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Saint Johns River conditions: manatees declining locally, microcystis detected at low toxin levels
Summary
Jacksonville University scientist reported lower manatee counts in August, normal-to-lower salinities after rainfall, and presence of Microcystis blooms with generally low toxin production in the Jacksonville area.
Dr. Jerry Pinto of Jacksonville University reported to the Jacksonville Waterways Commission on Sept. 10 that local manatee sightings and movement are declining as the season changes and that water-quality metrics are generally within expected ranges.
Dr. Pinto said “things are starting to calm down a little bit on the manatee front” and that, as fall begins, “most of the manatees are moving out of the area.” He reported that aerial surveys in August observed 15 manatees in the area.
On water quality, Pinto said salinities at Jacksonville University sampling stations range “7 9 to 13 parts per thousand,” which he described as typical. He reported water temperatures around 83–84 degrees Fahrenheit and higher-than-normal tides: about 3 feet above normal at high tide downtown and about 1 to 1.25 feet above normal at the Buckman area. Pinto said recent rainfall left the month of August roughly a quarter of an inch above normal, and that September data were incomplete at the time of his report.
Regarding algae, Pinto reported a presence of Microcystis — a genus that can include harmful blooms — “throughout pretty much” the stretch from Shands Bridge to Mandarin Point and Doctors Lake, but he said there was “no toxin production really in, Jacksonville area” and only low-level toxin production in Doctors Lake, below harmful thresholds.
On mortality, Pinto said local manatee deaths remained unchanged from the previous month at 14 total in the local area, including one watercraft death. Statewide, he reported 80 manatee watercraft deaths out of 525 total manatee deaths year to date, compared with 69 watercraft deaths and 434 total deaths at the same point last year.
A commissioner asked whether cooler temperatures will reduce algae; Pinto replied, “Yes. That should improve. Generally, high temperature and a lot of rainfall tends to kick up the algae in the system, but the lower temperatures, will help to reduce that growth.”
No formal action was taken on the status report; commissioners thanked Pinto and moved to public comment and other agenda items.
