Spatial and seasonal variation in macrozoobenthic density, biomass and community composition in a major tropical intertidal area, the Bijagos Archipelago, West-Africa

The coastal intertidal ecosystem of the Bijagos Archipelago, Guinea-Bissau, one of the largest and most important in West Africa, sustains a considerable proportion of the migratory shorebird populations of the East Atlantic Flyway and operates as a nursery area for benthic fish in the region. The macrozoobenthos in these mudflats constitute the main food source for both groups so that spatial and temporal variation in their abundance and community composition is likely to influence the abundance and distribution of fish and birds. In this study we described the spatial and temporal dynamics in the density, biomass, and community composition of macrozoobenthos across six intertidal flats in three islands of the Bijagos Archipelago. Overall, the Bijagos Archipelago was characterised by a highly species-rich macrozoobenthic community, with ca. 88 taxa identified across all sites, reaching a mean density of 1871 +/- 58.3 ind.m(-2) (mean +/- SE) and mean biomass of 5.65 +/- 0.41 g of AFDM.m(-2) (ash-free dry mass per m(2)), values much lower than what was described for nearby intertidal areas, namely the Band d'Arguin, Mauritania. Density and biomass of major macrozoobenthos classes (Bivalvia, Polychaeta, Malacostraca and Gastropoda) differed across sites and months, displaying an overall increase in density towards the final months of the dry season (March and April). Similarly, community composition also differed significantly between sites and throughout the season. The site with most distinct community composition (Adonga) supported low diversity and high abundance of a few bivalve species, whilst other two sites that hosted the most diverse communities, were also the most similar between them (Anrumai and Abu). These spatial and temporal patterns constitute an important baseline to improve knowledge of this intertidal ecosystem and will contribute towards a better understanding of the spatial and temporal distribution patterns of their consumers.

Automated summary

The Bijagos Archipelago in Guinea-Bissau is one of the largest and most important coastal intertidal ecosystems in West Africa, supporting a significant proportion of migratory shorebirds and serving as a nursery area for benthic fish. This study investigated the spatial and temporal dynamics of macrozoobenthos density, biomass, and community composition across six intertidal flats in three islands of the archipelago. Results showed variations in density, biomass, and community composition across sites and months, with higher density observed towards the end of the dry season.