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

• Published in: Marine ecology (Berlin, West) Vol. 28; no. 3; pp. 404 - 417
• Main Authors: Medina, Anibal, Brêthes, Jean-Claude, Sévigny, Jean-Marie, Zakardjian, Bruno
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.09.2007
• Subjects: Apsilus fuscus; Archipelago system; bathymetry; biogeography; Bodianus scrofa; ecological variability; Epinephelus marginatus; fish community structure; Galeoides decadactylus; geographic distance; isolation factor; Lethrinus atlanticus; Lutjanus agennes; Marine; multivariate analysis; Parapristipoma humile; Pomadusys incisus; Priacanthus arenatus; Pseudopeneus prayensis; relative dominance index; AE, Atlantic; ASE, Atlantic, Cape Verde Is
• ISSN: 0173-9565; 1439-0485
• DOI: 10.1111/j.1439-0485.2007.00163.x

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 (Di) 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, ΔDi, and at the community level, ΔD (sum of ΔDi). A physical isolation factor (Idb) combining distance (d) and bathymetry (b) is proposed. Covariance analysis shows that isolation factor is positively correlated with both ΔDi and ΔD, suggesting that Idb can be considered as an ecological isolation factor. The effect of Idb 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 Idb, independently of season. A principal component analysis on the monthly (ΔDi) for the 12 islands and the 18 species, complemented by an agglomerative hierarchical clustering, shows a geographic pattern of island organization, according to Idb. 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.