Nascimento Schulze, Jennifer C. (2017) Effects of temperature and salinity on the survival and physiology of Baltic Mytilus sp. early life-stages. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 53 pp.

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Abstract

Low salinity conditions of brackish and estuarine coastal systems represent a challenging habitat for marine organisms to survive and develop. Anthropogenic induced climate change is expected to change sea surface patterns, further increasing desalination and elevating temperatures. The Baltic Sea mussel populations are formed by hybrids of Mytilus edulis and Mytilus trossulus. To date, Mytilus populations inhabiting the eastern coast of the basin thrive at the lower limit of their salinity tolerance range. Early life-stages of marine invertebrates are found to be more sensitive to environmental change and extreme variations of abiotic factors. To understand how changes in salinity and temperature will act on Baltic Mytilus larvae, development of the full larval stage was monitored in a fully crossed lab experiment with three salinity levels (7, 9 and 11 psu) and two temperatures (12 and 15 °C). Mussels were collected from Ahrenshoop, Germany in May 2017. The combined treatment of 11 psu and 12°C represents the mean natural field conditions during larval season. Rates of survival, growth and settlement of larvae were strongly reduced at salinities of 9 and 7 psu. Higher temperatures alleviated the negative effects of low salinity. After a 67 day period, undeveloped D-stage larvae were still found present in adverse salinity conditions of 7 psu regardless experimental temperature. Physiology of the larvae was directly affected by desalination and temperature variation. Respiration rates increased with decreasing salinities of 9 and 7 psu. In addition, a +3°C temperature increase resulted in elevated respiration rates. The opposite pattern was observed for clearance rates. Lower levels of energy available for growth (scope for growth) of larvae reared under low salinity are a key finding in this study. Combining the adverse conditions of low salinity and temperature elevation of 3°C resulted in decreasing scope for growth with time. Predicted conditions for the Baltic Sea may represent a limiting factor for survival and development of Mytilus sp. early life-stages being bottleneck for survival redefining the distribution limits of mussel populations in this area.

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