ANNALES • Ser. hist. nat. ■ 13 • 2003 • 1
original sc ientific article	UDK 639.4:574.6(262.3-181
received: 2003-03-17
ESTIMATING THE CARRYING CAPACITY OF COASTAL AREAS POTENTIALLY SUITABLE FOR MUSSEL CULTURE IN THE UPPER ADRIATIC, CROATIA
Barbara SLADONJA Institute for Agriculture and Tourism, HR-52440 Poteč, P.O. Box 31 E-mail: bar.bara@iptpo.lir
Radovan ERBEN, Ivana MACUtRE, Goran KLOBUČAR & jasna LAJTNER Department of Zoology, Faculty of Science, University of Zagreb, HR-5000Q Zagreb, Rooseveftov ti:g 6
ABSTRACT
This papa deals with the application of a carrying capacity model, designed to evaluate the suitability often coastal inlets situated on islands in the upper Adriatic Sea for mussel production, and to estimate a potential produc tion quantity. I his approach allowed the estimai ¡on of a potential carrying capacity or the researched stations and suggestions for a possible launch of mussel production in these areas. The results or this study are considered to be useful for (he management of coastal areas suitable for bivalve, tanning, especially in this particular case of island development, it has been established that the model was suitable for evaluation and that all selected stations have flood conditions and carrying capacity tor mussel production. Mussel farming could, therefore, improve the island economy.
Key words: carrying capacity, mussel farming, dimensioning of mussel farms, island development, Croatia
VALUTAZIONE DI AREE COSTAL! POTENZiALMENTE IDONEE ALLA MITILICOLTURA
NEL NORD ADRIATICO, CROAZIA
SINTFSI
L'articob tratta l'appficazione del modelio di capacita portante clestinato alla valutazione dell'idoneita alla m/-tilicokura ui dieci Inscnature costali sitúate su isole del Nord Adriático e alla s rima délia quantité cfi produzierte Potenziale. L'approccio permette la valu tazlone delh?. capacita portante potenziale del le stazioni s ludíate, nonché la formulas tone di proposte per un possibile lancio délia mitllicoltura in tali aree. I risultati del presente studio ven-gono considérait vantaggiosi per la gestione de Ile aree costali idonee alla coltura di bivalvi, in particolare neü'ambito dello sviluppo insulare. Il modelio si è rivelato adatto alla valutazione e tutte le stazioni prescelte hanno dimostrato di avere condizioni e capacita portant' favorevoli alla mitllicoltura. La coltura di mitili perianto potrebbe mighorare ¡'economía insulare.
Parole chiave: capacita portante, mitllicoltura, climensionamento di mitilicolture, sviluppo insulare, Croazia
ANNALES • Ser. hist. nat. ■ 13 • 2003 • 1
Barbai» SIADONJA et ¿1: ESTIMA I INC n-lC CARRYING CAPACITY OF COASTAL AMAS POT CM AU V SUI ÎABI.l: FOR MUSS0. CU1.TURF .... 2S-Î2
INTRODUCTiON
The coast of Croatia and especially its islands have a number of areas potentially suitable for sea organism farming. Seashell farming has a long tradition on the eastern Adriatic coast, probably dating from the Roman period, but the first written documents originating from the 16,h century describe Mali ston Bay. In the 20'1' century, seafood farming intensified on over 30 localities from Slovenian coast down to Boka Kotorska Bay (Basioli, 1981). Former seafood production (during the Austro-Hungarian Empire) was much higher than today. The Austrian Fishery and Mariculture Society used several locations on the coast and islands for oyster and blue mussel culture (Quinto Congresso generale delta Società Austriaca di Pesca e piscicoltura marina, 1893), One of the main social and economical problems in Croatia today is maintaining the population on the islands and revitalising the economy. Aquaculture could be one of the main economy branches on the islands and on the coast in general.
Aquaculture is characterised by great dependence on the quality and productivity of the environment. Its development also bears a risk of negative environmental impact, such as pollution, landscape modification, or biodiversity change. Aquaculture development needs to follow the rtiies for use and conservation of natural resources in aquatic ecosystems (Bussani, 1983). Aquaculture as a renewable resource is a capital thai must ensure a sustainable flow of benefits to users.
Coastal zones are always subjects of different conflicting needs, which include recreational and tourist requirements, navigational access and traditional commercial fishing rights. Optimisation of available space is consequently a challenge that also faces the developing aquaculture industry.
Few mussel species are farmed all around the world. The world production in 2000 exceeded 1.5 million. More than 20 countries have significant production, although only two of them dominate the market, i.e. China with 40% of the total world production and Spain with 20%.
On the eastern Adriatic coast, the majority of shell production is located in Mali ston Bay (90% of total production), with other larger farms situated in Lim Bay, Piran Bay, mouth of the river Krka, and Budava Bay (Hrs-Brenko, 1985). In 1984, 300 t of mussels, 40 t of oysters and 2(>0 t of blue mussels were produced in Mali ston Bay (BenovsC, 1980, 1997), Considering the natural features of our coast, it could be said that the seafood production is still far from possible and satisfactory.
The most farmed mussels are those belonging to the genus Mytilus (M. eduiis - blue mussel), while the genus Perna (former green mussel) is (armed in warrnei waters, as around Thailand, China or New Zealand.
The capacity at the Gulf scalc depends on primary
production, trophic relationships, and modification of bio-geochemical cycles and community structure in the vicinity of culture sites (Foster-Smith, 1975; Frechette & Bourget, 1985; Frechette eta!., 1991, 1992).
On a smaller scale, however, the possibility of local food depletion should be considered. In many coastal ecosystems, bivalve suspension feeders, such as mussels, oysters and clams, occur in high densities. Feeding is performed by pumping and filtering large volumes of water through gills. Due to the filtration activity by bivalves, depletion of organic matter, bacteria and phyto-plankton in the overlying water has been observed in various ecosystems (Mohlenberg & Riisgard, 1979; Wright et at., 1982; Mantoura & Llewellyn, 1983; Frechette & Bourget, 1985). Indeed, dense arrays of long lines are likely to lead to a depletion of seston (Loo & Rosenberg, 1989), which c:ould affect the optimal size of growing sites, a problem thai has been considered by Incze et al. (1981 i. In addition, local depletion of seston raises the issue of determining the optimal distance between the sites, as they should be positioned in such a way to enable water replenishment by mixing and plankton growth before reaching next downstream site.
Early attempts to assess the impact of shellfish aquaculture focused on the issue of carrying capacity, or the ability of the system to support shellfish production were made (Incze eta!., 1981; Loo & Rosenberg, 1989). More recently, the emphasis has been on modelling the impact of shellfish (Rodhouse & Roden, 1987).
A carrying capacity model has been tested by applying it to ten island bays in the upper Adriatic. The model is based on particle and not on energy flow. The main objective was to test the model, and to apply it in specific conditions of the chosen bays.
A three-season field programme was undertaken to assess the spatial and periodical distribution of total and organic seston and transport mechanisms of water and seston in the vicinity of a site. These terms of the seston budget were used to determine the dominant processes involved, and thus to evaluate the possibility of launching mussel farming.
MATERIALS AND METHODS Location
The study was carried out in the upper Adriatic Sea, on four Croatian islands. Ten potentially suitable stations for mussel farming were investigated (Fig. 1): Cres Island: Pogana Bay (si. 1), Krk Island: Puntarska draga (st. 2) and Soline Bay (st. 3),
Rah island: St. Eufemija Bay (st. 4), Kamporska draga (st. 5), l opar Bay (st. 6) and Supetar Bay (st. 7),
Pag Island: Caska Bay (st. 8), Stara Novalja Bay (st. 9), and Stara Povljana Bay (st. 10).
ANNALES • Ser. hist. nat. -13- 2003 • 1
n»«Uu SlAOOUjA «I aJ; ESTIMATING M CARRYING CaPaCITV ot COASTAL A.RSAS POItNTlAUY SUIT ABIE fOR MUSSa CUUURC >5-3

sf s'ff^vL K«*
Fig. 1: Ten investigated stations along Croatian islands potentially suitable for mussel farming. SI. f: Deset raziskanih vzorčišč vzdolž hrvaških otokov, potencialno primernih za školjkarsho.
Sampling
Sampling took place in the winter (February} of 1998, and in the summer (July) and autumn (December) of 1999. Three replicates of water samples were taken at 0,5 and 10 m using a 5 ! Niskin bottle. Currents were measured by a pseudo-euferian method using Andria's cross (Mosetti, 1979). Compass recorded the direction.
Methods
Total particulate matter or seston (TPM) and particulate organic matter (POM) was determined as triplicates in the Zoology Department of the Faculty of Science.
Samples tor seston analysis in triplicates of 250 ml were filtrated on combusted and pre-weighted Whatman C.F/F tilters. Tite filters were transferred to a 60"C drying oven toi 24 hours. On the following day, filters were weighted to obtain values of TPM and combusted at 450 to 500°C for 24 h and re-weighted to estimate particulate inorganic matter (PIM) and POM (Magazzti, 1984) We used standard statistic equations (standard deviation and Mest).
Filtration rate is defined as the rate of removal of particles from a suspension in which the animals teed, or a measure of the equivalent volume of water that must have been filtered to account for the rate of rc-moval (CoughSan, 1969; Foster-Smith. 1975; Meyhofer, 1985; Prins ef a!., 1994; Riisgird, 2001). We used literature data for calculating the filtration rate. In Table 1, values
of blue mussel filtration rates are presented. Finally, we used the average filtration rate for the blue mussel.
Food supply is a function of water movement and quantity of particles in the water, whereas food demand is a function of filtration rate and food concentration. Carrying capacity is calculated by dividing food supply with food demand.
Tab. 1; Data of mussel filtration rate from bibliography. Tab. I: Podatki iz bibliografije o hitrosti filtracije skolik.
Mussel filtration rate (l/h)	Bibliographic source
2.06	Foster-Smith (1975)
0.33-1.25 (0.79)	Foster-Smith (1975)
0.35-1.05 (0.7)	Foster-Smith (1975)
1.54	Foster-Smith (1975)
1.47	Foster-Smith (1975)
1.2-3.4 <2.3)	Schuite (197S)
0.5-2.0(1.25)	Mohlenberj} & Riisgard (1979)
1-2.5 (1.75)	Widdows eta!. (1979)
2. SO	Martiniiif (199S)
! 1.60	average value
The modelfing approach itself has shown certain weaknesses, including sensitivity to a restricted set of underlying assumptions and Insensitivity to a potentially wide array of unspecified parameters. Despite these numerous limitations, approximations of carrying capacities for intensive cultivation remain of interest. The salient feature of both models is that it is based on particle flow, and not on energy flow. Clearly, the limitations of the modelling approach are not eliminated by these simplifications. This model is offered as an approach, and not as a unique solution.
The model is based on water movements and on the seston quantity in the area. A biological concept of the carrying capacity can be defined as the stock density at which production levels are maximized, without a negative environmental impact. The carrying capacity-model studied here is based on balance between mussel nutritive needs and food supply within the system. The estimation of the carrying capacity of bivalves in open systems is rendered difficult due to several factors: 1) seasonal and size-related changes in the energy demands of the cultured organisms;.2) seasonal changes in the abundance and nature of potential food substrates found in natural waters; 3) general lack of knowledge concerning the degree to which bivalves utilize various particles in the seston, and 4) difficulties of quantifying mixing arid flow through most culture areas.
The model of Carver & Mallet (1990) was developed in Canada (Nova Scotia). Authors used a somewhat simplistic but practical approach to determine estimates of carrying capacity for a mussel operation in a semi-closed coastal inlet on the Atlantic coast. Rather than
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ANNALES • Ser. hist. nat. - 13 • 2003 • 1
Batter» Sl.ADONSA hi ¿1.; tSTIMATtNG THF CARRYING CAPACITY Of COASTAL ARMS TOTFNTIAl I.Y SUITAfilF FOR MUSSEL CULTURE .... 2S-32
relying on laboratory-derived values, authors obtained extensive field data on water exchange, food levels and in situ mussel filtration rates. The volume of the Basin was estimated as well as the volume of water flowing in and out of the system in each tidal cycle, Data of suspended particulate matter was used in order to calculate food levels (food supply and food demand). Finally, carrying capacity was obtained dividing food supply by food demand. Equations are presented in Table 4.
RESULTS AND DISCUSSION Environmental study
Current velocities are shown in Table 2. As expected, the strongest currents were measured in winter as a consequence of meteorological conditions. We did not find significant differences between stations.
Measurements of the currents gave us results comparable with other authors (Princi et a/., 1980; Stravisi & Battista, 1992). Two current types are usually present in the Adriatic (Mosetti, 1966). On a large scale, there is a constant slow current below 10 m depth, parallel to the coast in the northern direction. On a small scale, currents are influenced by wind, tide and morphological circumstances. It is important for good water quality in mussel farms to have fast water exchange and currents able to replenish the water quite frequently.
The biggest bay is Caska on Pag Island, while the smallest is Pogana on Cres Island. As far as the bay volume is concerned, the largest goes to St. Povljana Bay on Pag, and the smallest to Punat Bay on Krk. In Table 4, all hydrologic data about bays is presented (water tidal oscillations, water surface and volume, water exchange).
Water exchange in all examined bays showed good results (from 5-30% of water exchange/day). For example, the Gulf of Trieste that is known for its high number of mussel farms (Martincic, 1998) has an average water exchange of only 7%. The bay studied by Carver & Mallet (1990) had a water exchange of approx. 50%. This is particularly important for water replenishment that depends not only on tidal currents but also on permanent currents and afso imports from the land.
Temperature, salinity and oxygen are parameters closely linked with each other and connected with external meteorological and hydroiogical conditions. Their variations are mostly of temporal character. During winter, the water column is homogeneous due to strong water mixing, while in spring it is possible to observe water stratification, which continues into and through the entire summer (Marchetti & Cotta Ramusino, 1992). Stratification is present both for temperature (presence of thermodine) and salinity (picnociine). in spring, superficial water in fact heats up, and due to the freshwater income from the land the salinity varies greatly between the sea's surface and floor.
Tab. 2: Current velocities at sampling stations. Tab. 2: Hitrosti tokov na vzorciScih.
juotrmnmiw | Stations	Winter	Summer	Autumn ]
1	9.5	15.2	0.07
2	0.6	12.5	10.0 j
3	5.9	0.9	0.9
4	18.0	1-4.7	8.3
5	12.8	16.7	0.1
6	26.3	16.7	8,3
7	10.2	9.5	10.5
8	12.5	7.1	14.9
9	15.0	8.3	8,3
10	0.3	0.3	0.3
Analysis of TPM showed a maximum concentration of particulate matter in summer {Tab. 3). Considering the low depth of water at most stations, high TPM values are probably a consequence of bottom resuspension. The obtained data were not significantly different between stations.
The relatively high standard deviations can be explained with the fact that these values are calculated as an average of three depths (0, 5 and 10 m). These are depths at which mussels are farmed and although different they were not statisticalfy significant. For further calculations, we thus decided to work with average data.
The lowest POM concentration was recorded in winter, the highest in autumn. Differences between winter and summer as well as between winter and autumn are statistically significant (l-test - 0.000828, t-test ~ 0.002804), while those between summer and autumn are not significant {West = 0.285358), Ail the examined stations had a good quantity of POM, ranging between 1.2 rng/1 (Lopar and St. Novaija Bays) and 4.2 mg/l in St. Povljana Bay.
TPM is related to land contributions and also to phytoplankton production (Schulte, 1975; Valli, 1980; Fonda Umani & Ghirardelii, 1988; Williams & Claustre, 1991). Suspended matter is usually composed of inorganic detritus, especially close to the shore or in shallow waters. Even by taking this into consideration, we found some relatively high concentrations of organic matter, with values ranging from 14% (winter) to 77% (autumn) of POM. Bayne & Widdows (1978) recorded, for the coastal area of Spain, values from 3 to 100 ntg/l of TPM, with only 5-30 % of organic: components. Our results can be well compared to data measured in the Gulf of Trieste (Adriatic Sea). Authors measured from 0.7 to 4 mg/l of TPM, with 25 to 31% of organic matter (Fonda Umani & Ghirardelii, 1988).
Since the organic component is formed by live planktonic organisms and organic, products of biodeposition, it is normal that we found the lowest concentration of organic matter in winter, when no planktonic
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ANNALES • Ser. hist. nat. - 13 • 2003 • 1
lí ¿tinta SI.ADONfA el ai: ESTIMATING THE CARRYING CAPACITY OF COASlAt AREAS POTCNTlAl.IV SUHABtE FORMOSSíL CULTURE .... ¿5-32
Tab. 3: Mean values (±s.d.) of total particulate matter (TPM) and particulate organic matter (POM) during three seasons at ten sampling stations. Relative contribution of POM as % of TPM is also shown.
Tab. 3: Srednje vrednosti (±s.d.) celotne suspendirane snovi (TPM) in partikulatne organske snovi (POM) v treh sezonah na desetih preučevanih vzorčiščih. Prikazan /e tudi relativni prispevek POM kot % TPM.
Station	Winter			Summer			Autumn		
	TPM (mg/l)	POM (mg/l)	POM (% of TPM)	TPM	POM	POM (% of TPM)	TPM	POM	POM (% of TPM)
1	3.3 (1.0)	0.4 (0.3)	14.0(11.5)	4.1 (1.7)	2.6(0.8)	68.0 (20.7)	3.5 (0.9)	2.0 (0.3)	60.0(11.0)
2	3.4 (1.4)	0.9 (0.11	28.7 (8.1)	3.3 U.0)	2.2(0.5)	69.0 (7.5)	3.8 (1.7)	i .5 (0.9)	39.7(15.6)
! 3	3.9 (0.8)	1.2 (0.1)	31.0 (2.8)	6.3 (3.3)	3.0(1.2)	48-0 (22.3)	3.5 (1.1)	1.3 (5.7)	37.0(15.5)
i 4	17.8(20.5)	1.7(1.1)	18.0(10.5)	7.4 (2.0)	1.8 (0.9)	25.3(12.5)	3.0(1.8)	2.1 (0.7)	75.3(15.9)!
5	3.0(1.6)	0.5 (0.3)	17.3 (4.2)	4.3 (2.9)	1.9 (0.6)	49.7(13.7)	2.6(1.0)	2.0 (0.7)	76.7(4.2)
6	4.8 (4.0)	0.7 (0.0)	21.0(13.1)	4.1 (2-3)	1.7 (0.7)	47.3 (15.3)	7.0 (5.8)	1.3 (0.5)	22.3 (8.1)
7	3.8 SI.41	0.8 (0.4)	22.0 (6.9)	4.3(1.9)	1.8(0.3)	44.7(11.7)	2.6 (0.6)	1.2(0.2)	48.3 (19.51
8	6.8 (4.8)	1.6 (0.8)	25.0 (5.6)	7.1 (4.0)	3.9(1.1)	62.0(17.1)	3.4(1.1)	1.7 (0.61	50.3 (4.5)
9	3.0 (0.7)	1.1 (0.3)	35.7 (7.8)	2.6 (0.3)	1.3 (0.4)	50.3 (19.8)	2.9 (0.4)	1.1 (0.4)	36.7(7.5)
1......<0 ....	2.3 (0.6)	0.5(0.1)	22.0(7.8)	18.0(6.5)	4.2 (.1.3)	23.0 (9.8)	_2.8 (1.3)	1.8 (6.0)	64.0(25.3)
blooms are present, and the highest percentage in autumn due to the active pianktonic bloom or scenes-cent phase of the bloom (Marchetti & Cotta Ramusino, ¡992).
Carrying capacity mode!
i here is an abundance of data in literature on the influence of water flow on the particles or food concentration (Dame el aL, 1980; Incze et at.. 1981; Cloern, 1982: Fr&chetre & Bourget, 1985; Loo & Rosenberg, 1989).
in estuaries, the seston movement is dominated by the river outflow, while in the coastal inlets it is primarily determined by tidal currents, which are often very weak. Food supply in the water depends not only on the water flow but also on the quantity and quality of particles present in it (Zentilin & Pellizzato, 1996).
Variations in food supply are in relation to tidal oscillations and thus to tidal volume, as well as to POM oscillations in the water. We observed that maximum POM levels at our stations were comparable to the values reported in other mussel studies (Bayne & Widdows, 1978; Widdows et ai, 1979; Wildish & Kristmanson, 1984; Carver & Mallet, 1990). Values lower than 1 mg/l are common along the Atlantic coast, while higher values are generally characteristic of estuaries and coastal inlets (Carver & Mallet, 1990). The lowest food supply was noted for the wintertime, as a result of the low primary production.
Among the stations, we calculated the highest quantity of food supply in Caska and St. Povljana Bays on Pag Island.
Rodhouse & Roden (1987) found that zooplankton compete with cultured mussels for food particles and
estimated that herbivorous zooplankton consume 29% of the annual phvtoplankton production in Killary Har hour, Ireland. On the other hand, recent evidence suggests that mussels can significantly reduce mtcrozoo-plankton levels (Incze et al., 1981), thereby effectively decreasing food competition. Given that increasing stock densities have a positive effect on primary production, our estimates of food supply should eventually include not only the POM delivered to the system, but also locally produced POM.
Food demand was calculated with estimates on filtration rate and food concentration. At our sites, there were always enough particles present in the water to satisfy the average filtration needs by mussels. Mussels consume live and inorganic particles in the water (plankton and detritus).
Since we did not find significant differences in carrying capacities measured in winter, summer and autumn, average data is presented (lab. 4). In the end, we concentrated on potential differences between stations.
Relatively large water volumes and high POM concentrations gave high carrying capacities. St. Novalja and St. Povljana Bays had a carrying capacity higher than 2000 t. The lowest carrying capacity was calculated for Pogana (about 600 t).
In estimating the carrying capacity, we assumed that the mussels had access to 100% of the available food supply. This approach does not allow factors such as incomplete mixing of particles in the Gulf, loss of particles in the outflow, and contamination of "new" particle-rich water by "old" particle-depleted water from the previous tidal cycle. A positive effect of mussel stock densities on nutrient regeneration, which can enhance local primary production, should also be considered.
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ANNALES • Scr. hist. nat. • 13 • 2003 ■ I
Barbara SI ADONjA ef al.: ESTIMATING THL CARRViNO CAPACITY OF COASTAL AktAS POTCNTIAUY SUITABLE ¡'OR MUSSIIt CULTURE .... 25-32
Tab. 4: Carrying capacity equations and hydrological dala for the ten sampling stations. Tab. 4: Enačbe za izračun nosilnosti okolja in hidrološki podatki za deset vzorčišč.
	Parameter	Equation	Cres	Krk	Krk	Rab	Rab	Rab	Rab	PaR	Pag	
			st. 1	si. 2	st. 3	st. 4	st. 5	St, 6	si. 7	st. 8	St. 9	st. 10
a	Average ebb tide (cm)		32.?.	32.2	32.2	32.2	32.2	32.2	32.2	3Z2	32.2	32.2
b	Average high tide !cm)		30.3	30.3	30.3	30.3	30.3	30.3	30.3	30.3	30.3	30.3
c	Daily useilations (cmi	(a+b) x 2	17.5	12$	125	125	125	125	12S	125	125	125
d	Tidal volume per day (x 1D1 rrr)	c x i	201	377	430	320	463	271	560	1398	675	1030
e	Tidal volume per week (x 104 m3)	d x 7	1407	2644	3016	2246	3244	1903	3920	9789	4731	7211
f	Bay volume in ebb tide (x 10" m3)	M/2	1217	878	1106	2344	9732	2426	6274	11487	10683	15714
8	Bay volume in high tide (x 10" m3}	j+d/2	1418	1255	1537	2665	10196	2697	6834	12886	11359	16745
h	Water exchange per day 1%)	d/g	14	30	28	12	5	10	8	11	6	6
i	Total by surface (Ami) m2		1609300	3024209	3449123	2569200	3710500	2176800	4482500	11194100	5410100	8245700
i	Bay volume (V.J x 104 in5		1318	1067	1 322	2505	9964	2562	65S4	12187	11021	16230 j
k	POM (mg/l)		1.7	2.6	2.4	1.9	1.5	1.2	1.3	2.4	1.2	4.2
1 m	Food supply (x 10" g ROM/week)	c x k	23.4	68.4	72.4	42.0	47.6	23.4	49.4	233.2	55.1	202.1
	Food demand (g POM/kg mussels/week)	k/1000 x 1.6 x 24h x 7 x 83	37.2	57.3	53.5	41.6	32.7	27.5	28.3	53.5	26.0	62.5
	Carrying capacity (Ions of mussels)	J/m	029	1193	1353	1010	1456	851	1746	4359	2119	3234
All the sites have shown to he suitable for mussel production. Carrying capacities higher than 500 t can be considered as high. The lowest recorded carrying capacity was in Pogana Bay on the island of Cres (600 t). Generally, the best island for mussel production should be Pag, where all three bays showed very high carrying capacities (higher than 2000 t).
CONCLUSIONS
It can be concluded that all the examined sites on Croatian islands are suitable for mussel farming. The present study only confirmed this statement already known to national experts. Mariculture could be an ad-
ditional motive and way of earning money for these island populations, as well as incentive for new people settling there.
Among 10 sites, the best are those on the island of Pag, but none turned out to be non-suitable for mussel farming. Similar study should be performed on other islands and new locations for this economic activity suggested.
ACKNOWLEDGEMENTS
The project was financially supported by the Croatian Ministry for Public Works and Reconstruction.
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ANNALE5 ■ Ser. hist, nat. • 13 • 2003 • 1
~	liariMi* SI aDONJA Trši: cSTIMAHNG THE CARRYING CAPACITY OF COASTA! AREAS POUNTiALLY SUITAfiLTFOlTMUSSnt CULTURE ..., 25-32
OCENJEVANJE NOSILNOSTI OKOLJA V SEVERNOJADRANSK1H OBALNIH OBMOČJIH, POTENCIALNO PRIMERNIH ZA VZGOJO ŠKOLJK
Barbara SLADONJA Institute for Agriculture and Tourism, HR-S244Q Poreč, P.O. Box 31 E-mail: barbara&iptpo.hr
Radovan ERBEN, Ivana MACUIRE, Goran KLOBUČAR & jasna LAjTNER Department of Zoology, Faculty of Science, University of Zagreb, HR-i 0000 Zagreb, Rooseveltov trg 6
POVZETEK
V desetih manjši!) zalivih ob severnojadranskih otokih je bil uporabljen mode/ za ugotavljanje nosilnost! tamkajšnjega morskega okolja. Študija, katere namen je bil ugotoviti primernost teh voda za gojenje školjk, je slonela na terenskih podatkih o izmenjavi vode in količini hrane v njej, dobljenih med vzorčenjem pozimi, poleti in jeseni leta 1999.
Rezultati so pokazali,, da so vse preučevane lokalitete primerne za školjkarstvo. Najnižja nosilnost okolja je bila ugotovljena v zalivu Pogana na Crew, sicer pa je bila izmenjava vode zadostna v vseh preučevanih zalivih (od 530% na dan).
Dobljene rezultate bi lahko uporabili za upravljanje obalnih območij, primernih za vzgojo školjk, posebno v primerih načrtovanega otoškega razvoja. Školjkarstvo bi lahko seveda močno izboljšalo otoško gospodarstvo.
Ključne besede: nosilnost okolja, školjkarstvo, dimenzioniranje školjčišč, otoški razvoj, Hrvaška
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