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Causes of Jellyfish Swarms Revealed

Tuesday February 7, 2012

Causes of Jellyfish Swarms Revealed

The recent spate of jellyfish swarms in the coastal waters around Lanzarote may well have been caused by a rise in the temperature of the sea and the drier weather conditions caused by climate change. Over the last two months, numerous beaches have had to be closed to bathers as a result of hundreds of stinging jellyfish washing up on the shore.

The Department of Fishing at the Cabildo of Lanzarote has just undertaken an in depth study to determine the causes of the plague and has already indicated that the temperature of the sea may be one of the primary causes for the occurrence. The results of their report is being distributed to the seven ayuntamientos on the island so that each municipality can prepare information to be posted by their beaches giving advice to bathers.

Amongst the findings of the study was that the waters around the Canary Islands contain as many as 170 different types of jellyfish, ranging in size from microscopic species to those that measure half a metre across. And those identified as the most dangerous to bathers are the Portuguese man o’war and the species known as ‘aguaviva’ which is the type of jellyfish that has been most in evidence in the last two months.

Although most of the time jellyfish live in open water, at certain times of the year the currents around the islands and the wind bring large numbers of them closer to shore, most commonly in January and February. Normal weather conditions mean that most years there isn’t a high volume of the creatures brought ashore.

What may require further study is why there is such a large presence of jellyfish in the waters around the archipelago at present. Amongst the factors that is likely to influence this are a rise in the temperature of the sea, a higher level of nutrients in the water, the movement of marine currents and lower levels of rainfall.

It has already been noted that historically it is in the drier years that large numbers of jellyfish appear, whilst when there is more rainfall, a coastal front makes it more difficult for the creatures to approach the shoreline. In addition, lower numbers of natural predators such as turtles and large fish may well account for higher than normal numbers of jellyfish.

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