Health Effects and Behavioral Response of Florida Manatees (Trichechus manatus latirostris) to Persistent Algal Bloom and Associated Loss of Seagrass Resources in Brevard County, Florida

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USGS researchers are working with partners to assess the health and foraging behavior of Florida manatees in the northern Indian River Lagoon and Banana River, areas that have experienced declining seagrasses due to an extended phytoplankton bloom. 

USGS works with partners to conduct manatee health assessments

USGS is working with partners to conduct health assessments on manatees in the DeSoto Park canal. Captured manatees are fitted with Argos satellite-linked GPS tags to record their movements and assess habitat use. Field observations of tagged manatees and habitat surveys will show forage preferences. (Public domain.)

The Science Issue and Relevance: Starting in 2011, seagrasses throughout the northern Indian River Lagoon (IRL) began to decline in abundance and extent due to turbidity and low light conditions from an extended phytoplankton bloom. Soon after this decline began, an Unusual Mortality Event (UME) was declared for manatee, dolphin, and some bird populations due to increases in mortality from unidentified causes. Most of the recovered manatee carcasses associated with the UME died acutely with signs of intestinal inflammation, and a change in diet from seagrass to macroalgae has likely led to shifts in microbial community composition.

Scientists with the U.S. Geological Survey’s Sirenia Project and cooperators are assessing the health and foraging behavior of Florida manatees in Brevard County, specifically the northern IRL and Banana River, where the severe loss of primary forage habitat and UME are centered. Goals for this study include investigating the dramatic loss of seagrasses, the subsequent changes in manatee foraging behavior, and any possible connections to the UME. High numbers of manatees (1,000+) use warm water refuges in the area during winter, and the species composition and density of nearby seagrass beds can be used to predict the long-term capacity of the area to support manatees and overall ecosystem health. To better understand these interlinked issues, we are investigating changes in seagrass resources and their spatial extent, as well as the intensity of seagrass use and health of manatees in the area. Defining such relationships among ecological factors and manatee health indices could inform management actions for manatees and other species in the region.

Manatee seagrass bed use in northern Indian River Lagoon and Banana River (Florida)

Manatee use of seagrass beds in the northern Indian River Lagoon and Banana River has changed dramatically since algal blooms began in 2011, following the functional edge of the seagrass beds that have recessed far into the flats (FWC and USGS data). (Public domain.)


Methods for Addressing the Issue: To investigate potential linkages between environmental stressors and manatee health in the area, USGS scientists are conducting health assessments of manatees in Brevard County, Florida, in cooperation with Florida Fish and Wildlife Conservation Commission, University of Florida, SeaWorld Orlando, and the City of Satellite Beach. These assessments allow for body condition to be rated and biomedical samples to be collected. Changes in manatee diet, microbiome, and immune system function will then be examined for their potential relationship to the UME. Gut samples will be analyzed for microbiome profiles to quantify levels of detrimental bacterial strains and perform manatee immune-marker panels to assess pathways stimulated by pathogens, stress, or chronic illness.

Following health assessments, released manatees are monitored with Global Positioning System (GPS) telemetry tags to track manatee movements and behaviors, and to identify foraging, travelling, resting, and other use areas. These data will be used to survey habitat used by tagged manatees to identify seagrass and macroalgal species assemblages in manatee foraging areas. 

In cooperation with the St. Johns River Water Management District, USGS scientists are documenting available submerged aquatic vegetation (SAV) in Brevard County. Physical environmental factors, such as depth, temperature and substrate, are being characterized in the region and in areas associated with manatee use. Through analysis of manatee movement data, scientists are identifying areas that are heavily used, lightly used, or not used by foraging manatees. Transects and monitoring sites will be selected to characterize benthic habitats and SAV across these different use areas, which provide insights on specific foraging areas, resources used, and potential forage carrying capacity for manatees.


Winter Manatee Foraging Behavior and the Decline of Seagrass Beds in the Northern Indian River Lagoon

Seagrass loss in the northern Indian River Lagoon and Banana River has been so extensive that manatees were observed feeding in locations that were so shallow that they were partially exposed. (Public domain)

Future Steps: USGS will continue manatee health and habitat assessments in Brevard County to establish relationships among ecological factors and health indices as environmental conditions change. This project will also compare manatee samples collected from the UME area with other population segments to better understand manatee health and ecosystem requirements. Information gathered from this study will have a direct bearing on future management actions adopted by the U.S. Fish and Wildlife Service and Florida Fish and Wildlife Conservation Commission to enhance recovery of manatees, and will be beneficial in informing decisions regarding conservation actions throughout the manatee’s range in the southeast U.S.