engleski

Biodiversity in anchialine caves: First record of the tubeworm Ficopomatus enigmaticus (Annelida, Polychaeta)

Ficopomatus enigmaticus (Fauvel, 1923) is a sedentary polychaete which has been found worldwide inhabiting coastal brackish waters, lagoons and estuaries of warm temperate areas of both hemispheres. This tubeworm builds calcareous tubes on any hard substrate (Serpulidae) with distinctive collar-like rings at irregular intervals and is relatively easy to identify. It is an efficient suspension-feeder, very tolerant and physiologically well adapted to temperature and salinity variations, eutrophic conditions and low dissolved oxygen content. Here we report on the first record of F. enigmaticus in two anchihaline caves which are located along the Mesozoic coastal carbonate rocks of the Mediterranean Sea, namely the Orljak cave in Krka River Estuary (Croatia, E-Adriatic) and the Bue Marino cave in the Gulf of Orosei (Sardinia, W-Tyrrhenian Sea). The Orljak cave has an entrance ca. 50 m from the coast without direct connection with the Krka Estuary. The cave is 23 m deep and 90 m long with two pools. The Bue Marino cave with entrance above the sea level and direct connection with marine water has a well developed underground drainage. An almost horizontal profile and several pools characterises the three branches of this karstic complex with a total length ca. 20 km. In Orljak cave salinity ranges from 2 to 8 in winter, and from 7 to 13 during summer. Water temperature varies from 15 to 17°C in summer and from 11 to 13°C in winter. Salinity values in the Bue Marino range from 28.4-32.3 in summer to pure freshwater during winter floods, and water temperatures at the surface were 19-20°C in summer. F. enigmaticus inhabits, in both caves, totally dark zones on rocky walls or submerged parts of speleothemes, of surfaces water layers until 1 m depth. The two populations share a low density with specimens growing solitary, with separate tubes. The two cave dwelling populations display a peculiar behaviour in growth strategy contrasting with the typical gregarious strategy of the species characterized by notable potentiality of bioconstruction. Environmental conditions confirm the well known extreme adaptability of the species, also to live in the dark, and suggest its ability to survive, although intermittently, in freshwater.

anchialine caves; Ficopomatus enigmaticus; Annelida; Polychaeta; Krka River Estuary

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