Award: OCE-1357140

There are about 3 billion tons of microscopic marine plankton that are photosynthetic, harvesting light energy to make food for all other marine creatures while producing about half of the oxygen we breath. These phytoplankton are just like the plants in a garden; they grow best when the environmental conditions are right, and when they have the essential nutrients they need. Those nutrients include major elements like nitrogen and phosphorus, but they also need a variety of trace element "micronutrients" that make their enzymes work (such as manganese, iron, cobalt, copper, nickel, and zinc). In many coastal regions, these essential micronutrients can be delivered from rivers and streams, but when you are far from land these trace elements are delivered with "dust", including mineral dust that blows off our desert areas and urban dust from human activities. Sometimes, the arrival of dust can enhance the growth of harmful microbes, such as triggering harmful algal blooms. We had some circumstantial evidence that the arrival of "Saharan dust" to the Florida Keys (a common phenomenon in the late summer) was responsible for the growth of certain species of Vibrio bacteria, and this might cause harm to the coral reefs. In our project, we wanted to see if we could understand why this might be happening, and what damage it might cause. The best time to find desert dust from the Sahara in southern Florida is in the mid-to-late summer when the trade winds blow dust all the way from northern Africa into the Caribbean. We set up our equipment in a marine laboratory on the Florida Keys in July and August from 2014 through 2016, and we started collecting samples. We collected air samples to measure the dust concentrations. We collected rain samples to measure how much dust the rainfall brought down. We collected seawater samples to measure the nutrient and trace element concentrations and to measure which bacteria and phytoplankton were present. We collected big tanks of sea water so we could add things like nitrate or phosphate or iron to see whether it would trigger a bloom of harmful bacteria. And we collected samples from the coral reef itself to see how healthy it was. We saw a significant increase in Vibrio bacteria within a day of dust arrival. The Vibrio population doubled and persisted for about 24 hr. Vibrio could be detected throughout the water column and in the coral mucus. From culturing experiments, we found that Vibrio alginolyticus, a pathogen for humans and corals, was the dominant species during the dust event, making up about 40% of the community. The next steps for this research are to find ways to measure how much stress the coral reef is feeling from this exposure, and to come up with ways to protect the reef. This should become even more important into the future since we believe that climate change will cause the desert areas in northern Africa to expand, leading to even more desert dust coming into the Caribbean and the Florida Keys. Last Modified: 09/11/2018 Submitted by: William M Landing