Davor Lučić

Incidence of spinal deformities in natural populations of sandsmelt, Atherina boyeri (Risso, 1810) in the Neretva river estuary, middle Adriatic

Information is presented on the occurrence of spinal deformities in natural populations of sandsmelt, Atherina boyeri in the Neretva River estuary, middle eastern Adriatic. During 1998 and 1999, the spinal deformity levels varied between 2.02% and 10.30% in four samplings, and 3.58% in total catch. The spine is deformed in one to a few places from vertical to horizontal angles, and the deformities are visible on the fish body immediately after catching. The possible reasons for such deformities are discussed.

Calycophorae (Siphonophora) in the open waters of the central and southern Adriatic Sea during spring 2002.

Twenty species of calycophoran siphonophores were identified from the central and south Adriatic Sea in spring 2002. Highest abundance and species diversity were noted at the deepest stations in the south Adriatic. Highest total abundance was found in the upper 100 m. The dominant species above 100 m were Lensia subtilis , Eudoxoides spiralis and Sphaeronectes gracilis , none of which showed diel migration. The first two species correlated significantly with the vertical abundance of microzooplankton, and the last with that of copepods. The most abundant species in the 100-400 m layer was Lensia meteori , whereas Lensia conoidea and Chlausophyes ovata were most abundant below 400 m.

First record of Idas simpsoni (Mollusca: Bivalvia: Mytilidae) in the Adriatic Sea

More then 127 specimens of the bivalve mollusc Idas simpsoni were collected from the skull of a fin whale Balaenoptera physalus. The skull was trawled up from a depth of 430 m near Mljet Island in the soiuth Adriatic Sea. This is first finding of I. simpsoni in the Adriatic Sea.

Microzooplankton in the open waters of the northern Adriatic Sea from 1990 to 1993: the importance of copepod nauplii densities

Zooplankton was sampled during 39 cruises, from 1990 to 1993, at four fixed stations in the open northern Adriatic. Hydrographic factors were important in determining the abundance of the smallest and largest components of the northern Adriatic food chain during this period. Nauplii—especially those of the smallest size fractions—were the major mediators of material transfer between primary producers and higher trophic levels. There was a significant difference in the vertical distribution of nauplii size fractions between the eastern and western parts of the northern Adriatic, but not in their population density. According to multiple correlation analyses, the abundance of naupliar size fractions in the western area correlated strongly with temperature and with certain biological factors. This study confirms the important influence of the Po River and of mid-Adriatic waters on the planktonic ecosystem of the northern Adriatic.

Population structure and diel vertical migration of euphausiid larvae in the open southern Adriatic Sea (July 2003)

The composition, bathymetric distribution, and diel vertical migration of larval euphausiids in the oligotrophic southern Adriatic Sea were studied during the summer of 2003. Larvae of 11 species were identified. Of these, Thysanoessa gregaria is reported for the first time from the Adriatic Sea. Information is presented on the distribution and diel migrations of the five dominant species. Nematoscelis megalops furciliae had the widest bathymetric range, extending from surface to the bottom (1200 m); larvae of Stylocheiron maximum were found from 100 to 1200 m. Euphausia krohnii (calyptopes and furciliae), Stylocheiron abbreviatum calyptopes, and Stylocheiron longicorne furciliae ranged over 800 m. S. abbreviatum (furciliae) and S. longicorne (calyptopes) had more restricted bathymetric distributions. Different populations were associated with layers characterized by specific light intensities. Three migration patterns were observed: (i) nocturnal ascent to upper layers (E. krohnii, N. megalops, S. abbreviatum); (ii) scattered population through the water column (S. maximum); (iii) migration to upper layers at midday and night, and descent during the morning and evening (S. longicorne). Different stages of the same species showed different preferences for light intensity.

The importance of vertical habitat gradients on zooplankton distribution in an enclosed marine environment (South Adriatic Sea)

Abstract The spatio-temporal patterns of a zooplankton community structure in a strongly stratified enclosed marine environment were studied over a one-year period. Copepods were by far the most abundant group, accounting for 69–91% of the total zooplankton, with a numerical dominance of the genus Oithona. Cluster analysis revealed four different groups of samples and a comparison was made of the hydrographical and biological properties of the resulting groups. Water temperature was the main force discriminating the zooplankton community. The strongest vertical separation was recorded in summer, while a salinity impact was noted during the autumn after a strong intrusion of open sea water. Most of the dominant zooplankters exhibited a distinct vertical separation over the study period, where thermophilic taxa (Cladocera, Centropages kröyeri, C. typicus, Oikopleura fusiformis, O. longicauda, Euterpina acutifrons) kept to the surface and cryophilic species (Diaixis pygmaea, Mesaiokeras hurei, Calanus helgolandicus, Parasagitta setosa) were concentrated below the thermocline layer (20 m depth) for most of the year. Due to the unique physical, chemical and biological properties of the study site, this research is an important step towards better understanding the distribution of zooplankton during stratified conditions.

Temporal patterns of the calanoid copepod community in Veliko Jezero, an isolated marine lake (South Adriatic Sea): links to a larger-scale climate changes

We complied and analysed a long-term calanoid community data set (1952–2009) with respect to environmental variations in nearly closed seawater lake Veliko Jezero (South Adriatic Sea). Changes in hydrographic properties were influenced by deepening and broadening the channel between Veliko Jezero and the sea in the early 1960s, which was in particular reflected by increasing salinity. Calanoid abundance displayed high intra- and inter-annual fluctuations but lacked any regular and recurrent pattern. Calanoids in the lake comprised 22 coastal and estuarine species, with five of them present over the entire study period (Calanus helgolandicus (Claus, 1863), Paracalanus parvus (Claus, 1863), Centropages kroyeri Giesbrecht, 1893, Isias clavipes Boeck, Acartia (Acartiura) clausi Giesbrecht, 1889). Four sample groups were identified by cluster analysis, with the highest degree of dissimilarity between samples from the 1950s and those from the 1990s and onwards. Observed changes – low densities in early 1980s; a shift in the dominant species; reduction and, finally, disappearance of Pseudocalanus elongatus (Boeck); increases in Paracalanus parvus and Diaixis pygmaea (Scott T., 1894) – can be associated with synchronous changes across trophic levels that have occurred in other European seas. The results presented here underline the importance of long-term studies of semi-closed marine lakes and lagoons, as these are particularly sensitive to global climatic changes.

Bacteria associated with jellyfish during bloom and post-bloom periods

This study is the first to investigate bacterial community associated with live medusa Aurelia sp. in the Gulf of Trieste (northern Adriatic Sea) using both culture independent and culture-based methods. We have analysed bacterial community composition of different body parts of medusa: exumbrella surface, oral arms (‘outer’ body parts) and of gastric cavity (‘inner’ body part) and investigated possible differences in medusa associated bacterial community structure at the time of jellyfish population peak and during senescent phase at the end of bloom, when jellyfish start to decay. Based on 16S rRNA clone libraries and denaturing gradient gel electrophoresis (DGGE) analysis, we demonstrated significant difference between bacterial community associated with Aurelia and the ambient seawater bacterial assemblage. Comparing bacterial community composition between different Aurelia medusa body parts, communities differed significantly, especially the one within the gastral cavity. The pronounced difference is dominance of Betaproteobacteria (Burkholderia, Cupriavidus and Achromobacter) in gastral cavity of medusa and Alpha- (Phaeobacter, Ruegeria) and Gamma- proteobacteria (Stenotrophomonas, Alteromonas, Pseudoalteromonas and Vibrio) on ‘outer’ body parts. This suggests that body-part specific bacterial association might have an important functional roles for the host. The results of bacterial isolates showed the dominance of Gammaproeteobacteria, especially Vibrio and Pseudoalteromonas in all body parts. Finally, comparison of medusa associated bacterial community structure, at the time of jellyfish population peak and during senescent phase at the end of bloom showed increased abundance of Gammaproteobacteria, especially Vibrio. Our results suggest members of Vibrio group are possible commensal opportunistic visitors, later becoming consumer of moribund jellyfish biomass and that the structure of jellyfish bacterial community might be affected by anthropogenic pollution in the marine environment.

Potential transfer of aquatic organisms via ballast water with a particular focus on harmful and non-indigenous species: A survey from Adriatic ports

Ballast water discharges may cause negative impacts to aquatic ecosystems, human health and economic activities by the introduction of potentially harmful species. Fifty untreated ballast water tanks, ten in each port, were sampled in four Adriatic Italian ports and one Slovenian port. Salinity, temperature and fluorescence were measured on board. Faecal indicator bacteria (FIB), phyto- and zooplankton were qualitatively and quantitatively determined to identify the species assemblage arriving in ballast water. FIB exceeded the convention standard limits in 12% of the sampled tanks. Vibrio cholerae was not detected. The number of viable organisms in the size groups (minimum dimension) <50 and ≥10 μm and ≥50 μm resulted above the abundances required from the Ballast Water Management Convention in 55 and 86% of the samples, respectively. This is not surprising as unmanaged ballast waters were sampled. Some potentially toxic and non-indigenous species were observed in both phyto- and zooplankton assemblages.

Zooplankton Community in the Boka Kotorska Bay

This study includes a review of recently published results regarding zooplankton in the Boka Kotorska Bay (since 2009), and comparison of these results with earlier investigations. Non-loricate ciliates were the most numerous microzooplankton in spring 2013 (37%). Loricate ciliates (tintinnids) values were low and similar to those recorded in the open Adriatic Sea. However, their diversity was quite high: 20 estuarine–neritic and 26 species typical of the open sea were identified. Copepod nauplii were dominant metazoan microzooplankton component (32%). Seven phylums and 81 mesozooplankton taxa were determined. Copepods were the most dominant group. Among them, Oncaea–cyclopoids and Oithona nana were the dominant copepod taxa at all stations. Heterotrophic dinoflagellate Noctiluca scintillans and cladocera Penilia avirostris were often extremely numerous during warm seasons. Changes in the zooplankton community noted during recent investigations can be linked with the observed climate changes identified in the Adriatic and Mediterranean Sea since the 1990s, which are reflected in: (1) zooplankton high densities in the winter period with a lack of spring peak; (2) domination of small-size cyclopoid copepods and decreasing of contribution of neritic calanoid species; (3) prolongation of high Penilia avirostris abundance in the autumn period; (4) spreading of invasive siphonophorae Muggiaea atlantica in the inner part of the Bay; (5) frequent outbreaks of gelatinous zooplankton; and (6) The first registered bloom of the ctenophore Bolinopsis vitrea in the Mediterranean in spring 2014, having a major impact on the regular planktonic food web system.