New technologies help identify culprit of the October-November 2013 Florida Bay algal bloom
In October 2013, FWC researchers in Marathon, FL were alerted to discolored water in a reef basin just north of Long Key in Florida Bay. Knowing that blooms caused by picoplankton (the tiniest microscopic algae, <0.0002 centimeters) have coincided with mass sponge mortality events in recent decades, FWC staff rushed to confirm initial bloom reports and collect water samples. Once bloom conditions were verified, the FWC Harmful Algal Bloom (HAB) group joined efforts to identify and quantify the blooming species to support research efforts focused on understanding connections between sponge mortality and water quality in Florida Bay. Sponges play an important role in creating habitat for commercially important animals such as the spiny lobster, Panulirus argus, and also help cycle nutrients and organic matter. Gaining a better understanding of these harmful events is important as we look for ways to better protect sponges and ecosystem health in the Florida Keys and Everglades National Park.
Though picoplankton blooms and associated sponge mortalities have been well documented in Florida Bay, the small size of these bloom organisms makes it challenging to definitively identify the culprit species and to effectively measure changes in abundance over the course of the bloom and in relation to sponge deaths. Traditionally, to identify harmful algae, scientists use microscopy to magnify the organisms. They identify HAB species by examining the size, shape and other characteristics of each cell. Pico-plankton cannot always be identified to the species level using light microscopy because they are too small. For those species that can be identified, counting the organisms is very time consuming. Researchers at FWC incorporated new technologies, including remote sensing, flow cytometry and molecular biology, to identify and quantify the bloom species.
A flow cytometer is a specialized instrument which uses lasers to record the properties of individual cells. Cells are condensed into a thin stream, exposed to 488nm light and then measured for size, shape and color. Cells are also very quickly counted.
Our flow cytometer can count 10,000 cells per second – much quicker than even our most skilled microscopists can count cells. Analysis of the Florida Bay samples revealed that the bloom culprit was a pico cyanobacterium, identified due to its distinct size, shape and color. The cyanobacterium is suspected to be a type of Synechococcus, an organism commonly observed in Florida Bay. Globally, there are more than 20 morphologically similar but genetically distinct types of marine Synechococcus and genetic tools are often used to help with identification in this group. These different types of Synechococcus vary widely in their ability to use nutrients, especially nitrogen, in the marine environment. We are evaluating genetic diversity within bloom samples using DNA sequencing to confirm the identity of the bloom organism and to determine how similar Florida Bay Synechococcusis to Synechococcus from around the world.
To determine the extent of the bloom within and beyond the study region, colleagues at the University of South Florida provided remote sensing data from satellites that detect chlorophyll pigments present in algal cells. Flow cytometry was also used to analyze a time series of field samples and together, these approaches allowed us to describe changes in the picoplankton community over space and time, during and after the bloom. We found that the bloom began in the early fall of 2013 and was primarily centered in the Arsnicker Keys basin north of Layton. Yet, sponge populations suffered substantially across all sampling locations. Additionally, preliminary nutrient data, provided by collaborators at the University of North Carolina-Chapel Hill, relates well to the bloom formation and decline. During peak bloom conditions, nitrogen, a critical phytoplankton nutrient, was very scarce as it was used to fuel the bloom. We are also using DNA fingerprinting to more specifically identify and track key organisms throughout the bloom to better understand how picoplankton communities change relative to nitrogen availability. Ultimately, the information gathered in this study will lead to improved statewide monitoring and management strategies, allowing FWC to better serve and protect Florida’s natural resources.