640262 event 1602852245 1602852245 "Ecologists have long debated the importance of top-down (the effects of consumers) versus bottom-up (nutrients and productivity) forces in structuring populations and communities.  There are numerous demonstrations of removing top consumers (wolves, sea otters, etc.) and the dramatic cascading effects on natural communities. Effects of removing lower trophic levels are relatively uninvestigated.  Here, we ask about the potential effects of removing a major class of detritivores from coral reefs and the possible roles of microbes in mediating the effects we demonstrate.  During recent decades, reefs have lost 50-90% of their live coral cover world-wide.  There are many drivers of the loss (overfishing, global warming, pollution, disease, etc.), but how these stressors may interact with low-level trophic alterations of reef communities has not been addressed. Over the past 200+ years, many thousands of tons of dried sea cucumbers have been removed from tropical coastal systems; these once abundant animals are now rare. The impacts of removing these detritivores is unknown (think of them as previously abundant vacuum cleaners on coral reefs).  In field experiments, we show that i) corals in areas with sea cucumbers produce extracts that are more suppressive of a common coral pathogen (Vibrio coralliilyticus) than corals where sea cucumbers have been excluded, ii) that corals without co-occurring sea cucumbers are more commonly killed by an apparent sediment-associated pathogen than corals with sea cucumbers, and iii) that damelfish that culture algal gardens on coral bases protect corals from these sediment-associated pathogens.  We are presently investigating the dynamics of coral microbiomes in these different treatments and in various stages of infection in hopes of identifying the pathogen(s) involved." 

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