ANNALES • Ser. hist. nat. • 13 • 2003 • 1 • Supplement short scientific article UDK 639.32:504.064 received: 2003-09-02 1SN ENRICHMENT IN FOULING COMMUNITIES INFLUENCED BY ORGANIC WASTE DERIVING FROM FISH FARMS Sonja LOJEN "¡oief SieiW Institute, Department of Environmental Sciences, S'-tOOO Ljubljana, Jamova 39 E-mail: sonja.tojen@ijs.si Dror ANGEL & Timor KATZ National Centre for Marieuiture, Israel Océanographie and Limnoiogical research, IL-Eilat 88112, POB 1212, North Beach Manolis TSAPAKIS Institute of Marine Biology of Crete, GR-71003 Heraklion, f'OB 2214 Nives KOVAC&Alenka MALE! National Institute of Biology, Marine Biology Station, SI-6330 Piran, Fornaie 41 ABSTRACT The nitrogen stable isotopic composition of fouling communities colonizing hard substrates at the fish farms and at unpolluted reference locations in N Adriatic IPiran, SI o venia!, E Mediterranean (Crete, Greece) and in the Red Sea (Eilat, Israel) was studied. An overall enrichment of the fouling community in 15-N at the fish farms has been detected at two of the three locations, indicating the incorporation of farm-derived particulate nitrogen into the organisms tissues. Key words: fish farm, stable isotope, nitrogen, biofilters, fouling organisms ARRICCHÍMENTO IN iSN IN COMUNITÁ Dl FOULING INFLUENZATE DA RIF1UTI ORGANIC! PROVENIENTI DA ALLEVAMENTi Dl PESCf SINTESI L'articoh riporta lo studio della composizione isotoptca stabile di azoto in comunita di fouling colonizzanti substrati solidí di allevamenti di pesci e in siti di controllo non inquinad, in Adriático seltenlrionale (Pirano, Sioventa), Mediterráneo orientate (Creta, Grecia) e Mar Rosso (Eilat, Israels). Un arricchimento complessivo in 15-N delle comunita di fouling negli atlevamenti di pesci é state riscontrato in due delte tre postazioni, indicando I'incorporazi-one del particellato di azoto derivante dagli allevainenti nei tessuti degli organismi. Parole chiave: allevamenti di pesci, isotopo stabile, azoto, biofiltri, organismi di fouling 73 ANNALES • Ser. hist. nat. • 13 • 2003 • 1 • Supplement Sonja LOJFN el gl.: "N CNRlCHMENT IN FOULING COMMUNITIES INTLUtNCED BY ORGANIC WASTE DERIVNC FROM FISH FARMS. 9-12 INTRODUCTION Fish farms release large amounts of soluble inorganic and particulate organic matter (POM) into the marine environment (McGhie el a/.., 2000). There is, therefore, a large interest in reducing the effluent load to the surrounding waters in order to ease the environmental impact of mariculture. In order to capture and remove effluents released from fish farms, removable hard substrates were deployed near a fish farm, in order to be colonised by filtering organisms. Stable isotopes of nitrogen were successfully used to trace the dispersion of organic debris and the sources of sedimentary organic matter in marine sediments and in aquaculture systems (Ye et al., 1991; McGhie et a I., 2000; Mazzola & Sara, 200!). In organisms, the nitrogen stable isotopic composition (§|SN) of tissues provides a powerful tool for determination of respective sources of nutrition for consumers and trophic relationships among organisms. In the trophic network among animals, >51:,N of their tissues systematically increase on average by 3.4%o per trophic level (enrichment ranging from 1,3 to S.3%0; Minagawa & Wacia, 1984!. The aim of the present study was to examine the influence of particulate organic nitrogen waste deriving from fish farms on the nitrogen stable isotope composition of fouling communities colonising hard substrates (hereafter referred to as biofilters) adjacent to the fish farm. MATERIALS AND METHODS Three study sites were selected: Crete (E Mediterranean), Eiiat (Red Sea) and Piran (N Adriatic). Samples of particulate organic matter arid fouling communities colonising the biofilters were taken at the fish farms and at reference locations, which had not been affected by aquaculture. Particulate organic matter (POM) was collected in sediment traps seasonally from autumn 2001 to spring 2003. Samples were filtered through GF/C glass fibre filters and dried in oven overnight at 50 °C. Samples consisting of entire fouling community on randomly selected biofilters (one per array) were removed from the substrate, dried, pulverised by grinding to particle size below 100am and subsequently analysed for nitrogen isotope composition. Nitrogen stable isotope composition (61SN) was determined using a continuous flow isotope ratio mass spectrometer Europa 20-20 with ANCA SL preparation module (PDZ Europa Ltd., U.K.). Samples were packed in tin capsules, combusted in elemental analyser arid gases produced were separated in a GC column. The results are expressed as relative 5 values in %», I.e. the difference in parts per mil of the isotopic ratios iSN/l,,N from those of atmospheric nitrogen. Laboratory working standards (urea and ammonium sulphate solutions with 100 jJ-g/ul. N) were calibrated versus IAEA N-1 and IAEA N-2 ). An exceptionally high enrichment in 1SN in POM was detected in Crete, where the large difference cannot be attributed only to the presence of organic waste from the farm, but is partially related to the seasonally dependent differences in nitrogen isotopic composition of plankton, where 5lSN values can change by several per mi! related to the temperature-dependent nitrogen cycling (Minagawa & Wada, 1984; Sigleo & Macko, 1985; Nakatsuka ef at.,. 1992; Montoya, 1994; Altabet et a/., 1999). The high average 5ISN value is a consequence of extreme enrichment of POM in ,;N in July 2001, when 5!SN values of 11-13 %o were determined. Later on the S'sN ranged from 7.2 to 8.6 %<,, yielding a seasonal average of 9.2 %,. Tab. 1: Average S'5N values of particulate organic matter and fouling communities at reference locations and fish farms in Crete, Eilat and Piran. Tab. 1: Povprečne vrednosti SrsN suspendiranih organskih snovi in združbe obrasti na referenčnih lokalitetah in v ribogojnicah na Kreti, v Eifatu in Piranu. Location 6,5N of POM (V"N of fouling community [%<>] CRETE Reference Fish farm 4.2 10.8 (9.2*) 4.5 6.3 EILAT Reference Fish farm 3.6 (3.8*) 4.8 (4.9*) 3.6 5.7 ¡PIRAN Reference Fish farm 5.3 (4.7*) 5.8 (5.7*) ksJMarreoiei «cvscarflMmaAduuMi m m 6.7 5.7 "seasonal averages 74 ANNALES - Ser. hist. nat. • 13 • 2003 • 1 • Supplement Sonja ¡.olfn « «f.. "n enrichment in fouling communities INFLUENCED by organic waste deriving FROM fish FARMS, 9-12 Fouling communities at reference locations were enriched in 1=N relative to the POM at all three sites, where the enrichment in Eilat was within the analytical error of the measurements. An enrichment of fouling communities in h'N al the fish farms relative to the reference locations was observed in Crete and Eilat, while in Piran the opposite occurred. The relation of 6t5N of POM to S'sN of fouling communities at the fish farms, however, seems controversial. The organisms are enriched in ,SN relative to their food sources by at least 1.3%», depending on the species (Minagawa & Wada, 1984), therefore the observed enrichment can be used for an overall estimation of the sources of nutrition of fouling organisms. Where the organisms are enriched in ,;>N relative to the POM, at least part of their nutrition derives from this source. Where the enrichment is very small or even negative, it is obvious that the particulate organic matter does not contribute to the average organisms' diet. Since the colonising communities are composed of different species, only average particulate nitrogen consumption of the whole community colonising the analysed biofilter can be detected. ^N-enrichment of organisms at the fish farms relative to those at reference locations indicates that some of the incorporated nitrogen derives from the fish farms, however, its fractions depend mostly on the composition of the colonising community, i.e. relative abundance of non-selective suspension feeders, which are able to ingest and retain nitrogen from particles of various sizes. In Crete, the fouling community at the fish farm is clearly enriched in 'SN relative to the reference location, however, depleted in ?5N relative to the POM. That means that suspension feeders present only a minor fraction of the whole community. Similar situation was observed in Piran. Figure 1 shows the enrichment of fouling communities relative to the POM at the fish farms and at reference locations. Different enrichments between POM and fouling communities at tire fish farms and al reference locations show that the compositions of fouling communities at both locations were obviously different and highly variable from biofilter to biofilter, as well as seasonally, which can be seen from the large range of measured 5'r'N values. Therefore they cannot be directly compared to each other. However, the overall enrichment of the organisms at the fish farms relative to the reference locations in Crete and Eilat shows thai they are enriched in l5N, i.e. at least part of their food is represented by ,SN enriched POM deriving from the cages. H-i 13121 1098 7 65 -4: 3 2-1 I 21 14 13 12 —, 11 .= 10 a .A 9 8 7 6 5 4 > Q S lo fish farms Crete Eilat Piran reference locations Crete Eilat Piran Fig. I: <5!i'i\' of particulate organic matter and fouling communities at the fish farms and at reference locations; solid symbols - POM, open symbols = fouling community. Horizontal bars represent average values of all measurements. SI. 1; d' TV suspendiranih organskih snovi in združba obrasti v ribogojnicah in referenčnih lokalitetah; polni simboli - POM, odprti simboli - združba obrasti. Horizontalni stolpiči ponazarjajo povprečne vrednosti vseh meritev. 75 ANNALES • Ser. hist. nat. -13' 2003 • 1 ■ Supplement Sonja Ï.OIFN e\ UN ENRtCRMtNT IN FOULING COMMUNITIES INFLUENCED SY ORGANIC WASTE DERIVING FROM FISH FARMS. 9-1 2 ¡ZOTOPSKA SESTAVA DUŠIKA V MORSKIH ORGANIZMIH V VPLIVNEM OBMOČJU RIBJIH FARM Sonja LOJEN Institut "ložel Stefan", Odiek za znanosti o okolju, bi-1000 Ljubljana, Jamova 39 E-mail sonja.bjen@ij5.si Dror ANGEL & Timor KATZ National Centu foi Mariculture, tsraei Oceanographic and I imnological research, ;L t Jat 88 f 12, POB 1212, North Beach Mamila TSAPAKIS Institute ot Marine Biology of Crete, GR-71003 Heraklio», POB .1214 & Nives KOVAČA Alenka MALEj Morska biološka postaja. Nacionalni Inilitut 7a Biolog jo, SI-6330 Pitan, Furnače 41 POVZETEK Analizirali smo izotopsko sestavo dušika v obrasli na umetnih substratih, lociranih v neposredni bližini ribjih rarm in na neonesnaženih referenčnih lokat ijah v severnem Jadranu (Piran, Slovenija',, v vzhodnem Sredozemlju 'Kreta, Grčija) in v Rdečem morju 'Eilat, Izraeli. Na dveh od treh lokacij smo izmerili povečano vsebnost S'sN v organizmih ob ribjih farmah, kar je posledica vgrajevanja izotopsko težjega dušika iz suspendirane snovi, ki se sprošča v okolico iz ribjih kletk. Ključne besede: ribja farma, stabilni izotop, dušik, umetni substrat, organizmi obrasti REFERENCES Altabet, M. A., C. Pilskaln, R. Thunell, C. Pride, D. Sigma», F. Chavez & R. Francois (1999): The nitrogen isotope biogeochemistry of sinking particles from the margin of the Eastern North Pacific. Deep-Sea Res Part !, 46, 655-679. Mazzola, A. & G. Sara (2001): The effect of fish farming organic waste on food availability for bivalve molluscs (Gaeta Gulf, Central Tyrrhenian). Aquaculture, 192(2-4), 361-379. McGhie, T. K., C. M. Crawford, I. M. Mitchell & D. O'Brien (2000): The degradation of fish-cage waste during fallowing. Aquaculture, 187, 351-366. Minagawa, M. & E. Wada (1984): Stepwise enrichment of1 N along food chains: Further evidence and the relation between or'N and animal age. Geochirn. Cosrno-chim. Acta, 48,1135-1140. Montoya, j. P. (1994): Nitrogen isotope fractionation in thé modern ocean: implications for sed.mentary records: in: Zahn, R., T. F. Pedersen, T. F. Kaminski & L. Labeyrie (eds.): Carbon Cycling in Glacial Ocean: Constraints of the Ocean's Role in the Global Change. Springer, Berlin, 259-279. Nakatsuka, T„ N. Handa, E. Wad a & C. S. Wong (1992): The dynamic changes of stable isotopic ratios of carbon and nitrogen in suspended and sedimented particulate organic matter during a phytoplankton bloom. J. Mar. Res., 50, 267-296. Sigleo, A. C. & S. A. Macko (1985): Stable isotope and amino acid composition of estuarine dissolved colloid material. In: Sigleo, A. C. & A. Hattort (eds.): Marine and estuarine geochemistry. Lewis publishers, Chelsea, USA, 29-45. Ye, L. X., D. A. Ritz, G. E. Fenton tS< M. E. Lewis (1991): Tracing the influence on sediments of organic waste from a salmonid farm using stable isotope analysis, j. Exp. Mar. Biol. Eccl , 45, 161-174.