Cultivating Palmaria palmata - Bord Iascaigh Mhara

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Salinity: Most sites around the Irish coastline will experience full salinity and are suitable sites for
Palmaria cultivation. Sites with brackish water, such as estuaries or where other large volumes of
freshwater run into the system from streams or rivers, as well as outflows from wastewater
treatment works or industrial sites must be avoided.
5.2 Materials for longline installation
The set-up of a seaweed farm varies with the demands of the seaweed species, the type of seeded collectors
used and economic considerations. For Palmaria cultivation at sea, a single-header longline structure is currently
used. Figure 5.1 shows a basic but versatile longline construction suitable for the cultivation of a range of
seaweeds. The structure consists of a method of anchorage, connected to a header rope on or near the surface
of the water, which is supported by buoys. The details of the equipment are outlined below, but longlines can
vary slightly between sites and between operators because of different challenges in the deployment, and also in
the amount of resources/materials available. No matter how the longline is constructed, two elements should
remain the same throughout. First, care should be taken over the tensioning of the header rope – this must never
be too slack as entanglement of the line becomes a problem. If it is too tight, however, rubbing can occur, with
the breakup of the line likely, and loss of the harvest. Second, the header rope must always be positioned
approximately approx. 0.5 m below the surface of the water. This is necessary as Palmaria develops and grows
better at this depth than at the surface since light levels are lower here and bleaching is less likely.
Equipment for one 100-m longline
Anchors/mooring blocks: Depending on the current at the site, the bottom substrate and the length of
the longline, the anchor devices can be either concrete anchor stones of suitable size, plough anchors
or other devices such as railway wheels. For a 100-m longline, the anchor stones should weigh at least
0.5 tonne, and preferably close to 1 tonne. Depending on the size, weight and number of anchor
stones, a barge may be required for deployment. Some method of attachment is required on the stone,
e.g. heavy metal ring, or eye.
Heavy link chain: Several metres of galvanised heavy-duty chain are required to connect
anchors/stones to the anchor rope. Chain with at least 16-20 cm links is suggested for use.
Anchor and header ropes: The length of anchor rope which is attached to the chain from the mooring
block or anchor is adjusted so that it is tight at high water without allowing too much slack at low tide.
This must be checked after installation at different states of the tide. A marker buoy is attached to the
end of each anchor rope. The headrope is then installed between the two marker buoys. Durable ropes
such as 3-core polypropylene rope (e.g. 32-mm for mooring, 16-mm for headrope) should be used.