Chromis Chromis fish / CRNEJ, Črnik in its natural habitat, Exploring the shallow waters part 3 ASMR

The damselfish Chromis chromis is typically the most abundant fish species in the rocky littoral environment of the Mediterranean Sea, where it feeds in huge shoals on incoming zooplankton and rests near the seabed each night. Research has shown that large populations of C. chromis play a fundamental role by transferring carbon, nitrogen and phosphorus directly from the pelagic system to the littoral in the form of solid and liquid wastes and therefore that this species acts as a vital conduit for nutrients. In addition, C. chromis represents a major prey item for predatory fish and seabirds, it has been shown to exert significant predation pressure on coastal zooplankton populations, but it is also a major consumer of fish eggs and hence may have a strong influence on the dynamics of other fish species. In this review paper the contention is that C. chromis represents a key species in the Mediterranean Sea rocky littoral. This view is supported by quantitative evidence that has been amassed over a number of years, but is collated here for the first time. Chromis chromis is of only minor importance to commercial fisheries (it is usually discarded), but trends in population abundance of this species can be indicative of levels of fishing pressure on other commercial species. It has been demonstrated that where predator numbers are able to recover from intensive fishing (e.g.in marine protected areas; MPAs), this is often mirrored by lower densities of C. chromis. Several papers have championed C. chromis as a possible indicator species for human disturbance. As well as being directly and indirectly affected by fishing, the species is also sensitive to a number of other anthropogenic pressures, most notably poor water quality and noise pollution.
The damselfish Chromis chromis (Linnaeus, 1758) is distributed in the eastern Atlantic along the coast of Portugal to the Gulf of Guinea (it may also reach Angola) and the Mediterranean Sea (QUIGNARD & PRAS, 1986). It is also distributed throughout the Adriatic Sea, living in schools in midwater, above or near rocky reefs, or above sea grass meadows, mainly at a depth of 3-35 m (JARDAS, 1996). It is the only representative of the family Pomacentridae in the Mediterranean Sea. The biology of this species has been well documented for the Adriatic.
The damselfish population of the middle Adriatic is relatively homogeneous although some morphological characters varied between sexes. The seven significant differences in morphometry could have resulted from phenotypic responses to the habitat in which they live, similar to those reported for Syngnathus abaster from the Danube River (CAKIĆ et al., 2002; MOVČAN, 1988). These authors indicated that differences may have been caused by varying features of the aquatic ecosystems. Modes of analyzed morphometric relationships were identical in males and females without a tendency toward bimodality in any characteristic, clearly indicating a homogeneous damselfish population in the Adriatic. Based on vertebra analysis, DULČIĆ et al. (1994) also reported that the damselfish population in the middle Adriatic is homogeneous. Adriatic Sea, Italian Mare Adriatico, Bosnian, Croatian, and Montenegrin Jadransko More, Albanian Deti i Adriatikut, arm of the Mediterranean Sea, lying between the Italian and Balkan peninsulas. The Strait of Otranto at its southeasterly limit links it with the Ionian Sea. It is about 500 miles (800 km) long with an average width of 100 miles, a maximum depth of 4,035 feet (1,324 metres), and an area of 50,590 sq mi (131,050 sq km). The Adriatic has been of great importance in the historical development of Mediterranean Europe and is of considerable scientific interest in itself. Modern study of the Adriatic has been carried out mainly under the auspices of several Italian and Balkan scientific institutes. There is a striking contrast between its two shores. The Italian coast is relatively straight and continuous, having no islands, whereas the Croatian coast is full of both large and small islands, generally oblong in shape and running parallel to the continental shore. Many tortuous straits form inlets between the islands similar to those of the Norwegian fjords and make the coastline very intricate.
The depths of the Adriatic near its shores bear a close relationship to the physiography of the adjacent coasts. Wherever such coasts are high and mountainous, the nearby sea depths are considerable, as in the case of the Istrian and Dalmatian areas of Slovenia and Croatia. Where low and sandy shores are found, the nearby sea is shallow, as in the vicinity of Venice or, farther south, near the delta of the Italian Po River. Generally speaking, the waters are shallow all along the Italian coast. The site of maximum depth of the Adriatic Sea is situated south of the central area; average depth is 1,457 feet (444 metres).

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