EVALUATING HEAT TREATMENT AS A METHOD TO REDUCE BIOFOULING IN OYSTER AQUACULTURE. Heat tolerance in Swedish grown Magallana gigas and Ostrea edulis.

Abstract: Aquaculture is a growing business in various parts of the world, Sweden included. As the commercial use of oysters increases, so does its demand. Farmers will need to produce a high quality product that is appealing to the customer and cost-effective for the farmer. One major issue for farmers is biofouling, as unwanted organisms settle and grow on the oysters, reducing their value and quality. This thesis explored a method for reducing the problems caused by a group of biofouling organisms, the calcifying tubeworms. The method included using a heated sea water treatment, in which the oysters were dipped into heated water for a short time period. Included in the experiment was the Swedish native oyster Ostrea edulis and the invasive species Magallana gigas. Due to its invasive status, M. gigas is prohibited to culture in Swedish water. The demand from the market has farmers wanting a legislation change, therefore its inclusion in this thesis was relevant. Using a range of temperatures based on previous successful studies on blue mussels, tests were conducted to see if the method could be applied to oysters too and if so, if the two different species had any differences in tolerance to stress from the heat treatment. Tubeworm mortality was also tested separately. The results indicate that M. gigas had a higher tolerance towards the stress from heat treatment while the mortality of O. edulis significantly increased with temperature. Alongside a surprisingly low threshold for high mortality in tubeworms, a conclusion was made that the method was suggested to be applicable to Swedish aquaculture, but the method must be optimized further to suit our native species to yield an effective result with low oyster mortality.