Browsing by Author "Mlay, Angela Peter"

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    Ecology of the intertidal zone of selected sandy/muddy shores in the Dar es salaam area
    (University of Dar es Salaam, 2000) Mlay, Angela Peter
    An ecological study was conducted on four shores in the Dar es Salaam area, Kunduchi, Ocean Road, Mjimwema/Kendwa, and Mtoni. The following were determined monthly for a period of one year: particle size, organic matter content, and percent pore water of the substrate; depth of the hydrogen sulphide layer; temperature; salinity; dissolved oxygen concentration in tidal pool water; and density, biomass, and species diversity of benthic macrofauna. In a comparison of the four shores, there was a very significant difference in density (randomized block analysis of variance, F = 22.751, p = 3.609 x 10"8), and biomass (Friedman’s test, Chi-square = 23.900, p = 2.576 x 105). Kunduchi and Ocean Road were similar in all the abiotic factors measured. Both shores had moderate species diversity, but low density and biomass of macrofauna. Besides being under environmental stress due to desiccation, these shores have been exposed to anthropogenic impacts due to excessive movement of boats and people, destructive fishing methods and pollution. In comparison with Kunduchi and Ocean Road, Mjimwema/Kendwa had higher percent pore water, lower organic matter content, thinner hydrogen sulphide layer, but approximately the same dissolved oxygen and salinity levels. Due to the physical contours of the surrounding area, this shore never completely drains and there are relatively few anthropogenic effects. Compared to the other three shores, Mjimwema/Kendwa had the highest biomass and species diversity of macrofauna. It also had high density. At Mtoni, the substrate was determined to be very fine silt, poorly sorted, with very low percent pore water, a high build up of organic matter, and a thick hydrogen suphide layer. Since it is in an estuary, salinity was lower than on the other shores and showed the greatest drop during the rainy season. Compared to the other three shores, Mtoni had the lowest species diversity, lowest biomass, yet highest density. This was due to the high density of two species of very small organisms that seem to be adapted to that stressful environment, i.e., Arcuatula arcuatula and Modiolus sp Mtoni had greater biomass of bivalves, crabs, and polychaetes than on the other shores. Gastropods were found in the greatest biomass at Mjimwema and were not observed at all at Mtoni. Total macrofauna, bivalve, and polychaete biomass were highest during the principal and secondary rainy seasons at Mjimwema/Kendwa. Crabs had greater biomass during the principal rainy season at both Ocean Road and Mjimwema/Kendwa. Kunduchi and Ocean Road showed the greatest biomass on the lower part of the shore, while Mjimwema and Mtoni showed the greatest biomass in the middle of the shore. All shores showed the lowest biomass on the upper part of the shore, which was dominated by crabs. In this zone, Dotilla fenestrata was dominant on all shores along with either Ocypode spp. (Kunduchi, Ocean Road and Mjimwema) or Uca spp. (Mtoni). At Kunduchi and Ocean Road, midshore was dominated by a variety of polychaetes, sipunculids, bivalves and crabs, while holothurians dominated the lower shore. At Mjimwema/Kendwa, midshore was dominated by a variety of gastropods, bivalves, sponges, holothurians, sea urchins, and brittle stars.