engleski

Survival strategy of semi-subterranean amphipod in intermittent karstic springs: case of the spring Krčić, Croatia

Aquatic invertebrates have developed different strategies to adapt and to survive the dry season in intermittent springs. Crangonyctid amphipod Synurella ambulans (F. Müller, 1846) is stygophile occupying various epigean and semi-subterranean freshwater habitats in Europe (Karaman 1974, 1990 ; Barnard & Barnard 1983 ; Sidorov & Palatov 2012). Although records of S. ambulans in intermittent water bodies seems usual, the response of population dynamic of the species to flow permanence within karstic springs was not examined before. The population structure, density (ind. m-2) and seasonal dynamic of S. ambulans were studied in the intermittent spring Krčić in Central Dalmatia (1) to determine the strategy of adaptation to flow oscillation ; (2) to understand how and where the species find refuge when a spring dries ; (3) to examine population density in relation to season, microhabitat and length of aquatic phase ; and (4) to determine the relative importance of major environmental parameters in the local distribution of the species. The sampling stations represents eucrenal and hypocrenal environment. Research was conducted once a month from April 2011 to December 2012, and with additional samples from April to December 2013. Samples were collected at three different types of substrates (microlithal, megalithal and moss/algae) and basic physico - chemical parameters of water were measured. The species was well adapted to changing currents, seasonal drying of spring and seasonal changing of living substrates, found hiding and feeding inside pockets of thin jelly coating of blue-green algae during autumn and at the end of spring, as well as under a thick layer of aquatic moss adhered to stones during the rest of the year. Algal periphytic mat is dominated by cyanobacteria species (Phormidium). Among the mat, there is rich diatom community forming mucilage pads, stalks and tubes dominated by Meridion circulare and Encyonema silesiacum. The reproductive season of S. ambulans in the intermittent spring Krčić was determined to be in groundwater at the end of the dry season of the spring source (September to November) because juveniles appeared in winter (December to January), soon after the spring was activated. The records of only few ovigerous females in samples indicate that its biological cycle is completely adapted to spring desiccation and the females appear to lay eggs in groundwater. Since the spring water temperature is lower than the mean annual air temperature of the area, gradual water table increase could be the initial key factor for the reproduction of the species in the stable environmental condition of the groundwater. The species is restricted to the ecotone around the point of groundwater up-welling and never drifting downstream into the hypocrenal zone of the spring Krčić.

eucrenal; amphipod population structure; diatom community; ecotone

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