Enviromental impacts of intensive mussel culture in the coastal waters of the gulf of Thessaloniki (N. Greece)

Abstract

The environmental impacts of mussel cultures are re-lated mainly to increased sedimentation and high filtration rates. Numerous mussel culture units are located in the shallow waters (maximum depth 20 m) in ΝW Thessaloniki Gulf (Greece). Evaluation of the impacts of the mussel units on the quality of the surrounding waters was the aim of this work. The sampling period lasted from January to August 2006, covering a complete culture cycle, from the larvae in the water column to the harvesting of mature mussels. Water samples were collected twice per month from three depths; 1 m and 5 m from the sea surface and 1 m above the bottom, from four sampling locations, three among the units and one outside of them. The parameters measured were dissolved oxygen, suspended solids, nutrients (nitrate, nitrite, ammonia, phosphate and silicate) as well as chlo-rophyll a as a measure of phytoplankton abundance. Low values of dissolved oxygen have been recorded in certain sampling periods. Relatively low values of nutrients were present throughout spring and summer. Chlorophyll α val-ues were below 0.2 mg/m 3 indicating a serious impact of the mussel culturing to the ecological status of the water column inside the mussel farming area. Multivariate sta-tistical analysis was applied on the data set in order to as-sess environmental impacts and reveal the association among the measured parameters.