Coralline algae, often seen as a hard, light pinkish algae on saltwater aquarium rocks, invertebrate shells, and glass was thought to be exclusive to saltwater and brackish water environments, but eastern European scientists have discovered the algae in the Cetina River in Croatia, a karst river located in the Adriatic Sea watershed. This river has a pH that is similar to marine environments, but without the saltwater.
The researchers, led by A. Žuljevic of the Institute of Oceanography and Fisheries, in Split, Croatia, discovered that Pneophyllum cetinaensis is endemic to the Cetina River and is the first known freshwater coralline algae discovered. Its marine genealogy puts it as a secondary freshwater immigrant. It cannot live in the estuary of the Cetina River which has diluted seawater and its sexual and asexual reproductive structures are conducive to a life in freshwater conditions. What makes the Cetina River ideal for the growth of this algae is the presence of carbonate rocks, limestone mostly, and hard water that is enriched with dissolved calcium carbonate and magnesium ions. The presence of these compounds are necessary for the growth of Pneophyllum cetinaensis.
The researchers found the coralline algae on rocks and on the shells of snails in the river system. The discovery of Pneophyllum cetinaensis dispels the notion that coralline algae is exclusively in the saltwater domain.