Elevated seawater temperatures have a limited impact on the coral immune response following physical damage

Abstract

Recurrent disturbances on coral reefs that cause injuries, like predation and storm damage, and elevated seawater temperatures reduce coral fitness and immunocompetence. An effective immune response is essential to prevent disease and enhance colony survival. To evaluate how elevated seawater temperatures affect the coral immune response following injury, fragments of Acropora aspera were exposed to ambient (27–29°C) or elevated (32–33.5°C) seawater temperatures for 8 days and subsequently experimentally injured. Expression patterns for 15 immune genes 24 h post-injury revealed that most genes involved in the Toll-like receptor pathway were unaffected by elevated seawater temperatures. Exceptions to this pattern were cFos and cJun, which were upregulated and likely played a role in repair processes, and TRAF-6 and NFκB, which were downregulated suggesting reduced immune function. Components of the complement system were upregulated (millectin, C3) or downregulated (Bf, Tx60, apextrin) in corals at high temperatures. However, corals that also sustained injury, showed normal Tx60 and apextrin expression, suggesting roles in the wounding response. Overall, basal expression levels of immune genes are sufficient to mount a response to injury in the short term, and the immune response of A. aspera following injury is not significantly affected by minor elevations in seawater temperatures.