Red tide patches move along Southwest Florida coast Fort Myers News-Press Sporadic reports of fish kills and respiratory irritation point to patches of red tide off the coast of Southwest Florida, aligning with data researchers have collected this week. Dead fish spotted were at Bonita Beach Friday morning and high counts of red tide, caused by the organism Karenia brevis, were reported along Sanibel earlier this week. “It hasn’t looked good for most of the week,” said Rick Bartleson, research scientist with the Sanibel-Captiva Conservation Foundation. “It started out pretty bad on Monday with about 20 million cells per liter, a significant jump from last week so I started increasing sampling.”