Behind the wall – Ronaldsay sheepOne of the earliest uses of seaweeds wasfeed for domestic animals. Ronaldsaysheep on the northernmost Orkney Islandstill have a staple diet of seaweed. Thesheep are confined to the foreshore by adry stone wall (the sheep dyke) that runsaround the island.
Non native seaweeds The ever increasing amount of marine traffic is transporting species of seaweed, and other marine species, large distances from where they originated, for example through the dumping of ballast water or as hitchhikers on the hulls of boats. Non native species have also been introduced in more curious ways, such as on oyster shells and seafood packaging, or through deliberate introduction for aquaculture purposes, e.g. pacific oysters.
Some introduced seaweeds, such as Wireweed (Sargassum muticum), have taken hold with dramatically adverse effects on the ecosystems they have arrived in.
Giants!Kelps are the giants of the seaweed world.They are the canopy species of underwaterforests.
In Scotland they can be several metres longwith large feathery fronds held on slenderflexible stalks, but the real kelp giants growon the Pacific Coast of North America, towering 30-50 metres above the seabed.
Hold on tightSeaweeds don't need the root systems we are familiarwith from land plants since nutrients such as nitrogen,phosphorus and trace elements are dissolved in seawater and can be taken up directly across all surfaces of the seaweed. It is only the mechanical features of a root system that are needed by seaweedsand many have holdfasts, which can be as big as footballs, holding them steady onto rocks and other firm structures no matter how turbulent the water is.
Great camouflage Decorator crabs adornthemselves with seaweedsand other materials fromtheir surroundings as ahighly effective form ofcamouflage.
How seaweeds reproduce Seaweeds reproduce by various methods at different stages oftheir life cycle. They can reproduce by fragmentation, where anew seaweed grows from a broken off piece. Or they producespores, which are sex cells, similar to pollen. Seaweeds cleverlyovercome the difficulty of bringing together male and femalespores in a turbulent sea using chemical signals, known aspheromones, released by the female spores, or by mass production of spores, which can turn the sea milky.
Want to know more about Scotland’s seaweeds?To find more about seaweeds in your area, contact the British Phycological
Society (www.brphycsoc.org), or Plantlife Scotland. The website
www.marlin.ac.uk is a treasure trove of seaweed information.
Join Plantlife today to
help us protect Scotland’s
special seaweeds
This booklet was written and produced by Plantlife Scotland, who would like to thank David Thomaswhose Life Series book Seaweeds was an inspiration for this leaflet.
ISBN: 978-1-907141-09-6
Plantlife International – The Wild Plant Conservation Charity is a charitable company limited by guarantee. Registered Charity Number: 1059559 Charity registered in Scotland Number: SC038951 Registered Company Number: 3166339, registered in England.
Reaching for the lightSeaweeds have techniques to reachthe light, which only penetrates a fewmetres in cloudy coastal waters full of plankton and suspended particleswashed in from the land or broughtdown by rivers. Some, like kelps, havelong stipes (‘stems’) supporting up to100 fronds at the top. Buoyancy aids or ‘bladders’ are another technique,lifting fronds of Knotted wrack (Ascophyllum nodosum) and other seaweeds towards the water’s surface’
Buoyancy aids or 'bladders' help seaweeds like this
Used by people For thousands of years seaweeds have been used for their potent healing properties, even supposedly helping to rejuvenate ageing skin. Seaweeds are also effective fertilisers, soil conditioners and a source of livestock feed. They are used in a huge range of products from ice cream to toothpaste, shaving foams, skin products and fabric dyes. Seaweed is heralded as an ultimate superfood, effective against heart disease, rheumatism and water retention while stabilising blood sugar
levels. It is also a superb source of vitamins and minerals. While cows chewed the cud, Scottish dairy farmers chewed the dulse whilst milking them. Carrageen seaweed is nature’s pudding maker – a natural gelatine. A Victorian amateur botanist, Reverend Allan McDonald, recorded over 40 words for seaweeds on the Western Isles from bragaire to gleadhrach to totan.
The beautiful shapes of Coral Weed Corallina officinalis
How long do seaweeds live? Some live for only a matter of weeks but they can growso fast that, despite this short lifespan, they still man-age to grow taller than many mature trees in a singleseason. Many seaweeds grow from the bottom ratherthan the top, so it matters less if the tops are damagedby waves. At the opposite end of the spectrum, brittlecalcareous seaweeds form extensive beds called maerlon the sea floor up to 25 metres below the surface.These extremely slow-growing seaweeds can take upto 800 years to reach a diameter of 30 centimetres.
The rigours of seaweed life The region between the open ocean and the land is a demanding place to live. It is a place of extremes dominatedby tides and waves. Depending upon their position on theshore seaweeds may have to spend hours out of the water,or may be trapped in rock pools where the chemical environment can change suddenly with a downpour of rain.Yet seaweeds have adapted to thrive in places where itwould seem impossible for immobile organisms to live.They survive desiccation and extremes of cold and heat bygrowing in layers so that only the top layer is exposed to theelements. Flexible stems protect some species against battering waves – if they had stiff trunks like trees theywouldn’t survive the turbulent waters.
Clean waters and an incredible variety of coastline, from rocky bays to sheltered tidal lochs, has made Scotland home to an amazingly rich and distinctive seaweed life. Species that are rare or absent from southern Britaincan be common in Scotland, such as the red seaweed Callophyllis cristata.Others can grow exceptionally large, like Dabberlocks, Alaria esculenta, a northern species which can reach 5 metres long.
What are seaweeds? Seaweeds are a group of simple, plant-like marine organisms called algae. Amazinglyvaried, they are the underwater equivalent of trees, shrubs, bushes and lawns. They photosynthesise like plants – that is they make food from carbon dioxide using energyfrom sunlight – but unlike plants growing on land, seaweeds are non-flowering and do not have roots, leafy shoots or sophisticated tissues for transporting water, sugar and nutrients. They are only remotely related to land plants. Generally seaweeds grow attached to surfaces that are bathed by water but can also be free floating.
Crucial to our coastal ecosystems Seaweeds are vital to the ecology of our beaches and seas, providing a rich variety of habitats and refuges from predators for many animals, such as sand hoppers and jellyfish. Lift up any weed that has been lying on a Scottish beach for a few hours and multitudes of sand hoppers will scramble for cover.Seaweeds also provide food for birds, marine snails, sea urchins and fish as well as for larger herbivores such as turtles, and for debris feeders such as crabs and sea cucumbers. Tiny broken off fragments are consumed by filter feeders such as mussels,barnacles and anemones. Some seabirds rest on floating mats of seaweeds or use seaweed as a nesting material.On exposed shores, kelp beds in deeper water protect fragile ecosystems, like sand dunesor coastal machair, from onshore storms.
Stunning shapes Seaweeds come in an amazing variety of shapes. Some have calcified tissues that are hard and brittle, such as Corallina’s red ribbons of segmented boxes that feel like a collection of small stones when you pick them up. Some are flattened fans, or clumps of delicate green, miniature inverted umbrellas known as Mermaid’s Wine Glass. Others are fragile sheets only a few cells thick, whilst some have tubes or sacks which fill up with seawater. Some of the large thick membranous seaweeds are often branched and studded with bladders, whilst others consist of whip-like single blades that resemble ropes as they lie in twisted masses on the shore.
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