By Victoria Metcalf 10/08/2017


The story has gone viral around the world  – a teenager, Sam Kanizay, dips his legs in the water after soccer practice in Melbourne and emerges bleeding profusely, and in hospital for days, with dramatic headlines of mysterious flesh eating sea creatures to blame. So what’s the likely culprit and do we need to fear getting in the water here?

Graphic warning.

Headlines such as “Strange Sea Creatures Chewed Up This Teen Boy’s Legs“, “Mysterious Flesh-Eating Sea Creature Causes Shocking Injury“, “Melbourne Teenager Bloodied By Swarm Of Meat-Eating Sea Lice“, “Tiny ‘meat-loving’ marine creatures ‘eat’ teenager’s legs at Melbourne beach“, “The Beach Is Canceled After This Teenager Got Attacked by Flesh-Eating Sea Lice“, and “Teen’s feet mangled by carnivorous ‘sea lice’” are enough to strike fear into every beach-goer,  potentially putting many off entering the water. For those that grew up with the movies Jaws or Piranha, it may seem, especially from the media reports, as if those horror movies are coming to life, albeit with a new much smaller terror, and that we perhaps best no longer dip our toes in.

The mystery

16 year old Sam, went for a soak in the waters of Dendy Street Beach last Saturday night. He’d been standing still in the water, aiding his tired legs for about thirty minutes before exiting. When he got out after noticing a “tingling sensation”, reports say that he was covered in sand, so went back in the water to wash it off. Upon returning to his shoes, he noticed that he was bleeding from his legs profusely, from hundreds of tiny pin-prick sized holes. Eventually Sam was taken to hospital, where medics were puzzled by the cause of the bleeding, which they struggled to get to stop. Theories from jellyfish larvae through to stingrays to small fish as the culprits were put forward.

 

Solving the mystery

Enter Sam’s father Jarrod, together with scientists to solve the mystery. Jarrod headed back to the beach the next night with some bait and captured and then filmed swarms of little sea creatures demolishing the bait back at his home.

At first the animals were identified as sea lice. This has since been corrected by Genefor Walker-Smith, a marine biologist from Museums Victoria, who correctly identified the animals on the video as lysianassid amphipods.

What are sea lice?

Sea lice are found all around the world in the oceans. Animals commonly described as sea lice cover two different types of crustaceans. In addition though, sea lice is a term sometimes given to the larval forms of jellyfish that may cause a painful and itchy rash when people in the sea come into contact with them, commonly known as ‘sea bather’s eruption’. Jarrod had bleeding wounds, which is why jellyfish were ruled out as the source of the injury.

Copepods

Some sea lice are small crustaceans belonging to the subclass Copepoda, of which there are over 500 different species. The marine ones feed on the mucus, epidermal tissue (skin) and blood of host marine fish. Once they exit their free swimming planktonic phase they look for and settle on a host fish to begin feeding and they can be aggressive feeders. They can cause many problems in salmon farms, damaging the fish.  I’m very familiar with this type of sea lice in the form of weird looking white ectoparasites located to the outside of Antarctic fish I have caught for research (similar to the one in the photo below).

copepod sea lice
Acanthochondria cornuta, an ectoparasite on flounder in the North Sea. Source: Wikipedia (Hans Hillewaert)

Isopods

Outside of the fishing industry, a different kind of crustacean called isopods are more commonly known as sea lice.  Isopods, of which there are more than 10,000 species, are found in marine, freshwater or terrestrial environments. Some land-based isopods you might be familiar with are woodlouse or slaters. There are over 4,500 marine species. Some marine species are parasitic and feed on blood with piercing and sucking mouthparts and strong claws for holding onto their prey.

My experience with marine isopods largely centres on the giant isopod (Glyptonotus antarcticus) found in Antarctic waters. Nearly the size of a hand, it’s an impressive animal, moving slowly with four antennae, two pairs of jaws, heavily armoured and with many large spiny legs. As intimidating as it looks, it’s a harmless opportunistic scavenger, that can roll into a ball when threatened, and also swim upside down.

Not an ordinary sea flea
Glyptonotus antarcticus, the giant Antarctic isopod. Credit: Victoria Metcalf.

What are sea fleas?

‘Sea fleas’, as shown in the video above are a lysianassid amphipod, a different type of scavenging crustacean to the sea lice (isopods and copepods). Sea fleas are found in both marine and freshwater and there are thousands of species. They tend to be smaller than the sea lice. Some amphipod species live in the water; others (non-lysianassid amphipods) are found in the sand often just below the surface when you scrape some sand back – sandhoppers. Lysianassid amphipods are commonly referred to as sea fleas because they resemble the fleas we might find on our pets in appearance. Most are scavengers and they have strong front legs armed with large claws to hold their food.

My experience with lysianassid amphipods is primarily again from Antarctic waters, when we strung bait down a hole to attract them, in order to take samples for dietary analysis of potential seal food. They were swarming around the bait in their thousands, looking much like the video Jarrod Kanizay took above.

Sea fleas
Antarctic amphipods (sea fleas) surround a Weddell seal, but aren’t attacking it.

Do we need to be concerned?

Firstly, with other users of the same body of water reporting no issues, this seems to be a highly uncommon event, rather than any concerning trend.  Secondly, I am not aware of copepods, isopods, or amphipods spreading disease to humans. The profuse bleeding from Sam’s legs may well have been due to an anticoagulant that the culprits ejected into the blood as they were feeding.

In addition, we can’t yet be certain what caused the bites and the bleeding. Attracting the amphipods with bait the next night, is not the same as definitively identifying that they were responsible for the injuries that Sam sustained. And although they make up the majority of the animals found in the sample Jarrod took, there are also cirolanid isopods (a kind of sea lice) present in the video, as identified by Niel Bruce, a curator at the Museum of Tropical Queensland. These are voracious feeders, capable of stripping carcasses in hours and are also very good swimmers with strong jaws. They will swarm in large numbers to a carcass and are likely to play a significant role in consuming dead and dying animals in the ocean. Bruce says he is aware of one incident where they attacked the face of divers cleaning pylons in the sea.

“It is possible that both groups of small crustaceans attacked the boy, possibly with isopods opening the wound and then both isopods and amphipods feeding at the injury,” says Bruce.

What about here in New Zealand? Although, we also have sea fleas and sea lice here, there is no need for panic. Generally, neither species would typically attack humans in this way. Earlier this year though, there was a report of sea lice attack on a New Plymouth swimmer. A 17 year old claimed she was the victim of a sea lice attack after emerging from the water covered in bites. However, there was no profuse bleeding and no certainty about what had in fact caused the bites.

My best advice is to keep moving, keep away from dead fish carcasses etc in the water, cover up, and swim at day rather than evening or nighttime.

The developmental stage of sea fleas is influenced by light and their behaviour can also be influenced by food availability, but I think it rather unlikely that the attack on Sam was a result of the full moon. One rather intriguing study on an Australian amphipod species (sea flea) suggested climate change could cause a population explosion due to increasing male attractiveness! So it remains to be seen what will happen in general to population numbers of sea flea species as water temperatures continue to rise in the future and what this may mean for beachgoers.


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