Trophic interactions between migratory seabirds, predatory fishes and small pelagics in coastal West Africa

摘要

Competition, predation and facilitation shape community structure. Yet facilitative behaviour is poorly studied, especially in marine ecosystems. We investigated the diet and foraging behaviour of 5 Afro-Palaearctic migratory seabirds during their non-breeding period in West Africa, focussing on their facilitative associations with predatory fishes. We used next-generation sequencing to describe the diet of 5 tern species, employing DNA metabarcoding for the identification of prey from droppings. This is the first time this method has been used for studying the diet of non-breeding migratory seabirds. Our results showed a high diet overlap among all seabirds, mostly due to the dominance of a single prey species, Sardinella maderensis (with a mean frequency of occurrence of 90% in tern diets). The subsurface marine predators identified in association with terns were crevalle jack Caranx hippos and West African Spanish mackerel Scomberomorus tritor, 2 predatory fishes which also rely on Sardinella maderensis as their most frequent prey in the study area, the Bijagos Archipelago. There were marked inter-specific differences in the reliance of terns on subsurface marine predators as facilitators, ranging from completely independent (little tern Sternula albifrons) to near-obligatory (black tern Chlidonias niger). The varied feeding strategies and small-scale spatial segregation may explain the co-existence of the 5 tern species during the non-breeding period, preying mostly on the same clupeids. Declines both in predatory fishes and in Sardinella maderensis and other clupeids are likely to impact the long-distance migrant seabirds studied here, calling for integrated management of fisheries in these coastal ecosystems.