Send nudibranchs: the alien invasion happening in the UAE's waters

The Arabian Gulf and Sea of Oman is home to 300 different varieties of nudibranchs — 10 per cent of the 3,000 species currently known to science

At the sight of their misshapen, oblong bodies, flush in bright streaks of nature’s most lurid colours, some might be convinced that these animals are aliens. And in many cases, they are.

The nudibranch is a jelly-like mollusc that lives in oceans around the world, from the Arctic to more temperate seas. Typically, the largest variety of species are found in shallow, warm-water reefs, but some specimens have been found at depths of 2,500 metres, living in waters too deep even for light to penetrate.

The Arabian Gulf and Sea of Oman are home to a surprisingly large number of these nudibranchs, with records of 300 varieties found in the UAE’s waters – 10 per cent of the 3,000 species currently known to science.

In the past 10 years alone, nudibranchs that were previously believed to be endemic to the shores of Malaysia and Zanzibar have been documented in the coastal waters of the UAE.

Although scientists are still researching how the slugs made their way to the Emirates, it is believed that the UAE’s shipping ports, among the busiest in the world, could be responsible for this alien invasion.

“They are an invasive species. The first thing you need to know is that nudibranchs travel as pelagic eggs. There is a lot of shipping in the UAE so you see that a lot of nudibranchs travel in ballast waters,” said Dragan Petkovic, founder of UAE Branchers – a citizen scientist research group.

The eggs of this hermaphroditic animal could be carried or even attach to shipping containers’ ballast compartments, which are commonly evacuated as they dock or depart from UAE ports. This process could be responsible for the introduction of species from the thousands of kilometres of routes along the UAE’s expansive trade network.

Heiko Seim, a member of the group, has spent much of his time scuba diving with an eye out for what he described as the “butterflies of the sea”.

“We have identified stuff only known in Japan – it’s a long way for the nudies [short for nudibranch]. How they came to our waters is a good question. It’s possible that they are part of the ocean worldwide soup plankton,” he said, referring to ocean currents changing from rising sea temperatures.


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For Mr Petkovic and his collective of scuba divers, this has been a unique chance to document a wide variety of these animals. But not all have been seen before. The UAE Branchers alone have documented 10 species that had previously not been discovered.

With their diversity, it is not hard to convince people that nudibranchs are shell-less relatives of their terrestrial cousins, the slugs.

Almost as if in a display of flamboyance, these marine molluscs strip themselves from their shells at the larval stage and expose their varicoloured soft bodies to the elements.

Despite their jelly-like outer layer, this animal’s defence system is one of nature’s most bizarre.

As they slowly graze on a wide range of limited mobility marine life, like sponges and coral, the nudibranchs use two tentacles to identify what is edible. But unlike other animals, the molluscs have an appetite for the oceans most unpalatable and toxic animals.

Over the past decade, scientists have discovered that nudibranchs are capable of absorbing the toxins of their prey and even use it in their own defence system.

A study in 2009 by Marine Biology (who or what is this?), found that nudibranchs feeding on jellyfish actually used the latter’s highly toxic stinging cells in their own defence.

“These are really one of nature’s most amazing animals, they eat, their digestive system has the ability to transform their own body,” Mr Petkovic said.

But much remains unknown about this bizarre oblong-shaped slug, but the goal of UAE Branchers, a team of scuba divers in the UAE, to contribute to a wider effort of research on these colorful critters.

Heiko Seim believes that perhaps it is the chance of discovering an unknown species that makes these animals so special to some scuba divers.

“All the other macro stuff in our water is more or less known, but on the nudies there is still a chance you can find stuff that hasn’t been recorded.

These colourful creatures will continue to be a pull for scuba divers interested in the smaller animals of the ocean, especially in a sea that is not necessarily known for its visibility.

But the Arabian Gulf is a young sea, and the visibility is a symptom of water that is full of nutrients creating an environment conducive to nourishing life. And, most importantly, it appears to be conducive to the nudibranch.

At any given time, photos taken by UAE Brancher and posted on theirt Facebook page could end up being of a species new to science.

As long as they keep appearing, these divers will continue to keep an eye out.

“I believe there are still two or three thousands more species to discover,” Mr Petkovic said.

Updated: June 17, 2018 04:20 PM


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