Kelp Forest

Scotlands Living Landscapes

• Foreword
• Introduction
• What is kelp and where is it found?
• Why kelp forests are important in Scottish coastal waters
• Scottish kelp plants
• Light – the critical factor
• Oarweed forests
• Cuvie forests
• Kelp parks
• Beyond the kelp zone
• Kelp productivity
• Uses of Kelp
• Kelp harvesting
• Afterword

Oarweed forests

The oarweed forest marks the junction between land and sea. It is probably one of the most ‘natural’ environments that can be explored by a land dweller, in that, around most of Scotland, it is only rarely affected by human activity. A close look at the world beneath the oarweed blades at low tide reveals a wonderland of delicately textured seaweeds and peculiar creatures, many of which have no counterpart on land.

Walking across the oarweed forest with the tide at its lowest means moving over a slippery, tangled brown mass of kelp blades, with clumps of other seaweed, such as crisp purple carragheen, Mastocarpus stellatus, dotted here and there on the rock. The rock surface itself is splashed in places with flashes of vivid pink. On closer examination, these are seen to be thin, chalky encrustations layered on top of the rock. These seemingly inert patches are in fact red seaweeds, which capture dissolved minerals from sea water to form their own chalky deposits.

Greyish-white encrustations can be seen on many of the kelp blades. These are bryozoans or moss-animals, also known as sea mats. Dull, irregular patches to the naked eye, they appear as regularly patterned mosaics under the microscope, each tile of the mosaic a small chamber containing a tiny animal. Superficially similar are the hydroids or sea-firs (once termed ‘zoophytes’ because they were considered part animal and part plant), which form small branching erect colonies. These have an outer supporting skeleton of horny material, interrupted by openings through which project the microscopic tentacled feeding heads or ‘polyps’ of the living animals.
Sea slugs grazing sea mats on kelp frond

Also present on the kelp blades is the translucent blue-rayed limpet, Helcion pellucidum, with its characteristic lines of vivid blue spots, reminiscent in their intensity of the colours of tropical fish. This limpet migrates down to the oarweed holdfast when it grows older; its shell becomes thicker and the colours fade.

A wide variety of animals live in the small chambers formed between the branching, root-like holdfast. These include fast-moving carnivorous bristle worms, with hooked, pincer-like black jaws, slow-moving cale-worms, and small, tube-dwelling crustaceans. Tiny, five-armed brittle stars and small crabs may also be seen.

Other animals attach to the rock surface between kelp plants and under boulders. Sponges form splurges of colour or tubular vase or purse shapes under overhanging rocks. Flower-like sea anemones are among the most strikingly coloured and patterned creatures of the shore, and orange or white soft corals, composed of many small polyps contained in a tough, rubbery mass, adorn the kelp stipes and rock surfaces in the shallow sublittoral.

Colonial sea squirts grow as thin sheets over rocks and seaweeds; many minute, brightly coloured individuals are arranged in double rows or starry patterns within a jelly-like matrix. Solitary sea squirts are bag-like animals, up to 7cm or 8cm high; two small openings squirt out water in fine jets when the animal is pressed.

Other animals of the oarweed forest live unattached to the rock surface or kelp plants. Close examination of clumps of seaweed may reveal grotesquely armoured sea spiders that feed on hydroids and sea anemones, tearing them apart with hooked pincers. A flash of bright purple or yellow may reveal the presence of a sea slug. Despite their name, these shell-less molluscs are among the most beautiful of marine animals, delicate in form and vividly coloured, although they are often very small.

Starfish glide slowly over the boulders between kelp plants, and an occasional sea urchin can be seen sheltering from the sun in the shade of an oarweed blade. A turned-over boulder may reveal a fast-moving blue and red squat-lobster, or an edible crab with ‘pie crust’ markings. When wading through shallow pools or peering under boulders you may disturb a butterfish, and glimpse its brown and black marbled back as it twists its eel-like body. You may also see the spiky-finned shanny, and the rounded, tadpole-like sea snail, which clings to the underside of rocks by means of a sucker.