Consumption rates and prey preference of the invasive gastropod Rapana venosa in the Northern Adriatic Sea

The alien Asian gastropod Rapana venosa (Valenciennes 1846) was first recorded in 1973 along the Italian coast of the Northern Adriatic Sea. Recently, this predator of bivalves has been spreading all around the world oceans, probably helped by ship traffic and aquaculture trade. A caging experiment in natural environment was performed during the summer of 2002 in Cesenatico (Emilia-Romagna, Italy) in order to estimate consumption rates and prey preference of R. venosa. The prey items chosen were the Mediterranean mussel Mytilus galloprovincialis (Lamarck 1819), the introduced carpet clam Tapes philippinarum (Adams and Reeve 1850), both supporting the local fisheries, and the Indo-Pacific invasive clam Anadara (Scapharca) inaequivalvis (Bruguière 1789). Results showed an average consumption of about 1 bivalve prey per day (or 1.2 g wet weight per day). Predation was species and size selective towards small specimens of A. inaequivalvis; consumption of the two commercial species was lower. These results might reduce the concern about the economical impact on the local bivalve fishery due to the presence of the predatory gastropod. On the other hand, selective predation might probably alter local community structure, influencing competition amongst filter feeder/suspension feeder bivalve species and causing long-term ecological impact. The large availability of food resource and the habitat characteristics of the Emilia-Romagna littoral makes this area an important breeding ground for R. venosa in the Mediterranean Sea, thus worthy of consideration in order to understand the bioinvasion ecology of this species and to control its likely further dispersal.     

The effects of northern italian rivers and Eastern Mediterranean ingressions on the phytoplankton of the Adriatic Sea

An analysis of the distribution of the phytoplankton standing crop during a period of high stability characterized the relative influence of northern Italian rivers and Mediterranean waters on the Adriatic Sea. The region influenced by northern Italian rivers was marked by low community diversities, relatively high chlorophyll a standing crops and cell densities, high microplankton to nannoplankton community volume ratios, and the dominance of Nitzschia seriata. To the contrary, the region influenced by Mediterranean waters exhibited high community diversities with prominent oceanic and warm water elements, low chlorophyll a standing crops and microplankton cell densities, low microplankton to nannoplankton ratios, and a relatively conspicuous coccolithophore flora.Nannoplankton populations remained relatively constant throughout the Adriatic. However eutrophication resulted in a marked increase in the microplankton component of the community, with the diatom Nitzschia seriata serving as a prime indicator of the process, even in regions several hundred kilometers downstream from nutrient sources.Even under relatively low rates of river discharge, the influence of northern Italian rivers could be traced along the entire western sode of the sea to the Otranto Strait, with low north to south and high west to east gradients resulting from the effect of a cyclonic surface circulation pattern on inflowing Mediterranean waters in the south and river discharge in the north.     

Reproduction of Pelagia noctiluca in the central and northern Adriatic Sea

The sequence of vitellogenesis as related to size increase of the oocytes of Pelagia noctiluca (Forskål) (Scyphozoa, Semaeostomeae) was examined to assess the influence of climatic factors on its reproductive period in the central and northern Adriatic Sea. From 1981 to 1985, 5 specimens with similar diameter were sampled each month. One ovary was excised from each individual and examined both with a videoanalyzer, to count the oocytes and to check their size distribution, and through histology to assess the stage of maturation in relation to the diameter. Oocytes of all stages were present in the ovaries of individuals down to a bell diameter of 3.5 cm. Thus reproduction occurs throughout the year in the central and north Adriatic Sea. However, the number of oocytes in different developmental stages in a gonad may range from a minimum value recorded in summer to two peaks in spring and autumn. The quantitative distribution is related to sea temperature and thus to metabolic rate, and to food availability.     

Correlation between the presence of Gonyaulax fragilis (Dinophyceae) and the mucilage phenomena of the Emilia-Romagna coast (northern Adriatic Sea)

The formation of massive amounts of suspended mucilaginous organic matter which periodically affects the Adriatic Sea, has been regarded as a complex physico-chemical phenomenon resulting from the production of extracellular material by phytoplankton. Although the exact cause has remained obscure, the mechanism of its formation has usually been considered to be a long-term process, starting after the late winter-early spring blooms, and involving the participation of various algal species, mainly within the diatom group. In this paper we report on the results of a phytoplankton monitoring programme in northern Adriatic seawaters off the Emilia-Romagna coast of Italy which revealed the constant concomitant presence of the dinoflagellate Gonyaulax fragilis (Schütt) Kofoid and mucilaginous formations. In the early stages of the phenomenon the dinoflagellate was clearly observable by microscopic examination in the mucilage, but as the mucilage aged this alga almost completely decomposed and diatom cells increased in number and became predominant. Although characterized by a slow growth rate in culture, in natural seawater G. fragilis was observed to reach cell densities of up to 7.0×10⁶ cells l⁻¹. The results of this study lead us to propose the hypothesis that the appearance of mucilage in the water column of the Adriatic Sea is the consequence of a seasonal growth of this dinoflagellate favoured by specific environmental circumstances.     

Seasonal and spatial distribution of bacterial production and biomass along a salinity gradient (Northern Adriatic Sea)

The Adriatic Sea is a semi-enclosed ecosystem that receives in itsshallow part, the northern basin, significant freshwater inputs whichmarkedly increase its productivity with respect to the oligotrophic featuresof the Mediterranean sea. In this area, especially on the western coastwhere river plumes diffuse, high physical (density) and chemical (nutrients)gradients occur on a small scale, both horizontal and vertical. Results ofbacterial production as ³H-thymidine incorporation, bacterialabundance as DAPI direct count, autotrophic biomass as chlorophyll a andtotal biomass as ATP from three areas in the Northern Adriatic Sea arereported. The three sites, differently influenced by the river waterdiffusion, were sampled seasonally over two days, every 24 h, in foursurveys from April 1995 to January 1996. Bacterioplankton production,strongly correlated with primary production, was extremely high near thecoast in low-salinity, high-nutrient waters, mostly as an indirectconsequence of riverine inputs causing an increase in phytoplanktonproduction stimulated by physically driven nutrient inputs. In the warmmonths bacterial activity was higher than in cold months. While bacteriaabundance did not appear related to the salinity gradients, bacterialproduction (from 0.6 to 372 pM ³H-thymidine h^™1incorporated, corresponding to 0.01–8.2 μg C l^™1h^™1) and the relative generation times (from 0.2 to 35 days)showed a high range of values, representing a variety of situations, fromestuaries to the ocean. The resulting role of the bacterial community in thecarbon cycle is very consistent, processing amounts of carbon which havebeen estimated as high as the 80% and the 260% of thosesynthesized by autotrophs in summer and winter, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Colonisation of Human-made Structures by the Invasive Alga Codium fragile ssp. tomentosoides in the North Adriatic Sea (NE Mediterranean)

Human-made structures, such as groynes, breakwaters, seawalls, pier pilings and floating pontoons, are becoming common features of the landscape in urbanised coastal and estuarine areas. Despite this tendency few studies have focused on their ecology or on their potential impacts on natural assemblages of organisms. When artificial structures are introduced in areas with little or no hard substrata, they not only provide novel habitats, which enables the colonisation of sandy areas by hard-bottom dwelling species, but they can also provide suitable habitats for exotic species. Along the north-east coast of Italy, sandy shores are protected from erosion by a line of breakwaters, which runs almost uninterrupted for about 300 km. These structures provide habitat for a variety of macroalgae and invertebrates and also for the invasive green alga Codium fragile ssp. tomentosoides. The aim of this study was, therefore, to investigate patterns of distribution of this alga on breakwaters in Cesenatico. In particular, we compared the density of thalli, biomass, length and degree of branching of C. fragile ssp. tomentosoides between the landward and the seaward sides of breakwaters, to test the hypothesis that sheltered habitats (landward) represent more suitable habitats than exposed habitats (seaward). In general, the landward side of breakwaters supported greater numbers of thalli of C. fragile ssp. tomentosoides than seaward sides. Thalli grew longer and more branched in sheltered habitats, leading to an overall larger biomass of the alga on the landward side of breakwaters. The presence of sheltered human-made hard substrata in the vicinity of major trading ports and sources of eutrophication could enhance the dispersal of invasive species across regional and geographic scales. Thus, the effects of artificial structures and introduced species on coastal assemblages cannot be evaluated separately, but their synergistic nature should be considered in planning strategies for conservation of biodiversity in coastal habitats.     

Dynamics and distribution of microphytobenthic chlorophyll-a in the Western Scheldt estuary (SW Netherlands)

The temporal dynamics and spatial distribution of microphytobenthic chlorophyll-a in the layer 0–1 cm were determined in the Western Scheldt estuary over the period 1991–1992. Connections between the annually averaged benthic chlorophyll-a and station elevation and sediment composition (as a measure of the hydrodynamic energy caused by currents and waves) were also examined.Microphytobenthic chlorophyll-a showed one main peak in early summer and a smaller peak in autumn. The mean chlorophyll-a concentration of 113 mg Chl-a m^–2 in the upper centimeter is of the same order of magnitude as in other estuarine areas. The average annual primary production of the microphytobenthos has been estimated at 136 g C m^–2 y^–1 The primary production of sediment inhabiting microalgae is at least 17% of the total primary production in the estuary.Considerable differences in annually averaged chlorophyll-a emerges between the stations. These differences are related mainly to the interaction between station elevation and clay content of the sediment.     

Phytoplankton growth rates in the freshwater tidal reaches of the Schelde estuary (Belgium) estimated using a simple light-limited primary production model

During the course of 1996, phytoplankton was monitored in the turbid, freshwater tidal reaches of the Schelde estuary. Using a simple light-limited primary production model, phytoplankton growth rates were estimated to evaluate whether phytoplankton could attain net positive growth rates and whether growth rates were high enough for a bloom to develop. Two phytoplankton blooms were observed in the freshwater tidal reaches. The first bloom occurred in March and was mainly situated in the most upstream reaches of the freshwater tidal zone, suggesting that it was imported from the tributary river Schelde. The second bloom occurred in July and August. This summer bloom was situated more downstream in the freshwater tidal reaches and appeared to have developed within the estuary. A comparison between phytoplankton growth rates estimated using a simple primary production model and flushing rate of the water indicated that no net increase in phytoplankton biomass was possible in March while phytoplankton could theoretically increase its biomass by 20% per day during summer. Chlorophyllaconcentrations at all times decreased strongly at salinities between 5–10 psu. This decline was ascribed to a combination of salinity stress and light limitation. Phytoplankton biomass and estimated annual net production were much higher in the freshwater tidal zone compared to the brackish reaches of the estuary (salinity > 10 psu) despite mixing depth to euphotic depth ratios being similar. Possible reasons for this high production include high nutrient concentrations, low zooplankton grazing pressure and import of phytoplankton blooms from the tributary rivers.     

Ecology and taxonomy of potentially toxic Pseudo-nitzschia species in Lim Bay (north-eastern Adriatic Sea)

The population dynamics of Pseudo-nitzschia in relation to environmental factors was investigated from March 2002 to July 2008 in Lim Bay, in the north-eastern Adriatic Sea. Domoic acid was monitored in the breeding population of Mytilus galloprovincialis from 2005 to 2008. The principal-component analysis of environmental parameters showed that the system is mostly temperature driven. The phytoplankton community was mainly composed of diatoms. Pseudo-nitzschia was the dominant diatom, present in 60% of samples, with a maximum (1.6 × 10⁶ cells L⁻¹) contribution up to 97% of the total diatom abundance. Morphological analysis revealed Pseudo-nitzschia manii and potentially toxic Pseudo-nitzschia pseudodelicatissima, Pseudo-nitzschia pungens, Pseudo-nitzschia fraudulenta and Pseudo-nitzschia calliantha as the dominant species in blooms. Pseudo-nitzschia abundance positively correlated to temperature, phosphate and ammonia in accordance with its maximal abundance in the summer/autumn period when fish farms had a maximum impact on the environment. Domoic acid was detected in M. galloprovincialis in concentrations below regulatory limits, ranging from 0.097 to 0.8721 μg g⁻¹ in five cases from April to October 2005 in Lim Bay, but so far it is not clear which of the species was responsible for DA production. This study is also the first record of P. manii, P pungens and P. fraudulenta species in the Adriatic Sea.     

Viral production in the Gulf of Trieste (Northern Adriatic Sea): Preliminary results using different methodological approaches

Although the temporal and spatial variability of virioplankton in the northernmost part of the Adriatic Sea has been repeatedly explored suggesting that viruses constitute an extremely dynamic component of the plankton community and hypothesizing their importance in marine food webs and mucilage events, there is still no information about viral replication rates. Hence, the contribution of viruses to bacterial mortality and the cycling of organic matter in this part of the Adriatic basin are still not fully comprehended. Assessment of the role of viral lysis requires a robust means of estimating viral production. Since, up to now, none of the available methods evolved to a state of a standard yet, in this preliminary study 3 different experimental approaches were simultaneously assayed (viral production estimated by radiotracer incorporation method [TdR], dilution technique for the estimate of viral production in already infected bacteria [DIL] and serial dilution method in manipulated phage-host assemblage [SER]). The present study provided the first evidence of viral production rates in this study area, that resulted in comprising between ∼ 3.5-15 × 10⁸ viruses L^− 1 h^− 1 and critically faced up the results obtained by different techniques with the consideration that they suffer from different biases. Based on TdR and DIL viral proliferation estimates, viral lysis was responsible for the loss of 54 to 95% of the bacterial standing stock, while the viral-induced mortality by SER (325% d^− 1) was likely consistently overestimated. These results indicate that viral lysis is a significant factor for prokaryotic mortality suggesting its implication as an important pathway for the cycling of dissolved organic matter in the Gulf of Trieste.     

Fish Farming Effects on Chemical and Microbial Variables of the Water Column: A Spatio-temporal Study Along the Mediterranean Sea

The effects of fish farming on chemical and biological variables of the water column were investigated in three coastal locations along the Mediterranean (Spain, Italy and Greece). Analyses of nutrients, chlorophyll a, particulate organic carbon and nitrogen (POC and PON), heterotrophic bacteria and cyanobacteria (Synechococcus) were carried out on integrated samples (0–30 m depth) taken at various distances from fish farms and the respective reference sites. At one of these sites, water samples were collected by means of Niskin bottles at 09:00, 13:00 and 16:00 h and at three different depths (0 m, 10 m and bottom). Integrated sampling showed no significant changes with distance in any of the variables measured, whereas all variables except PON showed significant changes between the three locations studied. However, changes were found in samples taken by Niskin bottles, with increased concentrations of NH₄⁺, POC, PON and decreased cyanobacteria densities at the surface layer in the immediate vicinity of the cages. Samples taken at the cages in the afternoon showed increased PO₄³⁻ concentrations in comparison to those taken in the morning. Dilution and grazing are probably both responsible for the lack of detectable signs of eutrophication.     

Seasonal changes in physiological responses and evaluation of "well-being" in the Venus clam Chamelea gallina from the Northern Adriatic Sea

Chamelea gallina is an infaunal bivalve, widespread in sandy bottoms along Mediterranean coasts. It is an important economic resource for fisheries in the Adriatic, although in recent years over-fishing, and other concurrent factors, have dramatically decreased clam harvesting. In this context, it is of great interest to gain information on seasonal variations in the physiological performance of clams, for an overall evaluation of their well-being. In this study, laboratory experiments were performed to define allometric relationships and effects of temperature on clearance and respiration rates of C. gallina. The mean values of b coefficients were calculated and used to correlate physiological measurements to 'standard' body mass, when seasonally collected clams were analysed. The highest clearance rate (0.42 L h(-1)) was measured in clams collected in July 2000; the highest respiration rate (12.22 micromol O2 h(-1)) was observed in July 2001, leading to a negative scope for growth (-2.8 J h(-1)). The influence of environmental and endogenous factors, mostly reproduction, was discussed. Survival in air and condition indices, showing higher stress conditions in December 2000 and July 2001, were in good agreement with the other physiological measurements. The physiological responses examined in this study appear to be suitable for providing detailed indications on the well-being of C. gallina and may be useful for future studies aimed at eco-sustainable management of the resource.     

Production characteristics of the population of the red algaAhnfeltia tobuchiensis in Baklan Bight (Peter the Great Bay, Sea of Japan)

Spatial distribution and production characteristics of the population of the unattached red algaAhnfeltia tobuchiensis (Kanno and Matsubara) Mak were studied in Baklan Bight (Sea of Japan) in September 1990 and June 1991. The following environmental factors were determined: the level of photosynthetically active radiation (PAR) penetrating the water column; the water temperature; and the content of oxygen, nitrogen, phosphorus, and dissolved organic substance. the main factor limiting the net primary production (NPP) of theA. tobuchiensis population in Baklan Bight appears to be PAR intensity at the surface of the stratum. In June and September, respectively it constituted about 10% and 0.2% of the PAR on the sea surface. By means of regression analysis, the following equations were obtained to describe the relationship between NPP at the surface of the stratum and the environmental factors studied, PAR intensity being the principal variable: NPP=0.02+0.81 PAR (in June) and NPP=0.02+0.23PAR (in September). In June and September, the NPP of theA. tobuchiensis stratum amounted to 17.2 and 1.3 g/(m² day), and the biomass to 21 and 31 thousand tons, respectively. During the eight months, its distribution changed considerably. In June and September, the daily biomass growth equaled 140.7 and 8.5 t, respectively. A 10-cm-thick layer displayed the highest production characteristics.     

Spawning of the colonial coral <Emphasis Type=Italic>Cladocora caespitosa</Emphasis> (Anthozoa,Scleractinia) in the Southern Adriatic Sea

Data on sexual reproduction of scleractinian coral species living in temperate zones, particularly in the Mediterranean Sea, are quite scarce. This paper describes sexual reproduction of the colonial coral Cladocora caespitosa from Veliko jezero (Mljet Island) in the Adriatic Sea. Spawned orange eggs and white sperm bundles were observed on the coral bank of C. caespitosa two nights before the full moon (20 June 2005) coinciding with increasing water temperature and correlated with the lunar cycle. Spawning was observed during five nights, involving about 30% of the colonies from the coral bank. Different colonies on the bank released only one type of gamete during the reproductive period. The diameter of the sperm bundles ranged from 100 to 200 μm (average 163 μm; SD = 47.08), while the female gametes diameter ranged from 300 to 500 μm (average 416 μm; SD = 73.12).     

Salinity tolerance of the barbel,Barbus callensis Valenciennes, 1842 (Pisces,Cyprinidae) and its ecological significance

The lethal salinity limits (LC₅₀ and mean survival times) of two populations of barbel, Barbus callensis, were determined. Conditions in Lake Ichkeul, Tunisia, are lethal for the fish in summer; this explains their seasonal migrations into Oued Sejnane and the other tributaries. Tolerance increased between 1984 and 1985 from LC₅₀ = 15.6 to LC₅₀ = 17.2 in a population from Oued Mejerdah; this may be connected with the dissolution of rock salt in the new Sidi Salem reservoir.

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Résumé Les limites létales de salinité (CL₅₀ et durée moyenne de survie) de deux populations de barbeaux tunisiens ont été déterminées. Nous avons montré que les conditions de salinité dans le lac Ichkeul sont létales pour ces poissons en été, ce qui explique leurs migrations saisonnières vers l'oued Sejnane et les autres affluents. Nous avons aussi constaté une élévation récente de la tolérance de la population de la Mejerdah, qui peut être en relation avec la dissolution des roches salines dans le nouveau réservoir de Sidi Salem.

     

The Reaction of the Starfish Asterias amurensisand Patiria pectinifera (Asteroidea) from Vostok Bay (Sea of Japan) to a Salinity Decrease

The reactions of the starfish Asterias amurensis and Patiria pectinifera that live in Vostok Bay at the salinity of 32–33 to a salinity decrease were studied under laboratory conditions. The lower limits of the desalination tolerance range of A. amurensis and P. pectinifera were, respectively, 24 and 20. A. amurensis proved to be less resistant to desalination. Under experimental conditions, all specimens of this species survived the salinity of 22, while those of P. pectinifera tolerated 18. At the same time, A. amurensis responded more actively than P. pectinifera to unfavorable changes in the environment. Turned to their dorsal side and exposed to a salinity of 16 to 32, the former reverted to the normal position within a shorter time than the latter. Being a more euryhaline species, P. pectinifera endured a salinity decrease to 6 or 8 over, respectively, 21 or 28 h. However, only 30–40% of all specimens could recover locomotory activity 12 or 8.5 h after being placed into water of normal salinity.     

Salinity tolerance and osmoregulation in the freshwater crab,Barytelphusa guerini (Milne Edwards)

The freshwater crab, Barytelphusa guerini, tolerates gradual transfer to higher salinities upto seawater, regulating its blood chlorides fairly well. Its metabolic rate shows a minimum in 50% seawater and increases on either side, during dilution as well as during concentration of the medium. However, this increase is more pronounced in hypotonic than in hypertonic media.     

Mitochondrial DNA phylogeography reveals the existence of an Evolutionarily Significant Unit of the sand goby Pomatoschistus minutus in the Adriatic (Eastern Mediterranean)

The sand goby Pomatoschistus minutus is a major component of marine shelf and estuarine food webs and an important study organism in behavioural research. Yet, despite the sand goby’s significance, its past and present patterns of migration and gene flow are poorly understood. Here we use the mtDNA control region and parts of the flanking tRNA genes of 63 fish from six localities in the Adriatic (Eastern Mediterranean), Western Mediterranean, Atlantic, and North Sea to investigate the phylogeography of this gobiid. Phylogenetic analyses and population genetics statistics reveal the existence of an Evolutionarily Significant Unit, sensu Moritz (1994), in the Adriatic and another in the Western Mediterranean, Atlantic, and North Sea. A possible biogeographical scenario for the separation of the ancestral population is that sand gobies in the Adriatic and Western Mediterranean split between 10,000 and 5000 years ago when due to the rise in sea temperature they migrated northwards and were bisected by the Italian peninsula. A testable prediction of this scenario is that sand gobies from the Western Mediterranean, Adriatic, and Aegean form three reciprocally monophyletic groups which are the descendants of a three-way diversification event.     

Relevance of the Diastereotopic Ligation of Magnesium Atoms of Chlorophylls in the Major Light-harvesting Complex II (LHC II) of Green Plants

The recent high-resolution crystal structure of LHC II [Liu et al. (2004) Nature 428: 287–292] makes possible an unprecedented insight into the stereochemical features of how chlorophylls (Chl)s are bound. The diastereotopic ligation generates four structurally different pigment types, two Chl a and two Chl b, which are distinguished not only by the groups in the 7-position (methyl in Chl a and formyl in Chl b) but also by the face of the tetrapyrrole to which the fifth magnesium ligand is bound. Within a LHC II monomer, out of the eight Chl a six have a ‚normal’ α-coordination and two are β-coordinated while out of the six Chl b only one has the ‚special’ β-coordination. In Photosystem I where a more meaningful statistical analysis could be made, out of 96 Chl a only 14 are β-coordinated, again indicating a preference for the ‚normal’ α-coordination [Balaban et al. (2002) Biochim Biophys Acta Bioenerget 1556: 197–207; Oba and Tamiaki (2002a) Photosynth Res 74: 1–10]. Astonishingly, all the special β-Chls are part of the stromal ring of Chls within the LHC II trimers and occupy key positions for the excitation energy transfer. Sequential energy traps are engineered with one hetero- and three homo-dimers. A careful pairing of carotenoids with the special β-Chls, which could quench their triplet states efficiently, implies a functional relevance of this diastereotopic ligation.     

Seasonal variations in carbon and nitrogen content of Acartia clausi (Copepoda,Calanoida) in the Gulf of Trieste (Northern Adriatic Sea)

A yearly study was made on total and cephalothorax lengths, dry weight, carbon and nitrogen contents and C:N ratio of the species Acartia clausi (Copepoda, Calanoida) which is always abundant, particularly in spring, in the net zooplankton community of the Gulf of Trieste (Northern Adriatic Sea). The samples of net zooplankton were carried out every month at the permanent station located 200 m offshore and preserved for about one year in 4% buffered formalin to insure weight loss stabilization. A. clausi was separated from other zooplankton specimens; washed and dried. For each monthly sample the average total and cephalothorax lengths and the average dry weight of adult organisms of A. clausi were measured. The mean carbon and nitrogen contents, as a percentage of dry weight, were determined by using a CHN analyser. Linear regression models were computed on the log-transformed data in order to check the relationships between dry weight, total and cephalothorax lengths, carbon and nitrogen contents and C:N ratio of A. clausi. The best of the various established correlations, was between dry weight and carbon content. Our study pinpointed a high seasonal variability of the C:N ratio, mainly due to seasonal fluctuations in the nitrogen content.