Kelp

Kelp Forests

The plants that comprise the kelp forest have to be strong but flexible to survive extreme wave activity. Due to storms kelp can only form forests on rocky surfaces.

To attach themselves they have evolved a holdfast. These structures appear to be roots however they are for anchorage and do not take up nutrients.

Holdfasts have a strong grip, storms will snap the stipes but the stipes mostly hold, instead if the storm is severe enough the plants are uprooted as a whole with their holdfast still connected to their anchorage rock.

Holdfast With Anchorage Stone

The kelp species making up a kelp forest depends on the exposure of the coast. On very exposed coasts, occur murlin Alaria esculenta; while on less exposed coasts furbelow Saccorihiza polyschides, tangle weed Laminaria digitata and cuvie Laminaria hyperborean; while on sheltered coasts sugar kelp Laminaria saccharina.

As for all plants, seaweed requires light to be able to carry out photosynthesis. Before the light reaches the kelp it has to travel through water reducing its “energy”. As with greater depth less light reaches the sea bed, this determines the depth as which a kelp forest can exist. The depth of course will vary depending on the turbidity of the water, the clearer the water the greater the penetration of light.

Light levels not only affect the depth of the forest but the species it is comprised of, as different kelp species have differing minimum light requirements. This leads to a zonation of the kelps, which is nowhere as distinct as with the wracks. The shallowest zone is that of Tangle Laminaria digitata, followed by Cuvie Laminaria hyperborean, and in deeper water Sugar Kelp Laminaria saccharina. On very exposed coasts, Murlin Alaria esculenta will replace Tangle Laminaria digitata.

The kelps forest is an extremely important ecosystem. They are tremendously rich in marine life. The forest is outside the harsh environment of the intertidal zone. The conditions in the kelp forest are conducive to a much larger number of marine species.

Kelp forests form convenient nurseries for fish fry as they offer shelter and food. This provides time for them to reach a larger size before they have to enter the more dangerous open sea, so improving their survival rates. The fry in turn attract predators, larger fish.

The kelps themselves provide shelter. Their holdfasts form an invaluable network of nooks and crannies between their “roots” perfect for small creatures. Freshly washed ashore hollow holdfasts of the furbelow or other kelp species still with their anchorage stone, are worth pulling apart, it is surprising the creatures you can find within.

The kelp plants act as platforms for plants and animals to live on particularly the stipes. The stipes in a forest together create a huge surface area. The stipes provide a good living environment, raising life to better light conditions, are good vantage points for those who depend on food brought in by the currents and are high enough to prevent the life on them from being smothered by silt.

Sponge Growing On Stipe

The kelps are food themselves and are grazed by molluscs. Of particular note is the blue-rayed limpet Helcion pellucidum, this small mollusc eats its way into the stipe eventually weakening the plant sufficiently, for it to break off during a storm.

More important kelps are the “power house” of an important food chain. Not only do they provide food directly, but as they die they decay and provide nutrients for plankton and filter feeders, which in turn are eaten by higher animals, which again are eaten by other predators and so on. Without the kelp forests these areas would be rock with relatively barren open sea above, rather than a rich environment with diverse range of species.

The profile of a kelp forest can be divided into three layers, the canopy, middle and ground.

The canopy is comprised of the fronds, which for the plants' benefit have evolved to absorb as much light as possible. Their strategies have proved effective meaning that the majority of the light is lost at this point, so that the lower layers are in relative shadow.

The middle layer includes the kelp stipe, here seaweeds grow on it that can survive with less light, which are mainly red seaweeds. As well as the plant life there are sponges, squirts, bryozoa and hydra to mention just a few.

At the lowest level the ground, least light reaches. Plant life here is limited just to encrusting red seaweeds. Life here does not depend on photosynthesis but instead feed on the kelp, on nutrients brought in by the currents or those that feed on others. Nevertheless this layer is very rich in life. Little light does mean that younger kelp plants are weakened as they are smothered by the older plants. It is a matter of them surviving until a storm denudes the mature kelp of their fronds so breaking the canopy and letting light in, allowing them to grow.