Population Dynamics of Three Polyplacophora Species from the Aegean Sea (Eastern Mediterranean)

Abstract

The present study is the first to examine spatio-temporal variations in the densities and morphometrics of three shallow water Polyplacophora species (Rhyssoplax olivacea, Acanthochitona fascicularis and Lepidopleurus cajetanus), native to the eastern Mediterranean, while also estimating several growth parameters. Two intertidal boulder fields located in the Pagasitigos gulf (central Aegean) were sampled monthly with SCUBA diving using quadrant sampling, to compare the spatial and temporal (month, season) effects on their size, population density and dispersion pattern. Region was the most significant factor influencing the abundance and size for all three species, while the temporal scales affected mostly Rhyssoplax olivacea. The effect of a boulder under the surface was only significant for the density of Lepidopleurus cajetanus. The standardized major axis method showed that the three species exhibited different allometric relationships between length, width and weight, while a slope comparison between regions yielded significant, in most cases, results. Using the standardized Morisita index for dispersion, a clustered pattern was observed for all species seasonally, with the exception of Acanthochitona fascicularis in Plakes in autumn and winter. To estimate the growth parameters, a bootstrapped Electronic Frequency Analysis (ELEFAN) utilizing a genetic algorithm was employed on pooled populations. L∞ and K varied among the three species with A. fascicularis exhibiting the highest L∞ and L. cajetanus the lowest K value.