SCUBA News 286
(ISSN 1476-8011)
May 2024

Welcome to SCUBA News. This month I feature the Giant Moray Eel, common around the Indo-Pacific. There is also 20% off my all time favourite liveaboard, the Duyung Baru.

Any questions, reviews or comments to news@scubatravel.co.uk.

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10 Fantastic Liveaboard Deals - Save up to $800

More great liveaboard diving deals, specially selected for us by Divebooker.com, the liveaboard specialists. Including the fabulous Komodo diving on the Duyung Baru, the best dive boat I've ever been on. But hurry, some of these offers need to be booked in May.

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Giant Moray Eel, large but only dangerous when provoked

Our Creature of the Month today is the the Giant Moray Eel, Gymnothorax javanicus

The largest of the moray eels, growing up to 3 m and the biggest encountered reaching a weight of 30 kg. Common throughout the Indo-Pacific, including the Red Sea.

Are Giant Morays Dangerous?

Although large, they are not normally dangerous to divers. But they are powerful fish with sharp teeth that can inflict serious wounds if provoked.

The famous Marine biologist John E Randall, writing in Australian Natural History recounts.

"The man was spearing a large moray eel for the Marine Toxins Program of the Hawaii Institute of Marine Biology. He followed a policy of spearing an eel and then returning to the boat for about 15 minutes...One good-sized eel was apparently little affected, for it extricated itself from the spear and bit the man in the shoulder.

Can you eat them?

No! They cause ciguatera fish poisoning. Ciguatoxin occurs in dinoflagellites, small organisms which stick to coral and algae. These are consumed by herbivorous fish. The fish in turn are eaten by larger fish and the toxin becomes more and more concentrated up the food chain until it reaches the giant moray eel. Once thought to be confined to the South Pacific and Caribbean, the toxin was recently isolated in the Red Sea and the Atlantic Ocean.

Symptoms of ciguatera toxicity include nausea, vomiting, diarrhea, headaches, muscle aches, numbness, vertigo, metallic taste in the mouth, blurred vision and hallucinations. Severe ciguatera toxicity can cause a feeling of a burning sensation on coming in contact with a cold object. Signs and symptoms can last from weeks to year and a relapse may be triggered by consuming alcohol, nuts, seeds, fish, chicken or eggs.

Co-operation between Giant Morays and other fish

The eel is being cleaned by a Bluestripe Cleaner wrasse (Labroides dimidiatus). It is eating parasites and dead tissue off the eel's skin. This keeps the eel's skin healthy whilst providing a meal for the wrasse. It's helpful cleaning duties give it protection from being eaten by the larger fish. An example of mutualism.

Giant morays also hunt with grouper. The grouper signals to the moray eel to start a joint search for prey, and recruits the eel to a prey hiding places. This works for both fish as they have complementary hunting skills

Normally grouper hunt during the day and giant morays during the night. Grouper hunt in midwater, so prey fish hide in crevices in the coral. Morays, though, squeeze through holes in the reef to corner their prey, which they locate with their excellent sense of smell. Consequently fish swim into open water to avoid them. When the grouper and the moray work together though, they are very difficult to evade.

A hungry grouper will seek out a giant moray and hover in front of it, shaking its head. The moray joins it and the hunt begins.

This behaviour lets the grouper catch five times as many fish as on its own. The moray caught even more fish than the grouper.

Lifestyle of Giant Morays

Morays undergo a sex change during growth, changing from male to female.

They feed primarily on fish, occasionally on crustaceans and octopus. You may see giant morays rhythmically opening and closing their mouths. They do this to maintain a respiratory current past the gills.

Giant moray eels are fascinating creatures with a complex social life and surprising hunting strategies. While their large size might seem intimidating, they generally pose no threat to scuba divers as long as proper respect is maintained. These underwater residents play an important role in the reef ecosystem, and understanding their behaviour helps us appreciate the delicate balance of life within the coral world.

References

Traylor J, Singhal M. Ciguatera Toxicity. [Updated 2023 Jun 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan.
Randall, J.E. 1969. How Dangerous is the Moray Eel? Australian Natural History. June 1969: 177-182.
Bshary R, et al. Interspecific communicative and coordinated hunting between groupers and giant moray eels in the Red Sea. PLoS Biol. 2006 Dec;4(12):e431.

Diving news from around the World

	The best place to dive in June? June is a great month for seeing ocean giants.
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	Stony coral tissue loss disease is shifting the ecological balance of Caribbean reefs Drastic change in the region's population of corals will disrupt the delicate balance of the ecosystem and threaten marine biodiversity and coastal economies.
	Fish deaths in England's rivers rise tenfold in four years More than 216,000 fish died in 2022-2023, when England recorded a 54% increase in sewage spills
	A rise in sea urchins and related damage to kelp forests impacts grey whales and their food When urchin numbers rise, the spiky creatures can devour kelp forests that are a critical habitat for zooplankton which are the primary prey of many marine animals, including grey whales.
	After hundreds of years, study confirms Bermuda now home to Cownose Rays Using citizen science, photographs, on-water observations and genetic data, new evidence that the Atlantic cownose ray (Rhinoptera bonasus) has recently made a home in Bermuda.
	Rapid Oyster Reef Restoration Gives Hope for Repairing the Sea Astonishing ecological recovery occurred within two and a half years of the reef being constructed, providing hope for the future of marine ecosystems around the world.
	Why are whales pooing on orcas? Researchers observed orcas fleeing from sperm whale faeces - but was this defensive defecation a tactic or just a coincidence?
	Saudi Arabia attempts to buy Red Sea resort in Egypt Saudi Arabia is negotiating to buy the Red Sea resort of Ras Ghamila from Egypt, reports the Middle East Eye.

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Photo credits: Diego Grandi, Tatiana Ivkovich, Steven Redmond, Andrea Izzotti/DepositPhotos, Tim Nicholson, Jill Studholme, Garry Frazer, Albrecht Fischer

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SCUBA News (ISSN 1476-8011)

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