The importance of diving in the study of marine biodiversity in the shallow Slovenian Sea (Gulf of Trieste)

The Slovenian sea represents the southern part of the Gulf of Trieste, which is the northernmost point of both the Adriatic and the Mediterranean Seas. It is a shallow semi-enclosed gulf with the maximum depth of ca. 33 m in waters off Piran. Slovenian coastline is approximately 46 km long.

The research on flora and fauna in the Gulf of Trieste has a centennial tradition, however there are several gaps in the knowledge of different taxonomic groups. Few years ago a research group was established at the Marine biological station in Piran, in order to assess the status of fauna, flora and habitat types of the Slovenian coastal sea, to obtain a comprehensive inventory and to identify the factors that are having (or might have) negative impact on the coastal and marine biodiversity.

The collection of data for this project is carried out primarily by SCUBA diving; on linear transects along the coastal belt. The field work is recorded with a photo- and video-camera. These techniques have been choosen because they are non-destructive methods; samples are collected only when the identification of organisms is not possible under water.

Figure 1.  Some inhabitants of the Slovenian coastal area (from: Lipej et al., 2000). 

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The research group has a particular interest in the assessment of infralittoral fish diversity. The accurate estimation of fish population is a current ecological problem, as long-term surveys of fish assemblages are being developed to study the impact of man-induced changes or to determine the protection status in restricted zones (Harmelin-Vivien & Francour, 1992). With the increasing number of marine protected areas in the Mediterranean, traditional fishing devices –prohibited in protected zones – could be well supplanted by visual counts methods.

Marine small-size fish, that by definition reach a maximum size of only 10 cm, have been the object of ecological investigations in several region of the world (Gibson, 1982). These fish escape from commercial fishing gears and remain undisturbed especially on rocky substrata. Therefore, it was not surprising that several gobiid and blennioid species of small size were described for the first time during the last 25 years from the European part of the Mediterranean Sea (Miller, 1986; Zander, 1990). The SCUBA techniques revealed that the infrequent capture of small fish in the past is not always an indication of true numerical rarity in the ecosystem. On the contrary, the introduction of such techniques has recently repeatedly demonstrated the abundance and diversity of small fish in the Mediterranean Sea (Ahnelt & Kovačić, 1997).

The blennioids of the Adriatic Sea have been discreetly investigated and from the check-list of Pallaoro & Števčić (1989) it can be seen that in the Adriatic area 20 species (1 Clinidae, 16 Blenniidae and 3 Tripterygiidae) have been established with certainty. Although few descriptions of the blennid fauna of the Northern Adriatic are available, there was still a lack of knowledge regarding the species inhabiting the Slovenian coastal waters. With the SCUBA diving Lipej & Richter (1999) recorded eighteen blennioids species toward the only 6 blennioids mentioned in the first report for this area, when samples were mostly collected with trawling nets (Matjašič et al., 1975).

Figure 2.  Some more inhabitants of the Slovenian coastal area (from: Lipej et al., 2000). 

The first survey of species from the family Gobiidae in the Adriatic Sea were in the last century, done by Steindachner and Kolombatović (Kovačić, 1994). Recently, the interest for this family has increased again. New gobiid species have been described (Kovačič, 1995, 1999; Kovačić & Miller, 2000), so the number of gobiids recorded in the Adriatic area has risen to 45.

With the SCUBA diving techniques it will be possible to have in a few years a quite complete inventory of the flora and the fauna of the Slovenian Sea, which includes also the nonindigenous species that are constantly reaching our waters. Although only a minor research of this kind has been carried out in the Adriatic Sea, scientists have recorded cases of introductions of alien species that could badly affect the indigenous ecosystems. SCUBA diving is one of the most appropriate techniques to be used to monitor the spread of nonindigenous species, in order to understand the impact they have once they are established in the new area, and take the right measures to protect the natural biodiversity of local ecosystems.

References

Ahnelt H. & Kovačić M., 1997. A Northern Adriatic population of Thorogobius macrolepis (Teleostei: Gobiidae). Cybium, 21 (2). 149-162.

Gibson R.N., 1982. Recent studies on the biology of intertidal fishes. Oceanogr. Mar. Biol. Ann. Rev., 20, pp. 363-414.

Harmelin-Vivien M. L. & Francour P., 1992. Trawling or Visual Censuses? Methodological Bias in the Assessment of Fish Populations in Seagrass Beds. P.S.Z.N.I: Marine Ecology, 13 (1): 41-51.

Kovačić M., 1994. Contribution to the knowledge of gobies, Gobiidae (Pisces, Perciformes) in the Rijeka Bay, Adriatic Sea. Periodicum Biologorum, Vol 96, No. 4, 463-465.

Kovačić M., 1995. Gobius roulei De Buen, 1928 (Pisces, Teleostei, Gobiidae), a fish new to the Adriatic fauna. Nat. Croat. Vol. 4., No 4, pp. 173-184, Zagreb.

Kovačić M., 1999. Gammogobius steinitzi Bath, 1971, a fish new to the Adriatic Sea. Nat. Croat. Vol. 8., No 1, pp. 1-7, Zagreb.

Kovačić M. & Miller P. J., 2000. A new species of Gobius (Teleostei: Gobiidae) from the Northern Adriatic Sea. Cybium, 24 (3): 231-239.

Lipej L. & Richter M., 1999. Blennioides (Blennioidea) of the Slovenian coastal waters. Annales 15/99, pp. 15-24.

Lipej L., Orlando M. & Makovec T., 2000. Pestrost življenja piranske Punte: naravna dediščina. Piran: Morska biološka postaja, Nacionalni inštitut za biologijo. 16 pp.

Matjašič J., Štirn J., Avčin A., Kubik L., Valentinčič T., Velkovrh F. & Vukovič A., 1975. Flora in favna severnega Jadrana. Prispevek 1. Slovenska akademija znanosti in umetnosti. Ljubljana, 54 pp.

Miller P.J., 1986. Gobiidae. In: P.J.P. Whitehead, M.L. Bauchot, J.C. Hureau, J. Nielsen & E. Tortonese (Eds.), Fishes of the North-Eastern Atlantic and Mediterranean. UNESCO, Paris: 1019-1085.

Pallaoro A. & Števčić Z., 1989. A check-list of species of Adriatic Blennioidea (Pisces, Teleostei, Perciformes). Studia Marina, N. 20, Kotor, Yugoslavia.

Zander C. D., 1990. The distribution and feeding ecology of small-size epibenthic fish in the coastal Mediterranean Sea. 21 EMBS, 369-376.