ANNALES • Ser. hist. nat. • 14 • 2004 • 1
original scientific article	UDC 595.3:504.06(262.35 Krk)
received: 2004-03-04
PRELIMINARY INVESTIGATION OF THE SEDIMENTARY BOTTOM DECAPOD FAUNA IN THE UPPER INFRALITTORAL OF THE ISLAND OF KRK (ADRIATIC SEA)
Marin KIRINCIC Rijeka Natural History Museum, HR-51000 Rijeka, Lorenzov prolaz 1, Croatia
ABSTRACT
The UNEP Mediterranean Action Plan Draft Reference List of Habitat Types of Conservation Interest includes sedimentary bottom infralittoral biocenoses. Such habitats are very rare on the eastern Adriatic coast. Therefore an investigation of the decapod fauna collected by means of a beach seine on the upper infralittoral (at the depth of ca. 0-1 m) has been carried out on three shores of Krk Island (northern Adriatic). Each locality is characterized by a different kind of sedimentary substrate (mud, sand, gravel). The species composition, their abundance and dominance are given for each locality, upon which a comparative study was conducted. Each locality has its specific dominant species. Carcinus aestuarii is the dominant species on the muddy bottom, Philocheras trispinosus on the sandy bottom, and Palaemon elegans in the biocenosis of coarse sands and gravels. Altogether, 14 benthic decapod species have been found.
Key words: decapod fauna, littoral, sedimentary bottom, northern Adriatic
STUDIO PRELIMINARE DELLA FAUNA A DECAPODI DI FONDO SEDIMENTARIO NELL'INFRALITORALE SUPERIORE DELL'ISOLA DI VEGLIA (MARE ADRIATICO)
SINTESI
La prima stesura della Lista di riferimento degli habitat meritevoli di salvaguardia del Piano d'Azione per il Mediterraneo dell'UNEP comprende i fondi sedimentari delle biocenosi infralitorali. Tali habitat sono molto rari lungo la costa orientale dell'Adriatico. Uno studio e stato pertanto eseguito sulla fauna a decapodi raccolta con l'ausilio di una rete da spiaggia nell'infralitorale superiore (profondita compresa tra 0 e 1 m) su tre spiagge dell'isola di Veglia (Adriatico settentrionale). Ogni localita e caratterizzata da un diverso tipo di substrato sedimentario (fango, sabbia, ghiaia). La composizione in specie, la loro abbondanza e dominanza vengono presentate per ogni localita, come pure uno studio comparativo tra di esse. Ogni localita ha una propria specifica specie dominante. Carcinus aestuarii e la specie dominante su fondo fangoso, Philocheras trispinosus su fondo sabbioso e Palaemon elegans nella biocenosi di sabbie grossolane e ghiaie. In totale sono state trovate 14 specie di decapodi bentonici.
Parole chiave: fauna a decapodi, litorale, fondo sedimentario, Adriatico settentrionale
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INTRODUCTION
The research on decapods in the Adriatic began in the 19th century (Stevcic, 1993). In 1918, O. Pesta integrated all knowledge hitherto acquired in his monograph Die Decapoden Fauna der Adria. That was the actual beginning of intensive submarine research along the Adriatic coast. Within the systematic expeditions, decapods were researched as well. In the northern Adriatic, the research was mainly conducted along the Is-trian coast (Manning & Stevcic, 1982; Stevcic, 1991), and the Kvarner islands (Stevcic, 1979; Gamulin-Brida et al., 1980). The research generated new knowledge on the composition of the crustacean population in the muddy bottom biocenoses of the lower infralittoral and circalittoral (Gamulin-Brida et al., 1972), and of the rocky mediolittoral and infralittoral (Pérès & Gamulin-Brida, 1973). The upper infralittoral of horizontal shores with sedimentary bottom was left open to research. Such areas have not been studied since up to that point the research was mostly conducted by means of trawl nets and bottom grabs drawn by ships. Scuba diving did not produce significant results due to fauna being burrowed in the sediment, well hidden or scared by the movements and bubbles produced by the scuba divers. The UNEP Mediterranean Action Plan Draft Reference List of Habitat Types of Conservation Interest, the title being self-explanatory, is a list drawn up by international scientists under the sponsorship of the UN Environmental Project, in order to protect rare and endangered marine habitats. The list includes sedimentary bottom infralittoral biocenoses as well. Such habitats are very rare on the eastern Adriatic coast. Therefore, an investigation has been carried out to document the decapod fauna collected by means of a beach seine from the upper in-fralittoral (at a depth of ca. 0-1 m) on three shores of the island of Krk (northern Adriatic). Each locality is characterized by a different kind of sedimentary substrate (mud, sand and gravel). Our intention is to carry out a qualitative analysis in order to prepare a list of species per each locality and to determine their relation to the substratum: whether they are strictly dependent to a certain type of the bottom or have adapted to different types. With a quantitative analysis we wish to determine the frequency of species and their dominance per locality, as well as relative dominance between the localities per species found at more than one station.
MATERIAL AND METHODS Study area
The decapods recorded here have been sampled at three localities: in Meline cove, St. Marak cove, and Baska cove (Fig. 1 ). The coves are situated on the southeastern coast of Krk Island.
The localities may be described as follows:
-	Meline (kr1) is a relatively large cove, sheltered from northern and southern winds. The maximum depth in the middle of the cove reaches about 3 m, increasing gradually to 6 m at the cove entrance. The substrate is muddy sand. In the mediolittoral zone, the biocoenosis of superficial muddy sands in sheltered waters has developed. In the sediment, the bivalve Cerastoderma ed-ule prevails. In the infralittoral, too, predominates the biocoenosis of superficial muddy sands in sheltered waters with communities of Cymodocea nodosa. The fauna is very rich in forms, composed of fishes, crustaceans, snails, bivalves, etc. The stream periodically flowing into the cove has a minor influence on the water quality. Sewage systems of the towns surrounding the cove (Klimno, Cizici, Dobrinj) may have a greater influence.
-	St. Marak (kr2) is a small cove, poorly sheltered from the waves and winds. The cove ends in the beach, which is somewhat better protected by the breakwater of the nearby port. The substrate is fine sand. Up to 0.5 m in depth predominates the biocoenosis of superficial sands in very shallow waters with bare bottom and en-dobionts' holes. Boulder stones are overgrown by algae Acetabularia acetabulum and Cladophora sp. In the eastern part of the cove, at a depth of 1.5 m, rocky bottom prevails, with pure sand between the rocks. A community of photophilic algae with low thalli has developed here. The predominant species here are: green alga A. acetabulum, brown algae Dictyota linearis and Dictyota dichotoma, and red alga Laurentia obtusa. Small thalli of the alga Padina pavonica and smaller settlements of the alga Dasycladus vermicularis were observed. Recently washed away shells of the bivalves Acanthocardia tuberculata, Callista chione and Paphia aurea are common on the sandy bottom. On the sandy bottom off the cove's western shore, at a depth of 2 m, biocoenosis of superficial muddy sands in sheltered waters with a meadow of C. nodosa has developed. The nearest town (Risika) is a few kilometres away.
-	Baska (kr3) is a bay, with gravel beach at its far end. The gravel substrate extends to a depth of 1 m. The bottom is bare, with a low bed of alga Cladophora sp. within the biocoenosis of coarse sands and fine gravels mixed by the waves. Further into the bay, there are boulder stones with thick settlements of the bivalves Mytilus galloprovincialis and Ostrea edulis. The rocky bottom is covered by a mossy layer of alga Cladophora sp., and to a lesser degree by algae Peyssonnelia sp. and Ceramium rubrum. In the area exceeding the depth of 2 m prevails the biocoenosis of superficial sands in very shallow waters. At the sampling point, the rivulet Ricina flows into the sea. As the town of Baska and its campground are situated close to the beach, the anthropogenic influence on the water quality could be considerable, especially in the summer period.
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Fig. 1: Study area. SI. 1: Raziskovano območje.
Material and methods
The material was collected in the mornings, in March 2002, once per each station, by means of a beach seine (Gibson et a!., 1993). Trawl hauls lasted for approximately 1 min and covered a mean distance of about 50 meters per each station. The seine net had 6 mm meshes. Its sides were 5 m long, it was 0.8 m high, its sack 1 m deep. The seine sampled animals of all sizes: from 10 cm long Carcinus aestuarii specimens to only few mm long specimens of Athanas nitescens. Apart from the decapods, the catch included some diverse fishes (Gobiidae, Sparidae, Soleidae, Callionymi-dae...). At the locality kr1, the seine was drawn perpendicularly to the shore from the depth of 1 m. At the locality kr2, it was drawn perpendicularly to the shore, from the depth of 1.5 m to the shore. Due to bottom configuration at the locality kr3, the seine was drawn horizontally to the shore covering the bottom up to the
depth of 1 m. The decapods were separated in the field and preserved in 5% formol solution, to be analysed and counted in the laboratory. The species composition, their abundance and dominance were given for each locality, upon which a comparative study was conducted.
RESULTS AND DISCUSSION
The research revealed 14 decapod species at the three investigated localities. Each locality exhibits different species composition and different dominant species. The results are given in Tables 1, 2 and 3, listing the number of specimens and percentages of species per locality.
Table 1 lists six species found in the seine at krl locality. It is evident that C. aestuarii is the dominant decapod, its share in the catch being 72.50%. This species lives in the intertidal and sublittoral zone, on every kind of soft bottom, frequently nearby estuaries and lagoons
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(Falciai & Minervini, 1992). Upogebia pusilla is also very common in this kind of environment. It lives in burrows 20 cm deep and is probably very hard to catch with seine net. Diogenes pugilator is a preferential characteristic hermit crab species of the well-sorted fine sands (Pérès & Picard, 1964). Palaemon adspersus lives on muddy sediment near sea grass meadows in brackish waters (Falciai & Minervini, 1992).
Tab. 1: Decapods collected at kr1 locality (Meline cove).
Tab. 1: Deseteronozci, ujeti na lokaliteti krl (draga Meline).
Furthermore, Crangon crangon is the only species with more than two specimens in the catch. This species is also frequent at the river mouths and/or lagoons. It lives in the burrows and exits during the night (Falciai & Minervini, 1992).
Tab. 2: Decapods collected at the kr2 locality (St. Ma-rak cove).
Tab. 2: Deseteronozci, ujeti na lokaliteti kr2 (draga Sv. Maraka).
St. Marak beach (Tab. 2) appears to be the locality with most diversified decapod population, where 9 different species of decapod crustaceans were found. Philocheras trispinosus, pursuant to the Adriatic decapod check-list (Stevcic, 1990) and a rare species in the Adriatic, appears to be fairly common at this station. It is the dominant species, its share in the catch being 53.23 %. Palaemon elegans is quite abundant on this beach as well, with the share of 22.58%. P. adspersus lives on muddy sediment near sea grass meadows in brackish waters (Falciai & Minervini, 1992). Macropodia rostrata
is also very common in a few meters on mixed sediments (Falciai & Minervini, 1992).
Table 3 demonstrates almost absolute dominancy of the species P. elegans, its share in the upper infralittoral of Baska beach being 97.18%. As opposed to the "dominant" shrimps P. trispinosus and P. elegans, the crab C. aestuarii has been found on the muddy bottom of the Meline cove beach only. C. aestuarii appears to be more dependent on the substrate of its habitat than the two other species. The environment of Meline cove seems to be suitable for the species listed above (apart from D. pugilator and M. rostrata). The relative abundances are probably strictly related to the catching method utilized for the research.
Tab. 3: Decapods collected at the kr3 locality (Baska bay).
Tab. 3: Deseteronozci, ujeti na lokaliteti kr3 (zaliv Baska).
Species	No. specimens	%
Palaemon elegans	69	97.18
Philocheras trispinosus	2	2.82
As far as other study sites are concerned, species like Clibanarius erythropus, Pisidia longicornis, Porcellana platycheles and Xantho poressa are normally found close to the stones or pebbles on the sandy bottom. In this case, too, their relative abundances are due to the catching method.
The species P. elegans and P. trispinosus were found at the sandy locality kr2, as well as in the biocenoses of coarse sands and gravels at locality kr3. Macropodia rostrata was found on the muddy bottom at the Meline cove station, and in the sandy infralittoral of St. Marak beach. These are the only three species caught on more than one type of substrate. The data reveals that P. elegans prefers coarse sedimentary bottom to sandy bottom and does not appear on muddy substrate at all. As opposed to P. elegans, P. trispinosus prefers sandy bottom to gravel and does not appear on muddy substrate. M. rostrata sporadically appears in the biocoenosis of superficial muddy sands in sheltered waters, yet it never inhabits coarse sedimentary substrate.
For the other listed species, not enough specimens were collected at the three localities to enable us to positively establish their exclusive connection with the type of habitat substrate.
CONCLUSIONS
The figure of 14 collected decapods is a relatively good result considering the number of times the beach seine was drawn. In comparison with the results of decapod collection nearby, at 25 stations along the southwestern coast of Krk Island at depths of 2-30 m (Gamu-
Species	No. specimens	%
Palaemon adspersus	2	2.50
Crangon crangon	16	20.00
Upogebia pusilla	2	2.50
Diogenes pugilator	1	1.25
Carcinus aestuarii	58	72.50
Macropodia rostrata	1	1.25
Species	No. specimens	%
Athanas nitescens	2	3.23
Palaemon elegans	14	22.58
Philocheras trispinosus	33	53.23
Clibanarius erythropus	3	4.84
Pisidia longicornis	3	4.84
Porcellana platycheles	1	1.61
Xantho poressa	4	6.45
Liocarcinus depurator	1	1.61
Macropodia rostrata	1	1.61
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lin-Brida et a!., 1980), where 16 species were caught, it in fact appears to be even better. The species C. aestuarii is dominant on the muddy bottom of the researched locality, P. trispinosus is dominant on the sandy bottom, and while P. elegans is dominant on the coarse bottom. The crab C. aestuarii was found exclusively on the muddy substratum. Decapods P. elegans and P. trispinosus do not depend on only one type of bottom substrata.
The acquired data on the dominancy of decapod species in specific sedimentary habitats, and their dependence on those habitats should be supplemented with data per season, and data on night time beach seine drawing at the above-mentioned localities. Drawing the seine in every season would determine possible
annual vertical migrations and changes in the decapod composition. Additional night time sampling would eliminate the shortcomings of the daily sampling resulting from certain species being covered up or inactive at daytime.
ACKNOWLEDGEMENTS
I would like to thank my colleague Milvana Arko-Pijevac for her assistance in biocoenology in this project, and my colleagues Marcelo Kovacic and Lado Bar-tonicek for assistance during the fieldwork. I am also grateful to Zdravko Stevcic and Cedric d'Udekem d'Acoz for reading the manuscript.
PREDHODNA RAZISKAVA FAVNE DESETERONOŽCEV NA SEDIMENTNEM DNU V ZGORNJEM INFRALITORALU OTOKA KRKA (JADRANSKO MORJE)
MARIN KIRINČIČ
Prirodoslovni muzej Rijeka, HR-51000 Rijeka, Lorenzov prolaz 1, Hrvaška POVZETEK
Osnutek referenčnega seznama habitatnih tipov varstvene pozornosti, pripravljen v okviru akcijskega načrta okoljskega programa Združenih narodov (UNEP), vključuje tudi sedimentne biocenoze spodnjega infralitorala. Zaradi dejstva, da so takšni habitati zelo redki vzdolž jadranske obale, je bila napravljena raziskava favne desetero-nožcev, in sicer ob pomoči mrež s plovci v zgornjem infralitoralu (v globini od 0 do 1 m) na treh obrežnih odsekih otoka Krka. Za vsako od teh treh lokalitet je značilna specifična sedimentna podlaga (glen, pesek, prod). Na vsaki lokaliteti je bila ugotovljena sestava vrst, njihova številčnost in prevlada, in na osnovi teh ugotovitev napravljena primerjalna študija. Vsaka raziskana lokaliteta ima svojo specifično prevladujočo vrsto: Carcinus aestuarii prevladuje na glenastem dnu, Philocheras trispinosus na peščenem, Palaemon elegans pa v biocenozi grobega peska in proda. Skupaj je bilo zabeleženih 14 bentoških dekapodnih vrst.
Ključne besede: favna deseteronožcev, litoral, sedimentno dno, severni Jadran
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