2) levels increase, coral reefs and other marine systems will be affected by the joint stressors of ocean acidification (OA) and warming. The effects of these two stressors on coral physiology are relatively well studied, but their impact on biotic inter- actions between corals are poorly understood. While coral-coral interactions are less com- mon on modern reefs, it is important to document the nature of these interactions to better inform restoration strategies in the face of climate change. Using a mesocosm study, we evaluated whether the combined effects of ocean acidification and warming alter the com- petitive interactions between the common coral Porites astreoides and two other mounding corals (Montastraea cavernosa or Orbicella faveolata) common in the Caribbean. After 7 days of direct contact, P. astreoides suppressed the photosynthetic potential of M. caver- nosa by 100% in areas of contact under both present (~28.5˚C and ~400 μatm pCO2) and

predicted future (~30.0˚C and ~1000 μatm pCO2) conditions. In contrast, under present con- ditions M. cavernosa reduced the photosynthetic potential of P. astreoides by only 38% in areas of contact, while under future conditions reduction was 100%. A similar pattern occurred between P. astreoides and O. faveolata at day 7 post contact, but by day 14, each coral had reduced the photosynthetic potential of the other by 100% at the point of contact, and O. faveolata was generating larger lesions on P. astreoides than the reverse. In the absence of competition, OA and warming did not affect the photosynthetic potential of any coral. These results suggest that OA and warming can alter the severity of initial coral-coral interactions, with potential cascading effects due to corals serving as foundation species on coral reefs. Introduction Though coral reefs cover <0.1% of the Earth’s surface [1], they are among Earth’s most eco- nomically and ecologically valuable ecosystems [2]. In recent decades, coral reefs have been negatively impacted by a wide range of anthropogenic influences such as eutrophication, over- fishing, and climate change [3–5] that have led to a 50–80% decline in global coral cover [6, 7]. PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.0235465 August 13, 2020 1 / 16 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Johnston NK, Campbell JE, Paul VJ, Hay ME (2020) Effects of future climate on coral-coral competition. PLoS ONE 15(8): e0235465. https:// doi.org/10.1371/journal.pone.0235465

Editor: Frank Melzner, Helmholtz-Zentrum fur Ozeanforschung Kiel, GERMANY Received: October 21, 2019 Accepted: June 16, 2020 Published: August 13, 2020 Copyright: © 2020 Johnston et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: Data are available in Dryad (https://doi.org/10.5061/dryad.7pvmcvdqr). Funding: This research was funded by a Smithsonian/Link Foundation Graduate Research Fellowship granted to NKJ and the Teasley Endowment to the Georgia Institute of Technology. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.