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In this study, we analysed the factors explaining the distribution and betadiversity of mesozooplankton species in shelf and coastal areas in the Bay of Biscay. Nonparametric multiplicative regression models showed that for 35% of the 26 species analysed, the geographical position was the main factor explaining distribution. The variation partitioning results of the betadiversity analysis indicate that niche adaptation (12–25%) and dispersal limitation (14–15%) influence the distribution of mesozooplankton species equally. Therefore, most of the variance (57–66%) remains unexplained suggesting there are other explaining factors not controlled or that a part of the variability is purely stochastic. A log-normal distribution fitted the species rank-abundance better than Hubbell's neutral model, which also indicates that the mesozooplankton distribution is not the result of pure neutral communities colonizing randomly from a large species pool. Overall, the combination of results suggests that mesozooplankton species have distribution centres that are often associated with geographical features, and from which they disperse randomly. [ABSTRACT FROM AUTHOR]