Transport, deposition and in situ decay of seagrasses in a tropical mudflat area (Banc D'Arguin, Mauritania)

Abstract

Extensive seagrass beds cover large areas of the mudflats and subtidal parts of the Banc d'Arguin (Mauritania, West Africa). The fate of seagrass biomass (mainly Zostera noltii and Cymodocea nodosa) was investigated during a 1-month expedition to the area (May 1988). Only minor amounts of leaf material were found to be transported by water currents at that time. Subtidal detritus depositions were not found in the area. Though conspicuous accumulations of leaf material were present on some parts of the shore, the amounts washed ashore per flood tide formed only a minor proportion of the daily seagrass production. Thus, transport of leaf litter away from the seagrass beds of the Banc d'Arguin appears insignificant. The major part of senescent leaves probably remains trapped within the seagrass beds and will decompose in situ. The observation that a large part of the particulate carbon present in the surface sediment of seagrass beds was derived from above-ground biomass (55% and 37% in Zostera and Cymodocea beds, respectively), is in agreement with this conclusion. Using the litterbag technique, the rate of leaf decomposition in a seagrass bed was investigated. The time required for 50% weight loss of Zostera and Cymodocea leaf litter in the intertidal zone of the seagrass bed was 158 and 50 days, respectively. In the subtidal zone these figures were 49 and 37 days.