Cobble beaches in oceanic islands : how they react to hydrodynamics and location in the island?

1st Mares Conference on Marine Ecosystems Health and Conservation. Olhão, Portugal 17-21 November 2014.

Cobble beaches are a particular part of the coastal scenery in the Azores. The islands are geological recent and most of its coasts are composed of cliffs and basaltic lava flows, leaving only few spots for the accumulation of cobbles and the construction of cobble beaches. The beach structure changes with the hydrodynamics intensity from summer to winter, but wit it will its biological communities necessarily change? Will the location of a beach in one island be important in the community structure? This study was made in the island of Terceira. Four beaches were assessed, two in the northern coast, with heavy hydrodynamics and two in the eastern coast, more sheltered from the surge intensity. Each beach was surveyed in the summer and in the winter of 2013. At Each beach a beach profile was made for each season, cobble size was measured in three fringes of the shore, and animal and algal communities abundances were assessed as well. Data concerning wave size, direction and intensity and sea water temperature for the island all year round was obtained through oceanic buoys. Comparisons were made between seasons for each beach as well as between beaches from the north coast and beaches from the east coast of the island. Results showed differences between beaches and at the same beach between seasons, showing that the location of a cobble beach can influence its biological community, ant that seasonal alterations made by wave intensity are important in shaping the biological communities.