Daily vertical migrations in the epifauna associated with Posidonia oceanica meadows

To estimate the importance of the vertical daily migrations in the structur e of the community of the epifauna associated with the leaf stratum of Posi donia oceanica, we compared to the vagil epifauna abundance in respect to t he period of the day and the height of the sediment. The study was develope d in the P. oceanica meadow of El Campello (Alicante, south-east Spain), du ring May of 1996, to a depth of 12 m, repeating the samplings in four sites to obtain a correct spatial interpretation. Three main behaviours were det ected. Decapods, amphipods, isopods, mysids, ostracods and polychaetes show ed a nocturnal increase in the leaf stratum of P. oceanica. By contrast, co pepods showed a nocturnal decrease in the leaves and gastropods did not sho w any temporal change. Chaetognaths and acari did not show statistical diff erences because of the considerable spatial heterogeneity. These vertical m igrations have an extreme importance in the configuration of the structure of the epifauna associated to P. oceanica, in addition to the diverse respo nse of the different taxa.