Cultivating Palmaria palmata - Bord Iascaigh Mhara

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Nutrient concentrations: Pre-prepared fertiliser usually provides very high concentrations of nutrients
compared to the concentrations found in ambient seawater. The concentrations available from slow-
release fertilisers are less controllable, but they provide a low-maintenance, easy-to-use source of
nutrients. If only N and P are added to the seawater, suitable concentrations for enhancing growth are
0.5 - 1.0 mmoles N L -1 seawater and 0.05 – 0.1 mmoles P L -1 seawater (N:P ratio of 10:1).
If Palmaria culture tanks are integrated into a re-circulating system with a double purpose of supplying
feed for the shellfish (e.g. abalone) and bioremediation, the nutrients present in the wastewater will be
taken up by the algae, thus cleaning the effluent. The major N source here is ammonium.
Nutrient application in a flow-through system: In a flow-through system the easiest way to provide a
continuous supply of nutrient is to use a slow-release fertiliser. This can be prepared by adding a
fertiliser solution or a mixture of crystalline salts to a porous clay vessel, which is tightly closed so that
the nutrients are released through the pores of the pot when submerged in the tank water.
Fertiliser can also be added at intervals by stopping the water-flow for a period, e.g. for 2-6 hours every
day. The algal fronds will rapidly take uo the nutrients during this period, and such “pulse-feeding” using
a high concentration of nutrients is just as effective as continuous application of fertiliser at a lower
concentration. Pulse-feeding may also be appropriate when seawater is supplied to the tanks by
“interval flushing” (see Chapter 8.2, Seawater supply), adding the nutrients just after the seawater has
been exchanged.
In winter, when nutrient levels in seawater are high and the growth rates of Palmaria are limited by low
light and temperatures, application of fertiliser has only a very limited effect.
Potential side effects of fertilisation: Nutrients added to the seawater stimulate not only the growth
of Palmaria but also that of other algae, which may be brought into the tanks either attached to the
fronds of collected Palmaria or through the seawater supply. Fouling algae with especially rapid growth
rates, such as some fine filamentous brown algae and some green algae, may develop quickly under
these conditions. Such species are generally adapted to higher irradiances than Palmaria, so that
reduction of light and/or increase in stocking density can reduce their growth.