Middle Adriatic Sea Research Articles

Organic matter stoichiometry based on oxygen consumption—nutrients regeneration during a stagnation period in Jabuka Pit (middle Adriatic Sea)

The Jabuka Pit, a continental shelf depression in the middle Adriatic Sea, acts as a collection basin for the dense water formed during winter in the northern Adriatic. Its deep waters are usually renewed at least every second year. The deep waters of Jabuka Pit remained practically isolated after the strong flushing occurred in early spring 1993. Our data from May 1993 to November 1994, permitted to follow, step by step, the oxygen consumption and the nutrient and carbon regeneration in the deep layer of Jabuka Pit during this period of isolation. Extremely high oxygen consumption and nutrients and carbon regeneration rates were estimated; the oxygen reduction rate is about 66.5 μmol/kg/yr, while the accompanying increasing rate of nitrate is 2.64 μmol/kg/yr, of silicate 4.2 μmol/kg/yr, of phosphate 0.24 μmol/kg/yr and of ΣCO 2 81.0 μmol/kg/yr. The temporal evolution of the regeneration ratios of nitrogen and carbon, as well as of the N inorg/PO 4 ratio, imply that possibly other processes, besides aerobic respiration, like denitrification, take place and modulate the values of the ratios. Furthermore, the changes of the concentrations of oxygen, nitrate, phosphate and ΣCO 2 in the deep layers of Jabuka Pit were exploited in order to estimate the elemental composition of the organic matter that is remineralised. Our results suggest that the most probable empirical formula that corresponds to the composition of the organic matter in the study system is (C 4H 6ON) 8; (C 6H 10O 5) 3; (CH 2) 108 being 11.4% carbohydrates, 20.3% proteins and 68.3% lipids. Furthermore, the investigation of our results show that there is evidence that the observed changes of the concentrations of the chemical parameters are better interpreted if additionally to the remineralisation of organic matter, small-scale CaCO 3 dissolution with simultaneous denitrification processes are considered.

Growth of juvenile salema, <i>Sarpa salpa</i> (Teleostei: Sparidae) in the Kornati Archipelago, eastern Adriatic Sea

Growth of juvenile Sarpa salpa from the Kornati Archipelago, eastern middle Adriatic Sea was analysed. A total of 1515 juveniles, ranging in length from 1.6 to 14.2 cm, were caught. Most individuals (94.65%) belonged to the 0+ cohort. The first settlers were aged 1.5-2.0 months, and probably entered shallow coves at the end of November. The relationship between total length and weight indicates positive allometric growth (b = 3.284). The condition factor, as a consequence of length-weight relationship, was CF = 1.41. The parabolic (c = 0.023 mm days-1; R 2 -1 2 = 0.897) growth models seem to be the most appropriate for the description of young S. salpa growth.

Dense water generation in the north Adriatic in 1999 and its recirculation along the Jabuka Pit

This paper describes thermohaline properties in the north and middle Adriatic Sea in 1999 based on temperature and salinity data collected along the Po-Rovinj, Jabuka Pit and Palagruža Sill profiles. The preconditioning, generation and spread of North Adriatic Dense Water (NAdDW), as well as their relationship to surface fluxes and river discharge are analyzed in detail. A strong Bora wind event in November 1998 resulted in heat loss exceeding 800W/m2, homogenizing and cooling the whole water column by 2.4°C, while another similar Bora episode in January/February with a cooling rate of 1.4°C ended with NAdDW generation. River discharge was low during the preconditioning and generation phases. Following its generation, the NAdDW flowed southeastward as a density current along the western Adriatic slope. Its northeastern part reached the steep edge of the Jabuka Pit and sank rapidly to the bottom, where it was observed a month after its generation. However, the core of the NAdDW current continued to follow the western slope as a density current, taking a detour around the pit on its southeastern side, and sinking to the bottom in the eastern segment of the pit. The detour and sinking at the Jabuka Pit slope was estimated with an analytical model to be 1.1m/km. Finally, the upper lighter part of the NAdDW current crossed the Palagruža Sill and followed the western slope entering the South Adriatic Pit and contributing to the water mass dynamics there. Another NAdDW branch was found at the very bottom of the middle of the Palagruža Sill, although being less pronounced than the one that moved over the western slope.

Effect of climatic fluctuations on the distribution of warm-water coral Astroides calycularis in the Adriatic Sea: new records and review

Three colonies of warm-water coral Astroides calycularis were found at the eastern part of the middle Adriatic Sea during the 1990–2001 period. For each specimen, depth distribution and habitat were recorded. Previous and recent knowledge of this species in the Adriatic Sea and in the Mediterranean Sea was discussed in relation to climatic changes. Occurrence of A. calycularis in the Adriatic Sea was related to the increased temperatures of the surface marine layer. Variable temperature conditions were connected to the climatic changes on the hemispheric scale through the North Atlantic Oscillation index. The prevailing sea current system together with the coastal configuration and bottom type favours the presence of the studied warm-water coral on the eastern Adriatic coast.

Seasonal and vertical distribution of planktonic bacteria and heterotrophic nanoflagellates in the middle Adriatic Sea

Temporal and spatial patterns of bacteria and heterotrophic nanoflagellates (HNF) were studied monthly from January 1997 to December 1998 in the middle Adriatic Sea. Bacterial and HNF relationships with phytoplankton biomass and temperature were analyzed to examine how the relative importance of bottom-up and top-down factors may shift over seasons and locations. For the coastal area, an inconsistent relationship between bacterial abundance and chlorophyll a and a stronger relationship between bacterial abundance and bacterial production suggest that other substrates than those of phytoplankton origin are important for bacteria. The analysis of simultaneous effects of temperature and bacterial production on bacterial abundance showed that the effect of temperature obscured the effects of bacterial production, suggesting that bacterial growth itself is highly temperature-dependent. The relationship between HNF abundance and bacterial abundance was slightly improved by the inclusion of in situ temperature, bacterial production or both parameters, as additional independent variables. About 60% of the variability in HNF abundance can be explained by bacterial abundance, bacterial production and temperature. In the open sea, tight coupling of bacterial abundance with chlorophyll a concentrations implied that phytoplankton-derived substrates have a dominant role in controlling bacterial abundance. During the colder months, bacterial abundance was high enough to support higher HNF abundance than observed, suggesting that predation exerted a minor depressing influence on bacterial abundance during that period. During the spring-summer period, HNF controlled bacterial standing stocks by direct cropping of bacterial production.

Deep chlorophyll-a maximum at one station in the middle Adriatic Sea

Deep or subsurface chlorophyll-a maximum (DCM) was studied at one station in the middle Adriatic from December 1996 to June 1998. Chlorophyll-a concentration, abundance, volume carbon concentration, size-fraction of phytoplankton and phytoplankton community structure were determined. In addition, physical and chemical factors as well as nutrients were determined. The DCM occurs during both the vertical mixing and stratification period in the middle Adriatic Sea. It is most frequent between 50 and 75 m. It is located below the pycnocline and it is associated with the nutricline. Phytoplankton size-fraction and community structure vary seasonally. The DCM is most pronounced during spring phytoplankton blooms with diatom dominance. Procaryotic picoplankton Synechococcus sp. was abundant in DCM during summer stratification. The DCM represents both a biomass maximum and a phytoplankton adaptation to low irradiance.

Benthic-pelagic coupling in frontal system areas of the Northern Adriatic Sea: Analysis of the carbon budgets

Sediment samples were collected between 1996 and 1998 during 4 cruises in the northern sector of the Adriatic Sea, facing the Po River outflow. In each sampling period, after identification of the front line, a grid of 6 sampling stations was selected in order to cover: the coastal area (largely affected by river waters), the inner and outer front areas, and the offshore waters. The biochemical composition of sedimentary organic matter (OM, lipids, proteins, carbohydrates and photosynthetic pigments) and enzymatic activity rates were studied to provide information on the potential organic matter turnover. Tentative estimates of the organic carbon budgets (input/production versus requirement by benthic consumers) are presented. Benthic carbon requirements, estimated from bacterial plus meiofaunal secondary production, was high (897 r mg r C r m m 2 r d m 1 ). OM concentrations in the Northern and Middle Adriatic Sea displayed high values, proteins being dominant, thus suggesting inputs of freshly produced material to the sea floor. OM turnover was generally rapid (11-30 r d m 1 ) and higher during summer. The uncoupled enzymatic rates ( i.e. faster protein than carbohydrate mobilisation in February, 1997) determined a decrease of the OM quality that plays an important role in biogeochemical cycles and OM diagenesis, limiting bacterial secondary production and sedimentary organic carbon utilisation. These data suggest that the efficiency of the system in the transfer of energy through the food web is generally higher in summer, especially during mucilage production.

The chemical and biogenotoxic characterization of organic xenobiotics in aquatic sediment materials: 1. The application and comparison of chemically non-specific and biogenotoxic methods

The aim of this work was to evaluate the Ames assay and mixed function oxidase (MFO)-Induct Test used in parallel with chemical group tests (ECD fingerprint and PAH estimation) for the characterization of the organic pollution of water sediment materials. Sediment materials were collected from “clean” and relatively heavily polluted locations in the Middle Adriatic Sea, and from some locations in continental Croatia polluted with wastewaters from different enterprises. Characterization of the organic extracts of the sediment materials investigated was performed chemically using UV spectrofluorometry for the determination polyaromatic hydrocarbons (PAH) and gas chromatography for the determination of volatile EC detector sensitive materials. Genotoxic analysis of the extracts was performed using the MFO-Induct Test and mutagenicity testing using the Standard Plate Incorporation Test as described by Maron and Ames with Salmonella typhimurium TA 98. Measurement of the BaPMO enzyme activity in the livers of carp treated i.p. with total extracts of the sediment investigated confirmed that the methanol extracts generally contained more inducing matter than the petroleum ether extracts. Ames assay showed that for all the samples following the elimination of the sulfur, there was an increase in the number of revertants in comparison to the control number, which indicates that the samples contained mutagenic substances. The larger doses of extracts generally demonstrated cytotoxicity, as evidenced by a reduced number of spontaneous revertants in the Salmonella/ Microsome Test. Investigation of the correlation of the chemical parameters with the biological parameter showed that the induction of BaPMO exhibited a statistically significant correlation with the level of the ECD fingerprint of the petroleum ether sediment extract.

Consumption of bivalve molluscs in Italy: estimated intake of cadmium and lead

Concentrations of cadmium and lead were determined in nine different species of mollusc bivalves(Modiolus barbatus, Venus verrucosa, Scapharca inaequivalvis, Tapes decussatus, Callista chione, Pecten jacobeus, Ensis siliqua, Venus gallina, Cardium tubercolata)collected from different coastal areas of the Adriatic Sea (north, middle and south Adriatic). The levels of cadmium and lead found in bivalves from the north Adriatic Sea were significantly (P<lt; 0.001) higher than those detected in those from the middle and south Adriatic Sea. In some species of molluscan bivalves(M. barbatus and T. decussatus)from the north Adriatic Sea, concentrations of cadmium and lead exceeded the maximum limit (2mg/kg w.w.) established by the Italian legislation. Weekly intakes were estimated and compared with the Provisional Tolerable Weekly Intake (PTWI) recommended by the FAO/WHO Expert Committee on Food Additives.

Seasonal Switching Between Relative Importance of Bottom-Up and Top-Down Control of Bacterial and Heterotrophic Nanoflagellate Abundance

Seasonal dynamics of bacterial and heterotrophic nanoflagellate (HNF) species assemblages were analysed in Kaštela Bay (middle Adriatic Sea). Dominant patterns identified were: (1) during summer and autumn bacterial abundance was mainly controlled by HNF grazing (top-down), whereas HNF abundance was controlled by bacterial abundance (bottom-up); (2) during winter and spring the coupling between bacteria and HNF was very weak, and bacterial abundance was mainly controlled by resources supply (bottom-up), whereas HNF abundance was controlled by micro-zooplankton grazing (top-down); (3) throughout the year, both bacterial and HNF species assemblages alternated with two periods of stable abundance, first with high and second with low values; (4) top-down effect was dominant in bacterial switching from stable abundance with high values to stable abundance with low values, whereas bottom-up model dominated in inverse process; and vice versa for HNF.

Evolution of Radiocontamination of the Northern and Middle Adriatic Sea in the Period 1979–1990

Abstract Several investigations were carried out on biotic and abiotic samples to determine the difference between Chernobyl and preChernobyl environmental radiocontamination of the Adriatic Sea. Special emphasis was put on the determination of 137Cs which resulted in the most abundant radionuclide in a wide variety of samples (sea water, sediment, pelagic and benthic species). Attention was also given to the neutron activation products 110mAg and 134Cs that were first discovered in the Adriatic ecosystem after the Chernobyl event in particular, although the 110Ag fallout deposition over the area was neglected in comparison to that of 137Cs, its bioaccumulation in macroalgae and molluscs was much higher suggesting some particular physiological accumulation mechanism.

Long-term production changes in the adriatic

Long-term fluctuations and trends in the rate of primary production were observed in the middle Adriatic Sea. Variability in the production rate was caused by oceanographic and meteorological factors affecting the advection of the Mediterranean waters in the Adriatic on long-term scale. Particular attention is given to a sudden and prolonged increase in primary production that started in 1978. This increase is related to the enhanced advection of the Mediterranean waters (richer in nutrients) into the Adriatic. Increased advection of Mediterranean waters to the Adriatic can be attributed to global climatic changes.

Age, growth and mortality of damselfish ( Chromis chromis L.) in the eastern middle Adriatic

Age, growth and mortality were analysed for damselfish collected in the eastern middle Adriatic Sea. Growth in length, not showing significant differences between sexes, was expressed for the whole sample using the Bertalanffy equation, L t = 142.0(1 − exp(− 0.26( t + 0.30)). Weight increased allometrically for both males ( b = 3.12) and females ( b = 3.08) during the spawning season. Total and natural mortality were found to be Z = 1.07 years −1 and M = 0.72 years −1. The exploitation ratio, E = 0.33, revealed underfished stock conditions in the studied area.

Mesoscale data assimilation studies in the Middle Adriatic Sea

In this paper we describe a mesoscale data assimilation experiment in the Middle Adriatic Sea. In order to perform dynamical forecasts we provide a quasigeostrophic numerical model with a set of initial fields regularly gridded via an objective analysis technique. Maps of this initial condition show a surface intensified jet meandering around a cyclonic eddy at the thermocline and deep levels. We dynamically forecasted the flow evolution for 30 days after initialization. The time scale of the variability is of the order of a few weeks and the cyclonic vortex seems to be locked to the topography. A set of numerical experiments with different initial bottom boundary conditions, with and without topography, are made to explore the influence of the topographic constraint on the mesoscale flow evolution. As expected the influence of the topography on the dynamical evolution of the flow is very strong and it confines the jet-cyclone along the bathymetric contours, strengthening the flow. On the other hand the flow is not sensitive to changes in the density bottom initial condition. Finally we analyze the energy and vorticity fields of the 1-month dynamical forecast experiment. It is concluded that a local frontogenetic process consisting of jet strengthening and cyclone development occurs and that available gravitational energy is converted into kinetic energy during the process.

A radioecological survey of Northern and Middle Adriatic Sea before and after the Chernobyl event (1979–1990)

Investigations to determine the presence and distribution of some anthropogenic pre- and post-Chernobyl radionuclides and to evaluate their behaviour and transport within different environmental components were conducted between 1979 and 1990 in Northern and Middle Adriatic Sea. Although the Chernobyl accident introduced many radionuclides into this environment, most of them had very short half lives and only Ru-103, Ru-106, Ag-110m, Cs-134 and Cs-137 were fully investigated on a long term basis due to their long persistency and abundance. In particular, neutron activation products, such as Ag-110m and Cs-134, not present in the environment before the event, were fully detected for the first time in the ecosystem shortly after the contamination. The results highlight the distribution of the considered gamma emitting radioisotopes in samples of seawater, sediments, mixed plankton, icthyofauna and benthic macrofauna, and allow a complete mapping and assessment of the Adriatic radiocontamination after 10 years of intense and extended monitoring of the ecosystem.

The mesoscale eddy field of the middle Adriatic Sea during fall 1988

The analysis of the first mesoscale experiment in the middle Adriatic Sea reveals the horizontal and vertical scale of the eddy field. The mesoscale variability is characterized by 10–20 km in diameter eddies. They are lower thermocline intensified, and the velocities in the upper and lower thermocline levels range from 10 to 1 cm s −1, respectively. The eddies are small because of the local Rossby radius deformation (5.4 and 2.8 km for the first and second internal baroclinic mode, respectively) and because they are second baroclinic mode intensified. The Levantine Intermediate Water is found in tongue-like features intruding between the intense eddy field.

Temporal fluctuations of zooplankton and bacteria in the middle Adriatic Sea

Year-to-year fluctuations in the abundance of zooplankton (1960-1982) and bacteria (1968-1988) were examined. Three main patterns of year-to-year changes in abundance were extracted by Principal Component Analysis (PCA): (1) Cyclical oscillations with 5.5 yr periodicity. This pattern is well correlated with salinity and southerly weather type (lower atmospheric pressure, southeasterly wind and higher precipitation) and can be accounted for by the water exchange between the Mediterranean and the Adriatic Sea. (2) Long-term trend of increasing abundance presumably due to the open Adriatic eutrophication. (3) Oscillations with 7.3 yr periodicity. This pattern is well correlated with temperature.

Long-term study of heterotrophic bacteria as indicators of eutrophication of the open middle adriatic sea

Results of the 20-year study, from 1968 to 1988, indicate a trend of increasing density of heterotrophic bacteria in the open middle Adriatic Sea. An identical trend has been observed for primary production resulting in an increase of oxygen saturation in the layer of maximum primary production. Transparency of seawater decreased during the investigated period. This suggests that fluctuations of hydrographic, chemical and biological parameters in the open middle Adriatic Sea are not only a result of the influence of natural factors but are influenced by coastal eutrophication as well. Eutrophication rapidly extended towards the open Adriatic Sea after the late 1970s.

Invertebrate hemoglobins: the dimeric hemoglobin from the mollusc Scapharca inaequivalvis.

The dimeric hemoglobin from the mollusc Scapharca inaequivalvis represents a beautifully simple model system for the study of cooperative phenomena in hemoglobins. The mollusc was brought to our attention due to an ecological problem. S. inaequivalvis is an indopacific species which has settled along the Middle Adriatic coast only in recent years. Its demographic increase has since been explosive and has been associated with the progressive disappearance of the native species Venus gallina. The adaptation and the survival of S. inaequivalvis can be easily explained in terms of the presence of erythrocytes in its coelomic fluid and of the periodical limitations in oxygen content of the Middle Adriatic Sea due to the process of eutrophization.1 KeywordsSedimentation VelocitySodium DithioniteOxygen BindingCoelomic FluidOxygen DissociationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.