SeaGrant Logo

August 14, 2020

This page last modified:
March 21, 2001

Causes of Seagrass Die-Off are Complex

By Tasha Marie Weinstein

Florida Bay Education Project of the

University of Florida/Monroe County Extension Service

Too much salt, too much sulfur, too many nutrients, too much phosphate, too many algae, too much seagrass. yes, that's right, even too much seagrass! These are just a few of the issues making Florida Bay researchers lose sleep at night, because all the "too manys" or maybe just a few, can periodically lead to a seagrass die-off. These die-offs can imperil the health of thousands of marine creatures and the myriad of other creatures that rely on them, including us.

Florida Bay's 850 square miles of backcountry creeks lined with mangroves, lush seagrass meadows and shallow interconnected basins makes it one of the most life-giving bodies of water in the world. In fact, USGS scientist Mike Robblee has counted as many as 141 fish, 70 pink shrimp & over 2,000 other crustaceans in a single square meter. He is quick to add that another square meter may be void of these creatures, but the truth remains that 90% of the products harvested from these waters either began life in the seagrass beds, sought shelter amongst the seagrass, dined on the seagrass or ate something that dined on the seagrass.

So, why bring all of this up now? Florida Bay seagrass is dying right now. Not a huge amount, like the massive die-off that occurred in 1987 but enough of a die-off that scientists are monitoring the situation very carefully. The areas affected are primarily Barnes Key and Twin Key Basin in the southern bay. In that area, the seagrass is very dense, sulfides are high and Labyrinthula, a parasitic slime mold disease, has been found. Researchers are calling the event "the 1987 die-off in miniature." Fortunately this time it does not appear to be spreading. Some good news from the research being conducted - Labyrinthula is not the primary culprit as some scientists once feared, however it may be responsible for perpetuating the die-off.

There are many theories about seagrass die-offs, which is why it is important to understand the entire ecosystem so that sound recommendations can be made for the Everglades Restoration Project. It's one thing to see a small die-off - those have been occurring for probably thousands of years. It is quite another thing, if in restoring the watershed, redirecting freshwater and combinations of nutrients, phosphates and sulfur, we weaken the acres of seagrass living in Florida Bay. In so doing we could leave the plants vulnerable to diseases such as Labyrinthula.

For now, the majority of scientists would agree that Florida Bay is doing well. The die-offs in the past primarily affected the genus Thalassia, commonly known as turtle grass. As a result other grasses, mainly shoal grass, have moved in creating a more diverse hydroscape. This diversity makes Florida Bay less populated with seagrass but results in habitats that support a greater number of organisms. Unfortunately, die-offs are not the only challenge to seagrass health. In 1997, an extremely dense population of sea urchins overgrazed a large area in western Florida Bay - uncommon, but damaging nonetheless, and in the weeks to come you will be reading a lot about the impacts of boat prop damage to seagrass beds.

Only one thing is constant in Florida Bay, change. Today's Florida Bay is a much different bay than in the past, and the bay of tomorrow will be much different than today's.

For more information on this research, contact the Florida Bay Education Project at 305-852-3592. Additional information on a variety of topics is available from the University of Florida/Monroe County Cooperative Extension Service, 5100 College Road, Stock Island or call at 292-4501; fax: 292-4415; email: or visit our web site Our services are free and available to all without regard to race, color, sex, or national origin.

The Florida Bay Education Project is an archived site. For more information go to NOAA's South Florida Ecosystem Education Project at