engleski

Is marine protected area of Lastovo island (Adriatic Sea) a natural laboratory ideal for testing the island trapped waves phenomena?

Island-trapped waves (ITWs) are a special case of coastal-trapped waves which occur along closed coastlines, such as islands or lakes. While surface ITWs usually have an amplitude of only a few centimeters, resonantly excited internal ITWs can surpass several tens of meters. Such ITWs can vertically transport nutrients to shallow waters with plenty of light available. Nutrients, combined with increased light availability, can trigger the primary production which is the base of the food web. The research related to ITWs was mostly focused on islands in the deep ocean, while the phenomenon was only recently recognized in a shallow and seasonally stratified sea like the Adriatic Sea. Temperature based measurements at Cape Struga (Lastovo Island), showed that geometric and stratification properties around the island can be close to resonant ones during summer. A recent field experiment was organized to determine the presence of the diurnal internal ITWs around Lastovo Island by placing thermistors on two opposite sides of the island. The thermistors were deployed at 9 equidistant depths between 5 and 45 meters on rocky cliffs facing north and south. The measurements were carried out between summer 2016 and summer 2017. During September 2016 and July 2017 significant diurnal internal waves were observed. Temperature oscillations at opposite sides of the island were out of phase, indicating the clockwise propagation of the internal wave around the island on the northern hemisphere. The question for future studies is if this resonant phenomenon can have an impact on primary production and consequently the whole food web dynamics. By using an interdisciplinary approach in investigating ITWs around Lastovo, we expect to connect physio-chemical processes in the euphotic layer with primary production and the functioning of the entire food web. We also aim to determine the parts of Lastovo Archipelago MPA which might have enhanced primary production.

Island-trapped waves, primary production, Lastovo, Adriatic Se

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