One Fish, Two Fish, “Red” Fish, Dead Fish?

Credit: Florida Fish and
Wildlife Research Institute

Libby Carnahan,  
Pinellas County Sea Grant Extension Agent  

We all remember the Gulf of Mexico beaches of 2005 littered with decaying fish. The fish kill was caused by “red tide” and recent reports of a patchy bloom of Florida Red Tide in southwest Florida from southern Pinellas County through Lee County is causing concern. So what is red tide and what are the impacts to us? 

Red tide is the result of a harmful algal bloom (HAB) of a tiny single-celled dinoflagellate algae called Karenia brevis. Red tide in Florida is a natural phenomenon, originating offshore from algae lying dormant as cysts in the sediment. It is unclear what causes the cysts to awaken and multiply. HABs occur under a particular combination of biology, chemistry, and physics.

Many red tides produce toxic chemicals that can affect both marine life and humans. The Florida red tide organism, K. brevis, produces brevetoxins that can affect the central nervous system of fish and other vertebrates, causing these animals to die. Fish can acquire the toxins through direct uptake (planktivorous fish), or by bioaccumulation through the food chain. Often the animals themselves do not exhibit any visible sign of contamination. Predatory fish, birds, marine mammals and humans that eat this fish can become poisoned. Blooms of K. brevis can kill millions of fish and birds in a few days, and blooms can last for weeks.

The red tide toxins can also accumulate in molluscan filter-feeders such as oysters and clams, which can lead to Neurotoxic Shellfish Poisoning in people who consume contaminated shellfish. Red tide also causes respiratory irritation in humans as K. brevis cells release toxins into the air as they are broken down by wave action. For people with severe or chronic respiratory conditions, such as emphysema or asthma, red tide can cause serious illness.

Although the occurrence of a red tide cannot be predicted, scientists can forecast its movement using wind and water current data once a bloom is located. Scientists also monitor the concentration of the red tide organism by collecting water samples routinely and in response to blooms. The information provided by forecasting and monitoring allows citizens to make informed decisions regarding their beach-going activities.

Some precautions that can be taken to avoid disease and/or discomfort due to red tide HABs include:

• Stay away from the water where HAB conditions have been identified or if water is foamy or discolored or contains dead fish. 
• Do not eat, use or collect any fish, crabs, shellfish, other life or items from those waters. 
• Do not let pets swim in or eat fish from those waters. 
• If contact is made with the water, rinse as soon as possible with fresh water. 
• If you suffer respiratory discomfort when near the water, moving a short distance away from the shore may alleviate the symptoms. In more severe cases, stay indoors in air-conditioned rooms as much as possible. 

Red tides can last as little as a few weeks or longer than a year. The duration of a bloom in nearshore Florida waters depends on physical and biological conditions that influence its growth and persistence, including sunlight, nutrients and salinity, as well as the speed and direction of wind and water currents. HABs can have consequences on human health, the environment, local and regional economies, and can impact natural ecological communities directly and indirectly.

For more information on active red tide events, visit the FWC website and access the resources below. http://www.myfwc.com/research/redtide/events/status/ 

References-

Rey, Jorge R. 2008. Red Tides. University of Florida, IFAS, EDIS ENY-851 (IN766), http://edis.ifas.ufl.edu/in766.

Staugler, Betty. 2012. Red Tide 101. University of Florida IFAS/ Charlotte County Extension. EAS-010412-002.

Summer Backyard Pond Problems: Gasping Goldfish!

By Michael Pettay, Horticulturist, University of Florida/IFAS Pinellas County Extension Educator

It’s a cool, misty morning, after one of our famous summer evening thunderstorms. You’ve gone out into the backyard to visit your ornamental pond and you see dead fish, possibly several, when just yesterday they seemed fine. Yikes, what happened? This is what the pond folks call summerkill.

Summerkill is an oxygen depletion event. Most fish prefer an oxygen concentration in the water of about 4 parts per million (ppm), but sometimes, during the heat of late spring and early summer, a layer of oxygen poor water may form at the bottom of the pond. This bottom layer will be cooler, darker, and may smell bad. If the water on the bottom contains less than 2 ppm of dissolved oxygen the fish will try to stay out of it, even if they are a species that normally prefers cooler temperatures (i.e. goldfish, koi). Bacterial decomposition of organic material causes this "bad" water. In the decay process, bacteria consume dissolved oxygen in the water to aid in breaking down plant and animal material, further dropping oxygen levels.

This condition occurs more frequently in deeper ponds, where excess water flows off of the surface layer. The bottom layer slowly accumulates while any overflow comes from the top.

If you happened to be back there during the event you would see the fish swimming with their heads poking out of the water, opening and closing their mouths rapidly, as though they were gasping for breath. This actually does help them to take in some oxygen as it diffuses in from the air, into the surface film of the water. If your pond has sloping sides, the poor things might be perched on their stomachs in the shallows as well. This helps them to conserve oxygen that would normally go to driving the muscles in their tails. From there, they continue to “gasp” heavily, trying to draw in as much oxygen as possible. If this situation is not soon corrected, the fish will begin to die. Larger fish, with their higher oxygen demand, tend to die before smaller ones. Small fish may be able to hold out longer, in those shallow areas where the big ones just can’t fit.

Summerkill begins with overcast skies, hot weather and the return of rainy days. Low water levels, brought on by one of our normal, dry springs contribute to the problem. A heavy rain, flowing into the pond, can cause the top and bottom layers of the water to mix. After mixing, the pond may change color from its normal green to brown. This mixing may happen a day or two following the rain, and the subsequent drop in dissolved oxygen need only occur for a short time to kill fish. It might even happen during the night, so the oxygen concentration could be on its way back up toward normal levels by the time you wander out there.

The best strategy for dealing with this situation is to prevent the buildup of that lower, oxygen poor layer in the first place by keeping the pond water circulating. This can be done by adding a submerged pump, a decorative fountain or an actual filter. If you discover an oxygen depletion event as it is happening, stirring the surface or adding water with a garden hose may help. This exposes more of the surface to the air above, so that more oxygen diffuses into the pond. Once the oxygen levels begin to rise, fish will stop acting like they just swam a marathon.

If you don’t have them already, adding live plants to the pond is helpful. Plants use sunlight to produce and add dissolved oxygen to the water, a process known as photosynthesis. When there are not enough plants, or when overcast skies keep sunlight from reaching the pond for several days, oxygen levels will drop. These plants can be anything from that suspended, microscopic algae that makes the water appear green, to broad-leafed aquatic plants, rooted in containers and submerged. Conversely, plants whose leaves float on the surface (i.e., water lilies) and other plants whose leaves are exposed to open air, do not contribute as much to the oxygen supply below the water surface.

Rain and wind from thunderstorms may also exacerbate the problems by stirring up bottom sediments, muddying the pond and further blocking the amount of sunlight penetrating the water. Rain can also wash in even more of the decaying organic material that our hungry bacteria in the bottom layer were decomposing to begin with.

You may experience oxygen depletion events for several nights running, until the pond stabilizes again. In this case it might be wise to add water or stir the surface each night until you are no longer greeted by gasping fish in the morning.

http://plants.ifas.ufl.edu/guide/fiskil.html
http://myfwc.com/whatsnew/07/statewide/fishkills.html