Dulse, Palmaria palmata, is an edible red algae (Rhodophyta) from the upper subtidal of the rocky coasts of the Atlantic from Greenland to Portugal and the North Sea. It is traditionally eaten dried in France, Ireland, Iceland and Canada, and is a source of minerals, vitamins, antioxidants and iodine.
The red alga propagates through spores. In aquaculture asexual reproduction is widespread, with apical tips used for the cultivation of new thalli from the branched thallus. P. palmata can be cultivated in tank culture with air to circulate. In Ireland, the red algae is grown in the sea after sowing of spores on ropes or directly attached to the ropes.
Palmaria palmata is a good candidate for integrated multi-trophic aquaculture (IMTA). In the project Offshore Site Selection (OSS), dulse showed specific growth rates (SGR) of 5-> 6 % d-1, at 16 hours of daylight and constant radiation in co-culture with turbot. The red alga also has a relatively high protein content (up to 21 % of dry matter), which can be increased by growing in integrated aquaculture. P. palmata needs a location with flow velocities of 5-10 cm s-1 for optimal nutrient and CO2 exchange on the surface of the thalli, as well as for the reduction of growth of epiphyts. In strong currents, the thalli of macroalgae become slimmer, which influences the surface:volume ratio and hence affects nutrient uptake and growth. For offshore site selection for growing dulse, wave exposure and flow rates have to be considered in order to achieve optimal growth conditions and to reduce the loss of biomass.
Another limiting factor for the growth of P. palmata in the German Bight is the relatively high water temperature in summer. Dulse does not tolerate temperatures above 19-22 ° C, depending on the sub-population. At 16.5 °C, dulse has a reduced growth rate of only 2.2 % d-1. Optimal growth of P. palmata is achieved at temperatures between 6 ° and 12 °C. Dulse is usually harvested at a length of 30-40 cm.