Last week, over a half million Ohio residents had no access to freshwater because of a harmful algal bloom (HAB). The toxic cyanobacteria Microcystis was to blame for this particular bloom but HABs are becoming more and more common, in part due to global climate change. Generally, the algae and bacteria that cause HABS need warm temperatures and high nutrient levels (think fertilizer and sewage) in order to reproduce in mass quantities, thus causing a bloom. Climate change is creating warming waters in many parts of the world, including the Great Lakes. Global warming is also creating more intense storms in some parts of the world, which can increase the nutrient runoff.
Many blooms have a toxin associated with them and as that toxin is accumulated in tissues throughout the food chain, it is generally those at the top that are most affected (i.e. manatees, dolphins, barracuda, and humans too). The bloom does not have to be toxic, however, to be harmful. Blooms can produce anoxic conditions in the water column- when algae is covering the surface, sunlight cannot reach the bottom, plants begin to die and decompose which then uses all the oxygen in the water, killing fish, etc. Eventually the massive blooms die as well, removing any additional oxygen from the water column. It is estimated that HABs contribute to an estimated 100 million dollar loss per year in the US. During harmful algal bloom events, there are closures of shellfish beds, lost production in fisheries, and reduction in tourism. Public illness, medical treatment and advisories cost money.
As HABs are becoming more common, they are also becoming more closely monitored. Here at MarineLab, in the past few years, we have partnered with NOAA on various HAB studies including the correlation of toxic phytoplankton at a healthy versus unhealthy reef, NOAA’s ongoing phytoplankton monitoring network program which requires us to monitor our site in Key Largo bimonthly, and the newest project, which is going to be making use of the Upper Keys community in assisting us in monitoring our phytoplankton populations throughout various bodies of water off of the Upper Keys.
Some of the target species we look for in our waters are pictured below.
Chaetoceros. Though not toxic, the whiskers on Chaetoceros can tear up fish gills like saw blades, causing mass fish kills.
Pyrodinium bahamense. Pyrodinium has a saxitoxin which can cause paralytic shellfish poisoning
Gambierdiscus. Gambierdiscus has a ciguatoxin that causes Ciguaterra Fish poisoning (why it is usually recommended not to eat large barracuda)