Abiotic Sponge Ecology Conditions, Limski Kanal and Northern Adriatic Sea, Croatia

Abstract

The Limski kanal, a semi-closed inlet (channel-like bay) located onthe western coast of Istria (Croatia), is an extraordinary spongehabitat. Research on the marine ecosystem has been conducted therefor more than 100 years. Today, 42 valid Porifera species are described.139 species are listed for the area around Rovinj and 159 speciesfor the northern Adriatic Sea. While several scientists describedthe sponge fauna, information on the abiotic situation or an explanationfor the diversity differences is missing. This study interprets physicochemicaland ecological parameters including depth profiles (temperature,salinity, pH-value, oxygen, water current velocity, photosyntheticallyactive radiation [PAR], water transparency and nutrients). Theirvariances are linked with the distribution patterns of the prevailingsponge fauna. The channel is characterised as predominantly marinehabitat. Although a shallow sediment barrier and a headland reducethe impact of the northern Adriatic Sea, differences between thechannel and the open sea seem to be limited. Compared to the morehomogenous water body of the Adriatic sampling locations, the channelshows variations and gradients of ecological parameters between differentlocations (e.g., due to freshwater influx: nutrients, temperature,oxygen content, salinity and water current velocity) – thisoffering habitat diversity. The sponge fauna changes along thoseecological gradients. It is dominated by the photophilic speciesAplysina aerophoba and Chondrilla nucula, but sciaphilic speciessuch as Dysidea avara, Axinella polypoides and Aplysina cavernicolacan be found, too. Some specialised species (e.g., Geodia cydonium,Tethya aurantium) even populate the muddy bottom of the channel.