Abstract
Global environmental change has the potential to disrupt well established species interactions, with impacts on nutrient cycling and ecosystem function. On coral reefs, fish living within the branches of coral colonies can promote coral performance, and it has been hypothesized that the enhanced water flow and nutrients provided by fish to corals could ameliorate coral bleaching. The aim of this study was to evaluate the influence of small, aggregating damselfish on the health of their host corals (physiology, recovery, and survival) before, during, and after a thermal-bleaching event. When comparing coral colonies with and without fish, those with resident fish exhibited higher Symbiodinium densities and chlorophyll in both field and experimentally-induced bleaching conditions, and higher protein concentrations in field colonies. Additionally, colonies with damselfish in aquaria exhibited both higher photosynthetic efficiency (FV/FM) during bleaching stress and post-bleaching recovery, compared to uninhabited colonies. These results demonstrate that symbiotic damselfishes, and the services they provide, translate into measureable impacts on coral tissue, and can influence coral bleaching susceptibility/resilience and recovery. By mediating how external abiotic stressors influence coral colony health, damselfish can affect the functional responses of these interspecific interactions in a warming ocean.
Highlights
Coral reefs are among the most biodiverse and climate change vulnerable ecosystems [1,2], largely owing to the thermal sensitivity of habitat-forming scleractinian corals
Under normal temperature conditions in the field, P. damicornis colonies with D. aruanus had significantly higher densities of Symbiodinium (ANOVA, F1,8 = 8.2, p = 0.02) and higher concentrations of total chlorophyll (ANOVA, F1,8 = 6.7, p = 0.03) than unoccupied colonies (Fig 1)
The effects of fish presence were consistent among sites for Symbiodinium density (ANOVA(treatment site): F3,30 = 1.81, p = 0.17, Fig 2)
Summary
Coral reefs are among the most biodiverse and climate change vulnerable ecosystems [1,2], largely owing to the thermal sensitivity of habitat-forming scleractinian corals. Aside from causing widespread coral bleaching and coral loss [2,3], sustained and ongoing changes in environmental conditions may threaten complex and critical interactions among coral reef organisms [2,3,4,5]. These complex interactions give rise to ecological processes that shape the structure and function of ecosystems, with feedbacks that are critical to reinforce or destabilize particular species-species and species-environment interactions [6,7,8].
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