About Croatia’s undersea world

The Adriatic Sea is a small, enclosed sea, but large enough to accommodate some of the most beautiful diving sites in the world with an amazing diversity of flora and fauna. Life in Croatia’s undersea world is part of the evolutionary heritage dating back to the prehistory of seas all over the world. A good example is the Mediterranean feather star which is 500 million years old, or jellyfish, evolutionary sea pioneers that continue to prosper to this day.

Kosmati samac (Dardanus calidus)

On the other hand, other segments of marine life are an evolutionary development in the division of seas and smaller sea oases, like the Mediterranean Sea. The Adriatic Sea is small and enclosed and likened to an evolutionary pool in which species developed and spread, and gained specific traits within a unique environment. The problem is how to divide marine life in the Adriatic Sea to afford a comprehensive overview for divers. A possible division would be according to relief characteristics above and below sea-level, type of seabed, current strength and other non-scientific descriptors used in the depiction of a diving site. The habitat also significantly influences the resident species.

Diving starts in the shallows along an indented coastline with 1246 islands, islets, crags and reefs. At the onset it gives divers insight into the interesting marine life in store among the rocky undersea crags and reefs. Shallower coves and bays where rocks have been pounded into pebbly beaches by the force of the sea may seem uninhabited at first, but are home to numerous unusual species, as are the few sandy beaches, which are covered in a variety of sediments, sand, silt and organisms, depending on diving depth. Characteristic of the karst relief along the Croatian coastline is the large number of caves, pits and holes, which are to be found in equal numbers both above and below the sea. Since the sea is sometimes ruthless, at times, these places appear to be uninhabited environments in eternal darkness, but are, in fact, home to some of the most fascinating species on the Adriatic. The science of marine life can be divided into habitats in regions on the open sea (pelagic) and those found on the seabed (benthos).

Veliki ježinac (Echinus acutus)

It is only natural that the imagination is fired up by species inhabiting the open seas – tuna, swordfish, and even schools of oily fish, without which life in the sea would be hard to imagine. Life at the bottom is far more interesting and more abundant for divers and diving, especially littoral regions reaching to a depth of 200 m. These regions are, in turn, divided into zones – the supralittoral, the mediolittoral, the infralittoral and, finally, the circalittoral, where the sun’s rays are too weak for flora or algae to prosper. The sunny shallows of the infralittoral zone are where most dives takes place.

Hobotnica (Octopus vulgaris)

Dives at a depth of up to 10 m among the sun-spangled algae, although less demanding, are often more gratifying, as far as diversity is concerned. The sun gives life to algae and plants, organisms that transform the inanimate into food at the beginning of the food chain. However, not all shallows are equally life-bearing. Pebbly shallows are constantly influenced by currents, waves and tides, so that many algae and plants cannot flourish. There are fewer crabs, fish, anemones, urchins, but some persist on surviving – the largest among the gobies, the rock goby, is one, as well as hermit crabs, snails and the unusual stone fish.

Kanjac (Serranus cabrilla)

Sandy beaches include species that dig into the sand to a depth of 1 m, like sea urchins, starfish, shellfish, and those that manage to take root, like Sargassum algae, or those that resemble fields – like the posidonia grasses. Diving in these conditions requires grace and elegance, as too much use of fins may reduce visibility, which is an advantage when diving at night since clouds of sand attract nocturnal species – mullets, striped bream, red sea bream, as well as the unusual snake blenny – that feed in the sand.

The sandy bottom is ruled by fish that like to dig in, like various soles, and by those that ambush their prey, like the star gazer or poisonous weever. The sandy seawater is also filtered by the largest shellfish in the Adriatic, endemic to the Mediterranean – the fan mussel, which grows to a height of 1 m. Fields of grasses are an important eco-system in the Adriatic, alongside a plant that only grows in the Mediterranean – the posidonia.

Up to 20% of species live, reproduce, grow and hide in this plant. Its roots are planted firmly in the sand, preventing erosion. The most common and attractive dives are those along crags around islands and along the coastline which may drop sheerly in places to 100 m. The marine life here depends predominantly on currents; currents that supply numerous filtrators with small particles of food.

The first and most primitive animals are sponges, which are actually colonies of small organisms living off what the sea provides. They are irregular in shape and often look like stones or chimneys, or even elephant ears.

Being an animal that spends its entire active life in one place is not so unusual in the undersea world. Cnidarians, gorgonians and corals are but a few of these beautiful and colourful creatures. Other marine life includes moray eels, congers and scorpionfish.

“Podmorski ples”

Caves

Life in caves is scarce – but they are a challenge to divers. Many still have stalactite and stalagmite remains dating from the Ice Age when they were part of the land mass. Due to the lack of sunshine and currents, life does not thrive here. The sediments at the bottom are frequently inhabited by Cerianthus membranaceus sea anemones and small leopard gobies. The cave entrances and openings and their vaulted ceilings are often covered in yellow cup-coral.



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