Mangrove palynology in recent marine sediments off Cameroon

Abstract

Based on a palynological analysis of marine sediment surface samples, we obtained the modern distribution of pollen and spores on the continental shelf off Cameroon, to examine their dispersal relative to vegetation sources on the adjacent continent. Special attention is paid to the mangrove pollen assemblage, whose dominant type is Rhizophora, which is the most abundant pollen in the overall modern assemblages. This mangrove grows mainly in the river deltas west and east of Mount Cameroon in the northern part of the study area, but patches also are found along smaller estuaries further south. Concentrations and percentages of Rhizophora are highest proximal to mangrove-vegetated coastline and decrease continuously southward, due to (1) the littoral position of the mangrove ecosystem, (2) the prolific pollen production of Rhizophora, and (3) their efficient dispersal by water. The other mangrove types (e.g., Avicennia, Pandanus and Nypa) along the Cameroon caostline are very poorly represented in the offshore pollen assemblage. The spores group was the second most common assemblage component with the highest concentrations and percentages of spores in the axis of the main estuaries. Common features in the distribution patterns of the two dominant taxa Rhizophora and spores, which are very different in terms of production zones, size and morphology, suggest that marine currents are crucial in distributing the palynomorphs in the open sea. The variation of mangrove pollen abundance in cores on the continental shelf can be indicative of palaeogeographical modifications of the environment.