Scottish Kelp Plants
Five kelp species are found in the Moray Firth. They each have a distinctive appearance, and they can also be distinguished by the situations in which they grow, defined by depth and range of exposure to wave action.
Oarweed (Laminaria digitata) is the kelp most likely to be seen by the casual observer. It grows at low-tide level on most open coast and rocky shores, where it forms the upper fringe of the kelp forest. It can also be found in lower shore rock pools. It has a flexible smooth stipe and a leathery blade, divided into thin straps which spread out like the fingers of a hand. It is tough in texture but smooth to the touch, and lies near flat on the shore when the tide is out. It is designed to move with the waves as they crash on the shore; its flexibility allows it to live and grow in situations where a more rigid plant would be torn off the rock.
On shores which are subject to severe wave action, even Oarweed cannot survive and is replaced by Dabberlocks (Alaria esculenta) as the dominant kelp at low tide level. Dabberlocks is a long, pointed, narrow plant with a short stipe; it is even more flexible than oarweed, and has a thinner frond with a distinctive midrib. On many shores, however, oarweed and dabberlocks are found together, with dabberlocks on wave exposed headlands and at cliff bases, particularly where these are steeply sloping, and oarweed in more sheltered areas. The fronds of dabberlocks are often eroded by the savage battering they take from storms.
Large, individual plants of Cuvie (Laminaria hyperborea) are occasionally visible in some oarweed forests. Cuvie is similar in appearance to oarweed, but can be distinguished by its large size and rough, stiff stipe which stands upright at low tide and is often covered by a profusion of attached red seaweed. Below the oarweed forest, and out of the immediate reach of the waves, cuvie is the most abundant kelp species, and is the dominant component of the extensive kelp forests which surround most of the open coast of Scotland.
Sugar Kelp (Laminaria saccharina) is an opportunist species which can sometimes occur on exposed shores, but which is most commonly encountered in areas sheltered from wave action, such as bays or the inner reaches of sea lochs. Sugar kelp has a long stipe and a long wavy, undivided frond without a midrib. It is found from low tide level to the limit of available light. In most sheltered areas, it adopts a 'cape form', characterised by a wide shapeless wavy frond, sometimes larger than a bath towel, which is attached to the sea bed by a small, weak holdfast.
Furbellows (Saccorhiza polyschides) is less common than the other scottish kelp species, but may be locally abundant. It is found at and below extreme low water, and is more common on sheltered shores than on the open coast. The blade is similar to that of oarweed and cuvie but the plant is distinguished by its frilled shape and bulbous, warty holdfast, which is hollow and often provides a home for small fish and other animals.
After Kelp forests have been hit by winter storms, the adjacent shore is covered by a brown carpet of glistening plants that have been ripped off the sea bed by the force of the waves. All this material eventually rots and enters the marine food web.
Kelps contribute organic material to the food web in other ways. Waves continually erode the tips of kelp blades, releasing flakes of plant matter. Every spring each cuvie plant sheds its blade from the previous year; and enormous input of detritus into the marine ecosystem, when the size of kelp forests is taken into account. In addition to the huge volume of rotting foliage produced by kelp forests, individual plants secrete as much as 40% of their net organic production directly into the sea. The productivity of kelp forests has been compared to the level of productivity found in a wheat field on land.
This huge amount of organic material is utilised by the animals of the kelp forest and, due to the action of waves and currents, by animals in other parts of the sea. Some animals, such as urchins, graze directly on kelp fragments. Bacteria absorb dissolved organic matter and in turn are eaten by filter-feeding invertebrates. Single-celled animals, small crustaceans, worms and molluscs trap minute particles of detritus. These in turn fall prey to larger animals such as fish and starfish.
The production of organic matter by kelp plants provides much of the fuel that drives the machinery of the inshore food web. Without the food source provided by kelp detritus and dissolved organic matter, inshore coastal waters would contain far fewer animals.