EFFECTS OF HARVESTING OF THE NAMIBIAN KELP (LAMINARIA PALLIDA) ON THE RE-GROWTH RATE AND RECRUITMENT

The split-fan kelp (Laminaria pallida) also known as the Namibian Kelp is one of the most important kelp resources along the Namibian coast. Harvested kelp is used mainly as feed supplements for abalone culture as well as sources of alginate for industrial and medical purposes. In this field study, the effect of harvesting kelp by cutting the fronds at various lengths (0, 15, 30, and 40 cm from the stipe for treatment T1, T2, T3 and T4, respectively) was investigated. A total of eighty matured plants were randomly selected and divided into the four treatments, consisting of two replicates each, with the various treatment plants receiving different coloured tags (blue, white, yellow and red, respectively). After cutting, the re-grown portions of the fronds were measured (from cut surfaces) weekly for 8 weeks and relative growth rate (RGR) was determined. Results indicated that among the various treatment groups, significant increase (P < 0.05) in the frond length after the harvesting was observed at the end of the eight-week experimental period. Kelps harvested by cutting 40 cm from the stipe (T4) recorded the highest frond length at the end of the period of investigation. However, during the period in which growth of the frond occurred in all treatments, the weekly mean RGR of frond per day was significantly higher (P < 0.05) in T1, than in the other treatments, while it was least in T4 with values of 3.13 and 1.10 % day-1, respectively at the end of the eight-week growth period. The mean relative growth rates for T2 and T3 were 2.54 and 1.34 % day-1 respectively. Results from this study are important for the management of Laminaria pallida and support the suggestion that non-lethal method of harvesting assures regeneration of kelp. The rapid recovery of kelp fronds in this investigation implies that non-lethal harvesting techniques will lead to sustainable management of the Namibian kelp.