Population structure and spatial distribution of the gastropod mollusc: Phorcus sauciatus in the rocky intertidal zone of Tenerife, Canary Islands.
Supervisors: Jose C Hernandez, Beatriz Alfonso (Univ La Laguna)
The present study analyses and compares the population structure as well as the horizontal (differences among 7 locations on the island), and vertical (differences among intertidal bands) distribution patterns of the intertidal gastropod mollusc Phorcus sauciatus (Koch, 1845), along the rocky intertidal zone of Tenerife, Canary Islands. Spatial variation in the abundance and size structure of P. sauciatus was detected, and a significant effect of the interaction terms (location and intertidal band) has been found on the densities of P. sauciatus populations. The total abundance of this species varied among locations, and higher abundances were generally found in the mid intertidal and supralittoral zones. The size frequency graphs of the populations of P. sauciatus in each site, including the minimum capture size in the Canary Islands of 15 mm width (BOC n°093 11th of May 2011), shows that four of the locations have high percentages of individuals larger than the minimum capture size, and two of the locations have individuals that are on average smaller in size, raising interest on the human activities such as harvesting in these sites and on “the implications for conservation of this species.

Key words: Gastropod, Phorcus sauciatus, abundance, intertidal zone, size structure