Opis strukture zajednica školjkaša u hrvatskom dijelu Jadranskog mora - istraživanje hidrauličnom dredžom

Hydraulic dredge surveys of bivalve communities in the Croatian part of the Adriatic Sea were conducted from the Island of Rab in the north to the river Neretva estuary in the south during 2007 and 2008. The main objective of the study was to describe distribution and community structure of bivalves on soft sediments along the eastern Adriatic, primarily focusing on commercially important species in five main bivalve harvesting areas. A total of 105 hydraulic dredge samples were collected at depths ranging from 1 to 11 m. Sampled bivalves were separated in the field and frozen for later laboratory analysis that included species identification, abundance and biomass determination. Live specimens of 54 bivalve taxa were collected during this study, while 87 taxa were represented by empty shells. Shells of the non-indigenous bivalve Anadara demiri were recorded for the first time in the Croatian part of the Adriatic Sea. In terms of biomass and abundance the dominant species were Acanthocardia tuberculata, Callista chione, Chamelea gallina, Glycymeris bimaculata, G. glycymeris, G. violascens, Laevicardium oblongum, Modiolus barbatus, Mytilus galloprovincialis, Ostrea edulis and Venus verrucosa. Statistically significant differences were noted in bivalve communities in the five main sampling areas including the island of Rab, Pag bay, Kaštela bay, Cetina estuary and Neretva estuary.Istraživanje zajednica školjkaša provedeno je tijekom 2007. i 2008. godine duž istočne obale Jadrana, od otoka Raba na sjeveru do ušća rijeke Neretve na jugu. Glavni cilj istraživanja bio je opis raspodjele i strukture zajednica školjkaša na mekim dnima duž istočne obale Jadrana, sa posebnim naglaskom na gospodarski važne vrste školjkaša u pet glavnih izlovnih područja. Hidrauličnom dredžom prikupljeno je ukupno 105 uzoraka na dubinama od 1 do 11 m. Prikupljeni školjkaši na terenu su odvojeni i zamrznuti za daljnju laboratorijsku analizu koja je uključivala identifikaciju vrsta te analizu brojnosti i biomase. U prikupljenim uzorcima 54 vrste školjkaša bile su zastupljene sa živim primjercima, dok je iz ljušturnih ostataka identificirano 87 vrsta školjkaša. Ljušture alohtone vrste školjkaša Anadara demiri zabilježene su po prvi puta u hrvatskom dijelu Jadrana. Maseno i brojčano najzastupljenije vrste bile su: Acanthocardia tuberculata, Callista chione, Chamelea gallina, Glycymeris bimaculata, G. glycymeris, G. violascens, Laevicardium oblongum, Modiolus barbatus, Mytilus galloprovincialis, Ostrea edulis i Venus verrucosa. Statistički značajna razlika zabilježena je u zajednicama školjkaša na pet glavnih područja istraživanja uključujući otok Rab, Paški zaljev, Kaštelanski zaljev te ušća rijeka Cetine i Neretve

Ciclo reproductivo de Glycymeris nummaria (Mollusca: Bivalvia), de la bahía de Mali Ston, Mar Adriático, Croacia

The reproductive cycle of the dog cockle, Glycymeris nummaria (Glycymerididae), was studied using specimens collected monthly from Mali Ston Bay, southeastern Adriatic Sea over the period from January to December 2010. We analysed sex ratios, gonad developmental stages, and oocyte diameters using standard histological techniques. There were no differences in the overall sex ratio and no difference in shell length with respect to sex. Results of a size-frequency analysis of oocyte diameters agreed with a qualitative analysis of gonadal developmental stages, confirming the occurrence of one annual spawning peak from May to July. A significant correlation was identified between mean gonad indices of males and females and condition index. This study provides the first data on the reproductive characteristics of G. nummaria, providing necessary information for the future sustainable management of its potential fishery.El ciclo reproductivo del bivalvo Glycymeris nummaria (Glycymerididae) fue estudiado en base a especímenes recolectados mensualmente entre enero y diciembre de 2012 en la Bahía Mali Ston (sudeste del Adriático). Analizamos la proporción sexual (sex ratio), los estadios del desarrollo gonadal y el diámetro de los ovocitos utilizando las técnicas histológicas estándares. No existen diferencias en la proporción sexual ni tampoco en la longitud de los especímenes en relación al sexo. Los resultados del análisis de la frecuencia de los diámetros de los ovocitos concordaron con el análisis cualitativo del estadio de desarrollo de las gónadas, confirmando la existencia de un pico de puesta anual entre los meses de mayo y julio. Asimismo se encontró una correlación significativa entre los índices gonadales promedio de machos y hembras y el índice de condición. Este estudio aporta por primera vez datos de las características reproductivas de G. nummaria que son necesarios para la gestión sostenible de la pesca potencial de esta especie en un futuro

Fuentes potenciales de alimento en Glycymeris nummaria (Mollusca: Bivalvia) durante el ciclo anual a partir del análisis de ácidos graso

Seasonal changes of food sources were investigated by analysing the fatty acid profiles of digestive gland and muscle tissues of the naturally occurring clams Glycymeris nummaria in Mali Ston Bay, Croatia. Total lipids in the digestive gland and the adductor muscle showed parallel changes, with a maximum after the main spawning event in September. In the digestive gland saturated fatty acids were highly dominant (up to 82%), indicating detritus as the main food source for this species. This type of food prevailed during the autumn/winter period, in contrast to the spring/summer period when detritus was enriched with phyto- and, to a lesser extent, zooplankton. Fatty acid composition of muscles indicated highly efficient utilization of ingested food through significant retention of polyunsaturated fatty acid from the clams’ diet during the entire period investigated.Se han investigado los cambios estacionales en las fuentes de alimentación de poblaciones naturales del bivalvo Glycymeris nummaria en la bahía Mali Ston (Croacia) por medio del análisis de los perfiles de ácidos grasos de la glándula digestiva y del tejido muscular. El total de lípidos tanto de la glándula digestiva como en el músculo aductor mostró cambios similares después del principal evento de freza (septiembre). En la glándula digestiva los ácidos grasos saturados fueron altamente dominantes (hasta el 82%), lo que señala a los detritos como principal fuente de alimentación de esta especie. Este tipo de alimento prevalece durante el otoño/invierno, mientras que en primavera/verano la alimentación se complementa con fitoplancton y, en menor medida, con zooplancton. La composición de ácidos grasos en el tejido muscular indica una alta eficiencia en la utilización del alimento ingerido mediante la retención de los ácidos grasos poliinsaturados (PUFA) de la dieta durante todo el periodo investigado

Veličinska struktura zooplanktonskog plijena kod četiri gospodarski značajne vrste školjkaša

Some bivalve molluscs are capable of zooplankton ingestion; however that aspect of their ecology is still relatively poorly studied. The objective of this investigation was to contribute to the understanding of size structure of zooplankters ingested by four commercially important bivalve species co-occurring in the same area. The study was performed in Mali Ston Bay – the most important bivalve aquaculture area in the eastern Adriatic Sea – from May 2009 to April 2010. We analyzed sizes of zooplankton ingested by cultured blue mussel Mytilus galloprovincialis and European flat oyster Ostrea edulis, and naturally-occurring bearded mussel Modiolus barbatus and Noah’s Ark shell Arca noae. Ingested zooplankton ranged in maximum linear dimension from 60.1 to 1398.5 μm. Zooplankton found in stomach contents of M. galloprovincialis and O. edulis suspended in the water column showed a wider size range than zooplankton found in stomachs of bottom living M. barbatus and A. noae. Sizes of ingested zooplankton significantly differed between O. edulis and the other three species.Iako neki školjkaši imaju sposobnost hranjenja zooplanktonom, taj aspekt ekologije školjkaša još uvijek je relativno slabo istražen. Svrha ovog istraživanja bila je pridonijeti poznavanju veličinske strukture zooplanktonskog plijena kod četiri gospodarski značajne vrste školjkaša koje žive na istom području. Istraživanje je provedeno od svibnja 2009. do travnja 2010. u Malostonskom zaljevu –najvažnijem području za uzgoj školjkaša u istočnom dijelu Jadranskog mora. Analizirana je veličina zooplanktona konzumiranog od strane uzgajanih vrsta dagnje Mytilus galloprovincialis i kamenice Ostrea edulis te vrsta koje na tom području žive u prirodnim populacijama dlakave dagnje Modiolus barbatus i kunjke Arca noae. Veličina konzumiranog zooplanktona kretala se u rasponu od 60,1 do 1398,5 μm. Veličinski raspon zooplanktona pronađenih u želucima vrsta M. galloprovincialis i O. edulis suspendiranim u vodenom stupcu bio je veći od zooplanktona pronađenog u želucima vrsta M. barbatus i A. noae. Statistički značajna razlika u veličini konzumiranog zooplanktona pronađena je između vrste O. edulis i tri ostale vrste

Edad, crecimiento y estructura de la población de Acanthocardia tuberculata (Bivalvia: Cardiidae) de la zona oriental del mar Adriático

A study of the age, growth and population structure of Acanthocardia tuberculata from the eastern Adriatic Sea was carried out. The condition index analysis identified one reproductive peak, which occurred between April and May, for a population of A. tuberculata in the Cetina River estuary with uni-modal recruitment. Annual growth rings on the external shell surface consisted of a dark ring deposited during the summer-autumn period and a light ring deposited during winter-spring. This was validated by acetate peels of shell sections and marginal increment analysis. Shell lengths of aged specimens ranged from 19.7 to 62.9 mm (mean = 41.21±8.96 mm). Estimated ages ranged from 5 months to 11 years, with mean values of 2.1, 2.4 and 3.1 years for Rab Island, Pag Bay and the Cetina River estuary respectively. Shell deposition is fastest during the first two years of life and significantly decreases after the 4th year. The growth parameters L∞ and k were estimated using the Gulland-Holt method and by fitting length at age data to a von Bertalanffy growth curve. Values of L∞ ranged from 52.6 mm (Rab Island) to 59.7 mm (Pag Bay). The growth constant k showed greater variations (0.49 to 0.77 year-1), while growth performance index values (ø’) ranged from 3.13 to 3.36.Se ha estudiado la edad, crecimiento y estructura de la población de Acanthocardia tuberculata de la zona oriental del mar Adriático. El índice de condición identifica un pico reproductivo que ocurre entre abril y mayo en la población de A. tuberculata del estuario del río Cetina, con reclutamiento unimodal. Los anillos de crecimiento anual en la superficie externa de la concha consistieron en un anillo oscuro depositado durante el verano-otoño y un anillo claro depositado durante el invierno-primavera. Se realizó una validación mediante el empleo de réplicas de acetato realizadas sobre secciones de la concha y el análisis de los incrementos marginales. La longitud de los especímenes datados osciló entre 19.7 a 62.9 mm (media =41.21±8.96 mm). Las edades estimadas oscilan entre 5 meses y 11 años, con valores medios de 2.1, 2.4 y 3.1 años en la isla de Rab, Pag bahía y el estuario del río Cetina, respectivamente. La deposición de concha es más rápida durante los dos primeros años de vida y disminuye significativamente a partir del cuarto año. Los pará- metros de crecimiento L∞ y K se calcularon utilizando el método de Gulland-Holt, ajustando los datos de longitud-edad a la curva de crecimiento de von Bertalanffy. Los valores de L∞ estimados variaron entre 52.6 mm (Isla de Rab) y 59.7 mm (Pag bahía). La constante de crecimiento k mostró grandes variaciones (0.49 a 0.77 año-1), mientras que el índice de rendimiento de crecimiento (ø’) osciló entre 3.13 y 3.36

Reproductive cycle of a non-native oyster, Crassostrea gigas, in the Adriatic Sea

The Pacific oyster Crassostrea gigas was introduced for the aquaculture purposes in many different parts of the world. However, the species has never been officially introduced for commercial farming in the Croatian part of the Adriatic Sea. Interestingly, in the 1970s, the Pacific oyster has been reported in the natural habitats of the Lim Bay, in northern Adriatic Sea. Although the species was recorded there, there is a lack of knowledge about its biology and ecology in this region, including a reproductive cycle. Information on the reproductive biology of non-indigenous species in new areas is crucial for prediction of their future survival and possible spread in invaded habitats. In this study, we provide the first data on the reproductive biology of the Pacific oyster in the Adriatic Sea, the northernmost part of the Mediterranean Sea. Quantitative and qualitative methods of gonad tissue analysis were conducted, and effects of environmental conditions on the gametogenesis were evaluated during two reproductive cycles. Our study confirmed that environmental conditions in the Lim Bay were favourable for the reproduction of the species. The Pacific oyster reproduced once per year and had a prolonged spawning period. Water temperature was the main factor affecting gonad development and oocyte size, while chlorophyll a concentration had an impact on the oocyte development in terms of their size.

Feeding of commercially important bivalve species in the Mali Ston Bay

Školjkaši su brojna skupina u većini obalnih morskih ekosustava te imaju veliku važnost u morskim hranidbenim mrežama. Poznavanje ishrane školjkaša od velike je važnosti posebno na područjima njihovog uzgoja gdje se školjkaši nalaze u velikom broju. U ovoj disertaciji predstavljeni su rezultati istraživanja ishrane četiri komercijalno značajne vrste školjkaša na području Malostonskog zaljeva. Istraživane su dvije vrste iz uzgoja – daganja Mytilus galloprovincialis i kamenica Ostrea edulis, te dvije vrste prikupljene iz prirodnog staništa – dlakava dagnja Modiolus barbatus i kunjka Arca noae. Istraživanje je provedeno u razdoblju od svibnja 2009. godine do prosinca 2010. godine. Ishrana školjkaša istraživana je primjenom tri različite metode: analiza sadržaja stabilnih izotopa dušika i ugljika, analiza sastava masnih kiselina te direktna analiza sadržaja želudaca školjkaša. Analize stabilnih izotopa i masnih kiselina, provedene na dvije vrste tkiva – probavnoj žlijezdi i mišiću zatvaraču, potvrdile su sezonske varijabilnosti u ishrani te preklapanje trofičke niše istraživanih vrsta tijekom toplijeg dijela godine kad je fitoplankton najviše doprinosio ishrani istraživanih vrsta školjkaša. Tijekom hladnijeg dijela godine doprinos dodatnih izvora hrane, kao što su detritus i zooplankton, bio je važniji u ishrani školjkaša. Direktnom analizom sadržaja želudaca potvrđeno je da se sve istraživane vrste hrane različitim skupinama zooplanktona, te da su uzgajane vrste školjkaša konzumirale veći broj zooplanktonskih organizama u usporedbi s školjkašima prikupljenih iz prirodnog staništa. Najbrojniji zooplanktonski organizmi u želucima školjkaša bile su ličinke školjkaša, što dovodi u pitanje održivi uzgoj na području gdje se sav uzgoj temelji na mlađi prikupljenoj iz prirode. Rezultati ovog istraživanja doprinose boljem razumijevanju trofičkih interakcija između različitih vrsta školjkaša, što može služiti kao dobra osnova za buduća modeliranja morskih hranidbenih mreža kao i održivo upravljanje prirodnim i uzgojnim populacijama školjkaša.Bivalves are an abundant group of organisms in majority of costal marine ecosystems and they play an important role in the marine food webs. Understanding of bivalve feeding ecology has great importance especially in aquaculture areas where cultured species usually occur at high densities. This thesis presents data about feeding ecology of four commercially important bivalve species cooccurring in the Mali Ston Bay including two cultivated species – black mussel Mytilus galloprovincialis and European flat oyster Ostrea edulis, and two species from their natural habitat – bearded horse mussel Modiolus barbatus and Noah's ark shell Arca noae. Study was performed in the period from May 2009 to December 2010. Feeding ecology was investigated applying three different methods: nitrogen and carbon stable isotope analysis, fatty acid analysis and direct analysis of stomach content. Stable isotope and fatty acid analysis, performed on two tissues – digestive gland and adductor muscle, revealed seasonal variability in food sources and overlapping of bivalve trophic niche during the warmer period of the year when phytoplankton contributed the most to the bivalves diet. During the colder part of the year additional food sources like detritus and zooplankton contributed more to the bivalves diet. Direct analysis of stomach content confirmed carnivory in bivalves, both from natural and cultured populations, but cultured species had higher numbers of zooplankters than those living on the seabed. The most abundant taxa were bivalve larvae, what pointed out a question of sustainable bivalve aquaculture in the area were all production relies only on seeds collected form the nature. Results of this study contribute to the understanding of trophic interactions between different bivalve species what is important for future modelling of food webs and sustainable management of wild and cultured populations

Feeding of commercially important bivalve species in the Mali Ston Bay

Školjkaši su brojna skupina u većini obalnih morskih ekosustava te imaju veliku važnost u morskim hranidbenim mrežama. Poznavanje ishrane školjkaša od velike je važnosti posebno na područjima njihovog uzgoja gdje se školjkaši nalaze u velikom broju. U ovoj disertaciji predstavljeni su rezultati istraživanja ishrane četiri komercijalno značajne vrste školjkaša na području Malostonskog zaljeva. Istraživane su dvije vrste iz uzgoja – daganja Mytilus galloprovincialis i kamenica Ostrea edulis, te dvije vrste prikupljene iz prirodnog staništa – dlakava dagnja Modiolus barbatus i kunjka Arca noae. Istraživanje je provedeno u razdoblju od svibnja 2009. godine do prosinca 2010. godine. Ishrana školjkaša istraživana je primjenom tri različite metode: analiza sadržaja stabilnih izotopa dušika i ugljika, analiza sastava masnih kiselina te direktna analiza sadržaja želudaca školjkaša. Analize stabilnih izotopa i masnih kiselina, provedene na dvije vrste tkiva – probavnoj žlijezdi i mišiću zatvaraču, potvrdile su sezonske varijabilnosti u ishrani te preklapanje trofičke niše istraživanih vrsta tijekom toplijeg dijela godine kad je fitoplankton najviše doprinosio ishrani istraživanih vrsta školjkaša. Tijekom hladnijeg dijela godine doprinos dodatnih izvora hrane, kao što su detritus i zooplankton, bio je važniji u ishrani školjkaša. Direktnom analizom sadržaja želudaca potvrđeno je da se sve istraživane vrste hrane različitim skupinama zooplanktona, te da su uzgajane vrste školjkaša konzumirale veći broj zooplanktonskih organizama u usporedbi s školjkašima prikupljenih iz prirodnog staništa. Najbrojniji zooplanktonski organizmi u želucima školjkaša bile su ličinke školjkaša, što dovodi u pitanje održivi uzgoj na području gdje se sav uzgoj temelji na mlađi prikupljenoj iz prirode. Rezultati ovog istraživanja doprinose boljem razumijevanju trofičkih interakcija između različitih vrsta školjkaša, što može služiti kao dobra osnova za buduća modeliranja morskih hranidbenih mreža kao i održivo upravljanje prirodnim i uzgojnim populacijama školjkaša.Bivalves are an abundant group of organisms in majority of costal marine ecosystems and they play an important role in the marine food webs. Understanding of bivalve feeding ecology has great importance especially in aquaculture areas where cultured species usually occur at high densities. This thesis presents data about feeding ecology of four commercially important bivalve species cooccurring in the Mali Ston Bay including two cultivated species – black mussel Mytilus galloprovincialis and European flat oyster Ostrea edulis, and two species from their natural habitat – bearded horse mussel Modiolus barbatus and Noah's ark shell Arca noae. Study was performed in the period from May 2009 to December 2010. Feeding ecology was investigated applying three different methods: nitrogen and carbon stable isotope analysis, fatty acid analysis and direct analysis of stomach content. Stable isotope and fatty acid analysis, performed on two tissues – digestive gland and adductor muscle, revealed seasonal variability in food sources and overlapping of bivalve trophic niche during the warmer period of the year when phytoplankton contributed the most to the bivalves diet. During the colder part of the year additional food sources like detritus and zooplankton contributed more to the bivalves diet. Direct analysis of stomach content confirmed carnivory in bivalves, both from natural and cultured populations, but cultured species had higher numbers of zooplankters than those living on the seabed. The most abundant taxa were bivalve larvae, what pointed out a question of sustainable bivalve aquaculture in the area were all production relies only on seeds collected form the nature. Results of this study contribute to the understanding of trophic interactions between different bivalve species what is important for future modelling of food webs and sustainable management of wild and cultured populations