In the Zone: The Hidden Patterns on our Shores

Common limpet © Tim Ferrero

Our shorelines are known for being busy and beautiful, but hiding in plain sight are clues to how wildlife copes with these challenging environments.

If you've been for a walk along our shores, you've likely noticed how varied they are. From sand to boulders, flat expanses to steep inclines, these spaces are as diverse as the wildlife that calls them home. Even individual shorelines are highly changeable; in fact they're known as intertidal ('between tides') zones because they transform with the rise and fall of the sea.

Intertidal zones are dogwhelk-eat-dogwhelk worlds* where conditions can be immensely tough. When exposed to the air, organisms risk desiccation (drying out) and experience greater extremes of temperature. Sunlight can cause cell damage, even in species that use photosynthesis. Being out of the water means safety from some predators, but vulnerability to others like coastal birds. Rockpools provide temporary refuges, but grow stagnant if not flooded regularly by the sea.

For species with the right adaptations, however, these watery Wild Wests have much to offer. Within each intertidal zone are distinct areas with their own unique challenges, and their characters are hinted at by the species managing to thrive there. So next time you're on our shores, see if you can spot the patterns hiding in plain sight!

*Just kidding - they prefer snacking on mussels and barnacles...

Make a splash

The splash zone is the area just above where the water reaches at high tide. It's technically its own zone called the supratidal ('above tides'), but can be submerged during especially high spring tides or stormy weather. Constantly sprayed by breaking waves, this space suits species that thrive out of sea water but have a high tolerance for the salt left behind when it evaporates.

Lichens are common residents of the splash zone. These hardy organisms are actually formed of two partners that would otherwise need gentler conditions to survive: a fungus and an alga. The fungus gathers moisture and nutrients from its surroundings, while the alga produces energy through photosynthesis. There are many different species, ranging in colour from white to grey to orange.

Sometimes seen munching on these lichens is the sea bristletail - one of only a few insects found on our shorelines. Only around a centimetre long, they get their name from the fringed bristles on their hind ends, which they can use to jump short distances. While they're naturally nocturnal, you might spot them scurrying off if they're disturbed during the day.

High and dry

The upper shore is the area at the limit of high tide. It's exposed for most of the day, enjoying only short periods under water. Residents must be able to combat desiccation, heat, and plenty of sunlight, as well as collision with breaking waves when the tide is in.

Only a few specialised seaweeds can live this far up the shore. Channelled wrack can survive up to eight days out of water thanks to the eponymous channels along its fronds - in fact it dies if submerged for too long! Spiral wrack, though not quite as hardy, can survive losing 80% of its water content. As it dries, it curls its fronds into spirals to conserve precious moisture.

Chitons, a group of molluscs, are also well adapted for the challenges of the upper shore. They have a powerful muscular foot which they use to clamp down tightly onto rocks - this helps them conserve moisture and stay securely attached in rough weather. Even in hot, dry conditions they can experience 75% water loss and live to tell the tale.

Best of both

The middle shore is a place of extremes, with residents having to be equally comfortable in and out of the water. They face desiccation when the tide is out, and buffeting by wave action when the tide is in, as well as long periods in dramatically different temperatures.

Animals with shells that can trap seawater are ideal candidates, as this ability can be used to both preserve moisture and maintain body temperature. The acorn barnacle clamps four hard plates over its opening, keeping them shut until the tide comes in. The flat periwinkle can also seal its shell, this time using a special plate called an operculum ('little lid').

The common limpet, meanwhile, will return to a favoured spot on a particular rock as low tide approaches. These repeat visits form an indentation called a 'home scar' which matches the limpet's shell exactly, allowing it to better form a tight seal that keeps the elements at bay.

Wet and wild

The lower shore is the last area to be uncovered by the tides. Only exposed for short periods, it's home to wildlife that can't stand a lot of air, heat, or direct sunlight. The easier living conditions result in a greater diversity of species in larger numbers, but also fierce competition.

The beadlet anemone uses special stinging cells called acrorhagi to deter predators and defend its territory; these bright blue beads are the source of its name. The fish known as a shanny, or common blenny, will also see off attackers and rivals - in this case with a bite from its strong, sharp teeth.

Of course, no mention of feisty lower shore animals would be complete without the velvet swimming crab. Whether this species is called the 'devil crab' for its bright red eyes, or for its tendency to dole out nips with its powerful claws, remains a mystery - just be sure to keep your fingers well clear!

Love our marine life?

The wildlife in our seas is truly amazing, and you can help to keep it that way. To learn more about our marine environment check out our project Secrets of the Solent, which includes surveys of the intertidal zone.