Search

Previous investigations of the northern Adriatic observed the changes in the hydromedusan fauna that demonstrate one aspect of the long-term consequences in marine ecosystem: decreased biodiversity. Following concern about substantial changes in these area, in this study we present the comparative results of the composition and abundance of hydromedusan fauna of northern Adriatic, pointing to the possibility of species repopulating recent years. During 2009-2011 we found considerably higher number of species and higher abundances in comparison with the results for the last 5 decades.

Hidromeduze su među prvim planktonskim vrstama opisanim u sjevernom Jadranu početkom 20. stoljeća. Ekološke promjene (eutrofikacija) i smanjenje otopljenog kisika uz dno od 1950.‐tih pa nadalje, uspostavili su nove ekološke uvjete u tom akvatoriju. Te promjene uzrokovale su znatno smanjenje biološke raznolikosti bentosa, uključivši meroplanktonske meduze. U ovom radu prikazani su rezultati istraživanja sastava i brojnosti faune hidromeduza sjevernog Jadrana, imajući u vidu njihovu moguću repopulaciju zadnjih godina. Uzorci planktona su sakupljeni mjesečno vertikalnim potezima od dna do površine s WP2 Nansenovom mrežom na četiri postaje. Predstavljeni rezultati obuhvatila su tri vremenska razdoblja: 1999.‐2002., 2003.‐2007. i 2009.‐ 2013. Rezultati jasno ukazuju na porast broja vrsta i njihove brojnosti od prvog razdoblja istraživanja prema zadnjem (2009.‐2013.). Pretpostavljamo da su neke od tih vrsta unesene ulaznim strujama u sjeverni Jadran, međutim, njihova brojnost je višestruko veća u usporedbi s prijašnjim vrijednostima. Zabilježene visoke prosječne i maksimalne vrijednosti za pojedine metagenetske vrste ukazuju ponovnu mogućnost uspostave stabilnih populacija. Ove promjene su u skladu s novonastalim stanjem sastava i brojnosti cjelokupnog planktona sjevernog Jadrana uzrokovanih klimatskim promjenama i posljedičnom oligotrofikacijom istraživanog područja.

During the last 50 years ecological changes were already noted in the northern Adriatic, and many species disappeared from this zone. Following concern about substantial changes in the northern Adriatic, in this study we present the comparative results of the composition and abundance of hydromedusan fauna of northern Adriatic, pointing to the possibility of species repopulating recent years. Presented data are results of investigations during three study periods: the first from 1999-2002, second from 2003-2007 and the third from 2009-2011. Our results clearly showed that the number of species and their abundance increase from the first to the third investigated period. We assume that some species were introduced by input currents in the northern Adriatic, which is confirmed by the increasing density of trachymedusa, but abundances of some species were several times higher than in previous records. Although the abundance of hydrozoan species vary during their life cycles, our high mean and maximum values of this metagenetic specimens could indicate the possibility of establishing stable populations in the area. These changes are consistent with the recent changes in the plankton composition and abundance, probably caused by a climatic forcing and recognized oligotrophication of the entire northern Adriatic.

During a one year study, an analysis was made on the species composition, abundance and biomass distribution of mesozooplankton in the semi-enclosed marine lake Veliko Jezero, in relation to the main physical-chemical properties of the water column. Copepods were found to be the dominant group over the entire sampling period. The highest abundance and biomass were recorded during the summer, while the lowest values were related to the bottom hypoxia during autumn. Increased salinity in the surface during autumn suggests a stronger inflow of open Adriatic waters and coincides with increased biodiversity.

A yearlong study of the mesozooplankton species composition, abundance and biomass distribution was conducted from February 2008 to February 2009 in the semi-enclosed marine lake Veliko Jezero. The degree of isolation strongly influences the composition of the community. Therefore, zooplankton populations in the lake were characterized by high abundance and a low number of species compared to the neighbouring open Adriatic. A total of 58 mesozooplankton taxa were identified. Copepods were found to be the dominant group over the entire sampling period and accounted for between 19% and 62% of total mesozooplankton density. The most abundant were cyclopoida-oithonids (Oithona similis and O. nana), and small calanoids Paracalanus parvus and Acartia clausi. The highest abundance and biomass were recorded during the summer, while the lowest values were related to the bottom hypoxia during autumn. Increased salinity in the surface during autumn suggests a stronger inflow of open Adriatic waters and coincides with increased biodiversity. Our analyses were based on the data available, indicating strong physical forcing as the primary influence on variation in zooplankton dynamics of the investigated area.

Rezultati ovog istraživanja donose prve podatke o sastavu, brojnosti i vertikalnoj raspodjeli razvojnih stadija eufauzida Jadranskog mora. Istraživanja su obavljena u području dubokog južnog Jadrana tijekom svih godišnjih doba. Rezultati mjerenja hidrografskih parametara potvrdili su da su godišnje varijacije temperature ograničene na površinski sloj do 100 m dubine, dok su varijacije saliniteta bile male za cijeli vodeni stupac. Postojanje takvih stabilnih hidrografskih uvjeta doprinosi održavanju relativno konstantnog sastava planktonske zajednice u južnom Jadranu te su ovi rezultati o sezonskoj raspodjeli i brojnosti ličinki eufauzida reprezentativni za otvoreni južni Jadran. Od 13 vrsta poznatih za Sredozemno more i 12 u Jadranskom moru, zabilježeni su razvojne stadije 12 vrsta. Prilikom određivanja vrsta primijećena su manja odstupanja od do sada poznatih ključeva za razvojne stadije eufauzida pa u posebnom prilogu donosimo njihovu nadopunu. Po prvi put je za Jadran zabilježena prisutnost vrste Thysanoëssa gregaria. Najbrojnije vrste ličinki eufauzida Južnojadranske kotline su: Thysanopoda aequalis, Euphausia krohnii, Stylocheiron longicorne, S. abbreviatum i Nematoscelis megalops. Najveća ukupna brojnost svih razvojnih stadija utvrđena je u proljeće. U usporedbi s oskudnim podacima za Sredozemlje, uočene su više vrijednosti razvojnih stadija eufauzida. Primijećena su četiri migracijska obrasca razvojnih stadija: (i) noćno podizanje u pliće slojeve (kaliptopisi i furcilije: Euphausia brevis, E. hemigibba, E. krohnii, Nematoscelis megalops; kaliptopisi Nyctiphanes couchii; furcilije: Stylocheiron longicorne, S. maximum, Thysaönessa gregaria); (ii) migracija u gornji dio vodenog stupca tijekom podneva i noći te tonjenje tijekom jutra i večeri (kaliptopisi S. maximum); (iii) slabo migrirajuća ili nemigrirajuća populacija (kaliptopisi S. longicorne), (iv) nepravilna migracija koja ne ovisi o dnevnonoćnim promjenama (kaliptopisi i furcilije: S. abbreviatum, Thysanopoda aequalis). Prema srednjoj dubinskoj raspodjeli razvojni stadiji eufauzida podijeljeni su na četiri dubinska sloja (površinski, subpovršinski, mezopelagijalni i dubinski), a ovisno o rasponu dubinske raspodjele na raspršene i neraspršene populacije. In this paper the first data on the composition, abundance and vertical distribution of developmental stages of euphausiids in the Adriatic Sea are presented. The research was performed in the deepest area of the southern Adriatic during all seasons. Hydrographic measurements confirmed that the annual temperature variations are limited to the surface layer up to 100 m in depth with minor salinity variations for the entire water column. Such stable hydrographic conditions contribute to maintaining a relatively constant composition of planktonic community in the southern Adriatic which makes these results on the seasonal distribution and abundance of euphausiid larvae representative for the open southern Adriatic. Out of the 12 formerly known euphausiids for the Adriatic and 13 known in the Mediterranean, developmental stages of 12 species were recorded. Minor deviations from the existing keys for euphausiid developmental stages were observed, and for this reason, we present their complement in the special chapter. Thysanoëssa gregaria has been reported in the Adriatic Sea for the first time. The most numerous species were: Thysanopoda aequalis, Euphausia krohnii, Stylocheiron longicorne, S. abbreviatum and Nematoscelis megalops. The maximum abundance of all developmental stages was determined in the spring. In comparison with the scarce data for the Mediterranean, we recorded higher abundance of euphausiids developmental stages in the Adriatic. Four migration patterns were observed: (i) nocturnal ascent to upper layers (calyptopes and furciliae: Euphausia brevis, E. hemigibba, E. krohnii, Nematoscelis megalops; calyptopes Nyctiphanes couchii; furciliae: Stylocheiron longicorne, S. maximum, Thysaönessa gregaria), (ii) migration to upper layers at midday and night, and descent during the morning and evening (calyptopes S. maximum), (iii) weakly-migrating or non-migrating population (calyptopes S. longicorne), (iv) irregular migration independent from the day/night cycle (calyptopes and furciliae: S. abbreviatum, Thysanopoda aequalis). According to the mean depth distribution, euphausiid developmental stages inhabit four depth layers (surface, sub-surface, mesopelagic and bathypelagic), and depending on the range of depth distribution they are characterized as scattered or non-scattered populations.

Plankton sampling (125-µm mesh Nansen plankton net) and hydrographic measurements were carried out weekly from March 2009 to July 2010 at a fixed station in the Kotor Bay, Montenegro (N 42026’ ; W 18045’). A bloom of ctenophore Bolinopsis vitrea was noted in the spring and summer of 2009. B. vitrea has been observed before in the Mediterranean, although it has not been reported to be dominant or to occur in massive blooms. During our investigation, ctenophores were only found below 5 m depth, where the hydrographic conditions were more stable. Results of the investigation indicate that mass occurrence of B. vitrea could have a great impact on the Kotor Bay ecosystem. Their predation on copepods would reduce grazing pressure on phytoplankton, favouring an uncommon bloom of the latter. It is evident that B. vitrea are capable of altering rapidly the composition and biomass of coastal plankton communities when present in large masses. Disappearance of B. vitrea from the Kotor Bay coincided with the appearance of their predator, the ctenophore Beoroe ovata, in December 2009. During 2010, neither Bolinopsis vitrea nor Beoroe ovata was observed in the bay system. This first evidence of such events for Bolinopsis vitrea along with recurrent recent blooms of the invasive ctenophore Mnemiopsis leidyi in the Mediterranean Sea may indicate changes in the functioning of this enclosed marine ecosystem. Gelatinous plankton blooms may thus pose an area of concern for the region indicating a risk of failure to achieve GES (Good Environmental Status) as high level objective of the MSFD (Marine Strategy Framework Directive).

Planktonic cnidarians were investigated at six stations in the Boka Kotorska Bay from March 2009 to June 2010 by vertical hauls of a plankton net from bottom to surface. In total, 12 species of hydromedusae and six species of siphonophores were found. With the exception of the instant blooms of Obelia spp. (341 ind. m-3 in December), hydromedusae were generally less frequent and abundant: their average and median values rarely exceed 1 ind. m-3. On the contrary, siphonophores were both frequent and abundant. The most numerous were Muggiaea kochi, Muggiaea atlantica, and Sphaeronectes gracilis. Their total number was highest during the spring-summer period with a maximum of 38 ind. m-3 observed in May 2009 and April 2010. M. atlantica dominated in the more eutrophicated inner area, while M. kochi was more numerous in the outer area, highly influenced by open sea waters. This study confirms a shift of dominant species within the coastal calycophores in the Adriatic Sea observed from 1996: autochthonous M. kochi is progressively being replaced by allochthonous M. atlantica in the coastal waters, especially in the eutrophicated areas. This study provides a detailed report on the composition and abundance of the planktonic cnidarians community in this region, and should be considered as a baseline for future studies on gelatinous zooplankton.

We present for the first time composition, numerical abundance and vertical structure of micro- and 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.

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.

Veliko Jezero (“Big Lake”) is a semi-enclosed marine lake formed in a submerged karstic valley in a Croatian marine protected area, the Island of Mljet. Over the second half of the 20 century, the Veliko Jezero ecosystem undergone human-induced modifications related to the water mass exchanges with the open sea, which consisted in a 2-fold increase of depth in the channel communicating the lake with open sea. In this work we examine historical and recent data on hydrology and zooplankton abundance and structure that cover the period 1950-2001. Both, temperature and salinity showed upward trends and a maximum of 2°C in temperature, while salinity rose from 35.84±1.19, observed in the 1950s, to 37.43±0.56 recorded in late 1990s. Such changes have modified the pelagic habitat and altered the zooplankton structure through invasive processes and local extinctions. In particular, an increasing number of open-sea species, i.e. copepods and appendicularians, become more frequent and abundant, and former dominant species, i.e. the copepod Pseudocalanus elongatus, have disappeared since the 1990s. Concurrent to these changes, the biomass of jellyfish has increased, with the schyphomedusan Aurelia sp. 5 as the dominant species reaching abundances nowhere observed. These long-term modifications are discussed in regards to resilience and compensatory responses of zooplankton community to disturbance in a changing environment.

Morning, midday, evening and night repetitive sampling was used to demonstrate calycophoran diel vertical migration (DVM) at fixed station in the oligotrophic southern Adriatic Sea at 8 depth intervals. Of 20 calycophoran species collected, most of them inhabited layers of specific temperature and light intensity, and migrated during night. The deep species Kephyes ovata is primarily non-migratory. Typical nocturnal movements to the surface were recorded for Lensia conoidea and Sphaeronectes koellikeri. Lensia subtilis and Eudoxoides spiralis migrated toward surface in the evening but sank deeper at night. Lensia meteori and Lensia fowleri reached upper layers at midday. The DVM of Sphaeronectes irregularis was irregular and independent of diel light patterns. Though low in numbers, some calycophorans were found above the thermocline at night. For mesopelagic species, however, higher summer surface temperatures proved an effective barrier to migration above 100 m. Thus, certain species could be represented as key species of planktonic cnidarians assemblages found within a certain depth range. Though not homogenous, and while some undertake nocturnal migrations in both directions, all are interrelated by preferences of bathymetric distribution and specific DVM behavior.

Calanus helgolandicus is a key pelagic copepod in trophic food webs of the North Atlantic and surrounding ecosystems. Changes in the population size of this species have rarely been investigated in the Adriatic Sea. In this work, we examine the seasonal habitat utilization of C. helgolandicus in regards to environmental variations and predation pressure in the Marine reserve of Mljet Lake “Veliko jezero”, a pristine ecosystem that offers a natural mesocosm to investigate ecology of zooplankton. In the marine lake “Veliko jezero”, C. helgolandicus is one of the dominant species reaching abundances up to 249, 6 ind/m3 and contributing up to 15, 86% of the total copepod abundance. We show that predation by jellyfish and chaetognaths act as major controls of the population size of C. helgolandicus. Pronounced seasonal vertical migration was observed. During the colder time of year, abundance is higher in upper layers. As temperature increase and upper layers become food depleted, C. helgolandicus migrate to concentrate in deeper layers, where they are faced with a trade-off between predatory risk and feeding opportunities. Such ecological interactions appear to be the main control on the population size of the species, although modifications in the functional responses might also occurs as consequence of food diet changes. Our results suggest large predator impact on zooplankton production in stratified marine environments.

U Mljetskim jezerima (Veliko 1.45 km2 i Malo 0.241 km2) 2008. – 2009. g. istraživan je sastav i biomasa mrežnog zooplanktona na postajama Vrbovačka (VJ), Malo jezero i u uvali Gonoturska. Uzorci su uzimani Nansen mrežom finoće tkanja 200 µm i promjera otvora 57 cm. Prikupljeni uzorci odmah su konzervirani 2.5% neutraliziranim formaldehidom. Ukupna suha i organska tvar izvagane su na METTLER TOLEDO XS analitičkoj vagi. Zooplanktonska fauna jezera karakterizirana je malim brojem vrsta i visokim vrijednostima gustoće. U ukupnom broju dominiraju kopepodi: Oithona similis, Oithona nana, Acartia clausi, Paracalanus parvus, Centropages kroyeri. Veliko jezero je prema zooplanktonskoj biomasi visoko produktivno područje, čije su srednje vrijednosti suhe (15, 13 mg/m3) i organske tvari (11, 98 mg/m3) najsličnije vrijednostima za sjeverni Jadran. Srednje vrijednosti suhe mase u Malom jezeru su znatno niže (7, 38 mg m-³). Visoke vrijednosti gustoće kopepoda Calanus helgolandicus, skifomeduze Aurelia sp.5 pteropoda Limacina spp., brojnost i veličina hetognata Sagitta setosa, te hiperbentički kopepod Mesaiokeras hurei neke su od specifičnosti zooplanktonske faune Velikog jezera

Jellyfish are conspicuous components of marine ecosystems and recognized as valuable indicators of ecosystem performance and change. Although changes in their population size have been described for long time, recent reports indicate an increase of jellyfish proliferations in different shelf seas worldwide. In this study we used a comparative approach based on time series data and ecosystem modeling to evaluate how food web complexity and ecosystem degradation interact with the dynamics of jellyfish. The ecosystems investigated represent two contrasting environments, the Kiel Fjord, south-western Baltic Sea, and the Marine Protected area of the National Park Mljet, in the south Adriatic Sea. The results show that jellyfish dynamics is favored by food web degradation, which together with global warming, allow higher variability in jellyfish outbreaks. The consequences of such dynamics may jeopardize the ecosystem resilience under global warming scenarios.

This review compares historical data sets (1967-68, 1974-1976, 1993-1995)to the most recent data (2003-2004)on the composition, abundance and vertical migration of cnidarians of the deep southern Adriatic. 18 species of medusae are typical open-ocean holoplanktonic species and 6 of these were either always or frequent found in samples, namely Rhabdon singulare, Aglaura hemistoma, Persa incolorata, Rhopalonema velatum, Sminthea eurygaster, and Solmissus albescens. The most common calycohore siphonophores are Lensia subtilis, L. meteori, Eudoxoides spiralis, Sphaesonectes gracilis, and S. irregularis, followed by Hippopodius hippopus, Vogtia penthacantha, Lensia comoidea, L. fowleri, Chelophyes appendiculata, Kephyes ovata, and Bassia bassensis. Some difference in presence and abundance betwen historical and recent data are noted.

Dnevne vertikalne migracije ličinki eufauzida su istraživane u južnom Jadranu na postaji dubine 1200 m u srpnju 2003. godine. Obavljeno je 19 serija uzorkovanja planktonskom mrežom na zatvaranje finoće tkanja 200  m u različitim dobima dana unutar osam dubinskih slojeva u vremenskom intervalu od 96 sati (152 vertikalna poteza). Od ukupno 11 zabilježenih vrsta po učestalosti nalaza i brojnosti izdvajamo vrste Euphasia krohnii i Stylocherion abbreviatum, te Stylocherion longicorne, Nematoscelis megalops i Stylocherion maximum. Isključivši malobrojne kaliptopise N. megalops, svi razvojni stadiji navedenih vrsta pokazuju velike dubinske raspone raspodjele pojavljivanja: E. krohnii - kaliptopisi 0-800 m, furcilije 0-1200 m ; N. megalops - furcilije 0-1200 m ; S. abbreviatum - kaliptopisi 200-1200 m, furcilije 0-400 m ; S. longicorne - kaliptopisi 100-600 m, furcilije 0-800 m ; S. maximum - kaliptopisi i furcilije 100-1200 m. Izračuni središnje tendencije dubinske distribucije za svaki stadij i vrstu pokazali su da sve ličinke obavljaju opsežne dnevne vertikalne migracije, a najveće su zabilježene za kaliptopise vrsta E. krohni (552 m) i S. longicorne (280 m), a među furcilijama za vrste S. maximum (811 m) i N. megalops (447 m). Naši rezultati su prvi podaci za ličinke eufauzida u Jadranu te predstavljaju znatan doprinos poznavanju sastava i uloge mrežnog zooplanktona u hranidbenoj mreži ovog dubokog oligotrofnog ekosustava.

U Mljetskim jezerima (Veliko 1.45 km2 i Malo 0.241 km2) 2008. – 2009. g. istraživana je gustoća i biomasa mezozooplanktona na postajama Vrbovačka, Jejevići i Babine kuće te na po jednoj postaji u Malom jezeru i u uvali Gonoturska. Uzorci su uzimani Nansen mrežom finoće tkanja 200 &micro ; m, promjera otvora 57 cm okomitim potezima u dva dubinska sloja. Prikupljeni uzorci odmah su konzervirani 2.5% neutraliziranim formaldehidom. Suha i suha organska tvar izvagane su na METTLER TOLEDO XS analitičkoj vagi. Najveća srednja vrijednost gustoće je u svibnju na postaji Babine kuće (10 317 ind m&macr ; &sup3 ; ) i srpnju u Malom jezeru (7044 ind m&macr ; &sup3 ; ). Postaja Babine kuće ima najviše srednje godišnje vrijednosti gustoće (3237 &plusmn ; 3077 ind m&macr ; &sup3 ; ), postaja Gonoturska najniže (1063 &plusmn ; 604 ind m&macr ; &sup3 ; ), kao i najniže srednje godišnje vrijednosti suhe tvari (3.74 &plusmn ; 2.18 mg m&macr ; &sup3 ; ). Najveća srednja vrijednost suhe tvari je na postaji Jejevići u veljači 2009. g. (62.53 mg m&macr ; &sup3 ; ). U Velikom jezeru srednja vrijednost gustoće populacije je 2437 ind m&macr ; &sup3 ; , srednja vrijednost suhe tvari je 15.13 mg m&macr ; &sup3 ; i organske tvari 11.98 mg m&macr ; &sup3 ; , što je najsličnije vrijednostima za sjeverni Jadran. Srednje vrijednosti suhe mase na ostale dvije postaje su znatno niže, Malo jezero 7, 38 mg m&macr ; &sup3 ; , Gonoturska 3.74 mg m&macr ; &sup3 ; , što je najbliže vrijednostima za Kvarner, odnosno otvorene vode srednjeg i južnog Jadrana.

Uzorci mezozooplanktona su sakupljeni istraživačkim brodom “Vila Velebita”na četiri stalne postaje tijekom 15 krstarenja u sjevernom Jadranu od svibnja 2003. do svibnja 2004. godine. Materijal je uzet vertikalnim potezima od dna do površine planktonskom mrežom površine otvora 0, 25 m2 i finoće tkanja 200 µm. Manji upliv rijeke Po u 2003. godini u usporedbi s višegodišnim prosječnim vrijednostima uzrok su stabilnijim hidrografskim prilikama i manjim koncentracijama klorofila a. Utvrđene su niske vrijednosti mezozooplanktona za sjeverni Jadran. Veća brojnost nađena je na zapadnim postajama, a veća raznolikost sastava mezozooplanktona na postajama uz istočnu obalu. Kopepodi su imali veliki udio u ukupnim vrijednostima mezozoplanktona, osobito tijekom jeseni i zime. Dominatne vrste su: Paracalanus parvus, Acartia clausi, Ctenocalanus vanus, Calanus helgolandicus, te Oithona plumifera i Temora stylifera. Tijekom ljetnih mjeseci najbrojnija je bila neritička kladocera Penilia avirostris. U svibnju 2003. dinoflagelat Noctiluca scintillans je bio izrazito dominantan na svim postajama. Smanjena brojnost pojedinih dominantnih neritičkih i estuarijskih vrsta sjevernog Jadrana, te povećanje gustoće površinskih vrsta otvorenog mora, dovodimo u svezu s čimbenicima okoliša, prvenstveno smanjenim upliva slatke vode i prodorom slane oligotrofne vode.

Uzorci mezozooplanktona su sakupljeni istraživačkim brodom “Vila Velebita”na četiri stalne postaje tijekom 15 krstarenja u sjevernom Jadranu od svibnja 2003. do svibnja 2004. godine. Materijal je uzet vertikalnim potezima od dna do površine planktonskom mrežom površine otvora 0, 25 m2 i finoće tkanja 200 µm. Manji upliv rijeke Po u 2003. godini u usporedbi s višegodišnim prosječnim vrijednostima uzrok su stabilnijim hidrografskim prilikama i manjim koncentracijama klorofila a. Utvrđene su niske vrijednosti mezozooplanktona za sjeverni Jadran. Veća brojnost nađena je na zapadnim postajama, a veća raznolikost sastava mezozooplanktona na postajama uz istočnu obalu. Kopepodi su imali veliki udio u ukupnim vrijednostima mezozoplanktona, osobito tijekom jeseni i zime. Dominatne vrste su: Paracalanus parvus, Acartia clausi, Ctenocalanus vanus, Calanus helgolandicus, te Oithona plumifera i Temora stylifera. Tijekom ljetnih mjeseci najbrojnija je bila neritička kladocera Penilia avirostris. U svibnju 2003. dinoflagelat Noctiluca scintillans je bio izrazito dominantan na svim postajama. Smanjena brojnost pojedinih dominantnih neritičkih i estuarijskih vrsta sjevernog Jadrana, te povećanje gustoće površinskih vrsta otvorenog mora, dovodimo u svezu s čimbenicima okoliša, prvenstveno smanjenim upliva slatke vode i prodorom slane oligotrofne vode.

During two cruises of the MEDUZA experiment conducted in July 2003 and May 2005 various data were obtained over the deepest part of the southern Adriatic Pit. Temperature, salinity, light transmission and fluorescence were measured in July 2003. During May 2005, except CTD measure- ments the samples were taken for laboratory determination of phytoplankton pigments with HPLC technique. During both cruises irradiance and radiance were measured at 14 wavelengths in the range 340-715 nm with optical probe to about 100 m depth. Bad weather conditions during both cruises caused interruption of measurements that continued after 24 to 48 hours. Stormy conditions have resulted in a slightly different structure of the water column. In the periods of measurements recorded were diurnal rhythms in a series of parameters, caused by solar radiation cycles in the surface layers as well as fluctuations in the deeper layers under the influence of the internal tide. Meteorological conditions and changes in sea level are also described. The analysis included the principal component and correlation analysis between the measured and derived parameters in order to establish a link between the in-situ pigments and multispectral data. During both cruises diurnal vertical oscillations were observed in biotic and abiotic parameters. Chlorophyll pigments prevailed over other pigments preventing other pigments to be distinguished spectrally. Regression models for chlorophyll a were established from radiance and reflectance ratios.