Gongolaria barbata forest in the shallow lagoon on the southern Istrian Coast (northern Adriatic Sea)

The Gongolaria barbata forest inhabiting Scuza lagoon on the southern Istrian coast (northern Adriatic) represents the last significant refuge for this species among the shallow waters of the Istrian Coast. The lagoon is characterised by extreme winter and summer temperatures. Moreover, the absence of certain grazers could be one of the main factors favouring the development and growth of G. barbata forest. Two morphologically distinct forms of G. barbata inhabit the lagoon: attached and detached. Abundance and morphological characteristics of each form were analysed in randomly sampled thalli. The wet weight, thallus length, number of cauloids and total cauloid length were significantly higher in the detached than in the attached form. Although the main cauloid was highly branched in both forms, its total length was up to three times higher in the detached than in the attached form. Our study suggests that this population of G. barbata can thrive in the extreme conditions found in the lagoon, while also exhibiting two distinct forms. Furthermore, this large population could serve as a donor for future restoration attempts on the western Istrian Coast where a decline of G. barbata has been confirmed in recent years.