Croatia’s Adriatic Sea: Beyond the Sparkling Surface
The Adriatic is an elongated bay of the Mediterranean Sea, connecting to it via the Strait of Otranto and the Ionian Sea. Italy occupies the western coast and Croatia the eastern, with bits also belonging to Slovenia, Bosnia and Herzegovina, Montenegro and Albania. Croatia hogs almost all the islands, making the difference of the eastern and western side striking.
Claiming nearly ¾ of the entire Adriatic shoreline, the coast of Croatia is the Mediterranean’s most indented one. If you unravelled it into a single string, it would amount to 6278 kilometres – the air distance between New York and Berlin. Of this total, more than 4300 kilometres are the islands. The official count is an impressive 1244, but truth be told, this includes islets, rocks and flyspecks. Only 78 of these are larger than 1 square kilometre and qualify as islands; out of those, 67 are inhabited.
Along with the spectacular coastline, the fascinating traits of the Adriatic are its colour and its warmth. The shades of blue depend on the depth and the sea bottom, but the incredible clarity of the water is mostly thanks to the rocky shores with little run-off. In the northern Adriatic, where Po River joins, visibility ranges around 20 metres, while in the far-flung Palagruža island, up to 50 metres. Diving, anyone?
The water temperature reaches up to 26° C in the summer but drops to between 9° and 12° C in wintertime. As the northern Adriatic is fairly shallow, the swimming season kicks off earlier while in the south, like in Dubrovnik, it lasts longer, with swimming well into October. The salinity follows a similar pattern. It is at 33‰ in the northern Adriatic, where there are many tributary rivers; it is higher in the south and areas distant from the coast, reaching 38‰.
For a relatively small area, the Adriatic is a treasure trove of life, claiming nearly half of all Mediterranean biodiversity. The current estimates put the number of species between 7000 and 8000, but some studies suggest there might be more than 12,000. Those include 5500 maritime invertebrates, over 600 algae, more than 280 sponges, 116 kinds of coral and 449 species of fish.
Due to climate change, human activity as well as species migration across to Suez Canal, these numbers are ever-changing. In the two decades of the 21st century, nearly 40 new fish have been identified in the Adriatic.
But not all newcomers are welcome, and especially not the invasive species. While mostly not dangerous to humans, they do not have a local enemy and so spread easily, ultimately reducing biodiversity. Such are the “killer algae”, Caulerpa taxifolia, whom aquarium lovers will recognise with ease, as their fluorescent green colour makes them favourite décor in fish tanks. Blue Atlantic crabs are another one. Good swimmers, they can go between rivers and seas; they multiply easily, and as omnivores, though competition for food, are a danger to local crab species.
To report spotting of any of these is praise-worthy support to the beauty of the Adriatic. Along with the Croatian Ministry of Environment contact (email@example.com), there are also local centres like the Invasive Species Centre in Poreč, available at 052-408 304 or firstname.lastname@example.org.
But some invasions are no cause for alarm. In springtime, blooms of common jellyfish can be seen floating in bays and along the shores, especially in Istria and the Kaštela bay. You can recognise them by four horseshoe-shaped gonads, easily seen through their translucent bell. If you see them, fear not. They are not dangerous to humans, and their appearance usually means the spring is about to bloom, too.