Exoenzymatic activity and organic matter composition in sediments of the Northern Adriatic Sea: response to a river plume

Exoenzymatic activities (aminopeptidase and b-glucosidase) and organic matter composition were investigated in June 1996 and February 1997 in the sediment of two areas of the Adriatic Sea differently influenced by the Po river. Protein, carbohydrate, and lipid concentrations were comparable to those reported in most productive systems. Sediment chlorophyll a and biopolymeric carbon concentrations in June were twice as high as in February, but highest exoenzymatic activities and organic matter turnover rates were observed in February (with aminopeptidase activities 10 times higher than in June). The accumulation of organic matter and lower protein and carbohydrate turnover rates observed in June were the result of a different biochemical composition of organic matter in the two sampling periods. In June, organic matter was characterized by a more refractory composition. The consequent reduction of available organic substrate was associated with a decrease in the exoenzymatic substrate affinity. Lower organic matter turnover rates were also observed in deeper sediment layers. In February, the freshwater plume was almost completely confined to the northern area, whereas in June it was extended to the southern area. The results suggest that river inputs influence the biochemical composition and distribution of the sediment organic matter and exoenzymatic activities in coastal marine sediments.     

Copepod and barnacle nauplius distributions in the Irish Sea: relation to springtime hydrographic variability

The distributions and abundances of copepod and barnacle naupliiare described along a five-station transect in the Irish Seafrom Liverpool Bay, England, to Dundalk Bay, Ireland, in May1989. Correspondence analysis revealed that various hydrographicregions in the Irish Sea are characterized by distinct naupliusassemblages. Acartia, Centropages and Temora nauplii were associatedwith the Welsh coastal water east of the Liverpool Bay front.The western stratified water to the west of the seasonal, westernIrish Sea front was distinguished from the mixed water to theeast by abundances of Calanus, Pseudocalanus, Oithona, Microcalanusand harpacticoid nauplii. The Liverpool Bay and western IrishSea fronts are, apparently, boundaries between coastal and offshoreassemblages of crustacean nauplii.     

Ectoenzymatic ratios in relation to particulate organic matter distribution (Ross Sea,Antarctica)

The results of a study on ectoenzymatic activity (the enzyme activity bound to particles larger than 0.2 micro m) and its relation to organic particle concentration are reported here. The sampling was carried out during the 1994 Antarctic spring, at a fixed station (Station 11) in the polynya of the Ross Sea, an area characterized by quick changes in sea ice cover. The sampling was repeated 4 times over a 20-day time period. The particulate organic matter distribution followed the physical structure of the water column, which depends on ice dynamics and is mainly determined by salinity. In the mixed-water surface layer (0-50 m) the concentrations were higher (on average 65.6 micro gC/L) than in the deeper water layer (50 m-bottom) (on average 19.1 micro gC/L). This distribution and quality, expressed by the protein:carbohydrate ratio, linked the particulate organic matter to the phytoplanktonic bloom which was in progress in the area. We determined the kinetic parameters of the glycolytic and proteolytic ectoenzymes and also the total activity for the proteolytic enzyme, in order to evaluate the contribution of the particle-bound activity. We observed higher values in the surface layer than in the deeper layer. b-Glucosidase activity ranged between 0.03 and 0.92 nmol L(-1) h(-1); b-N-acetylglucosaminidase activity was in the range of 0.04-0.58 nmol (L-1) (h-1). The total proteolytic activity (leucine aminopeptidase) ranged between 0.85 and 33.71 nmol L(-1) (h-1). The ectoproteolytic activity was about 35-60% of the total. The Km values were slightly higher for the proteolytic activity (on average 0.43 micro M for ectoproteolytic activity and 0.58 micro M for total proteolytic activity) than for the b-glucosidase (on average 0.36 micro M) and b-N-acetylglucosaminidase (on average 0.17 micro M), showing no remarkable variations in the water column. The ectoenzymatic ratios and their relationship with particulate organic substrates confirm the close link between organic substrate availability and degradation system response. The significant and positive correlations are not specific and suggest a prompt and efficient systemic response to the input of trophic resources. Nevertheless, changes in ectoenzyme activity and synthesis may act as adaptive responses to changing features of the ecosystem. In particular, variations in the proteolysis:glycolysis ratio depend on the functional features of the ecological system. In our study area this ratio is higher (about 10 or more) during production (particularly autotrophic) and lower (about 5 or less) during degradation/consumption events. The analysis of previous data, collected over a larger area characterized by different environmental conditions due to the changes of the pack ice cover, during the same cruise, confirms the existence of a significant relationship. Furthermore, the analysis of enzyme-uptake systems, expressed as Vmax:Km ratio, suggests that glycolytic ectoenzymes, although poorly expressed, may encourage microconsumers to grow rapidly on a wide range of organic substrates, including the refractory ones such as cellulose and chitin. However, low ectoenzyme potential exploitation rates of available organic substrates (on average about 5% for glycolytic and 12% for proteolytic ectoenzymes) would suggest that, during spring, zooplankton grazing or vertical and lateral transport are likely to play an important role in the removal of organic materials from the system.     

Pelagic larvae of bivalve mollusks and polychaetes in winter plankton of the Kara Sea

Quantitative zooplankton samples were obtained by vertical tows with a Juday plankton net, in the southern Kara Sea, from November 28 to December 11, 2005 (by an expedition of the Murmansk Marine Biological Institute KSC RAS aboard the nuclear ice-breaker “Soviet Union”). The most abundant meroplankton forms were juveniles of Bivalvia and larvae of Polychaeta (the maximum abundances were 106.2 ind/m³ and 7.5 ind/m³, respectively). The results are discussed in relation to changes in the thermal regime of the Arctic Ocean observed during the recent decades.     

Changes in particulate and dissolved organic matter in nutrient-enriched enclosures from an area influenced by mucilage: the northern Adriatic Sea

This study examined the partitioning of organic matter intoparticulate organic carbon (POC) and dissolved organic carbon(DOC) pools in nutrient-enriched enclosures containing naturalplankton from the Gulf of Trieste (northern Adriatic), an areaaffected by mucilage. The strategy of nutrient additions wasto introduce a pulse of new nutrients in concentrations thatmimic natural inputs and to survey community structure and organicmatter fluxes long enough so that plankton became nutrient-limited.Maximal bacterial biomass attained roughly double the initialvalue, while autotrophic carbon increased by nearly an orderof magnitude. The microflagellate-dominated community releasedmore DOC per unit biomass (5.5 ± 7.2 to 50.6 ±28.0 µg C µg Chl a^-1 day^-1 versus 3.4 ± 3.4to 10.8 ± 4.6 µg C µg Chl a^-1 day^-1 for diatom-dominatedphytoplankton), POC increase was modest (~300 µg C l^-1)and there was little change in DOC. Organic carbon partitioningduring two experiments in which diatoms prevailed was dominatedby POC (>800 µg C l^-1) in the exponential growth phasewith an increasing contribution of particulate carbohydratesthat paralleled gradual nutrient depletion. Transition to thestationary phase and the decay of autotrophic communities wereaccompanied by the net accumulation of a carbohydrate-rich DOC.     

Zooplankton biomass variation in relation to climatic conditions in the Barents Sea

Over the last two decades, there have been large changes in the zooplankton biomass in the Barents Sea. These biomass variations are mainly attributed to predation pressure and environmental factors (e.g. advective transport). When stock size of capelin (Mallotus villosus), a major planktivorous fish in the Barents Sea ecosystem, was quite low as in 1986 and 1994, the zooplankton biomass showed marked increase. However, the increase in the zooplankton biomass occurred in different water masses during 1986 and 1994. In 1986, a climatically cold year, the plankton biomass was highest in the Arctic waters of the northeastern Barents Sea. This is probably due to the increase in larger Arctic amphipod species, such as Themisto libellula. In 1994, a climatically warm year, the zooplankton biomass was high in the Atlantic waters of the southwestern Barents Sea. The large increase in zooplankton biomass in the Atlantic waters in 1994 was presumably due to the higher inflow of advected organisms, e.g. Calanus spp., as well as high temperatures, which may lead to high growth rates of zooplankton. Throughout the studied region, the plankton biomass in the "cold year" of 1986 was generally much lower than in the "warm year" of 1994.     

Temporal variability of particulate organic carbon,nitrogen and phosphorus in the Northern Adriatic Sea

The particulate organic carbon (POC), nitrogen (PN) and phosphorus (PP) vertical distribution along the water column and temporal variability in coastal and offshore waters of the Northern Adriatic Sea were related to the hydrodynamic conditions and biological processes. Fresh water inputs from the Po and Adige rivers enhance primary production, resulting in high POC, PN and PP concentrations at the surface. In offshore waters, POC and PN concentrations were about 3–4 times less than in the coastal waters, while PP were up to 10 times lower, highlighting a marked phosphorus depletion. In the bottom layer, the POC content decreases due to the strong density gradients which separate bottom waters with prevailing degradation processes. Short term 48 h-variability of POC, PN and PP in the coastal waters was determined to a great extent by variations in the spreading of river plumes at the surface and by nepheloid layers and resuspension processes in the bottom waters. The particulate matter in the Adriatic offshore waters is extremely depleted as regards particulate phosphorus and is characterised by C_org:P and N:P ratios higher than the Redfield ratio.     

Pelagic Food Chain of the Bering Sea

Journal of Ichthyology - The order of magnitude of biomass and production at various trophic levels in the epipelagic community has been calculated, and the main pathways for the transformation of...     

Concepts of soil organic matter transformations in relation to organo-mineral particle size fractions

Summary Changes in the composition of organo-mineral particle size fractions as a result of cultivation of a grassland soil are discussed with reference to models of soil organic matter formation and turnover. The data presented indicated that physically stabilized organic matter is an important reservoir, with an intermediate turnover time, which is responsible for nutrient supply in agricultural soils. Possible mechanisms of stabilization and mobilization of organic matter are presented in the light of the arrangement of organic and inorganic components of the soil.     

Benthic ciliates in Adriatic Sea lagoons

Sediment samples were collected from four sandy and muddy bottom sites at both Sacca di Goro lagoon (northern Adriatic Sea) and Lesina lagoon (southern Adriatic Sea) on one occasion in May and one occasion in July in order to make a comparative study of ciliate abundance and diversity. The temperature, pH, dissolved oxygen, and redox potential were measured at the time of collection, the water content of the sediments was determined, and samples subjected to granulometric analysis. The ciliated protozoa in sub-samples from the top centimeter of sediment were identified to genus and species level and enumerated. Ciliates belonging to 38 and 33 species were found in the sediment of Sacca di Goro and Lesina, respectively, the diversity of ciliates varying widely between stations. Total ciliate numbers ranged from 32 to 759 cm(-2) and from 2 to 256 cm(-2) at Sacca di Goro and Lesina, respectively; the ciliate biomass ranged from 1.1 to 30.3 microg C cm(-2) in the samples collected at Sacca di Goro, and from 0.01 to 157 microg C cm(-2) in the samples collected at Lesina lagoon. Aspidisca lynceus, Aspidisca steini, Chilodonella uncinata, Frontonia marina, Pleuronema marinum, Strombidinopsis minimum, Strombidium sp., and Urotricha sp., were observed at the two lagoons but not in all stations; Keronopsis flavicans and Trachelostyla pediculariformis were often numerous at Goro lagoon, A. lynceus, Condylostoma patulum and Tracheloraphis teissieri were the most abundant ciliates observed at Lesina lagoon.     

Invasion of amphisteginid foraminifera in the Adriatic Sea

Amphisteginid foraminifera are larger symbiont-bearing foraminifera that are abundant in tropical and subtropical reef and shelf regions of the world’s oceans. There is now unequivocal evidence that climate change has led to an expansion of tropical belts. As temperatures rise, surface isotherms are shifting poleward and habitat ranges are moving towards higher latitudes. Fueled by substantial warming, the Mediterranean has been identified as one of the most severely affected areas. This study documents for the first time that amphisteginid foraminifera have now crossed the Strait of Otranto and invaded the eastern Adriatic coast along southern Albania. Sampling on the opposite side along the southern part of the Italian boot shows, however, that amphisteginid foraminifera have not yet colonized the western coast of the Adriatic. The asymmetric invasion of the Adriatic displays spatial heterogeneity, where the progressive colonization follows the major surface currents with a northerly flow along the eastern coast and a southerly return along the western coastline. Previous sampling along Ionian Sea sample sites provides a baseline chronology allowing computations of range expansion rates. The observed recent rate of range expansion in Amphistegina is computed between 4.0 and 10 km/year^?1 and provides strong support for current species model projections. Based on the new data, the range boundary shift is projected to lead to a total northward range expansion of 5.2° latitude in the year 2100. The latitudinal range extension computed for the Mediterranean is thus almost twice as large as those computed for the southern hemisphere. The ongoing range extension into new areas of the Mediterranean Sea is shown to trigger changes in community structures with potential consequences for ecosystem functioning. Numerical abundances and impacts of invasive amphisteginids are greatest at shallow depths <20 m. Evidence is now accumulating that the invasion of amphisteginid foraminifera results in (1) a loss of benthic foraminiferal biodiversity, (2) alterations of foraminiferal community structures and (3) shifts in abundances of functional groups of foraminifera.     

The genus Dinophysis in the Southern Adriatic Sea

Abstract

Some preliminary results of a survey carried out along the Southern Adriatic coasts (Brindisi-S.M. Leuca) are reported in order to contribute to the knowledge of the phytoplankon community of this area. Ten Dinophysis species had been identified, four of them are known to be involved in DSP mussel contamination. Spatio-temporal distribution of Dinophysis spp. is shown.     

Soil microbial activity in relation to dissolved organic matter properties under different tree species

Background and aims

The total concentration of dissolved organic carbon (DOC) has often been observed to correlate positively with soil microbial respiration. The aim was to explain the correlation with the properties of dissolved organic matter (DOM).

Methods

A dataset from previously published papers was gathered together and subjected to multivariate analyses. Samples were collected from five tree species experiments in Finland. The degradability of DOM was assessed by measuring bacterial and fungal growth in DOM. The chemical properties of DOM were assessed by XAD resin fractionation and molecular weight. Soil microbial activity was assessed as C and N mineralization and microbial biomass.

Results

Both low and high molecular weight compounds, as well as hydrophilic neutral compounds, seemed to be relatively easily degradable. In contrast to our presupposition, easily degradable DOM seemed to be less abundant in soil where variables describing microbial activity were higher. Birch soil with higher microbial biomass N seemed to contain less easily degradable DOM than spruce soil.

Conclusion

We suggest that DOM collected and characterized at a certain point reflects more the accumulation of refractory compounds following high microbial activity than the easily degradable compounds that microbes would be using when measured.

     

南海环境微生物对聚球藻有机物质的响应

【背景】海洋浮游植物产生的有机物质与异养细菌之间的相互作用是上层海洋物质和能量循环过程中的重要组成部分。【目的】探究寡营养海域微生物群落对聚球藻有机物(Synechococcus-derived organic matter,SOM)的响应和代谢利用过程,加深对海洋微生物介导的生物地球化学循环过程的认识。【方法】利用南海海域微生物群落,添加聚球藻有机物质后黑暗培养,对培养过程中有机碳、营养盐和活性微生物群落结构的变化进行追踪。【结果】在短期的培养过程中,有60%-73%的SOM被微生物所利用。γ-变形菌(Gammaproteobacteria)在培养过程中响应最快,也是最优势微生物类群。SOM的加入改变了原位微生物群落结构,并且随着活性有机物质逐步被消耗,微生物群落结构也发生了演替。【结论】SOM中的大部分物质都属于活性有机物质,可以快速地被微生物所降解利用。不同微生物类群响应不同生物可利用性有机物质,推动了海洋物质和能量的循环。     

Long-term changes in Wadden Sea nutrient cycles: importance of organic matter import from the North Sea

The Wadden Sea is a shallow tidal area along the North Sea coast of The Netherlands, Germany and Denmark. The area is strongly influenced by rivers, the most important of which are the rivers Rhine, Meuse and Elbe. Due to the increased nutrient load into the coastal zone the primary production in the Wadden Sea almost tripled during the past few decades. A conceptual model is presented that links nitrogen input (mainly nitrate) via Rhine and Meuse with the annual nitrogen cycle within the Wadden Sea. Three essential steps in the model are: (1) nitrogen limits the primary production in the coastal zone, (2) a proportional part of the primary produced organic matter is transported into the Wadden Sea and (3) the imported organic matter is remineralized within the Wadden Sea and supports the local productivity by nitrogen turn-over. The conceptual model predicts that during years with a high nutrient load more organic matter is produced in the coastal zone and more organic matter is transported into and remineralized within the Wadden Sea than during years with low nutrient loads. As a proxy for the remineralisation intensity ammonium plus nitrite concentrations in autumn were used. Based on monitoring data from the Dutch Wadden Sea (1977–1997) the above mentioned model was statistically tested. In autumn, however, a significant correlation was found between autumn values of ammonium and nitrite and river input of nitrogen during the previous winter, spring and summer. The analysis supports that in years with a high riverine nitrogen load more organic matter is remineralized within the Wadden Sea than in years with a low nitrogen load. A comparison with older data from 1960 to 1961 suggests that the remineralisation intensity in the Wadden Sea has increased by a factor of two to three. This is not reflected by a two to three-fold increase in riverine nitrogen load from 1960 to present. It is suggested that the increased remineralisation rates in the Dutch Wadden Sea between the 1960s and the 1980s/1990s are largely caused by an increased nitrogen flux through the Channel and the Strait of Dover and by an increased atmospheric nitrogen input.     

Changes in the microzooplankton assemblages in the northern Adriatic Sea during 1989 to 1992

Microzooplankton were sampled at five fixed stations in theopen waters of the northern Adriatic during four cruises in1989, nine in 1990, six in 1991 and 12 in 1992. Changes in thequalitative-quantitative composition, together with the spatial-temporaldistribution of the microzooplankton assemblages in the northernwaters of the open Adriatic, were the result of atypical oceanographicand productivity conditions in the entire region of this sea.Owing to low values of ciliated protozoa, which comprised only26% (1989) and 36% (1991) of the total number of microzooplankton,primary production cannot be controlled through grazing. Thismay possibly explain the occurrence of marine snow. The presenceof the larger mucous aggregates in the later phase causes asignificant decrease in the density of the naupliar copepodpopulation. Therefore, the usual dominance of copepods in summerdoes not occur and their development cycle is displaced to lateautumn. Consequently, only Olihona nana, a species of widerecological tolerance, comprised up to 73% of the total numberof postnaupliar copepods during the presence of mucous aggregatesin 1989. Thus, this small copepod plays an important role inthe processes of remineralization in the northern Adriatic.     

A sketchy outline of the fate of organic matter in the Dutch Wadden Sea

Conclusion In ecosystems like the Dutch Wadden Sea a carbon budget can be made roughly However, there are in space as well as in time a lot of gaps in the observations. Especially from subtidal sediments of inlets and gullies are no observations available. Also the quantification of the different functional groups of the anaerobically respiring organisms (manganese reducers, denitrifiers, iron reducers, methane formers) in the decomposition is absent. And what is the role and quantitative importance of fermenting organisms? Finally, the quantification of the use of the reduced end products of anaerobic respiring organisms is unknown.