A. Phillips et al., HORIZONTAL ZONATION OF EPIPHYTIC ALGAE ASSOCIATED WITH AVICENNIA-MARINA (FORSSK) VIERH PNEUMATOPHORES AT BEACHWOOD MANGROVES NATURE-RESERVE, DURBAN, SOUTH-AFRICA, Botanica marina, 37(6), 1994, pp. 567-576
A sampling technique designed to study the distribution of macroalgae
associated with Avicennia marina (Forssk.) Vierh. pneumatophores was a
pplied. Eighteen species of algae were recorded growing epiphytically
on the pneumatophores. A variety of environmental factors were measure
d simultaneously. Resultant data were subjected to Correspondence Anal
ysis and grouping patterns which influenced the two major axes on the
scatterplot revealed the presence of ecological gradients through the
mangrove swamp. Algal cover was dominated by Bostrychia moritziana (Se
nder) J. Ag., B. radicans (Mont.) Mont. and Caloglossa leprieurii (Mon
t.) J. Ag. Clustering of these species on the scatterplot corresponded
to a salinity gradient through the swamp from isosalinity in the sout
h to hyposalinity towards the north. A second gradient, lateral in inf
luence, corresponding to wetting frequency was apparent from the perma
nent water supply (the creek) outwards to the drier outer pneumatophor
e perimeter. Microcoleus chthonoplastes Thuret ex Gomont and Lyngbya c
onfervoides C. Ag. ex Gomont were the most abundant Cyanophyceae, but
were usually inconspicuous within the mass of Rhodophyceae. Rhizocloni
um implexum (Dillw.) Kuetz. and R. riparium (Roth) Harvey, which were
visually obvious in the field when clustered together in macroscopic c
olonies, were the most abundant members of the Chlorophyceae. Distribu
tion of the blue-green and green algae was similar to that of the red
algae, although they tended to be more apparent in the drier areas as
the red algae became less dominant. Salinity, tidal inundation and the
related wetting frequency appeared to be the main environmental facto
rs governing horizontal zonation of epiphytic algae associated with ma
ngroves in this estuarine ecosystem.