Quantifying recent regional changes in symbiont prevalence
Data from recent studies suggest that the prevalence of thermtolerant symbiont Durusdinium trenchii may be increasing on Caribbean coral reefs (Kennedy et al., 2015), likely due to chronic and acute thermal stress throughout the region (Kennedy et al., 2016). Large-scale symbiont community shifts in favor of D. trenchii may have important implications for the future of reefs, since this symbiont type may increase coral thermal tolerance while potentially causing eco-physiological trade-offs (Ortiz et al., 2013). However, there are no studies to date that analyze data spanning multiple decades to confirm this long-term trend.
The Coral Reef Futures Lab has a unique collection of hundreds of coral samples collected between 1995 and 2002 from several sites in the western Atlantic that differ in thermal regime and bleaching history. These samples come from up to 18 different scleractinian (hard coral) species per site and cover a range of depths from 2 - 33 meters.
In 2018, I began to analyze these historical samples using qPCR to assess the historical incidence and relative abundance of thermotolerant Durusdinium trenchii on Caribbean reefs.
In 2019 and 2020, I will travel to Key Largo, Belize, the Bahamas, and Bermuda to collect new samples from the same coral species at the same locations and depths in order to investigate how symbiont communities on entire reefs have shifted throughout the region over the past few decades. I will contextualize my findings by assessing each location’s history of bleaching events and other disturbances/stressors.
I hypothesize that the prevalence and abundance of D. trenchii has increased over time on reefs throughout the Caribbean, largely due to increasingly frequent and severe bleaching events that favor corals hosting this thermotolerant symbiont type.