The effect of simulated harvesting on biomass and agar of Gelidium abbottiorum R.E. Norris at Reunion Rocks, KwaZulu-Natal, South Africa

Abstract

The effect of simulated harvesting on the biomass and agar content and quality of Gelidium abbottiorum was investigated at Reunion Rocks, KwaZulu-Natal for the period July 1995 to July 1996. There are no previous published records of biomass assessment for seaweeds on the KwaZulu-Natal coast, many of which are of potential economic value. Seaweed samples were collected from Reunion Rocks every three months. This included harvesting the seaweed using two methods, i.e. 'plucking' and shearing'. Biomass was assessed and dry mass values of 255–384 g.m −2 were recorded for the period July 1995 to July 1996. No seasonal differences in biomass were Found for the period July 1995 to July 1996. Standing stocks in commercial beds elsewhere in the world vary from 0.5-1.5 Kg.m 2 fresh mass. The fresh mass of Gelidium abbortiorum was between 0.9–1.4 Kg.m −2 . Therefore, it was concluded that biomass was comparable to that in commercial beds in other areas of the world. Both harvesting methods had the effect of decreasing the biomass over the study period (i.e. from July 1995 to July 1996). It is recommended that 'plucking' be used as a harvesting method if harvesting is to occur at this site. It is suggested that harvesting take place once a year either in spring (September-December) or summer (January-March), Agar was extracted and the quality tested, i.e. gel strength, gelling temperature and melting temperature. Mean agar yields of between 17.5–36.6% were obtained. Gel strength of agar was measured to be between 64.9–291.2.g.cm −2 Gelling temperatures of between 26–34.7 °C were recorded. Melting temperatures of the agar were between 66–77 1 °C. There was no seasonal difference in any of the agar characteristics. It was concluded that agar from this source could be used commercially if blended with superior material from other sources.