Interannual size changes of adult Aurelia sp.5 medusae stage in the Marine Protected Area of Mljet Island South Adriatic

Aurelia aurita s.l. is the most widespread scyphozoan jellyfish that recurrently appear "en mass" and forms large aggregations mainly in coastal waters, embayments and estuaries. Beside anthropogenic factors controlling jellyfish populations climate change may play an important role. The aim of this study was to assess whether climate-related factors in absence of other anthropogenically induced stressor influence medusae size. We investigated seasonal and interannual changes in the size of Aurelia in a "jelly lake" in the National Park of Mljet Island (Croatia) where minimal human impact on the environment makes the Veliko Jezero a natural mesocosm for understanding the impact of climate change on the Aurelia population. The observed changes suggest Aurelia medusa population response to changing environment, in particular to enhanced temperature, by reduced body sizes. Comparison of Aurelia population dynamics from different regions in the Mediterranean Sea revealed the unique feature of the Veliko Jezero population. Despite the similarity of the environmental windows of medusae occurrences in the Veliko Jezero and regions in the Mediterranean Sea, medusae in the Veliko Jezero are present all year round. It seems that the lake bathymetry enables medusae to vertically migrate to deeper and cooler water layer, avoiding the limiting temperatures developed in the upper layer during the summer. These conditions may prolong the Aurelia medusae life span and together with continuous strobilation support the stability of the Aurelia medusae population all year round

Godišnje promjene veličine adultnih primjeraka meduze Aurelia sp.5 u zaštićenom području otoka Mljeta, južni Jadran

Aurelia aurita s.l. is the most widespread scyphozoan jellyfish that recurrently appear “en mass” and forms large aggregations mainly in coastal waters, embayments and estuaries. Beside anthropogenic factors controlling jellyfish populations climate change may play an important role. The aim of this study was to assess whether climate-related factors in absence of other anthropogenically induced stressor influence medusae size. We investigated seasonal and interannual changes in the size of Aurelia in a “jelly lake” in the National Park of Mljet Island (Croatia) where minimal human impact on the environment makes the Veliko Jezero a natural mesocosm for understanding the impact of climate change on the Aurelia population. The observed changes suggest Aurelia medusa population response to changing environment, in particular to enhanced temperature, by reduced body sizes. Comparison of Aurelia population dynamics from different regions in the Mediterranean Sea revealed the unique feature of the Veliko Jezero population. Despite the similarity of the environmental windows of medusae occurrences in the Veliko Jezero and regions in the Mediterranean Sea, medusae in the Veliko Jezero are present all year round. It seems that the lake bathymetry enables medusae to vertically migrate to deeper and cooler water layer, avoiding the limiting temperatures developed in the upper layer during the summer. These conditions may prolong the Aurelia medusae life span and together with continuous strobilation support the stability of the Aurelia medusae population all year round.Aurelia aurita s.l. je najrasprostranjenija vrsta meduze unutar razreda režnjaka (Scyphozoa) koje se opetovano pojavljuje u nakupinama. Stvaraju velike agregacije većinom u obalnim vodama, zaljevima i estuarijima. Osim antropogenog, važan utjecaj na populaciju meduza mogu imati i klimatske promjene. Cilj ovog istraživanja je procjeniti u kolikoj mjeri utjecaji povezani s klimatskim promjenama, u odsutnosti drugih antropogeno induciranih stresova, utječu na veličinu meduza. Istraživali smo sezonske i godišnje promjene veličine vrste Aurelia u morskim jezerima Nacionalnog parka Mljet (hrvatska), gdje se Veliko jezero pokazalo kao idealan prirodni mezokosmos za istraživanje i razumijevanje utjecaja klimatskih promjena na populaciju ove vrste. Uočene promjene ukazuju da populacija meduze Aurelia odgovara na promjene okoliša, posebno na povišenu temperaturu smanjujući veličinu tijela. Usporedba dinamike populacije Aurelia u različitim dijelovima Sredozemlja otkriva jedinstvenu značajku populacije u Velikom jezeru. Unatoč sličnosti uvjeta okoliša u kojima se meduze pojavljuju u Velikom jezeru i ostalim područjima Sredozemlja, u Velikom jezeru su prisutne tijekom cijele godine. Očigledno, batimetrija jezera omogućava meduzama avertikalnu migraciju u dublje i hladnije slojeve, izbjegavajući površinski sloj sa povišenim vrijednostima temperature koje se razvijaju tijekom ljeta. Ovi uvjeti mogu utjecati na produžen životni vijek meduza te omogućiti stalnu strobilaciju i stabilnost populacije ove vrste tijekom cijele godine

Ingresija hidromeduse Neotima lucullana (della chiaje, 1822) u ekosustavu estuarija rijeke Neretve (jugoistočni Jadran, Hrvatska)

Hydromedusa Neotima lucullana is an endemic species of the Mediterranean Sea. In this study we document the first numerous and permanent occurrence of N. lucullana in the estuary of the Neretva River, an unusual habitat for this typical marine species. We provide COI barcode sequence of this species, which is also first genetic sequence ever published of N. lucullana. Weekly data on the occurrence and abundance of N. lucullana were obtained from reports and records of autonomous divers and local fishermen in the area from Opuzen to Metković from mid-June to the end of October 2021. The individuals were always located in the layer above the bottom with salinity between 35.2 and 38.2. The diameters of the jellyfish bells ranged from 15 mm to 72 mm, most of them between 40 mm and 58 mm. Differential development of the gonads was observed in all specimens larger than 25 mm. In mid-June, the specimens were common but solitary. A week later, the jellyfish were more frequent and in smaller aggregations. From late June to mid-September, the jellyfish were constantly observed in larger aggregations. Toward the autumn, the number of individuals gradually decreased, and by the last week of October, only single individuals were observed. Our results indicate significant changes in the ecosystem of the Neretva estuary and confirm the observed composition of zooplankton communities dominated by marine species in summer and autumn.Hidromeduza Neotima lucullana je endemska vrsta Sredozemnog mora. Ovim istraživanjem dokumentiramo prve zapise o brojnoj i dugotrajnoj pojavi meduze N. lucullana u estuariju rijeke Neretve, neobičnom staništu za ovu tipično morsku vrstu. U sklopu ovog istraživanja dobivena je sekvenca podjedinice i citokrom oksidaze (COI), što je ujedno i prva genetička sekvenca ikad objavljena vrste N. lucullana. Tjedni podaci o pojavi i brojnosti N. lucullana dobiveni su na osnovi izvještaja i zapisa autonomnih ronilaca i lokalnih ribara na području od Opuzena do Metkovića od sredine lipnja do kraja listopada 2021. Jedinke meduza su uvijek bile u sloju iznad dna unutar vrijednosti saliniteta između 35,2 i 38,2. Promjer zvona meduza kretao se od 15 mm do 72 mm, glavnina između 40 mm i 58 mm. Diferencijalni razvoj spolnih žlijezda uočen je kod svih primjeraka većih od 25 mm. Sredinom lipnja jedinke su bile uobičajene, ali prisutne pojedinačno. Tjedan dana kasnije, meduze su bile često viđene i u manjim skupinama. Od kraja lipnja do sredine rujna, meduze su bile prisutne u većim agregacijama. Broj jedinki postupno se smanjivao prema jeseni i samo pojedinačni primjerci bili su uočeni tijekom posljednjeg tjedna listopada. Naši rezultati ukazuju na znatne promjene ekosustava donjeg toka rijeke Neretve što potvrđuje zabilježen sastav zooplanktonskih zajednica u kojima dominiraju morske vrste tijekom ljeti i jeseni

Sastav i raspodjela zooplanktona duž obalnih i otvorenih voda Albanije (južni Jadran) u kasno proljeće

We present for the first time composition, numerical abundance and vertical structure of microand mesozooplankton in the Albanian coastal and open sea region. Zooplankton was sampled at six stations on the 75-km long continental shelf slope transect in May 2009. The most numerous microzooplankton were copepod nauplii (maximum: 39 ind. L-1), followed by calonoid and cyclopoid copepodites (maxima: 5 and 4 ind. L-1, respectively). The most abundant of fourteen tintinnid species was Tintinnopsis radix, found in the surface to 50 m layer. The species composition of the coastal and open sea mesozooplankton was similar to that previously reported for the south Adriatic Sea. The copepod Oithona similis was the dominant species at all stations, followed by Oithona plumifera, Acartia clausi, Paracalanus parvus, Oithona nana and cyclopoida-oncaeids at the shallower coastal stations, and Clausocalanus pergens, Oithona plumifera and Oithona nana offshore. Mesozooplankton diversity rose considerably from the coast to the open sea. Mesozooplankton abundance exhibited the opposite trend, with the maximum (2286 ind. m-3) noted at the shallowest station. Findings of typically open sea tintinnid and copepod species at the coastal station indicate the high influence of currents from the open sea area during our investigation. Our results suggest the low influence of fresh water on zooplankton population densities, even at the shallow stations where penetration of fresh water in the surface layers was notable.Po prvi put su prikazani sastav, abundancija i vertikalna struktura mikro- i mezozooplanktona u albanskim obalnim i otvorenim vodama. Istraživanje je obavljeno na šest postaja duž 75 km dugom transektu od šelfa do kontinentskog slaza. Najbrojniji predstavnici mikrozooplanktona su bili kopepodni naupliji (maksimum: 39 ind. L-1), iza kojih su slijedili kalanoidni i ciklopoidni kopepoditi. Od 14 zabilježenih vrsta tintinida, najbrojnija je bila vrsta Tintinnopsis radix, nađena od površine do 50 m dubine. Sastav zajednice mezozooplanktona obalnog i otvorenog mora u skladu je s prijašnjim istraživanjima južnog Jadrana. Kopepod Oithona similis bila je dominantna vrsta na svim istraživanim postajama. Na plićim postajama slijede je vrste Oithona plumifera, Acartia clausi, Paracalanus parvus, Oithona nana i cyclopoida-oncaeids, a u otvorenim vodama vrste Clausocalanus pergens, Oithona plumifera i Oithona nana. Bioraznolikost mezozooplanktona značajno raste od obale prema otvorenom moru. Nasuprot tome, najveća gustoća mezozooplanktona (2286 ind. m-3) zabilježena je na najplićoj postaji. Prisutnost karakterističnih vrsta tintinida i kopepoda otvorenog mora na obalnim postajama ukazuju na utjecaj struja otvorenog mora za vrijeme ovog istraživanja. Naši rezultati ukazuju da povećani upliv slatke vode nije znatno utjecao na gustoću zooplanktonskih populacija čak i na plitkim postajama gdje je prodor slatke vode u površinskim slojevima osobito izražen

La poco nota medusa Drymonema dalmatinum Haeckel 1880 (Scyphozoa, Discomedusae) nel Mare Adriatico

Authors report historical and recent records of the little-known medusa Drymonema dalmatinum in the Adriatic Sea. This large scyphomedusa, which may develop a bell diameter of more than 1 m, was fi rst described in 1880 by Haeckel based on four specimens collected near the Dalmatian island Hvar. The paucity of this species records since its description confi rms its rarity, however, in the last 15 years sightings of D. dalmatinum have been more frequent.Gli autori riportano segnalazioni storiche e recenti della poco conosciuta medusa Drymonema dalmatinum nel mare Adriatico. Questa grande scifomedusa, che può sviluppare un cappello di diametro di oltre 1 m, è stata descritta per la prima volta nel 1880 da Haeckel, in base a quattro esemplari catturati vicino all’isola di Lèsina (Hvar) in Dalmazia. La scarsità delle segnalazioni di questa specie dalla sua prima descrizione conferma la sua rarità. Tuttavia, negli ultimi 15 anni gli avvistamenti di D. dalmatinum sono stati più frequenti

The lesser-known medusa Drymonema dalmatinum Haeckel 1880 (Scyphozoa, Discomedusae) in the Adriatic Sea

Authors report historical and recent records of the little-known medusa Drymonema dalmatinum in the Adriatic Sea. This large scyphomedusa, which may develop a bell diameter of more than 1 m, was first described in 1880 by Haeckel based on four specimens collected near the Dalmatian island Hvar. The paucity of this species records since its description confirms its rarity, however, in the last 15 years sightings of D. dalmatinum have been more frequent.Avtorji v prispevku predstavljajo malo znano klobučnjaško meduzo Drymonema dalmatinum (dalmatinska lasasta meduza). Prvič jo je opisal Haeckel (1880) ravno na osnovi vzorcev meduz iz Jadranskega morja. Klobuk dalmatinske lasaste meduze lahko doseže premer preko enega metra, vendar so bili primerki iz Jadranskega morja manjši, največji so imeli premer okoli 60 cm. Na osnovi historičnih virov in novejših opazovanj avtorji v prispevku podajajo časovni pregled opazovanj te meduze od konca 19. stoletja do danes. Stiasny (1940b) je predlagal 30-letni ciklus pojavljanja, vendar smo v zadnjih desetletjih zabeležili pojave l. 1984, 2001, 2010 in 2014. Dalmatinska lasasta meduza je bila bolj pogosto zabeležena v južnem Jadranu, opazovani primerki pa so bili manjših dimenzij kot v severnem Jadranu, kar nakazuje njen transport z vodnimi masami ob vzhodnojadranski obali proti severu. Podatki iz literature kažejo, da so pomemben plen dalmatinske lasaste meduze uhati klobučnjaki, za katere v obdobju po letu 1980, zlasti pa po l. 2000, v severnem Jadranu ugotavljamo pogostejše masovno pojavljanje

Composition and diel vertical distribution of euphausiid larvae (calyptopis stage) in the deep southern Adriatic

Summary: Diel changes in the vertical distribution and abundance of calyptopes were studied in the deepest area of the southern Adriatic over four seasons (July 2003, February 2004, October 2004, April 2009). Temperature variations were limited to the upper 100 m and salinity variations were small. Of previously known adult euphausiid species – 12 for the Adriatic (Gangai et al., 2012) and 13 for the Mediterranean (Mavidis et al., 2005) – calyptopes of 11 species of euphausiids were recorded. Abundance of calyptopes of all species was the highest in spring. Species were characterized according to their mean depth: surface (0–50 m), sub-surface (50–200 m), mesopelagic (200–800 m), or bathypelagic (800–1200 m) and vertical dispersion (scattered or non-scattered). Four diel patterns emerged: (i) nocturnal ascent to upper layers (Euphausia brevis, E. hemigibba, E. krohnii, Nematoscelis megalops, N. couchii), (ii) migration to upper layers at middle of the day and at night, and descent during the morning and evening (Stylocheiron maximum – only winter), (iii) weakly-migrating or non-migrating (S. longicorne), (iv) irregular migration independent of the day/night cycle (S. abbreviatum, S. maximum – during spring, summer and autumn, T. aequalis). Keywords: Euphausiid larvae, Mediterranean Sea, Secondary production, Vertical distribution, Weighted mean dept

Mass occurrence of the ctenophore Bolinopsis vitrea (L. Agassiz, 1860) in the nearshore southern Adriatic Sea (Kotor Bay, Montenegro)

The ctenophore Bolinopsis vitrea has been rarely observed in the Mediterranean Sea. A bloom of B. vitrea is here reported for the first time in the southern Adriatic Sea..

Long-term Monitoring of Carnivorous Gelatinous Macrozooplankton in the Area of Dubrovnik-Neretva County (Croatia)

In the southern part the Adriatic, gelatinous macrozooplankton fauna is poorly known compared to the other taxa. Therefore, our goal was to collect and systematize all available phenological data and abundances of gelatinous organisms based on scientific surveys from 1996 to 2020 and a ”citizen science“ sighting program in the southern Croatian waters. The inter-annual variability and seasonality of planktonic Cnidaria and Ctenophora were described. A total of 590 reports was received from citizens, which summed up to result in 870 data together with the scientists’ records. In total, 15 species were recorded. Of these, scyphomedusa Pelagia noctiluca accounted for 34 %, followed by ctenophora Cestum veneris (19 %) and the scyphomedusa Cothylorhiza tuberculata (17 %). Mass occurrence was most frequently found in P. noctiluca and then in C. tuberculata and C. veneris. Isolated mass occurrence was recorded for the freshwater hydromedusa Craspedacusta sowerbii, found in Lake Kuti near the mouth of the Neretva River, and for the scyphomedusa Aurelia cf. solida. The three species A. solida, Mnemiopsis leidyi and C. sowerbii are not native to European waters. Considered that alien species are invading the Adriatic Sea and human impact and global warming are increasing, it is crucial to carefully monitor the occurrence of gelatinous zooplankton taxa and to conduct studies focused on deciphering their ecological impact in marine ecosystems. Therefore, our empirical analysis of 25 years of observations provides essential information on the variation of gelatinous zooplankton in the Southern Adriatic region

Planktonski ožigalkarji v odprtih vodah južnega Jadranskega morja: primerjava podatkov iz preteklih in novejših raziskav

Planktonic cnidarians in the open southern Adriatic Sea: a comparison of historical and recent dat