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Post-Ian nutrients feeding red tide and other algae blooms along SWFL coastline

Posted at 6:39 PM, Nov 03, 2022
and last updated 2022-11-03 18:59:23-04

FORT MYERS, Fla — In the wake of Hurricane Ian, red tide is now blooming along the Southwest Florida Coastline from Sarasota to Collier County. Scientists are blaming the rapid increase in nutrients for feeding this and other algae blooms.

In a report from the Florida Fish and Wildlife Conversation Commission report last Friday, red tide expanded from 3 samples off Sarasota County to 56 samples across 4 counties positive for red tide.

FGCU Professor and member of Florida’s Blue-Green Algae Task Force Doctor Mike Parsons is investigating the current red tide.

“With more red tide showing up off of Collier County, for example, is this part of one bigger bloom coming in,” said Dr. Parsons. “So, we just saw the tip of it showing up between Venice and Sarasota and now the rest of it is starting to move in onshore, or it is probably too early for that to be a second bloom moving in.”

Dr. Parsons is looking at past red tide blooms to understand what might be happening post-Ian. He says if we look back to post Hurricane Irma, we had a small red tide bloom in the Fall with a larger bloom that came during the springtime.

“Similar to what we are seeing with Ian, we did have a red tide starting right after Irma,” said Dr. Parsons. “And it kind of stayed small for a little bit, but it just persisted. Then in the springtime, it really started taking off. It made it through the summer which is atypical.”

Dr. Parsons says it is too early to know if that will happen again. With the expansion of red tide to the south last week, Dr. Parsons says he was a little surprised to see that movement, with ocean current models showing a push more onshore.

“What that tells me, is that maybe there was more of it offshore that was moving inshore, rather than having this move down the coast,” said Dr. Parsons. “In that case, it is a little bit surprising, in that we were just out there on the Hogarth a couple of weeks and collecting water samples 60 miles off of Naples and didn’t see it.”

So far, FWC hasn’t reported any fish kills due to the red tide. Dr. Parsons says they have found a few locations with low oxygen levels from the current red tide, but nowhere near the extent that we saw during the spring post-Irma.

“But as this red tide develops, as soon as we start to see more of those orange and red dots on the maps that means the cell concentrations are getting high enough where the toxin levels will be high enough to kill the fish,” said Dr. Parsons. “So that is a big concern and something we don’t want to see.”

Dr. Parsons says there are other algae blooms that are feeding on Ian’s nutrients right now as well. As those die off, red tide can feed on them expanding the existing bloom. That said there is still a lot of freshwater runoff causing a barrier between those blooms and the existing red tide

“There is still that question of where those blooms are happening in that salinity environment. So is the water too fresh, because when you look at red tide it really needs salinity above 24,” said Dr. Parsons.

“So, it has to be mainly Gulf water and that dilutes a lot of nutrients out from that freshwater discharge, but by the time it mixes if there are a lot of nutrients there or recycled nutrients, it could be a significant source of nutrients for it,” said Dr. Parsons.

Florida Department of Health in Sarasota County on Thursday issued a county alert for elevated red tide levels at several beaches in the county. DOH said that people can still enjoy the beaches during red tides as respiratory irritation and dead fish are not always present. They also advised people with severe or chronic respiratory conditions to avoid red tide areas.

The Florida Fish and Wildlife Conversation Commission will issue an update on the ongoing red tide on Friday.