Coral larvae avoid substratum exploration and settlement in low-oxygen environments
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Coral larvae avoid substratum exploration and settlement in lowoxygen environments Hendrikje Jorissen1
•
Maggy M. Nugues1,2
Received: 18 September 2019 / Accepted: 7 October 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Oxygen is a critical resource that mediates a multitude of essential processes and interactions at multiple scales on coral reefs. In adult corals, it can directly or indirectly impact physiological processes, such as photosynthesis, respiration, and calcification. Moreover, many corals bleach as a consequence of being exposed to low oxygen. The sessile adult phase of corals makes habitat selection crucial for post-settlement survival and thus their pelagic larvae use a diverse array of cues to determine a suitable spot for settlement. However, the effects of oxygen on the early life stages of corals are still poorly known. This study investigated the importance of oxygen as a potential settlement cue and its effect on swimming and settlement behavior of coral larvae of two Acropora species. Two experiments were performed, one investigating coral larval swimming behavior under different oxygen conditions and the other studying coral larval settlement along an oxygen gradient. Bottom exploration, expressed as the percent of A. cytherea and A. pulchra larvae in the bottom section of experimental cylinders, was reduced by 96% and 100%, respectively, in hypoxic water compared to normoxic water. When offered the choice to settle on an otherwise preferred settlement substrate (Titanoderma prototypum) along an oxygen gradient, larvae of both coral species settled almost exclusively on T. prototypum fragments placed in well-oxygenated environments, with
Topic Editor Morgan S.Pratchett & Hendrikje Jorissen [email protected] 1
EPHE, USR3278 CRIOBE, UPVD-CNRS, PSL Research University, 66860 Perpignan, France
2
Labex Corail, CRIOBE, 98729 Moorea, French Polynesia
settlement rates increasing nonlinearly with oxygen concentrations. These results suggest that low-oxygen areas can negatively influence the settlement success of coral larvae and that oxygen concentration may be used as a cue for coral larval swimming and settlement behavior. Keywords Oxygen Hypoxia Settlement Coral larvae Larvae behavior Acropora
Introduction Oxygen is a fundamental driver of the functioning and health of coral reef ecosystems, and the dynamics of coral reefs cannot be understood without comprehending the role of oxygen (Altieri and Gedan 2015; Nelson and Altieri 2019). It has recently been called the universal currency of coral reefs, as it is produced by photosynthetic organisms such as corals and algae, consumed by nearly all reef species, exchanged between mutualists, and suppressed by competitors and disease agents (Nelson and Altieri 2019). However, research on the drivers behind the degradation and decline of tropical coral reefs has so far mainly focused on elevated ocean temperatures, ocean acidification, eutrophication and overfishing (Pandolfi et al. 2003;
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