Award: OCE-1947522

Coral reefs are declining dramatically, with appreciable portions of this loss being due to coral disease, bleaching, and algal overgrowth of corals.  Our investigation conducted field experiments on reefs in French Polynesia and demonstrated:

1) corals grow and survive better in multispecies stands than in single species stands, with multispecies stands experiencing less predation from fishes and less competition from seaweeds than single species stands;

2) coral disease is strongly suppressed by co-occurring sea cucumbers, but sea cucumbers have been severely overharvested – putting reefs at risk and facilitating the increasing outbreak of coral disease documented in recent decades;

3) water extracts from corals growing with co-occurring sea cucumbers are much more suppressive of a known coral pathogen than the same corals growing without nearby sea cucumbers;

4) when common sea cucumbers feed on reef sediments, they suppress microbial abundance by about 75% during gut passage and they selectively remove some groups of microbes (especially cyanobacteria) that are known to produce toxins,

5) turf algae that commonly overgrow the bases of some corals can be allelopathic to those corals, but this is seasonally variable, is not correlated with alterations in coral microbiomes, and may become more damaging as oceans warm;

6) coral replanting efforts on reefs may profit from selectively planting more hearty, and often slower growing, corals rather than the faster growing, but less stress or disturbance resistant, species that are more commonly used; and

7) in many cases changes in coral microbiomes that are often interpreted as a cause of coral demise may more commonly be a response to other drivers killing or suppressing corals.

Finally, it has been suggested that corals living in stressed areas may be pre-adapted to various stresses and could thus be useful as source populations to help damaged reefs recover.  When we reciprocally transplanted corals between reefs experiencing differing stresses and manipulated exposure to competing seaweeds and corallivores, corals were affected by macroalgal competition, corallivory, transplant location, or some combination thereof, but we found limited evidence that the habitat of origin significantly impacted intraspecific performance.

Overall, our findings suggest that maintaining coral diversity and re-establishing previously common detritivores like sea cucumbers may suppress the loss and aid the recovery of these at risk, but valuable, ecosystems.

 

Last Modified: 04/29/2026
Modified by: Mark E Hay