Distribution and population dynamics of Porphyra (Bangiales, Rhodophyta) in the southern Western Cape, South Africa

Although Porphyra is commercially farmed in many countries, in South Africa only small harvests of wild populations for sale as nori have been carried out. The discovery that Porphyra improves growth of South African abalone ( Haliotis midae) farmed in land-based tanks has led to increased pressure to harvest wild populations. This paper reports on a survey of the distribu tion and seasonality of Porphyra in the southern Western Cape. Porphyra was present at all sites surveyed, and showed considerable temporal variation. A significant amount of the Porphyra present is in reserves and therefore protected from harvesting. Closer examination of one site revealed seasonal populations of Porphyra that occupied different niches dependent on season . Recruitment peaked in spring and autumn, leading to dense summer and wint er populations. Summer populations generally grew lower in the eulittoral t han winter populations. No pattern in the mortality of larger thalli was de tected, though sporeling mortality was high following recruitment peaks. Al though it seems that most sites in the southern Western Cape are suitable f or harvesting, the taxonomy of the genus in the region urgently needs revis ion if populations are to be appropriately managed.