As I write this we are well into the extended period of lockdown and we are all experiencing a touch of the blues. But let’s not dwell too much on that and look at some fascinating marine animals generally known as ‘the blues’.

‘The blues’ float at the sea surface and because they have no means of propulsion they are at the mercy of sea currents and the wind. PHOTO: Getty Images

The blues, as might be expected from the name, hang out in the deep blue ocean. Or perhaps more accurately, they sail the seven seas. The blues all have some sort of floatation device that allows them to float at the sea surface. And yes, they really are blue, the colour being camouflage against predators spotting them on the surface from above. 

However, they have no means of propulsion, so the blues are all at the mercy of sea currents and the wind. This is why the on-shore winds will cause them to wash out on beaches around the world.

Portuguese Man o’ War or ‘Bluebottle’

Most people are familiar with the bluebottle (Physalia physalis), also known as Portuguese Man o’ War, which often wash out on beaches. PHOTO: Wikimedia

Most people are familiar with the bluebottle, also known as Portuguese Man o’ War (Physalia physalis). People who have experienced their stings may wish they were less familiar with them.

A bluebottle is not just one animal, but a colony of specialised individuals, which all have the same genetic makeup but different functions (like the organs in our bodies). 

One type of animal forms a blue gas-filled float; others are specialised reproductive and feeding animals that hang beneath the float. Yet other individuals form long trailing tentacles with vicious stinging cells. These tentacles are designed to catch and immobilise fish and other prey. They then retract the tentacles to bring the prey closer to the specialist feeding animals.

The best way to treat a sting from a bluebottle is to rinse the wound with vinegar to remove any residual stingers or bits of tentacle left on the skin, and then immerse the wound in hot water – ideally at a temperature of 45° C for 45 minutes. A hot pack will substitute nicely for the hot water. 

This remedy works for jellyfish stings as well. Both toxins are proteins and the hot water denatures the protein (breaks the 3D structure), rendering it inactive. Peeing on the sting will not help, despite what you may have seen on TV programmes such as Survivor or Friends.

Bubble-raft shell

This bubble-raft shell (Velella velella) is also called a ‘by-the-wind-sailor’ because of its translucent triangular vane that acts like a small sail. PHOTO: IFL Science

Another fascinating blue floater is the bubble-raft shell. These beautiful blue snails look fragile, but they’re hardy travellers and fascinating hunters! The violet sea snail (Janthina janthina) is a pale purple gastropod found in tropical and subtropical waters all around the world. It spends its entire life adrift on the ocean surface using a raft made of bubbles. 

It excretes mucous from a gland on its foot, and agitates the water around it to create bubbles that it traps inside the mucous. The bubble-raft is critical to its survival as the snail lacks the ability to swim. If the bubbles become dislodged from the shell, the snail will sink and die. 

Beyond worrying about keeping its bubble-raft intact, life isn’t care-free for the violet sea snail, because it is food for a wide range of predators, including birds, turtles and fish.

Violet snails are protandric hermaphrodites, meaning they are born male and develop into females over time. Fertilisation is internal, but males lack a penis, so there is no direct mating. Instead, the males release their sperm into a case that drifts to a female, where the sperm fertilises the eggs. The eggs develop internally and are born live, with the tiny purple snails immediately able to build their own rafts. 

These baby snails are protected from day one by a great camouflage strategy known as countershading. It works by having the underside of their shell – which sits on the surface of the ocean when they’re floating – be much darker in colour than the top.

By-the-wind-sailor and Sea Swallow

The bubble-raft shell (Janthina janthina) is a beautiful violet sea snail. PHOTO: Project Noah

So what is the advantage of floating at the surface? The bubble-raft shell has evolved this ability in order to feed on other ‘floaters’ such as jellyfish, bluebottles and particularly Velella velella, also called ‘by-the-wind-sailors’.

By-the-wind sailors have a stiff translucent triangular vane that acts like a small sail. Interestingly, the sail runs diagonally across the top of the float, so that the animals sail at a 45-degree angle to the prevailing wind, just like a sailing boat.

Another member of the ‘blues band’ is Glaucus atlanticus, a species of sea slug (Nudibranch), locally known as a ‘sea swallow’. The sea swallow uses its blue coloration to its advantage as it floats on the ocean’s surface. The blue side of the body faces upward to camouflage it against the blue of the sea, while the silver side faces downward to camouflage it against the bright surface of the water.

The Blue Dragon (Glaucus atlanticus), locally known as a ‘sea swallow’, has an even more powerful sting than the bluebottle. PHOTO:

Like other nudibranchs, the sea swallow stores the stinging cells (nematocysts) created by the creatures on which it feeds, including Portuguese man o’ wars. These cells are stored and concentrated, so when it’s touched, the blue dragon can release these stinging cells to pack an even more powerful punch than the man o’ war. That’s some punch.

These beautiful but dangerous sea slugs can be found throughout oceans around the world, from temperate to tropical waters. So if you come across one, it’s best to admire its beautiful blue colours from a distance and not be tempted to touch it.

About the Author

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Whale Coast Conservation passionately lives by its slogan “Caring for your environment”.

Its small staff and volunteers are dedicated to

  • raising community and visitor awareness of the unique, biodiverse natural resources of the Cape Whale Coast region and
  • to projects that convert awareness into practical actions that lead towards living sustainably.

WCC ensures expert representation in public participation processes that contribute to environmental and developmental policies and legislation.  We monitor regional development; and ensure compliance with legislation and guidelines.

WCC increases general public awareness of sustainability through environmental education, citizen-science research projects, community projects and campaigns.

WCC communicates with its audience through exhibitions, signage, technology demonstrations, workshops, talks, film shows, newsletters and articles.

WCC places emphasis on educating future generations through its Youth Environment Programme (YEP).  YEP is offered to 24 schools in its target area with a total of over 10,000 learners.

WCC facilitates schools’ participation in special events such as Earth Day, Walking for Water, Arbor Day and Coastal Clean-ups.

WCC facilitates educator development programmes to improve the capacity of educators to offer informed environmental content in their lessons across all learning streams.

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