COMPOSITION AND BIOLOGICAL IMPLICATIONS OF A NEPHELOID LAYER OVER THE INNER AGULHAS BANK NEAR MOSSEL BAY, SOUTH AFRICA

• Published in: Transactions of the Royal Society of South Africa Vol. 47; no. 2; pp. 187 - 197
• Main Authors: Zoutendyk, P., Duvenage, I. R.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.01.1989
• ISSN: 0035-919X; 2154-0098
• DOI: 10.1080/00359198909520162

Water from the nepheloid layer associated with the mud belts on the inner Agulhas Bank near Mossel Bay contained a concentration of 19,0 mg.l 1 total suspended particulate matter. Particulate organic matter (POM) formed only 7 per cent of this and was 3-4 times less than that of comparable coastal waters. Particle size distribution was skewed to the lower size range with a peak at 30 üm. With the aid of the Shields curve for incipient motion of fine sediment, grain sizes that would be entrained from the bottom by orbital velocities resulting from waves were calculated; such grains will be present over the mud belts for most of the year. Considerable differences in community structure between two reef systems at the same depth were recorded and may be attributed to nepheloid water. Where turbidity was high, macrophyte cover amounted to only 0,3 gC.m −2 compared with 111 gC.m −2 in the absence of nepheloid water. Nepheloid water also affected filter-feeders; Porifera appeared to benefit from the percentage of POM falling into the correct size range, while other groups, e.g. tunicates, appeared to be affected adversely by the high inorganic fraction. Particulate organic carbon (POC) requirements of reef filter feeders of 467 mgC.m −2 ,d −1 appear fulfilled by nepheloid POC of 670 mg POC.m −3 .