exactly what the name suggests - hold fast to the rock. Seaweeds must produce some amazing adhesives, as quite small holdfasts seem to be sufficient for quite large plants. As the plant grows, its holdfast increases in size by the addition of haptera (finger like extensions) that enclose increasing volumes of space. These spaces become occupied by a variety of animals, both immobile and free swimming. The surface of the holdfast is usually colonised by encrusting filter-feeding animals - over fifty-three species having been identified from an individual holdfast. Kelp plants are composed of
three distinct parts: the blade or lamina, which is supported by the stipe and attached to the substratum by a holdfast. The holdfast resembles a collection of roots, but serves only as an anchor having no nutrient gathering role. The kelp beds around the west coast of Ireland, from where we source our raw material, support a diverse assemblage of invertebrate fauna. Kelp communities are three dimensional in structure, providing a vertical addition to the seabed. This, effectively, increases the surface area and habitat variety, which is differentially exploited by various species. There are several physically distinct parts of the kelp plant. Each supports a different type of community, consisting of possibly thousands of individuals from hundreds of species, physically supported by an individual plant. In particular, the holdfast of kelp species provides a physically complex matrix, ideal for habitation by invertebrate animals. We can now see that a complex eco-system is dependent on seaweed, and we must be mindful of this when we harvest it for our own needs.
Seaweed harvesting in
Ireland currently employs about 400 people in a mostly part-time capacity. It is quite clear, however, that the situation is deteriorating rapidly. Recruits are few as people are less and less willing to engage in such ‘dirty’ work that is so weather and tide dependent.
In general, it will become
increasingly difficult to get the younger people of the western seaboard to collect seaweed. It became obvious that there was a need to urgently examine the
mechanisation of wrack and kelp collection, and seaweed cultivation in general. Mechanisation has been successfully applied in similar situations in a number of other countries, notably Norway and France. In Norway, both Ascophyllum and Laminaria are harvested mechanically, using a range of custom-built devices and boats. It is collected by special designed seaweed trawlers that use a dredge trawl. Traditionally, in France, L.
digitata was harvested by hand and dragged up the coast by horses. However, due to increased demand for this seaweed, more effective methods of kelp harvesting have been developed. To effectively harvest large amounts, a mechanical kelp harvester was developed called “Scoubidou”. The scoubidou is a curved iron hook which is suspended from a hydraulic arm mounted on the boat. It is lowered into the kelp bed and rotated. The blades of the seaweed are wound around the rotating scoubidou and the hydraulic arm pulls them out of the sea.
Short blades are missed by the device and form the next year’s crop. Studies compared the difference between kelp cut using a scoubidou and kelp cut by hand, and found no difference in the recovery time of the harvested populations. This indicates the machinery is leaving enough of the L. digitata behind to allow adequate regeneration of the kelp and production of spores for the next generation. Ascophyllum Nodosum is the primary seaweed used in the production of our seaweed extracts used in amenity, horticultural and agricultural applications. Harvesting techniques for the sustained exploitation of Ascophyllum have been arrived at by observation over a number of years. If a relatively small stump is left behind - about 25cm - this will regenerate to allow another crop in 3, 4 or 5 years, depending on location. The situation is not so simple with kelps, as the whole plants would be harvested. From existing scientific data, we can roughly predict how long regeneration of a bed would take, but we cannot be certain that data from areas would be applicable to Irish situations.
Additionally, we do not know 131 Top: Red Algae
Middle: The small holdfast (about 1cm across) of an Ascophyllum nodosum
Below: Kelp farm with seeded rope wrapped around long line
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