Production and biomass of the seagrasses Zostera noltii Hornem. and Cymodecea nodosa (Ucria) Aschers. at the Banc d'Arguin (Mauritania, NW Africa): a preliminary approach

Abstract

During May 1988 a study on Zostera noltii Hornem. and Cymodocea nodosa Ucria (Aschers.) was carried out at the Banc d'Arguin, Mauritania. Sediment grain size distributions indicated that all habitats studied were extremely muddy (40–70% silt). For Z. noltii, the aboveground gross relative growth rate varied between 0.02 and 0.04 g g −1 ash-free dry weight day −1, while for C. nodosa it was 0.02 g g −1 ash-free dry weight day −1. Net relative growth rate of both species varied between −0.05 and 0.02 g g −1 ash-free dry weight day −1. Usually a greater loss than increase of leaf biomass in the samples during the period of observation occurred. Both relative growth rate and biomass production per unit area were higher in the low intertidal populations of Z. noltii than in the high intertidal ones. It is suggested that these differences are due to the negative, indirect effects (e.g. dehydration) of the high insolation on the high intertidal populations. Data on morphology, leaf area index, pigment pool and elementary carbon, nitrogen and phosphorus of Z. noltii supported this suggestion.