Search

Južni Jadran je najdublji dio Jadranskog mora (1242 m) i jedno od tri mjesta dubokog vertikalnog miješanja u Sredozemnom moru. Analizom uzoraka zooplanktona uzetih na otvorenom moru južnog Jadrana u veljači i lipnju 2021., istražili smo utjecaj zimskog vertikalnog miješanja na rasprostranjenost i abundanciju četinočeljusta od površine do 1200 m dubine. Krstarenje u veljači bilo je nakon epizoda jake bure i posljedično znatnih gubitaka topline na površini mora. Također, u intermedijarnom sloju zabilježen je ulaz slane istočnomediteranske struje (> 38, 9, LIW) koja uz navedene vremenske prilike stvara uvjete za vertikalno miješanje. Stoga je u veljači dubina miješanog sloja (DMS) bila do 600 m. U isto vrijeme zabilježena brojnost četinočeljusta bila je niska i gotovo jednaka od površine do DMS- a. Također, zabilježena je neuobičajena vertikalna raspodjela epipelagičkih vrsta u relativno visokom broju od 200 do 600 m dubine. U lipnju, kada je uočena izražena toplinska stratifikacija zabilježeno je izrazito povećanje brojnosti četinočeljusta u epipelagičkom sloju. To je vjerojatno povezano s proljetnim cvjetanjem fitoplanktona pojačanim unosom hranjivih tvari u eufotičnu zonu zbog zimske faze miješanja.

Želatinozni zooplankton se pokazao kao dobar indikator termohalinih promjena u Jadranu. Brojnost i pojavnost stranih ili nedavno uspostavljenih želatinoznih vrsta su direktno povezani s promjenama u obrascima cirkulacije, a potencijalno i s razinom zagrijavanja Jadrana. U posljednjih deset godina u Jadranu su otkrivene dvije nove želatinozne planktonske vrste za znanost: Brooksia lacromae (Thaliacea, Tunicata) i Aurelia pseudosolida (Ulmaridae, Cnidaria). Indopacifička vrsta Paracytaeis octona (Cytaeididae, Cnidaria) je zabilježena od 2015. godine pa nadalje, dok su mediteranske vrste Doliopsis rubescens i Pegea bicaudata (Thaliacea, Tunicata) zabilježene u Jadranu prvi put 2016. godine. Sporadično su se bilježile i relativno rijetke vrste Pyrosoma atlanticum (Thaliacea, Tunicata), Porpita porpita (Porpitidae, Cnidaria) i Flaccisagitta hexaptera (Chaetognatha). Naši podaci sugeriraju da se ubrzavaju promjene u sastavu zajednica želatinoznog planktona u Jadranskom moru što upućuje na potrebu provođenja sustavnih programa monitoringa na državnoj razini. Da bi se procijenila mogućnost korištenja metoda sekvenciranja sljedeće generacije u praćenju promjena u sastavu Jadranskog zooplanktona proveli smo istraživanje u Sjevernom i Južnom Jadranu u trajanju od godine dana. Naši preliminarni podaci pokazuju da se rijetke vrste zooplanktona i pelagički plaštenjaci ne bilježe konzistentno upotrebom fragmenta gena podjedinice I citokrom oksidaze (COI).

Copepod community structure was investigated on a short time sampling scale during a 24-h cycle at one fixed station in the open Adriatic Sea in June 2020 and February 2021 (from 0 to 300 m) using Nansen opening-closing net (250 µm mesh size). In June, the upper oceanic waters were characterized by vertical gradients of environmental factors while in February oceanic waters showed relatively homogeneous physicochemical conditions. During the winter vertical mixing, the bulk of the copepod population remained in the epipelagic zone (0- 100 m) over the entire 24-h cycle, with calanoids remained the dominant group. An increasing trend of copepod standing stocks from midnight to early morning in the surface layer found in June is in agreement with previous records of copepod day- night variations in the Mediterranean Sea. Average Shannon-Wiener diversity index was lower in July (2.21±0.27) than in February (2.54±0.18) with the most pronounced differences in a 200-300 m layer, during the whole sampling period. Day-night differences in diversity and number of taxa of the epipelagic area were more pronounced in June, confirming the higher intensity of diel vertical migration in summer as well as deficiency of calanoids during the most intensive daylight. Although the epipelagic community was composed of numerous weak diel vertical migration species, for the majority of investigated copepod taxa migration patterns differed between the seasons suggesting significant influence of environmental conditions on their vertical positioning.

Vertikalna migracija je rašireno ponašanje mnogih svojti zooplanktona kroz koje organizmi aktivno sudjeluju u transportu tvari i energije u morskom okolišu. Cilj ovog istraživanja bio je razjasniti promjene u vertikalnoj distribuciji zajednica kopepoda pod dva različita okolišna uvjeta: ljetna stratifikacija (lipanj 2020) i događaj duboke zimske konvekcije (veljača 2021). Uzorci su uzeti tijekom ciklusa od 24 sata na jednoj postaji u južnom Jadranu od površine do 1200 m (u osam dubinskih slojeva). U lipnju je najveća brojnost kopepoda zabilježena u površinskom sloju tijekom ranog jutra, dok je tijekom intenzivnog dnevnog svjetla najveći dio populacije kopepoda bio koncentriran na sloju od 200-300 m. U veljači su maksimalne vrijednosti gustoće bile u površinskom sloju (0-50 m) tijekom cijelog ciklusa od 24 sata. Ukupno je identificirano 90 svojti kopepoda. Vertikalni obrasci raznolikosti pokazali su veće vrijednosti u srednjim slojevima (400-600 m) tijekom podneva u oba godišnja doba. Izračunata srednja dubina pojavljivanja (WMD) za većinu istraživanih vrsta kalanoida bila je dublja u veljači nego u lipnju, što ukazuje na njihovo zadržavanje u dubljim slojevima tijekom razdoblja miješanja, a time i smanjuje rizik gubitka putem vizualnih grabežljivaca. Naši podaci naglašavaju važnu ulogu gradijenata okoliša u vertikalnom strukturiranju zajednica kopepoda u obje vremenske skale (dnevne i sezonske), u dinamičnom oligotrofnom pelagičkom sustavu.

The coverage of Thaliacea species has been relatively good regarding 18S. The 18S gene is highly conserved, therefore of limited use in delimiting closely related species and unsuitable for population-level studies. This is demonstrated by the fact that Thalia democratica and Thalia longicauda, which are morphologically quite distinct, possess identical 18S sequences. COI has been traditionally the most common barcode gene, because of its ability to differentiate species and populations and relative ease of amplification across taxa, but thaliacean COI sequences are scarce, so much so that COI barcodes of only five Thaliacea species are available. The general absence of available thaliacean sequences is likely due to a combination of factors: lack of taxonomists as well as inability of the commonest COI primers (namely, LCO1490 and HCO2198) to reliably amplify COI gene fragments across thaliacean taxa. Within the framework of SpaTeGen project, in an effort to produce COI sequences of Adriatic thaliaceans, we combined multiple primer pairs and produced doliolid and salpid COI sequences of more than 800 bps, encompassing HCO2198 binding site. Our preliminary results show that pyrosomatid and doliolid sequences are 6 aminoacids longer than salpid sequences, in the first 300 aminoacid stretch. Preliminary phylogenetic analysis based on COI sequences place salpids as a sister clade to pyrosomatids and doliolids. This is in contrast to published phylogeny based on 18S, which place pyrosomatids as the most ancestral group from which doliolids and salpids branch off in succession.

New species of Doliolida is found in the South Adriatic in autumn 2021. Blastozooids of this species are similar to Dolioletta gegenbauri in endostyl position (from MII 1/2 to MIV 1/3), overall body consistency (both species are fragile and easily damaged in net tows), position and length of the testis and ovary and the position of the branchial bar. The main difference in Dolioletta sp. nov. and Dolioletta gegenbauri is in that intestine does not form a tight coil and after forming a right loop as in Doliolum nationalis, it sharply turns left so that anal aperture is facing left body wall. The other difference between these two species is in that the ganglion is positioned between MIII and MIV, but closer to MIV in Dolioletta sp. nov., while in Dolioletta gegenbauri it is positioned closer to MIII. COI pyhlogenetic analysis showed that Dolioletta sp. nov. forms a clade with Dolioletta gegenbauri (100% bootstrap support), while the COI sequence difference between these two species is 16.8%. The finding of a new doliolid species in the Adriatic Sea continues the worrisome trend in recent decades of new gelatinous species being described every couple of years in this well investigated area. The geographic origin of this species is still unknown.

In summer 2020 a bloom of Aurelia solida occurred in the Adriatic Sea. Among A. solida individuals, new Aurelia species was detected. The individual was sequenced (COI, 16S, 18S- ITS1- 5.8S- ITS2- 28S) and the obtained sequences were searched against the GenBank database using the Blast tool. The search showed that no identical sequence existed in GenBank. Subsequent phylogenetic analysis associated this newly discovered species the most closely to Aurelia solida. Aurelia solida is a known Lessepsian migrant which is now widespread throughout Mediterranean. Given its close genetic association to the new Aurelia species it is possible that the newly discovered Aurelia species is also a Lessepsian migrant. In addition to genetic differences the two species differ most prominently in the way manubrium arms fold as well as in the morphology of the rhopalium.

An unknown hydromedusa species belonging to the genus Paracytaeis (Anthoathecata, Cytaeididae) is collected from the open sea of the southern Adriatic in winters of 2016., 2020. and 2021. Only two species from this genus are known, P. octona and P. meteoris. So far, only medusa stage of both speies are described. The last one is doubtfoul species due to inadequate description of only single specimen from near the Cape Verde Islands (Atlantic Oceans). However, our species can be distinguished from its congeners, among others features, by the number of oral tentacles in adult specimens. Specimens were sequenced (COI, 16S) and the obtained sequences were searched against the GenBank database using the Blast tool. The search showed that no identical sequence existed in GenBank. However, no data of any of two Paracytaeis species existed in the Genbank. Nevertheless, this analysis confirm that species belong to the family Cytaeididae. Relatively high number of specimens (1.0 ind/m3) were occurred in a situation with high salinity conditions (38.8 - 39.3) in all years when they are registered. High salinity condition indicates strong inflow of Eeast Mediterranean water into Adriatic Sea. Therefore, our Paracytaeis species might be a Lessepsian migrant of Indo-Pacific origin.

Investigation of deep sea plankton is limited because the deep sea net sampling is time consuming especially is specialized equipment such as multinet systems is not available. We here present rare insight in yearly cycle and size distribution of mesopelagic appendicularian Oikopleura villafrancae. Appendicularians are a group of pelagic tunicates known for their short life cycle and unique mode of feeding using a structure called the appendicularian house. Their house contains a set of filters which enables them to feed on submicron particles. Appendicularians have not been known to exhibit any substantial vertical migration. In order to investigate ecology of mesopelagic appendicularian Oikopleura villafrancae we sampled open South Adriatic from the surface to the 1200 m depth during the course of three years in following layers using Nansen closing nets: 0-50, 50-100, 100-200, 200-300, 300- 400, 400-600, 600-800, 800-1200 m. The samplings were contucted during all seasons. We determined abundance of the O. villafrancae in each layer as well as measurements of tail length, tail musculature width, trung length and endostyle length. Our results show that population of O. villafrancae is vertically distributed in depth layers from 200-1200 m in a way that shortest inndividuals are consistently found only in top layers while progressively larger individuals are found in deeper layers. The abundance of O. villafrancae is lowest in winter and autumn months while in spring and summer it is the greatest. Morphological data does not show any discrepancies within the population which would indicate presence of cryptic species or subspecies as indicated by Fenaux (1992) by describing subspecies Oikopleura villafrancae indentacauda in addition to species Oikopleura villafrancae.

Gamulin (1979), during his investigations of thaliacean abundance and distribution in the Adriatic Sea in the period from 1947 to 1952, found only larvae of Pyrosoma atlanticum, most commonly in the tetrazooid form, and in the greatest abundance near the Vis island. Nevertheless, he states that Pyrosoma atlanticum is common in the South Adriatic were it is occasionally caught by the fishermen in the fishing nets. For the period 1974-1975 Katavić (1976) states that he found 7 tetrazooids and 3 small adult colonies in the South Adriatic. In the period from 2007 to 2020 only few tetrazooid colonies were caught by zooplankton nets and adult colonies were never observed on the surface. In 2021, during zooplankton sampling trip in the open South Adriatic on 9th and 10th of September, we observed 13 adult colonies of P. atlanticum. Three of them were caught by hand nets and their identity was confirmed by inspection under the binocular. At the time of collection the surface salinity was extremely high (39.3) and surface temperature was 25.4°C. It seems that P. atlanticum is not as common in the Adriatic now as it was in the past. It occurrence seems to vary and it is possible that it is governed by circulation changes in the Ionian Sea, most notably BiOS (Bimodal Ocillating System). Due to the termophilic nature of P. atlanticum and on-going climate changes it is possible that P. atlanticum will become more common in the Adriatic Sea than it was in last decades.

Thalia democratica inhabits warm and temperate waters around the globe and is one of the most ubiquitous Thaliacea of coastal waters. Currently, within Thalia democratica there are two accepted forms: Thalia democratica democratica (Forskål, 1775) and Thalia democratica indopacifica van Soest, 1975. The two forms differ quite substantially in morphology. The most notable difference is in presence/absence of lateral cuticular projections as well as in size of medioventral projections. In order to test if the two forms of T. democratica represent different species, we sequenced 1758 bp long fragment of 18S gene. The 18S sequences of the two T. democratica forms differed 0.17%, or in 3 positions out of 1758. In the view that T. democratica and T. longicauda, which are considered separate species, have identical 18S sequences it is likely that Thalia democratica democratica and Thalia democratica indopacifica are separate species.

Chaetognaths comprise a phylum of marine organisms which is considered among the most important zooplankton groups, as they are often second in abundance after copepods in the mesozooplankton. Some basic aspects of chaetognath distribution and biology particularly for meso- and bathypelagic species are not well known in the Mediterranean Sea as well as other seas and oceans. Vertical distribution of Sagitta lyra abundance and biomass were studied at open-sea stations from surface to 1200 m depth in the northern part of the South Adriatic Pit during four seasonal cruises in 2019/2020. S. lyra displayed ontogenetic vertical distributions, with older stages occurring at greater depth. They were more abundant in the upper 100 m, their abundance decreased conspicuously with depth, and were captured only rarely between 600 and 1200 m. Increase in abundance and biomss were found in early spring after winter convective events and early summer in time of intensive reproduction. Mean carbon and nitrogen content (as a percentage of dry weight) among maturity stages varied from 21.2 to 36.1% and 6.1 and 8.6% respectively. Higher values were recorded in greather depths where they consumed prey at high rates and where the contribution of older specimens increased.

Oikopleura longicauda is cosmopolit appendicularian species with a preference for warm and temperate waters. In order to determine genetic diversity of Oikopleura longicauda we sequenced 307 bp long fragment of subunit I of mitochondrial cytochrome oxidase (COI) of 34 individuals collected in July 2017 at a coastal station in South Adriatic. Our data revealed 4 groups of sequences with more than 16% of uncorrected p-distances indicating that Oikopleura longicauda is likely a complex of species with at least 3 different species existing in the Adriatic.

A planktonic tunicate determinated as Thalia orientalis Tokioka, 1937 was recorded for the first time in the Adriatic in 2007, when prevalent circulation pattern in the North Ionian Gyre was changing from cyclonal to anticyclonal, thus starting to bring more of western Mediterranean waters into the Adriatic Sea. Since T. orientalis is present in Red Sea as well as in Atlantic, it was hard to determine where from exactly did it arrive. In order to determine the origin of the Adriatic specimens we sequenced 757 nucleotide long fragment of 18S rRNA gene from the Adriatic and Pacific specimens of the T. orientalis. Uncorrected p-distance between sequences was 1.98%, which suggests that the specimens are of separate entities. The Adriatic and Pacific specimens differ also morphologically in the shape of atrial palps and medioventral projections. As Thalia orientalis was described based on specimens from the Pacific, Adriatic specimens should be considered as a new, still undescribed species. Our results emphasize importance of DNA methods in determining the origin of alien species as well as the mechanisms of their dispersal.

In this study we investigated diatom colonization during period of first 6 months of artificial substrate (glass slides) exposure. From April to October 2016 microscopic glasses were submerged in the marine lake Mrtvo more (island of Lokrum, Dubrovnik area, South Adriatic, NE Mediterranean, Croatia). This semi-closed shallow marine ecosystem is connected with the open sea by an underwater passage, and is during summer season under significant anthropogenic influence (swimmers). The parallel oriented glass slides (against the surface) were placed on a seafloor at 1 m beneath the water surface. The samples were collected weekly. For light microscopy (LM) observations diatom frustules were cleaned from the organic material using method with hydrogen peroxide and hydrochloric acid. In order to determine the relationships between diatom community and environmental variables, water samples for analysis of physicochemical variables were taken weekly from the same place where diatom sampling was carried out. Water temperature ranged from 18.3°C (May) to 27.3°C (July). Salinity varied from 26.6 (October) to 37 (August). Oxygen saturation (O2/O2′) ranged 0.58 (September) to 1.3 (June). TIN ranged from 0.96 (May) to 10.2 (September) µM. Phosphate (PO4) ranged from 0.112 (May) to 0.578 (July). Silicate (SiO4) ranged from 3.925 (May) to 13.016 (July) µM. The benthic diatom flora was investigated and diversity was determined in relation to the concentrations of phosphate, silicate, and nitrogen compounds. The composition (% relative abundance) of a total of 133 diatom taxa within 47 genera found in the benthic diatom community of studied artificial substrates were identified in 21 samples. Species Cocconeis scutellum Ehrenb. var. scutellum, Cocconeis dirupta var. flexella Grunow, Pinnularia Ehrenb. sp., Diploneis crabro (Ehrenb.) Ehrenb., Navicula salinicola Hust., and Licmophora paradoxa (Lyngb.) C. Agardh were the most abundant. Genera with the greatest number of taxa were: Nitzschia Hassall (20 taxa), Mastogloia Thwaites ex W. Sm. (11), Amphora Ehrenb. ex Kütz. (9) and Cocconeis Ehrenb. (9). Altogether, only three taxa were presented in more than 85% of samples: Cocconeis scutellum var. scutellum, Cocconeis dirupta var. flexella and Cocconeis pseudomarginata W. Greg. In total, 60 taxa were found only once (sporadic) with average relative abundances lower than 1.3%. The number of taxa per sample ranged from 9 (May, June) to 52 (August), with an average of 25.4. The species diversity index varied from 0.74 to 4.51. Pielou’s species evenness ranged from 0.23 to 0.86 (the average 0.63).The amount of biofilm increased through study period. Diatom assemblages were significantly different (ANOSIM, P

Doliopsis rubescens was a very common species in the Mediterranean in 19 th and in the beginning of the 20 th century. In the past it was a very abundant species, so much that it formed large blooms at the coast of France. Afterwards it has become extremely rare with sporadic records in the Atlantic. D. rubescens was found in the Adriatic for the first time in 2016 and 2017, in the depth layer from 50 to 200 m. Two individuals preserved in ethanol were sequenced and the phylogenetic tree was constructed based on 18S rRNA gene sequence. The phylogenetic position of D. rubescens is discussed in relation to other Thaliacea and its morphological peculiarities.

Data of phytoplankton abundance in winters of 1994 and 1995, and surface chlorophyll satellite- derived data(1997-2012) are the basis for investigation of characteristics and intensity of phytoplankton blooms in the open South Adriatic. Special attention is paid to the relation of different circulation regimes in the Ionian Sea (prevalently anticyclonic or cyclonic direction of Northern Ionian Gyre - NIG) to intensity of phytoplankton blooms. Different circulation regimes in the Ionian Sea cause inflow of water of different physical and biochemical properties into the Adriatic. Relatively high winter production events were evident in the open South Adriatic during both anticyclonic and cyclonic regimes. In the nutrient rich anticyclonic years, shallow vertical mixing is sufficient for enrichment of euphotic layers with the nutrients and development of the bloom, while in nutrient poor cyclonic years deep vertical mixing is necessary. Moreover, intense blooms have occurred in the years of specific hydroclimatic properties (i.e. East Mediterranean Transient – EMT and during extremely cold winters) and reversal years (from anticyclonic to cyclonic circulation of NIG and vice versa). In conclusion, winter season is important for production in the open South Adriatic waters and could not be omitted in the total yearly production estimates. Winter bloom intensity in the open South Adriatic depends on synergistic effects of local meteorological conditions and large time scale climatic variabilities in the Eastern Mediterranean on one hand, and water masses of different properties entering the Adriatic on the other.

The Adriatic Sea is a semi-enclosed sea and its ecosystem is influenced by the regular exchange of water with the Eastern Mediterranean. Levantine Intermediate Water and Ionian Surface Water flow into the Adriatic along the sea’s eastern border. The volume of this flow depends on climatic oscillations that occur from the Atlantic to the Southeast Mediterranean. The South Adriatic, the deepest part of the Adriatic Sea, represents a key area for both the Adriatic Sea itself and the entire Eastern Mediterranean basin. Tintinnids are the best known ciliates in the marine plankton. Their high frequencies and identifiable morphology have been suggested as indicators of oceanographic conditions including water temperature and origin, such as neritic, oceanic, and even upwelling water. Samples in South Adriatic were collected at four stations with a 53 µm mesh Nansen net. The spatial and temporal distribution of tintinnids was investigated at monthly intervals in the South Adriatic Sea during 2016. Of the 68 species identified, there were 47 surface, 15 subsurface, 3 mid-water, and 1 deep sea species. The dominant surface and subsurface species were Codonella aspera, Codonella amphorella, Undella claparedei and Salpingella accuminata. Species Parundella lohmanni predominated in the mid-water layers and Xystonellopsis scyphium in the deep-sea layers. While the majority species are always present in the South Adriatic Sea, some species were occasionally immigrates from the Mediterranean Sea. The highest variability in the number of species occurred in the surface and subsurface layers. A mid-water community of species Parundella lohmanii indicated inflowing South Adriatic Deep Water. Some other species such as Poroceus apiculatus, Undella subcaudata and Eutintinnus elegans appeared with strong inflows of the Levantine Intermediate Water during winter and spring. Based on these results, tintinnids may be used as a biological indicator of the state or possible changes in the marine ecosystems of the South Adriatic Sea.

The E2-M3A Station is deployed in the southern Adriatic Sea, at about 1200 m depth, in the center of the cyclonic gyre where deep convection process takes place, involving both the atmosphere and the ocean dynamics and forming new dense and oxygenated waters, thus triggering the solubility and the biological pump. In particular, the E2M3A is equipped with an upward looking 150 kHz RDI- Acoustic Doppler Current Profiler (ADCP) positioned between 265 and 320 m depth, with a vertical resolution of 5 m and a range of 250-300 m. The mooring line has been in water since November 2006, with an interruption from September 2010 until May 2011. ADCP backscattering signal is very useful in determining zooplankton distribution and variability at various time scales, including seasonal/annual behavior and diel vertical migration (DVM). From ADCP backscattering signal, backscattering strength (Sv) was calculated for the entire dataset. Sv permits to quantify qualitatively the scatters present in the water, i.e. the particulate and/or the phyto/zoo-plankton. Zooplankton distribution is dependent on phytoplankton presence and blooms, which on its own depend on nutrients availability (related to wind-induced vertical mixing), but also on sunlight. The variation in time of Sv together with vertical velocity allows for measuring DVM of zooplankton and its variability with seasons and years. Alternation of high and low values for Sv are present all year long with differences in intensities in particular in the surface layer. Quite high values for Sv are found in spring and summer ; in spring they are found along a large part of the water column, while in summer they are detected prevalently in the upper part of the measurement range. This behavior is related to the conditions of the water column, i.e. mixing and nutrients availability, which influence phytoplankton blooms and therefore zooplankton growing and movements. Correlating Net Primary Production obtained from model and Mixed Layer Depth, a delay of two months in the bloom of phytoplankton with respect to deepest mixing is found. Power Spectra of Sv show a major peak at 24 h that corresponds to the classical nocturnal- diurnal migration, and a secondary important peak at the period of 12 hours that indicates a different type of DVM pattern, the twilight migration. The ultimate factor behind DVM seems to be the minimization of the risk of predation from fishes and other carnivorous groups. Calculating the monthly mean daily cycle of the Sv, it is evident that there is a decrease in Sv at sunrise, while it increases at sunset. The highest values in the derivative of Sv, as well as highest values in the vertical velocity (w), coincide in time with sunset and sunrise. In particular, w is negative (downward movement) at sunrise while it is positive (upward movement) at sunset, and in some cases absolute value of w (|w|) reaches 5 cm/s. The hour of occurrence of |w| greater than 4.5 cm/s follows the curves in time of the hours of sunset and sunrise, which are changing throughout the year.

Brooksia lacromae sp. nov. urn:lsid:zoobank.org:act: 2B9ACCBD-8B20-437D-B013-468F8E956864 Figs 1–4 Diagnosis Oozooid (solitary form; Fig. 2) Muscles II and III fuse dorsally before fusing with muscle I mid-dorsally. Muscles III and IV fuse briefly dorsolaterally. Muscles IV and V fuse before approaching muscles VI and VII mid-dorsally. There is one longitudinal ventral muscle which extends anteriorly into the proboscis. In addition, the proboscis contains two lateral longitudinal muscles. The ventral longitudinal muscle branches posteriorly into two branches. There are two slit-like openings in the ventral longitudinal muscle, one below the anterior end of the endostyle, and the other slightly anteriorly from the first one. Muscle I fuses with branches of the ventral longitudinal muscle at their anterior part, while muscles VI and VII fuse with them posteriorly. Muscles II, III, IV and V converge ventrally towards the junction between muscle I and the branches of the ventral longitudinal muscle. Muscle II can be slightly fused with muscle I just before its connection with branches of the ventral longitudinal muscle. Endostyle straight. Stolon emerges from the test ventrally, slightly posteriorly from the nucleus. There is one test processus just posteriorly from the stolon (Fig. 4D). Muscles I–VII with 52–58 muscle fibers in total, measured laterally in two examined individuals. Blastozooid (aggregate form; Figs 3, 4 A–C) Sinistral individual – Four muscles on the left side, three muscles on the right side. Dorsal IM1 continues ventrally as the ventral muscle IM1, without extending to the anterior attachment processus (ap1). A branch of dorsal muscle IM1 (IM1-a) extends to the anterior attachment processus (ap1). Dorsal muscles IR, IIR and IIIR branch dichotomously. Dorsal muscle IR-a continues ventrally as ventral muscle IR. Dorsal muscle IR-b continues ventrally as muscle IIR-c. A small branch from muscle IR-b/IIR-c enters the lateral attachment processus (ap2). Dorsal muscle IIR-a continues ventrally as ventral muscle IIR-a. Muscle IIR-b ends blindly on the ventral side of the animal without entering the posterior attachment processus (ap3). Dorsal and ventral muscles IIIR enter the posterior attachment processus (ap3) without joining. Muscles IVL-a and IIIR-a extend from muscles IVL and IIIR, respectively, towards the nucleus. Endostyle curved anteriorly. Muscles IL-IIIL, IR-a,b and IIR-a,b,c with 3 muscle fibers each in all examined individuals. Muscle IVL with from 3 to 9 muscle fibers, muscle IIIR with from 5 to 7 muscle fibers. Dextral individual Mirror image of sinistral individual. Etymology Brooksia lacromae sp. nov. is named after the island of Lokrum near which it has been found. The Latin name of the island of Lokrum is Lacroma. Material examined Two oozooids and 19 blastozooids. Holotype One oozooid (14.8 mm body length, 23.9 mm total length including proboscis), collected from a 0–50 m depth layer on 3 Oct. 2014 in a 53 μm mesh plankton net. It is deposited in the Tunicata collection of the Croatian Natural History Museum under inventory number CNHM Inv. br. 44/1. Allotype One sinistral blastozooid (4.2 mm body length, without attachment processes), collected from a 0–50 m depth layer on 3 Oct. 2014 in a 53 μm mesh plankton net. It is deposited in the Tunicata collection of the Croatian Natural History Museum under inventory number CNHM Inv. br. 44/2 Paratypes One oozooid (11.5 mm body length, 18.2 mm total length including proboscis) and one dextral blastozooid (4.8 mm body length, without attachment processes), collected from a 50–100 m depth layer on 3 Oct. 2014 using a 53 μm mesh plankton net, deposited in the Institute for Coastal and Marine Research (University of Dubrovnik) under inventory number IMP-002; one dextral blastozooid (4.1 mm body length, without attachment processes) collected from a 0–50 m depth layer on 3 Oct. 2014 with a 200 μm mesh plankton net, deposited in the Dubrovnik Natural History Museum under inventory number PMD 2106. Other material 16 blastozooids deposited in the Institute for Coastal and Marine research (University of Dubrovnik) under inventory number IMP-003. Type locality 42°37'21"N, 018°06'05"E, off Dubrovnik, South Adriatic (Mediterranean Sea; Fig. 1). The temperature average in the 0–50 m layer was 19.0°C, with a range between 16.2°C and 22.2°C, while the salinity average was 38.36, with a range between 37.79 and 38.68. In the 50–90 m layer the temperature average was 15.8°C, with a range between 15.5°C and 16.1°C, while the salinity average was 38.71, with a range between 38.67 and 38.77. Remarks Oozooid. Brooksia rostrata and Brooksia berneri oozooids are very similar, differing only in the fact that in B. berneri oozooid muscle I, joined with the intermediate muscle (im), is separated from muscle II and discontinuous mid-dorsally. Due to this fact we will only compare the B. lacromae sp. nov. oozooid to the B. rostrata oozooid. The Brooksia lacromae sp. nov. oozooid has one ventral longitudinal muscle which extends into the proboscis, while B. rostrata has two (Fig. 2). The proboscides in both collected oozooids broke off during collection, but were found in the sample (Fig. 2c). The proboscis of Brooksia lacromae sp. nov. seems to be thinner at the base than in Brooksia rostrata and in both species it contains two lateral longitudinal muscles. The ventral longitudinal muscle in B. lacromae sp. nov. has two small slit-like openings anteriorly, one below the endostyle and the other just anteriorly to it, partly overlapping with the anterior end of the endostyle. In Brooksia lacromae sp. nov., in contrast to B. rostrata, body muscles are not arranged in a barrel-like structure where muscles are perpendicular to the body axis dorsally, as well as ventrally, but they converge to the posterior third of the body. Only muscles I, VI and VII fuse with the branches of the ventral longitudinal muscle, while muscles II, III, IV and V converge to the connection between muscle I and branches of the ventral longitudinal muscle, without fusing with either. Only muscle II can sometimes be slightly connected with muscle I ventrally. The stolon in Brooksia lacromae sp. nov. seems to emerge from the test, slightly posteriorly from the nucleus (Fig. 4D), while in B. rostrata it emerges from the anterior part of the nucleus (Thompson 1948). Blastozooid (sinistral individual). The Brooksia lacromae sp. nov. and Brooksia rostrata blastozooids are very similar. In Brooksia lacromae sp. nov., muscle IIR-b ends blindly on the ventral side of the animal without entering the posterior attachment processus (ap3), while in Brooksia rostrata it enters the posterior attachment processus (ap3). The left intermediate muscle (IM1) in Brooksia lacromae sp. nov. is continuous dorsally and ventrally. Its branch IM1-a enters the anterior attachment processus (ap1). In Brooksia rostrata the left intermediate muscle is discontinuous. Its dorsal and ventral counterparts both enter the anterior attachment processus. Because of this, the anterior attachment processus in B. lacromae sp. nov. possesses two muscles (IM1-a and IM2), while in B. rostrata it possesses three muscles (dorsal and ventral left intermediate muscle and right intermediate muscle). According to Thompson (1948), the right intermediate muscle of the sinistral individual of B. rostrata ends blindly, while after Tokioka (1954) and Godeaux (1998) it connects to muscle I. In B. lacromae sp. nov. the right intermediate muscle (IM2) ends blindly. Genetic analysis There were no differences between blastozooid and oozooid 18S sequences. Between two cox1 sequences there were 7 substitutions out of 837 nucleotides, which results in 0.84% uncorrected pairwise distance. Cox1 sequences were translated using ascidian mitochondrial code and there were no differences in amino acid sequence between them. The uncorrected pairwise distance between the Brooksia rostrata 18S sequence (HQ015403) and the Brooksia lacromae sp. nov. 18S sequence (KR057223) was 1.5% (including gaps). Out of 26 differences in 1740 nucleotides between these two sequences, there were 21 transitions, 4 transversions and one single nucleotide gap.

Mali Ston Bay is a coastal region in the southern Croatia (eastern Adriatic) where the European flat oysters (Ostrea edulis) and mussels have been cultivated for centuries. In 1983, due to its ecological and economical importance, the area was proclaimed a special reserve, both in marine and terrestrial zone. The European flat oyster has high economic potential in the European Union market because it has almost disappeared over a European territory due to outbreaks in farms caused by bonamiosis and marteiliosis. Mali Ston Bay is a rare remaining habitat of European flat oysters in Europe and it has optimal conditions for the reproduction and production of shellfish in relation to the highest standards and health requirements. In 2016, Dubrovnik-Neretva County and Municipality of Ston have accepted of amendments to the Spatial Plan for the construction of tourist resorts in the Bay on the surface area of 13 hectares with the capacity of 550 tourist beds. The Croatian scientific community strongly opposed the proposals and has advised to invest in tourism infrastructure on the southern slopes of the Pelješac Peninsula, where the coast for this type of activity is more attractive and thus encourage the development of two complementary economic activities which in principle cannot successfully coexist together.

In the last two decades 21 species of non-crustacean zooplankton were observed for the first time in the South Adriatic, two species were recorded after years of absence, while four recorded species were new to science. Origin and the timing of the arrival of non-indigenous species tracked the changes in salinity in the South Adriatic driven by Bimodal Oscillating System (BiOS). According to recently postulated BiOS theory, the direction of the circulation of North Ionian Gyre (NIG) drives the inflow of different water masses into the Adriatic, which in turn modifies the Adriatic water outflow and reverses the circulation in the NIG. The occurrence of Atlantic/Western Mediterranean species coincided with the anti-cyclonic circulation in the NIG which brings Modified Atlantic Water into the Adriatic Sea, while the presence of Lessepsian species coincided with the cyclonic pattern in the NIG, which governs the entrance of Eastern Mediterranean waters. The impact of newcomers has translated into a larger contribution within the zooplankton community and, in particular cases, into the replacement of native species. The synergistic effects of these processes, together with warmer Mediterranean waters, raise concerns on dramatic changes in the marine biodiversity of the Adriatic Sea.

We investigated potential connections over the past two decades between mesoscale circulation regimes in the Ionian Sea and newly-observed planktonic tunicate species and concurrent rise in sea temperature in the Adriatic Sea. Analyses of plankton samples from 1993 to 2015 in the southern Adriatic revealed marked changes in the planktonic tunicate community. Eleven appendicularian and three thaliacean species were recorded for the first time in the Adriatic. We found that incoming of these species are in connection with circulation regimes in the Northern Ionian Gyre (NIG). The occurrence of Atlantic/Western Mediterranean species coincided with anti-cyclonic circulation in the NIG, owing to the advection of Modified Atlantic Water into the Adriatic, while the presence of Lessepsian species coincided with the cyclonic pattern, which governs the entry of Eastern Mediterranean waters. The impact has been that some newcomers now make a larger contribution to the zooplankton community in the southern Adriatic and, in certain cases, have replaced native species. The synergistic effects of these processes, together with warmer Mediterranean waters, raise concerns over dramatic changes in the marine biodiversity of the Adriatic.

In the last two decades multiple new gelatinous planktonic species were recorded in the Adriatic. Their arrival has been positively correlated with increasing sea temperature as well as with different circulation patterns in the Ionian Sea. The direction of the Ionian Sea Gyre causes advection of different water masses in the Adriatic. During its cyclonic phase it brings mainly warm and saline Eastern Mediterranean water, while during anticyclonic phase it brings more of Atlantic and Western Mediterranean waters. Here we present first record of Fritillaria helenae (Tunicata, Appendicularia) for the Mediterranaen Sea (Garić and Batistić, 2016). Fritillaria helenae was so far only known from the Atlantic. It was found in the South Adriatic in autumn 2014 when a marked drop in salinity was recorded, which suggests increased inflow of Atlantic/Western Mediterranean waters into the Adriatic.