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How geographic distance and depth drive ecological variability and isolation of demersal fish communities in an archipelago system (Cape Verde, Eastern Atlantic Ocean)

2007; Wiley; Volume: 28; Issue: 3 Linguagem: Inglês

10.1111/j.1439-0485.2007.00163.x

1439-0485

Anibal Medina, Jean‐Claude Brêthes, Jean‐Marie Sévigny, Bruno Zakardjian,

Isotope Analysis in Ecology

Abstract Cape Verde is a tropical oceanic ecosystem, highly fragmented and dispersed, with islands physically isolated by distance and depth. To understand how isolation affects the ecological variability in this archipelago, we conducted a research project on the community structure of the 18 commercially most important demersal fishes. An index of ecological distance based on species relative dominance (D i ) is developed from Catch Per Unit Effort, derived from an extensive database of artisanal fisheries. Two ecological measures of distance between islands are calculated: at the species level, ΔD i , and at the community level, ΔD (sum of ΔD i ). A physical isolation factor (I db ) combining distance (d) and bathymetry (b) is proposed. Covariance analysis shows that isolation factor is positively correlated with both ΔD i and ΔD, suggesting that I db can be considered as an ecological isolation factor. The effect of I db varies with season and species. This effect is stronger in summer (May to November), than in winter (December to April), which appears to be more unstable. Species react differently to I db , independently of season. A principal component analysis on the monthly (ΔD i ) for the 12 islands and the 18 species, complemented by an agglomerative hierarchical clustering, shows a geographic pattern of island organization, according to I db . Results indicate that the ecological structure of demersal fish communities of Cape Verde archipelago, both in time and space, can be explained by a geographic isolation factor. The analytical approach used here is promising and could be tested in other archipelago systems.