Coral physiology and growth response to heat stress and hypoxia: a case of Patong reef, Phuket

Abstract

Coral reefs around the world are under threat from multiple global and local stressors. Understanding the responses of different coral species to these stressors is essential to develop effective management and conservation strategies and mitigate the impacts of climate change on coral reefs. This study examines the responses of three coral species - Porites lutea (massive), Montipora tuberculosa (tabular), and Pocillopora verrucosa (branching) - to rising seawater temperature and low dissolved oxygen (DO) levels, which are expected to intensify as a result of climate change. Coral nubbins were collected from Patong Bay, Phuket, Thailand, and subjected to experimental investigations under ambient conditions (29 °C, DO > 6 mgL−1), heat stress (32 °C), hypoxia (DO < 2 mgL−1) and heat stress + hypoxia treatments. Photosynthetic performance indicators Fv/Fm and Fv/F0, and physiological parameters - Symbiodiniaceae density, pigment concentration, and growth rate were quantified. Results indicate that P. verrucosa is the most sensitive and severely affected by heat stress and hypoxia, more so than P. lutea and M. tuberculosa. The combination of heat stress and hypoxia had less impact on these species, except for a decline in growth rate of M. tuberculosa. Moreover, the coral species respond differently to high temperature and low oxygen, with their sensitivity depending on the species. These responses may differ according to the lighting, especially in hypoxic conditions. Additional research is required to better understand the combined impacts of heat stress and hypoxia, and to enhance the mechanistic comprehension of synergistic and antagonistic responses in the three scleractinian corals. The study fills a research gap and provides useful information to predict the vulnerability of these three coral species in shallow reef habitats under climate change scenarios, helping to devise effective mitigation strategies for the preservation of coral reefs globally.