Fish Kills Along North Naples Beaches

some victims of the recent fish kill in Naples, FL

In the past week there have been several reports of dead and dying marine life along Collier County beaches from Clam Pass up to Wiggins Pass. The event is thought to the be result of an offshore algal bloom which is a natural event. Results from FWC's Fish and Wildlife Research Institute indicate a mixed bloom of dinoflagellates (Takayama tuberculata, unidentified microphytoflagellates) and diatoms (Proboscia alata and Hemiaulus sp.) at multiple locations. Unlike the dinoflagellate that causes red tide, Karenia brevis, these organisms are not thought to be toxic.

Why does the water appear to be discolored in some areas?
When environmental conditions are "just right" (i.e. the right nutrient levels, currents, winds, water temperature, etc) many types of microscopic organisms called phytoplankton (i.e. dinoflagellates and dioatoms) can quickly proliferate or "bloom" into dense visible patches along the water's surface. These blooms can span several kilometers in some cases. Because of the pigments in these organisms' bodies some blooms can cause the water to appear greenish, brown, black or even reddish orange if the concentrations are high enough. This is where the term "red tide" comes from although many red tide events and other algal blooms result in no changes in water color at all.

What causes the fish to die?

A dead butterfly ray
 along the beach

Most of the species found washed up are bottom-dwelling organisms such as sharks (mostly nurse and bonnethead), rays, skates, toadfish, puffers, cubbyus, barbfish, grouper, spadefish, eels, lobsters, and crabs. Their deaths are thought to be a result of low oxygen levels caused by the bloom. Like all plants, phytoplankton produce oxygen through photosynthesis. During the night when these species are not photosynthesizing they are consuming oxygen. If bloom concentrations are large enough they can remove large quantities of oxygen from the water resulting in low or no oxygen levels.  In addition, as these microorganisms die, more oxygen can removed from the water through the decomposition process, thus adding to the problem.
How long will this last?
While some algal blooms can occur for months, it is impossible to know for sure how long the current bloom will last. Initial indications, however, suggest it is already diminishing. It is likely, though, that marine life will continue to wash up on beaches in the next several days.

Is it safe to swim in these waters?
Generally speaking yes, but this usually depends on people's tolerance to swim around dead fish! The County has not closed any of the beaches are issued any health warnings; remember, the species thought to be responsible for this bloom are not considered toxic. Some people, however, have been known to develop skin and eye irritations when swimming in waters with other types of algal blooms. When in doubt, stay out!

Safety Precaution!

Juvenile sharks affected by the low
oxygen conditions
 swimming in the surf zone

One last note.... many of the affected species are still alive swimming in the surf zone as a result of low oxygen levels forcing them close to shore. Some of these animals can bite and/or sting so be cautious when walking along this area. It is not recommended  to pick them up.