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The interrelation of climate, mangrove soils and population densities of Anopheles gambiae melas in the Gambia.
Summary only. Chloride content of the soils and groundwater was very high and varied in different parts of the swamp but each profile showed little seasonal variation. The high Cl content of dry season surface waters was not derived from the saline waters of the supply creek but resulted from leaching and redistribution of existing Cl. Most of the soils were very acid when dried and previous colonization by Rhizophora was evident. Land accretion was by replacement of Rhizophora by Avicennia and with it the barren mud flats typical of the Sene-Gambian region and climate, leading eventually to formation of soils similar to those of the uplands. Avicennia was instrumental in forming the highly saline soils associated with it. The sudden decline in salinity caused by the first rains affected the mass hatching of viable eggs and presumably the subsequent mid-rains population decline was due to the effect of decreasing salinity on the microfauna and flora providing larval food. Avicennia was the typical habitat of Anopheles gambiae melas since it provided the best available microclimate for egg survival and adult resting during the dry season although its soils and surface water were at times chemically unfavourable to the eggs.