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manatee in bed of seagrass

Manatee deaths spike as seagrass disappears

June 08, 2021

Algae blooms decimate seagrass linked to Florida manatee fatalities

Manatees are having a difficult time in Florida. The lumbering underwater mammals have been challenged by boat collisions and habitat degradation, but a food shortage is hastening their continued decline.  So far 749 manatee fatalities have been recorded by the Florida Fish and Wildlife Conservation Commission through May 21, surpassing 637 total deaths last year.  The hardest-hit areas are a few counties on the Atlantic Coast south of Duval County. Since December 1, 2020, over 300 manatees have died in the Indian River Lagoon which has suffered a series of harmful algal blooms, leading to massive losses in seagrass coverage.  So far this year, 15 manatees have died in Jacksonville, according to the FWC.
Manatee diets depend on seagrass but manatees are finding fewer underwater plants. That is due in part to pollution from out of nutrient-rich wastewater spiking blooms of harmful algae. The nutrients in pollution combine with warmer average water temperatures and trigger abundant algae growth.  The shallow coastal areas where seagrasses occur are limited by water clarity because most species require high levels of light. Algae mats block sunshine and the grass beds die.
Pollution from the recent phosphate wastewater being pumped into Tampa Bay out of Piney Point Reservoir can make the problem worse. The average estuary depth of just 12 feet sustains thousands of seagrass bed acres drawing hundreds of manatees to the area. Scientists from the University of South Florida discovered a 15-mile-wide diatom bloom that formed in response to the discharge. The bloom of phytoplankton dissipated over time. Scientists will continue to monitor any impacts to seagrasses and other marine life.
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