Low macroinvertebrate biomass suggests limited food availability for shorebird communities in intertidal areas of the Bijagós archipelago (Guinea-Bissau)

Abstract

Knowledge of the macrozoobenthic community and its interactions with predators is critical for understanding intertidal ecosystems but this information is still lacking for many tropical sites. We core-sampled three intertidal areas in the Bijagos archipelago, Guinea-Bissau, one of the largest intertidal wetlands in West Africa, to evaluate macroinvertebrate abundance and diversity, investigate ecological variables influencing macroinvertebrate distribution, and estimate food availability for several shorebird species. We found a low macroinvertebrate biomass, which mostly consisted of bivalves and polychaetes. The fiddler crab Afruca tangeri was also among the more abundant species. Both Shannon diversity and rarefied species richness indicate macrozoobenthic communities in the Bijagos have low diversity but there is large variation in species composition among sites. Sediment fine fraction, organic content and distance to the coast were correlated with the abundance of several macroinvertebrate taxa. Harvestable biomass for the shorebird species studied was very low, below the values described for intertidal sites in temperate areas and some other sites in the tropics. Although this fits with low shorebird densities in the Bijagos, it also suggests that wintering shorebird communities must depend on secondary production by macrobenthic invertebrates during the winter, in the same way as has been proposed for other tropical intertidal systems.