Porphyra 

Description

At low tide in winter and spring Porphyra spp. are easily recognizable by their dried, black refuse sack, look-alike appearance, stuck flattened against vertical rock faces, piers and slipways. The rose-purple colour of the thin fronds is only apparent under the water when the plant frond unfurls regaining their usual elasticity. Generally it grows up to 20 cm long. In its earlier stages it is green becoming brownish purple, then light chocolate before turning black when it is ready to harvest. Porphyra is a winter crop that flourishes in temperatures between 4-9¡ãC. Like most inter-tidal seaweed¡¯s it can be bleached by strong sun to a light brown colour normally in late spring, while in winter it appears like black plastic. The fronds have no definite shape, they can be narrow or broad, divided by lobes, thin, but always have a double layer of tissue which differentiates them from the single tissue layer of Ulva lactuca (Sea lettuce). Porphyra is attached by a cord of interwoven strands to the rock or shell substrate. The major problem with harvesting Porphyra from the wild is the relatively small amount of naturally occurring plants in an area and the relative low biomass of individual plants.

Distribution

Porphyra umbilicalis growing on mussels

Porphyra umbilicalis like most species of Porphyra is found from the high shore down to the mid-lower shore on rough-surfaced rocks, mussel spat shells, concrete breakwaters and sometimes settled on other seaweed species. There are about 140 species of Porphyra world-wide but only a few species such as Porphyra umbilicalis, Porphyra tenera, Porphyra linearis and Porphyra yezoensis, have served as sea-vegetable foods. In Ireland Porphyra spp.are found all around the coast where suitable substrate is available.

Porphyra dioca looking like flat shiny black plastic 

These quantities are generally insufficient to sustain the type of harvest quantities necessary for a commercially realistic operation. The aquaculture trials aspire to develop the farming and husbandry techniques in order to meet the requirements for the production of large quantities of Porphyra spp. in a controlled cycle, at one site.

Nutritional analysis

Porphyra linearis, a desirable species however, difficult to harvest and to cultivate