Seasonal Growth and Agar Contents in Gelidium pristoides (Gelidiales, Rhodophyta) from Port Alfred, South Africa

Abstract

Seasonal growth rates, Standing crops, agar contents and thallus nitrogen levels were recorded in an intertidal population of the agarophyte, G. pristoides, in order to assist with the management of this commercially exploited species. Growth (linear elongation of fronds) was seasonal,, with highest values recorded in late summer (February 1984 = 0.38 mm day" 1 , January 1985 = 0.37 mm day-1 ) and lowest values in late winter (August 1983 = 0.15 mm day" 1 , August 1984 = 0.07 mm day" 1 ). Standing crops were highest (approximately 450 g dry wt m~2) in March 1984 (late summer) and generally throughout the following spring and summer (October 1984 to March 1985, and lowest (approximately 300g dry wt m~2) in winter. The highest agar content (48% of dry wt) was recorded in midsummer, and lowest content (30% of dry wt) in winter. The agar contents were inversely related to thallus nitrogen levels, which varied from 2.3 to 3.5% (of dry wt). The agar contents of distal halves of plant thalli were higher (8 to 15% of dry wt) than from the proximal halves.

Commercial seaweeds in southern Africa: a review of utilization and research

“…No national policy for the conservation and management of natural resources in Transkei has materialized (Dye 1988) and access to seaweed resources is uncontrolled except within declared nature reserves (no accurate information is to date available). Gelidium species are harvested by between 600 and I 000 pickers operating on a casual basis (Carter 1986). In Ciskei, the Division of Nature Conservation of the Department of Agriculture, Forestry and Rural Development is responsible for the administration of the Ciskei Nature Conservation Act of 1987, which precludes unauthorized activities that might disturb "the natural state of the vegetation, the land or any water" (Coleman 1988).…”

“…Gelidium-harvesting in the Eastern Cape is carried out by between 60 and 100 harvesters (almost all women), picking plants by hand and operating in teams of 10-15, each under the control of a supervisor (Carter 1986). The official permit issued to the concession-holder requires that harvesters wear distinctive clothing and carry appropriate authorization, and that a notice explaining harvesting activities be erected temporarily in the vicinity.…”

“…Five commercial companies hold the designated concessions in South Africa and some have access to other sections of the southern African coast. The industry employs about I 000 part-time Gelidium-pickers in Transkei and the Eastern Cape (Carter 1986), and about another 1 000 elsewhere. Total annual income for South Africa (but excluding Namibia and Transkei) is estimated for the late 1980s at US $1,5-2 million.…”

“…Each tuft may consist of up to 40 or more individual plants, with brownishpurple fronds up to 200 mm long and 5 mm wide, and is attached very firmly by a network of coarse filaments to almost any hard surface in the midintertidal zone (Carter 1986). Carter examined the distribution of Gelidium on various hard substrata at Port Alfred in the Eastern Cape and found that a high percentage of plants occur on limpet shells (Patella oculus) as a result of limpet grazing of rock surfaces and of strong attachment of Gelidium rhizoids to the shells.…”

“…Criticism of the practice was raised even in Parliament and it became necessary to provide scientific analyses of the situation. Extensive studies by scientists of the Sea Fisheries Research Institute and others have been carried out on G. pristoides since 1983, and results indicate that harvesting practices have a minimal effect on the environment and that increased yields might result if activities are limited to summer and autumn (Carter 1986, Jarman et al 1988, Robertson 1988.…”