REU students Carmen Denman and Andrew Kledzik collect water samples in Devil's Hole</p>

REU students Carmen Denman and Andrew Kledzik collect water samples in Devil's Hole

Once a subterranean oceanic cave fed by the Atlantic Ocean, Devil's Hole eventually collapsed and is now a large water-filled sinkhole. Prior to its collapse, Devil's Hole was one of the island's most popular (and oldest!) tourist attractions, serving as a natural aquarium and offering up close views of Bermuda's indigenous marine life. Since the 1950s scientists from around the world have studied a variety of natural marine processes and organisms in Devil's Hole, including carbonate sedimentation, the ecology of boring sponges, and nutrient flux of sediments. Today, Devil’s Hole forms a natural laboratory that scientists are using to understand how marine organisms and sediments are responding to changing physical and chemical seawater conditions.

Each year Devil's Hole undergoes reliable transitions: there is a period of summer stratification that causes lower waters to be seasonally hypoxic (low in oxygen), followed by an overturn during the winter months during which the entire water column returns to typical oxygenated waters. As a result, observations of bacterioplankton in Devil's Hole can demonstrate how the community changes in response to low pH and O2 and increased levels of pCO2. Researchers are particularly interested in bacterioplankton and associated microbial processes because they are believed to be of increased importance as ocean surface warming creates more numerous and more frequent oxygen minimum zones. 

In 2008 the temporal dynamics of bacterioplankton communities were analysed at Devil's Hole, Bermuda during the 6-week annual transition from a strongly stratified water column with suboxic and high-pCO2 bottom waters to a fully mixed and ventilated state. During stratification, the oxygenated surface waters were dominated by the SAR11 clade and the cyanobacterium Synechococcus. In the suboxic bottom waters, Chlorobiales prevailed. These autotrophs use sulfide as a source of electrons for photosynthesis. The abundance of the ammonia-oxidizing Thaumarcheota and the methane producing Euryarcheota were elevated in the suboxic bottom waters. Following convective mixing, the entire water column returned to a community typical of oxygenated waters.

The results of this study have been published in Environmental Microbiology:
Parsons, RJ, Nelson, CE, Demnan, CC, Andersson, AJ, Kledzik, AL, Vergin, K, McNally, SP, Treusch, AH, Carlson, CA, and Giovannon, SJ. (2014) “Marine bacterioplankton community turnover within seasonally hypoxic waters of a sub-tropical sound: Devil¹s Hole, Bermuda.” Environmental Microbiology DOI: 10.1111/1462-2920.12445.

Additional research done at Devil's Hole includes:
Andersson, AJ, Bates NR, and Mackenzie, FT. (2007) "Dissolution of Carbonate Sediments Under Rising pCO2 and Ocean Acidification: Observations from Devil's Hole, Bermuda." Aquatic Geochemistry 13(3): 237-264.

Bates, NR. (2017) "Twenty Years of Marine Carbon Cycle Observations at Devil's Hole Bermuda Provide Insights into Seasonal Hypoxia, Coral Reef Calcification, and Ocean Acidification." Front. Mar. Sci. 14. https://doi.org/10.3389/fmars.2017.00036