Red Tide

Written by Georgie Pendell

Gansbaai holds a very special place in my heart as it has one of the most unique marine ecosystems in the world. Gansbaai is rich in biodiversity and we are lucky enough to have a variety of animals including the infamous Great White Shark within a short boat ride away. It is important that these ecosystems are balanced as even something as tiny as microscopic algae – simple plant like organisms that live in the sea can have a huge impact on marine life.

Photograph of the awesome Great White Shark taken in an area called Jouberts Dam, Gansbaai – Photo credit, Georgina Pendell

These microscopic algae are usually important for a healthy marine ecosystem. However, if the concentrations of algae are higher than normal they can create an algal bloom. Certain species of microalgae discolour the water a brown to red colour and therefore are commonly known as red tides. Some red tides are also described as harmful algal blooms (HABs) as they can deplete oxygen and produce toxins that are harmful to marine life, birds and humans. Animals can inhale these toxins through the air or consume them through their food. Red tides are more likely to occur when there are warm ocean surface temperatures, low salinity, high nutrient levels, calm seas, or rain followed by sunny days during the summer (oceanservice.noaa.gov).

Photograph of a red tide event – Photo © NOAA

Florida is currently in a state of emergency as a red tide catastrophe has spread along 130 miles of Southwest Florida’s coastline, making it the worst red tide event they have seen in over 10 years. It has been caused by a huge influx of the microalgae called Karenia brevis that is unique to the Gulf of Mexico. Karenia brevis releases toxins that effect the central nervous system of animals and is fatal to marine life. It is also known to have harmful respiratory and gastrointestinal effects on animals.

Image of Karenia brevis taken under an electron microscope
Photo© University of Maryland, Center for Environmental Science.

This red tide event actually started in October 2017 but has gotten severely worse over the past few weeks. What was some of the most beautiful beaches in Florida are now covered with dead animals. Devastatingly, over 100 tonnes of dead animals have been washed up on the shore of Southwest Florida. As well as thousands of fish, the red tide is responsible for the deaths of at least 97 manatees, 150 sea turtles and may even have caused the death of a 26 foot juvenile whale shark according to the Florida Fish and Wildlife Conservation Commission. Also, in the past week 12 dolphins have been washed up, including a 12 year old male named Speck who was known to researchers in the Sarasota Bay area. The red tide releases vapours that have also caused respiratory irritation in people who live near the beaches.

Photograph of a dead 26 foot long juvenile whale shark that washed up on Sanibel Island, Florida
Photo © Florida Wildlife Conservation Commission

It is thought that climate change and increased nutrient run off from agriculture may have exacerbated the current red tide event. However, a lot more research needs to be done to determine the cause. Scientists at the Mote Marine Laboratory in Sarasota are currently trying to find a way to tackle red tide events. They are currently field testing a process that uses ozone – a disinfection technique to purify red tide sea water. As well as being an ecological disaster the red tide is also having an economic impact through a loss of tourism and fishing in the area.

Photograph of thousands of dead fish by a boat ramp on Bradenton Beach, Florida – Photo © Chris O’Meara

In 2017, the Gansbaai area also suffered a red tide event caused by three microalgae species. Although not as ecologically severe as the current red tide event in Florida, it had an economical impact on the abalone farms in the area. The South African abalone (Haliotis midae) or perlemoen as the locals call it is a type of large ocean dwelling snail. This species is endangered in the wild due to its high demand on the food market so is sustainably farmed along our coast. Unfortunately, during the red tide that started in January 2017 and lasted two months, the abalone farms around our coast lost a significant amount of stock. Divers also reported seeing lots of dead wild abalone and sea urchins that had lost their spines.

The South African abalone (Haliotis midae). Also known as perlemoen, meaning “mother of pearl”
Photo © Two Oceans Aquarium

It is important to remember how fragile these ecosystems are and that even the tiniest life can have a disastrous effect on the whole ecosystem. We are so lucky to have a rich diversity of marine animals right on our door step. If you would like to learn more about Gansbaai’s wildlife including the magnificent Great White Shark then read more on our last blog.

Cage diving with Great White Sharks.
Photograph taken on board White Shark Projects cage diving vessel – Shark Team

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