On the outer side of Telašćica Bay vertical cliffs rise into the most prominent steep slope of the Adriatic Sea – the famous “stene” of Dugi otok. The steep slope stretches from Cape Mrzlovica in the southwest to the mountainside of Veli Vrh in the southeast reaching a height of 161 m in Grpašćak. The greatest depths can reach 85 m. The area is rich in interesting flora and fauns, and dolphins may be seen swimming along the cliffs. Different corals, including the already endangered red corals, live underwater on the cliffs. The cliffs are interesting above sea level, too. Croatian Centaury (Centaurea ragusina) grows on the cliffs, which are also the northernmost habitat of tree spurge (Euphorbia dendroides). The cliffs are also a nesting place of the peregrine falcon (Falco peregrinus), and Eleonora’s falcon (Falco Eleonore). Because of the presence of a large number of birds of these two protected species, Telašćica has been included in the Important Bird Areas-IBA areas).
The cliffs of the steep slope are also home to two endemic species of land snails of the family of door snails (Clausiliidae): Delima edmibrani and Agathylla lamellosa. The Delima edmibrani has only been found within the boudaries of the Nature Park, therefore it could be considered as its endemic species, i.e. a stenoendemic species of the Nature Park.
The Croatian Centaury is a rare endemic species. It is present only in Croatia, in several locations, but with a scarce population: in areas around Cavtat, and in islands of Central and South Dalmatia. The species has two subvarieties in the area of Nature Park Telašćica: Centaurea ragusina ssp. ragusina located on steep slopes and in Čuška Dumboka Bay, and Centaurea ragusina ssp. lungensis which is present only on the steep slopes.
Along the cliffs, in the depths of the sea, you can find the Eunicella cavolinii and Paramuricea clavata gorgonians, and sponges such as Axinella cannabina. The underwater of the cliffs, to a depth of 20 km, is dominated by a community of photophyllic algae made of Halimeda tuna, Acetabularia acetabulum, Padina pavonica and many others. Colonies of red coral Corallium rubrum, which is an endangered species, can be found at greater depths. Several types of sea urchins, a large number of different species of fish and crabs also live in the area surrounding the cliffs.
The underwater hollows cliffs are featured with half-dark caves inhabited by a variety of sponges, cnidarians, corals, etc.