Above: Bird on Seaweed © Dorset Wildlife Trust
Below: Cuttlebones © J Mead, Sugar Kelp © J Mead, Mermaid's Tresses © J Mead
Cuttlefish are cephalopods, closely related to squid and octopus. Their large body can grow up to 45cm long and around their mouth they have 8 tentacles covered in suckers as well as 2 extendable arms for catching prey.
Mating occurs during the summer after a spectacular mating display where males use chromataphores (ink filled sacks) in their skin to rapidly change their colour to attract a female. Afterwards the female then deposits the eggs in clumps, attaching them to anchored objects such as seaweed or rope on the seabed.
After mating both males and females die as they have used all their energy giving their offspring the best start possible in life. The mantle (soft part of the cuttlefish) is easily broken down but their hard bones can often be found washed up on beaches especially after bad weather. Whilst alive the cuttlefish use their cuttlebone to control their buoyancy, it is filled with hundreds of chambers and by changing the amount of air inside it the cuttlefish can move up and down in the water.
As with plants on land, many types of seaweed begin to die back as summer begins to draw to a close. Some seaweeds are perennial (meaning they live for many years) whereas others are annual (only lasting one year). Annual seaweeds start growing in the spring as the amount of sunlight increases, they then last the whole summer and finally, during stormy weather in the autumn and winter, they get ripped off the rock and washed up on the shore. Perennial seaweeds may also loose fronds in bad weather, which will reduce their growth rate throughout the winter months.
So at this time of year it’s a great time to wander along the beach and see what species were growing just off shore. Some of the more notable species are:
- Japanese Seaweed (Sargassum muticum) - golden in colour, this non-native seaweed can be several metres long and covered with hundreds of tiny air bladders.
- Sugar Kelp (Saccharina latissima) - this long belt like seaweed has a beautiful frilly and crinkly texture.
- Oyster thief (Colpomenia peregrina) - this seaweed is small in size but quite distinctive. It is a hollow sphere 3-7cm across that may be ripped or torn by the time it washes up on the beach.
- Bootlace Weed/Mermaid’s Tresses (Chorda filum) - these are extremely long (up to 8m), unbranching cylindrical tubes. They are covered in short transparent hairs that mean they feel slimy to the touch when out of water.
Migrating birds feeding on the strandline
The seaweed that is left behind by the ebbing tide forms a line along the beach which we call the Strandline. This is an extremely important habitat for both marine and terrestrial wildlife. As the seaweed begins to rot, flies lay their eggs in the seaweed- the flies, eggs and resulting maggots are a valuable source of food for animals such as bats, birds and foxes. A common sighting is Rock Pipits, which are exclusively coastal in their distribution and spend a lot of time feeding on the strandline. At this time of year you will be able to see migrating birds making use of this last chance to feed before crossing the channel and continuing their long journey south. It’s not just seabirds, like terns and gulls that you can see but more inland birds such as Swallows, diving and swooping along the beach.