Mining extraction in the ocean depths: a baseline to understand and reduce acoustic impact on biodiversity.

Throughout history, man has exploited the earth's mineral resources for its survival and for technological development without regard for their regeneration. Given the growth of the world population and given the fall in resources, man started looking for new deposits, which were found in 1960s in the ocean depths. Humankind then began to consider extracting minerals from these deposits and this gave origin to Deep Sea Mining (DSM). The consequences of mining activities in the deep sea are not entirely known and the effects can be varied: noise pollution, light pollution, chemical pollution, habitat destruction, habitat fragmentation and the loss of species which we consider the basis of many life systems. The acoustic impact of these activities could have significant consequences on marine species; nevertheless, this has been the most overlooked issue to date. The aim of this PhD project was to provide baseline knowledge of possible acoustic impacts of DSM on biodiversity before mining begins. In order to do this, the PhD project was organised into 3 different stages. First, during an indoor experiment, the biochemical responses of invertebrates Arbacia lixula and Mytilus galloprovincialis subjected to acoustic stress were analysed. The results showed significant changes in cytotoxicity activity, expression of heat shock proteins (HSPs), and enzyme activities (esterases, alkaline phosphatases, peroxidases) in the coelomic fluid of sea urchins subjected to acoustic stress. Significant effects were also observed in glucose levels, cytotoxicity and enzyme activities (esterase, alkaline phosphatase, peroxidase) in the digestive gland of the mussel. Second, the biochemical responses of vertebrates and invertebrates subjected in-situ to watergun emission were analysed: Chromis chromis, Holothuria tubulosa and Arbacia lixula. Significant effects on fish cortisol levels and on enzyme activities in sea urchin peristomes were found. Furthermore, the enzyme biochemical responses analysed in the coelomic fluids of echinoderms showed significant effects only in A. lixula sea urchin and only in peroxidase activity. Third, behavioural changes in experimental conditions were studied in juveniles of Sparus aurata subjected to 4 different acoustic emission frequencies. This experiment showed that only low frequencies had effects on all the behavioural responses analysed: swimming height, motility and dispersion of the group. Based on behavioural data obtained in vivo on juvenile fish, a numerical model was created to predict the impacts of different acoustic emission frequencies. Using the results obtained and literature, a first technical standard useful for mining activities was drawn up