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By Kashmi Ranasinghe 18 December 2019 6 min read

Oceans take up 70% of the Earth's surface. But did you know that 95% of our oceans are unexplored? It's safe to say that the deep blue is so big because it's full of secrets.

That's why it's always exciting when we find something at the beach. There is so much biodiversity down by the sand - from the fauna to the flora, there is always something for you to look at.

But what’s the story behind them? Get your best David Attenborough costume on (beach-appropriate of course), because we’re deep-diving into the world of Aussie ocean critters!

Snail sacs

You've no doubt stumbled upon these clear jelly-looking sacs on the sand at your local beach. You probably thought they were baby jellyfish. You might know them as sausage blubber or shark poo. But they’re not. They’re the egg sacs of snails from the family Naticidae. Some sacs grow to about 5cm in length, reaching up to 10cm. They can even weigh as much as 200g!

The female moon snail lays her eggs at night. She lays the eggs in a single line, embedded in a sand grain matrix (a combination of mucus and sand). There are thousands of little snail eggs in this jelly matrix. The matrix takes on the water and it develops into what we know as this little crescent-shaped goop. Interestingly, the sac grows three-to-five times the size of the snail who laid it. The sac then breaks up in the water after a few days, releasing the larvae. 

If you do find one, don't throw them at your family and friends. Gently place them back into the water!


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Salps are nature's jellybean. This is what a bloom of salps look like.

Another strange jelly-like glob you might find on the beach are salps. Salps are semi-transparent barrel-shaped marine animals that form chains with each other. But salps are not jellyfish, they’re tunicates (a type of zooplankton also known as sea squirts).

They’re fast growers. You won’t have time to pull out the grey-lead and the ruler - they reproduce at a rapid rate. They grow to their full size at 48 hours - about 10 per cent of their body length every hour.

This growth is driven by an insane amount of food. Salps contract their muscles to bring in a huge amount of water to their 'mucus net' (a filtering system inside their bodies), which they'll flush out their rear. Anything that’s small enough to get into their mucus net is eaten. They’ll eat larvae and fish eggs, but they really prefer eating plant plankton (phytoplankton).

However, they play a key role in absorbing carbon dioxide from the sea. The phytoplankton they eat absorbs carbon dioxide from the ocean. So, they could help with oceanic warming as they remove carbon dioxide from the environment simply by eating.

They’re a cute salty snack for most ocean fish species, coral, turtles, molluscs, jellyfish and seabirds. Turns out humans aren't the only ones who love eating gummy lollies! You can find them in huge blooms in and around spring. But they don’t stay around for long - they usually survive between two weeks and three months before they are eaten by mackerel or tuna.


It’s seaweed, right? Wrong.

Seagrass is often mistaken for seaweed when it washes up on shore. But they’re more than a way to bamboozle you on our oceans’ flora. Seagrasses are flowering plants which grow underwater in the ocean. They evolved from land plants and turned into marine grass about 100 million years ago. They also come in a range of different sizes - from the teeny Halophila spp. (a few cm) to the giant Posidonia sinuosa (30-40cm)

They’re an ecosystem engineer, providing many important functions for the environment. They feed and house a whole heap of marine life, as well as purify water, take carbon dioxide out of the water and generate oxygen - they’re the trees of the water. They’ve also evolved to thrive in low nutrient areas, so they’re really sensitive to nutrient increases (like a kid when it comes to vegetables). 

So how can you tell the difference between seaweed and seagrass? They do look super similar. But seagrasses produce flowers, fruits and seeds during their reproductive cycle. 

You can find them all over Australia - pretty much confirming at least someone in every coastal state or territory has confused them for seaweed. 

Blue-ringed octopus

Proof that size doesn’t matter, these guys pack a punch. There are four described species of blue-ringed octopus which span the waters of Japan to Australia. All are identified by their yellowy skin and characteristic blue rings or lines on their body and arms.

But don’t stress too much. Blue-ringed octopuses aren’t aggressive. But their rings aren’t for show, it's a trait to tell predators - and wary beachgoers - to stay away.

Each of the 50-60 rings reflects iridescent blue. Beneath and around each ring, there are darkly pigmented chromatophores (light-reflecting cells) to enhance the ring’s colour. When the octopus is threatened, the muscles around the rings relax, resulting in more of the ring being visible. The simultaneous darkening of the surrounding chromatophores dramatically increases contrast, resulting in the rings appearing to flash.

So what happens if you get bitten? Apply pressure to the wound, immobilise the limb and seek immediate medical assistance. Their venom contains a compound known as tetrodotoxin, which is 1200 times more toxic to humans than cyanide. The venom generally causes numbness, difficulty breathing, nausea, vomiting, paralysis and in the absence of medical care, cessation of breathing and death. Tetrodotoxin is contained in the octopus’ salivary glands and throughout its body tissues. So best stay away if you come across one.

Blue bottle jellyfish

Beautiful, but enough to make you shudder just looking at if you've been stung before.

When the sun’s out, the guns aren’t the only ones coming out. You can expect to see blue bottles making an appearance along the east coast. But blue bottle species are found globally. 

Blue bottle jellyfish are part of a weird group of jellyfish made up of several colony members called zooids. These members generally include individuals which feed, float, reproduce and sting. 

The most common blue bottle you’ll find here in Australia is Physalia utriculus, the Pacific Man-o-war. It’s a small relative of the larger and more venomous Portuguese Man-o’-war (Physalia physalis). Our blue bottles reach about 6cm in length and have one main fishing tentacle that grows up to a metre long. 

So why do blue bottles wash up on shore? It depends on ocean currents and wind direction. Jellyfish are 98 per cent water so they’re highly susceptible to these environmental factors. If you head down to the beach and find a full bloom of jellyfish, it’s best to turn right back around and find another location. But here’s what you should do if you do get stung.

With all of our little ocean friends, it’s better to look and not touch. Stay safe and science-y this summer friends!


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