…Mom Continues to Ask About Red Tide

As Catie discussed in last week’s blog post, red tide can put a serious damper on your seafood consumption. But why does red tide seem to be particularly bad some years and less so others?

As a quick refresher, check out last week’s post to learn about the creatures causing red tide and why it’s so harmful in the environment.

Because of the risk to human health, scientists work hard to track water quality conditions and concentrations of red-tide-causing plants in order to better predict when and where harmful algal blooms will occur so that environmental managers may close fisheries when necessary. But every year these red tide events differ in location, timing, and severity.

But what allows a harmful algal bloom to occur?

Remember, these are tiny plants, so they need food! In general, scientists believe that some of the factors contributing to these events include: water temperature, nutrient availability in the water column, and sunlight. The specific conditions necessary for an algal bloom, however, are unique to each region and each species of dinoflagellate.

Recently, scientists at the University of South Florida have been studying red tide in Florida to better understand why some years see worse blooms than others. They have discovered that ocean circulation is actually a defining factor in determining the severity of red tide in Florida. In other words, how the water flows around in the Gulf of Mexico and back out into the Atlantic Ocean plays a critical role in harmful algal bloom severity.

Let’s back up for a minute and walk through this…

The dinoflagellate Karenia brevis is responsible for harmful algal blooms that occur

2005-karenia-brevis
Microscopic view of Karenia brevis. (Source: noaa.gov)

regularly along Florida’s west coast. This single-celled plant is slow growing, so in order for it to cause a harmful algal bloom, a couple of things need to happen:

1) There need to be enough of the tiny plants to reach a critical mass

2) There need to be enough nutrients to feed these plants.

Offshore waters in the Gulf of Mexico provide the perfect environment for K. brevis to have an advantage over others.

But if these plants are blooming offshore, how does the harmful algal bloom reach Florida’s Gulf Coast?

Well, that’s where the research from USF can help us to understand what’s going on. Scientists have long known that current systems increase ocean productivity by introducing both nutrients and plankton. And this system is no different. This study found that the position of Gulf of Mexico Loop Current (see image below) is a deciding factor in the severity of red tide seasons along the west coast of Florida.

gulfcurrentsmap
Map of ocean currents in the Gulf of Mexico. The Gulf Loop Current is at the right, closest to Florida. (Source: NOAA).

Because current systems are fluid, their specific position can change from year to year. In years where the Gulf Loop Current is positioned closer to the shallow-waters  of Florida’s west coast, conditions are not favorable for red-tide-causing plankton. Instead, the current system brings nutrients to coastal waters, which supports the growth of other, faster-growing phytoplankton.

When the current stays further from the continental shelf, fewer new nutrients are added to the system and K. brevis is able to outcompete other plant species, potentially leading to a red tide.

So what does this mean?

By understanding the factors contributing to at red tide, scientists and fishery managers may better predict when, where, and how severe harmful algal blooms will be. And that will help keep those of us who love to eat shellfish safe from red tide toxins.

Understanding the factors contributing to red tide may also help fishermen prepare for, and adapt to shellfish closures.

Let’s take a quick look at the West Coast.

westcoast-habs
Fishermen digging for clams in Washington after the clam fishery reopened. Source: NOAA

The presence of a harmful algal bloom toxin in coastal waters along Washington, Oregon, and California during summer 2015 had devastating effects on a number of shellfish fisheries, including the Dungeness crab fishery. High levels of toxins were found in shellfish and as a result, several fisheries were closed to prevent consumption of contaminated organisms.

This not only impacted these species’ availability to consumers, but also industry revenues. The closure of the razor clam fishery  resulted in an estimated $9.2 million in lost income in Washington alone and also impacted the state’s $84 million Dungeness crab fishery.

Harmful algal blooms can have serious impacts on marine systems as well as coastal communities. Better understanding the dynamics of harmful algal blooms will allow us to better predict when, where, and how bad these events will be. And better prediction of these events can help to keep humans safe and can help the fishing industry and communities prepare and adapt to these blooms.

Innovative research is advancing science across many fields, and especially in the marine sciences. The more we understand about the marine world around us, the better we are able to ensure we keep it healthy while enjoying its bounty!


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