The magical world of the rocky shore

The Northumberland coastline has it all when it comes to scenery – long sandy beaches, dramatic rocky shore, soaring cliffs, expanses of mud flats and diverse salt marsh. Being coastal, all habitats change dramatically with the tide, governing how much space is available to enjoy. Wildlife that lives on the coast must adapt to changes in the amount of available space during the day as the tide rises and falls, and none more than those that live on the rocky shore.

So, let’s take a closer look at this particular habitat, and the factors that make it such a special place…

Here in the UK, the tide rises roughly every six and a half hours and takes the same amount of time to go back out again. How high the sea rises and falls depends on the gravitational pull of the sun and the moon. As the tide retreats, a magical world is exposed which is home to some of the UK’s most weird and wonderful creatures. Most have gills and therefore need to be underwater in order to breathe. Therefore when the tide is out, they must adapt to living out of water for long stretches of time. How long this is depends on where they live on the rocky shore – areas are exposed for longer the higher up the shore they are. This creates separate sections on the shore which have different creatures living in them – this is known as Zonation.

Rockpools may be one of the most obvious features of a rocky shore and provide an underwater haven for a vast array of marine life. The ecosystem that exists within a rockpool is extraordinary. Hidden away under rocks or seaweed are snappy crabs, and fish that swim away at the speed of lightening. Hermit crabs scurry across the sand in search of their next meal, and anemones sway their arms about in the water hoping to catch a piece of food drifting past. Taking a closer look at the underside of a boulder you could find sea squirts or sponge carpeting the rock surface. These animals are sessile, in that they do not move around once they are settled on the rock surface, so it’s very important to replace boulders you have moved when exploring the rockpools to ensure they don’t dry up and can still find food.

Common Hermit Crab in a Dog Whelk shell

All rockpool dwellers have adapted special features to keep them safe from predators, as well as safe from the elements when the tide is out. Limpets and periwinkles have hard shells which protects them from potential predators, as well as helping them to trap water inside them allowing them to breathe and keeping them from drying out. Barnacles use a similar technique, although they are more closely related to crabs than they are limpets! One of the rockpool’s most veracious predators is also a firm fan favourite – the starfish! They creep along the ground using their long arms and tubed feet in search of a tasty limpet or mussel to eat and use chemicals to create a hole in their shell and scoop out the insides.

Common Starfish

Competition between animals is fierce on the rocky shore, especially in zones which are exposed by the tide for longer. The best place to be is tucked away safely in a sheltered rockpool, but with many animals having the same idea, fights can break out for the best hidey hole, as well as for food. For sessile creatures, finding a nice patch of suitable bare rock to settle on can be a hard job, which is why you may find sponges and tunicates making the most of a cool damp crevice or overhang to call home.

Breadcrumb Sponge on a rock amongst kelp holdfasts 

One often overlooked feature of the rocky shore is actually one of the most important marine organisms – seaweed! There is more algae in the ocean than there are stars in the sky and it forms the base of the whole ocean food chain, supporting tiny marine animals all the way up to ocean giants such as whale sharks. On the rocky shore, species of seaweed (or algae) also follow zonation patterns, as some are more tolerant of dry, warm conditions than others. Usually only exposed at very low tide, kelp grows in dense forests just below the low tide mark. It is a type of brown seaweed and has long stipes (stems) and fronds. Kelp forests are a secret kingdom bursting with life, and because they are almost always underwater, they provide shelter and food for a high diversity of creatures.

At the extreme opposite – at the highest zone of the shore – green algae dominates as it is most tolerant to long periods of sunlight exposure. BE WARNED! Green seaweed can be extremely slippy, so take extra care if walking on the rocks! Brown seaweed takes over the further down the shore you go, and are a favoured food for grazers such as periwinkles and small crustaceans. Taking a closer look at the algae in the mid zone of the shore, you will see some species which have a pink colouration. These are known as red algae and come in many shapes and sizes. The most obvious is a type of encrusting seaweed which covers underwater patches of bare rock, looking extremely rock-like itself!

Pink encrusting seaweed

The marine creatures that live on the rocky shore must be tough! It’s a very harsh environment with long periods of exposure to sunlight and high temperatures when the tide is out, but also at high tide if the seas are big and powerful wave action is another threat they must face. Animals and algae attached to the rock surface must be strong enough to hold on tight to avoid being washed away, and rockpool dwellers need to watch out for boulders being thrust around by the waves.

Because of the rich diversity of organisms inhabiting the rocky shore, it is an incredibly important feeding ground for our shorebirds. Each bird has evolved to have features to help them find food amongst the boulders and seaweed. In our next instalment, we will take a closer look at the creatures that make up a significant portion of our shorebirds’ diet, and how they have adapted to become the rocky shore experts that they are today!

A big thank you goes to the Berwickshire and Northumberland Marine Nature Partnership for the use of the amazing photos of the Hermit Crab and Common Starfish! Please do have a look at their website for more information about the amazing marine life that calls the Northumberland Coast home – https://www.xbordercurrents.co.uk/