Spanning nearly a quarter of a million kilometres, Canada’s coastlines are home to one of the toughest habitats for any creature to live in: the intertidal zone, a place where the ocean meets the land.
To survive here, creatures have to endure intense changes in their surroundings. They have to go from an underwater environment to practically dry land twice a day. Some areas even face hurricane-force waves every 10 seconds.
In Kingdom of the Tide, a documentary from The Nature of Things, we meet some of the unusual and quirky characters that have adapted to survive in such a harsh environment.
Sea stars have an unusual stomach
Sea stars, relatives of the sea urchin, have an unique way of obtaining and consuming their food. They have to move fast to catch their prey before the tide goes out, leaving them stranded in place. Hundreds of tiny tube feet allow them to move quickly underwater. But those feet are also designed for another purpose: opening the shells of mussels.
Once the sea star has latched on to and pried open a mussel shell, even just a crack, it ejects its stomach from within its body and inserts it into the shell. Once inside, the stomach begins to digest the mussel into a gastric soup. Then, it’s as simple as pulling its stomach, and its liquid lunch, back inside its body.
Being well-endowed is key to barnacles’ breeding success
Barnacles are crustaceans often found in the upper parts of the intertidal zone. By secreting a natural glue, they cling to the rocks — and once they’re attached to something, they’re really stuck. But while this might help them when the tide roars in and out, it leaves them unable to move and seek out potential mates.
Barnacles have an impressive adaptation to get around the problem. They’re hermaphroditic, meaning they have both female and male sexual organs; this means they can reproduce with any of their neighbours.
WATCH: Barnacles seeking out new mates.
They’re also very well-endowed, having the longest penis to body size of any animal in the world. A barnacle’s penis can be up to eight times its body length, says Alyssa Gehman, an intertidal ecologist with the Hakai Institute on Calvert Island, B.C. This feature helps them reach out to nearby barnacles more easily to reproduce.
Limpets have super strong teeth
Limpets are aquatic snails that have an important job in the intertidal zone: keeping algae under control. They graze on algae that grows on the rocks by licking it off with their tongues, which are lined with super strong, spiky teeth.
These teeth are made out of protein and very small fibres of goethite, an iron-based mineral. It’s been found to be the strongest material in the natural world, even beating out spider silk, which is five times stronger than steel!
WATCH: A limpet using its impressive teeth to graze.
The nudibranch has a thrifty defence
Nudibranchs are a type of mollusk that are a part of the sea slug family. While they may not have a shell to protect themselves, that doesn’t mean they’re defenceless. Instead, they get a little help from their diet.
WATCH: An opalescent nudibranch finds a new weapon.
Many nudibranchs love to eat hydroids, an animal related to jellyfish with toxic stinging cells. They swallow these cells and move them through their body, storing them in the spine-like structures on their backs. Then, when these nudibranchs need to defend themselves, they fire away!
Adaptive anemones have toxic tentacles
Like barnacles, anemones are stuck in their places in the intertidal zone. They can’t swim or crawl to find their food, so they can’t be picky eaters. Their crowns of toxic tentacles paralyze any prey that passes by, allowing the anemone to grab them and eat them whole — even spiny sea urchins. What they can’t digest, the anemones simply spit back out the next day.
Aggregating anemone colonies use their tentacles to protect themselves from predators and other encroaching colonies. Warrior anemones are positioned on the perimeter of the colony for protection. They can stretch up to three times their length in order to strike at competing colonies, firing tiny poisonous harpoons from their tentacles.
This fish can breathe air to stay safe during the low tide
This beautiful sea slug has a secret weapon
The intertidal zone keeps serving up new discoveries
The black prickleback can breathe air
For many fish, a receding tide spells disaster — but not for the black prickleback. This fast, eel-like fish can avoid its enemies by staying in the intertidal zone during low tide while its predators are swept away.
WATCH: A prickleback stays safe during the low tide.
But how does it survive the completely foreign habitat of the exposed intertidal zone? It can breathe air through its skin! The prickleback can stay out of water for up to 23 hours because of a slimy mucus coating that keeps it moist.
Watch Kingdom of the Tide on The Nature of Things.