Litter production by mangroves. II. St Lucia and Richards Bay

Abstract

Litter fall was measured in two mangrove communities at St Lucia and at Richards Bay. At St Lucia one community comprised almost pure Avicennia marina (Forssk.) Vierh. while the other was dominated by Bruguiera gymnorrhiza (L.) Lam. At Richards Bay one community consisted almost entirely of A. marina while the other was dominated by Rhizophora mucronata Lam. Mean litter production by the A. marina community was 2,78 g dry matter m− 2 d− 1 and 2,89 g dry matter m− 2 d− 1 for St Lucia and Richards Bay respectively, while for the B. gymnorrhiza and R. mucronata communities, mean production was 2,00 and 2,66 g dry matter m− 2 d− 1 respectively. Higher litter values were generally obtained during the warmer, wetter months. Mean annual leaf yields comprised 44,1 % of the total litter in the older A. marina community at St Lucia compared with 73,3% in the young, vigorous community at Richards Bay. Reproductive material made an important contribution to litter (mean value 41,1 %) in the former community. In the B. gymnorrhiza and R. mucronata communities the mean contribution of leaves to total litter was 48,8% and 52,3% respectively. In the B. gymnorrhiza community the most variable major component of litter was the propagules. In all communities stem material generally made a small contribution to total litter. From a calculation of the area occupied by mangroves in each estuary it was estimated that total litter production was 1322,7 and 4684,1 t yr− 1 at St Lucia and Richards Bay respectively. It is suggested that this provides a significant input of litter to these systems. Plantafval in twee manglietgemeenskappe by St Lucia sowel as Richardsbaai is gemeet. Die een gemeenskap by St Lucia bestaan hoofsaaklik uit ’n suiwerstand van Avicennia marina (Forssk.) Vierh. terwyl die ander een gedomineer word deur Bruguiera gymnorrhiza (L.) Lam. By Richardsbaai bestaan een gemeenskap hoofsaaklik uit A. marina terwyl die ander oorheers word deur Rhizophora mucronata Lam. Die gemiddelde plantafvalproduksie in die A. marina-gemeenskap was 2,78 g droë materiaal m− 2 dag− 1 en 2,89 g droë materiaal m− 2 dag− 1 vir St Lucia en Richardsbaai respektiewelik, terwyl die gemiddelde produksie vir die B. gymnorrhiza- en R. mucronata-gemeenskappe, 2,00 en 2,669 g droë materiaal m− 2 dag− 1 respektiewelik was. Hoër waardes vir plantafval is gewoonlik in die warmer, vogtige maande verkry. Die gemiddelde jaarlikse blaarafval maak 44,1 % van die totale plantafval in die ouer A. marina-gemeenskap by St Lucia uit in vergelyking met 73,3% in die jong, vinniggroeiende gemeenskap by Richardsbaai. Voortplantingsmateriaal maak ’n belangrike deel van die plantafval (gemiddelde waarde van 41,1%) in eersgenoemde gemeenskap uit. In die B. gymnorrhiza-en R. mucronata-gemeenskappe was die bydrae van blaarafval tot plantafval 48,8% en 52,3% respektiewelik. In die B. gymnorrhiza-gemeenskap het propagule die mees veranderlike hoofkomponent van die plantafval uitgemaak. In al die gemeenskappe het stingelmateriaal ’n baie klein bydra tot die totale plantafval gemaak. ’n Berekening van die area wat deur mangliete in een strandmeer bestaan, het aangetoon dat die totale produksie van plantafval, 1322,7 en 4684,1 jaar− 1 by St Lucia en Richardsbaai respektiewelik was. Dit word aangevoer dat dit ’n aanmerklike bydra tot plantafval in hierdie sisteme lewer.