Viral abundance and distribution in mesopelagic and bathypelagic waters of the Mediterranean Sea

Despite the fact that marine viruses have been increasingly investigated in the last decade, knowledge on virus abundance, biomass and distribution in mesopelagic and bathypelagic waters is limited. We report here the results of a large-spatial-scale study (covering more than 3000 km) on the virioplankton distribution in epi-, meso- and bathypelagic waters in 19 areas of the Mediterranean Sea, from the Alboran Sea and Western Mediterranean, to the Tyrrhenian Sea, Sicily Channel and Ionian Sea. Integrated viral abundance in epipelagic waters was significantly higher than in deep-sea waters (on average, 2.4 vs. 0.5×10¹² viruses m⁻³). However, abundance of viruses in the deep-Mediterranean waters was the highest reported so far for deep seas worldwide (7.0 and 3.1×10¹¹ viruses m⁻³ in mesopelagic and bathypelagic waters, respectively) and their biomass accounted for 13–18% of total prokaryotic C biomass. The significant relationship between viral abundance and prokaryotic abundance and production in deep waters suggests that also deep-sea viruses are closely dependent on the abundance and metabolism of their hosts. Moreover, virus to prokaryote (and nucleoid-containing cell (NuCC)) abundance ratio increased with increasing depths suggesting that deep waters may represent optimal environments for viral survival or proliferation. Overall, our results indicate that deep waters may represent a significant reservoir of viruses and open new perspectives for future investigations of viral impact on the functioning of meso-bathypelagic ecosystems.     

Hydrobiological studies of the ballast waters of cargo ships in Russian Sea ports

The results of the first studies on the ballast waters of commercial vessels in Novorossiysk and Vladivostok ports are presented. Data on the composition of the flora and fauna, their abundance, viability, and the origin of the species were obtained. In the zooplankton from the ballast waters sampled in the Novorossiysk port, 31 species of holoplankton and 15 species of meroplankton were found. The total number of zooplankton varied from 1.3 to 60 thousand ind./m³. The Mediterranean basin, providing 62% of the ballast waters, represents a vector of the greatest risk. In the port of Vladivostok, in the ballast waters of the vessels of the Russian-Japanese and Russian-Chinese lines, 45 species of microalgae, 24 species of zooplankton, 22 species of meroplankton, and 10 groups of meiofauna were revealed. In addition, 24 species of microscopic filamentous fungi were identified and 28 morphologically distinguishable strains of bacteria were isolated (in total not less than 153 species). The basic “groups of risk” for bioinvasions in the basins of the Black Sea and the seas of the Far East were revealed. The need for control of ships’ ballast waters in Russia, which is presently lacking relevant national methodical guidelines and legislation, is substantiated.     

Changes in the species composition and ichthyoplankton abundance along transects in the Baltic Sea

Correlations have been revealed between the distribution of the different ichthyoplankton species and the fluctuations of the environmental factors along transects in the Baltic Sea during the autumn of 2005 and spring and autumn of 2006. The early ontogenetic stages of the cod and other bottom fish species were confined to the Bornholm Basin located in the southwestern part of the sea with near-bottom salinity of more than 16?? and the absence of an oxygen deficiency in the isohaline zone of 11?C14??. Eggs and larvae of the Baltic sprat were distributed in June throughout all the deep-sea regions with near-bottom water salinity of no less than 8%., up to the western Gulf of Finland. In the spring of 2006, the abundance of sprat eggs was found to drop significantly compared with the average long-term data for the recent period; this was due to the cold winter of 2006.     

Variations in the abundance of fisheries resources and ecosystem structure in the Japan/East Sea

Evidence supports the hypothesis that two climatic regime shifts in the North Pacific and the Japan/East Sea, have affected the dynamics of the marine ecosystem and fisheries resources from 1960 to 2000. Changes in both mixed layer depth (MLD) and primary production were detected in the Japan/East Sea after 1976. The 1976 regime shift appears to have caused the biomass replacement with changes in catch production of major exploited fisheries resources, including Pacific saury, Pacific sardine and filefish. Both fisheries yield and fish distribution are reflected in these decadal fluctuations. In the 1960s and 1990s, common squid dominated the catches whereas in the 1970s and 1980s, it was replaced by walleye pollock. In the post-1988 regime shift, the distribution of horse mackerel shifted westward and southward and its distributional overlap with common mackerel decreased. The habitat of Pacific sardine also shifted away from mackerel habitats during this period. To evaluate changes in the organization and structure of the ecosystem in the Japan/East Sea, a mass-balanced model, Ecopath, was employed. Based on two mass-balanced models, representing before (1970–75) and after (1978–84) the 1976 regime shift, the weighted mean trophic level of catch increased from 3.09 before to 3.28 after. Total biomass of species groups in the Japan/East Sea ecosystem increased by 15% and total catch production increased by 48% due to the 1976 regime shift. The largest changes occurred at mid-trophic levels, occupied by fishes and cephalopods. The dominant predatory species shifted from cephalopods to walleye pollock due to the 1976 regime shift. It is concluded that the climatic regime shifts caused changes in the structure of the ecosystem and the roles of major species, as well as, large variations in biomass and production of fisheries resources.     

南黄海浮游动物主要种类数量分布年间比较

分析对比1959年、1982年、1998-2000年以及2007-2010年4个不同时期南黄海中部（34.25°~37.45°N,122.00°~124.00°E）浮游动物主要优势种中华哲水蚤（Calanus sinicus）、太平洋磷虾（Euphausia pacifica）和强壮箭虫（Sagitta crassa）数量时空变化及其与温度、盐度和太平洋年代际震荡指数（Pacific Decadal Oscillation,PDO）变动的关系。结果显示,温度可能对中华哲水蚤和太平洋磷虾数量分布影响较大;强壮箭虫则受盐度影响较大。PDO暖位相时期中华哲水蚤和太平洋磷虾数量显著低于冷位相时期,强壮箭虫则相反。中华哲水蚤和太平洋磷虾丰度与提前3个月PDO值呈显著正相关,强壮箭虫丰度仅与当月PDO值呈显著正相关。     

Satellite observations of synoptic eddies and the geostrophic circulation of the Sea of Japan waters

Currents and eddies in the Sea of Japan are investigated on the basis of shipboard multiyear averaged hydrologic measurements over 1925–2005 and satellite images over 1988–2002. The schemes of geostrophic currents are constructed and the positions of quasi-stationary eddies on the sea surface are determined. It is shown that eddy formations are concentrated along jets of the main currents. A construction of the scheme of surface currents with consideration for eddies is attempted.     

Latitudinal changes (6°S-20°N) of summer ciliate abundance and species compositions in surface waters from the Java Sea to the South China Sea

Ciliates play a curial role in energy transfer from pico-and nano-phytoplankton to mesozooplankton in marine ecosystems. In order to visualize their geographical distributions from the Java Sea to the South China Sea (6°S to 20°N), the authors investigated the ciliate abundance and species composition in surface waters during May 18 to 27 of 2010. The ciliate abundance decreased latitudinally from 3 080 ind./L (～6°S) to 40 ind./L (～3°N), and then increased to 1 180 ind./L (～16°N) at the end of the survey. A total of 22 ciliates belonging to 15 genera were identified with the tintinnids accounted for 50% (11 species); and the species number showed a same spatial change as the ciliate abundance. Moreover, the Strombidium occupied over 50% of total ciliate abundance in most stations and Mesodinium and Tintinnopsis contributed to about 18.7% and 11.4%, respectively. In particular, our results indicate that the geographical changes in ciliate abundance were positively regulated by larger nano-and micro-phytoplankton biomass, rather than smaller pico-phytoplankton in the investigated waters.     

Standing stocks and production rates of phytoplankton and abundance of bacteria in the Seto Inland Sea, Japan

Standing stocks and production rates of phytoplankton and abundance of bacteria were investigated at 39 stations in the Seto Inland Sea, Japan during four crulses in October 1993, January, April and June 1994. Primary productivity was measured by the¹³C tracer method. Photosynthetic rate varied from 0.41 to 32.1 μgC/1/h with an average value of 4.67 μgC/l/h. Annual primary production was estimated to be 218 gC/m²/year. Annual primary production in this study was 1.8 times as high as the values which were previously reported at same area. The reason for the disagreement between our primary production value and previous values is not thought to be due to the difference of methods used for measuring primary production or the different Chl.a concentrations but to the method of estimating the primary production in the euphotic zone from thein vitro measurements. The distribution of bacterial cells in surface seawater was examined during the same cruises. Bacterial cell density ranged from 0.32 to 3.4×10⁶ cells/ml. The density was relatively high in the eutrophic regions of Hiroshima Bay and Osaka Bay In addition, a high density of bacteria was also observed in an area within Suo Nada where Chl.a was relatively low. The disparity between Chla and bacterial density in Suo Nada suggests that bacterial abundance can be controlled by the availability of substrates other than phytoplankton exudate.     

Resources and habitat conditions of the bivalve mollusk Anadara broughtonii in the northern part of Amur Bay (Sea of Japan)

The population of ark shell Anadara broughtonii inhabiting the northern part of Amur Bay (Sea of Japan) is prone to the effects of the unstable environmental factors characteristic of the estuarine zone. The significant proportion of individuals with a decreased growth rate is due to the ecological and physiological peculiarities of the species at the northern limit of the geographical range. During the period of 2004?C2009, the temperature and salinity characteristics in the habitats of A. broughtonii showed no significant fluctuations. The commercial fishing for the ark shell was performed taking into account the scientifically approved maximum allowable catch size. The current condition of the population can be considered as stable.     

Dynamics of planktonic foraminiferal community in the Sea of Japan during the last 2 My

Based on the analysis of the foraminiferal assemblages in 118 sediment samples from the 210-m-long core of ODP Hole 798 drilled near Honshu Island, it is shown that the structure of their tanathocoenoses experienced three large reorganizations during the last 1.9 My, namely 0.68, 1.21, and 1.36 My B.P. The first reorganization coincides with the Matuyama-Brunhes boundary marked by the magnetic polarity reversal. The second reorganization corresponds to the sharp and progressive temperature fall caused by general climate deterioration. The third event is poorly interpretable thus far. Using the K-average method, the assemblages were differentiated into two types differing in their taxonomic structures. The replacement of one type of community with another occurred simultaneously with the cooling onset 1.21 My B.P. Spectral analysis of the variations in the integral characteristics of the taxonomic structure revealed three groups of cycles with average periods of 136, 59, and 33 ky. These estimates are one-third higher as compared to the duration of the Milankovitch climatic cycles. The species structure of the foraminiferal community is shown to be well consistent with the rank model of geometric series.     

Oceanic distribution and life cycle of Calanus species in the Norwegian Sea and adjacent waters

The distribution and demography of Calanus finmarchicus, C. glacialis and C. hyperboreus were studied throughout their growth season on a basin scale in the Norwegian Sea using ordination techniques and generalized additive models. The distribution and demographic data were related to the seasonal development of the phytoplankton bloom and physical characteristics of water masses. The resulting quantified relationships were related to knowledge on life cycle and adaptations of Calanus species. C. finmarchicus was the numerically dominant Calanus species in Coastal, Atlantic and Arctic waters, showing strong association with both Atlantic and Arctic waters. C. hyperboreus and C. glacialis were associated with Arctic water; however, C. glacialis was occasionally observed in the Norwegian Sea and is probably an expatriate advected into the area from various origins. Demography indicated one generation per year of C. finmarchicus, a two-year life cycle of C. hyperboreus, and both one- and two-year life cycles for C. glacialis in the water masses where they were most abundant. For the examined Calanus species, young copepodites of the new generation seemed to be tuned to the phytoplankton bloom in their main water mass. The development of C. finmarchicus was delayed in Arctic water, and mis-match between feeding stages and the phytoplankton bloom may reduce survival and reproductive success of C. finmarchicus in Arctic water. Based on low abundances of C. hyperboreus CI–III in Atlantic water and main recruitment to CI prior to the phytoplankton bloom, we suggest that reproduction of C. hyperboreus in Atlantic water is not successful.     

Structure and species diversity of the zooplankton community of the Inland Sea of Japan

Seasonal fluctuations in composition and abundance of zooplankton of the Inland Sea of Japan were investigated in 1979–1980. Some of the areas in the environment were found to be eutrophic and sharp temperature variations occurred with seasons. In this scenario, zooplankton populations peaked in autumn. Copepods were the dominant component and six species of this group formed about 88% of the total zooplankton counts. Species groups are categorized based on distributional characteristics. Zooplankton composition was more or less homogeneous in each season within the area studied and a few oceanic species which occurred had only limited influence on community structure. Species diversity was low and competition among species was weak. The results indicated a poor quality biotope probably resulting from a deterioration of water quality and an environment which favours r-selection.     

Spatial variability in the primary productivity in the East China Sea and its adjacent waters

Primary productivity in the East China Sea and its adjacent area was measured by the¹³C tracer method during winter, summer and fall in 1993 and 1994. The depth-integrated primary productivity in the Kuroshio Current ranged from 220 to 350 mgC m⁻²d⁻¹, and showed little seasonal variability. High primary productivity (above 570 mgC m⁻²d⁻¹) was measured at the center of the continental shelf throughout the observation period. The productivity at the station nearest to the Changjiang estuary exhibited a distinctive seasonal change from 68 to 1,500 mgC m⁻²d⁻¹. Depth-integrated primary productivity was 2.7 times higher in the shelf area than the rates at the Kuroshio Current. High chlorophyll-a specific productivity (mgC mgChl.-a⁻²d⁻¹) throughout the euphotic zone was mainly found in the shelf area rather than off-shelf area, probably due to higher nutrient availability and higher activity of phytoplankton at the subsurface layer in the shelf area.     

Geographical and seasonal variations in abundance,biomass and estimated production rates of microzooplankton in the Inland Sea of Japan

We measured abundance and biomass of 3 major groups of microzooplankton, i.e. tintinnids, naked ciliates and copepod nauplii, at 21 stations in the Inland Sea of Japan in October 1993, January, April and June 1994. The average abundance of the microzooplankton over the entire Inland Sea of Japan ranged from 2.39×10⁵ indiv. m^–3 in January to 4.00×10⁵ indiv. m^–3 in April. Ciliated protozoans, i.e. tintinnids plus naked ciliates, numerically dominated the microzooplankton. The average biomass of the microzooplankton was exceedingly high in October (8.62 mg C m^–3) compared to that in the other months (2.06, 2.79 and 2.68 mg C m^–3 in January, April and June, respectively). The ciliated protozoans also dominated in terms of biomass except in October, when copepod nauplii were more important. Estimated production rate of the microzooplankton was highest in October (average: 6.02 mg C m^–3d^–1) and followed in order by June, April and January (1.94, 1.14 and 0.54 mg C m^–3d^–1, respectively). Due to higher specific growth rate, the production rate by the ciliated protozoans far exceeded that by the copepod nauplii. The trophic importance of the microzooplankton in the pelagic ecosystem of the Inland Sea of Japan was assessed by estimating carbon flow through the microzooplankton community.     

Annual cycle of zooplankton abundance and species composition in Izmit Bay (the northeastern Marmara Sea)

The monthly abundance, biomass and taxonomic composition of zooplankton of Izmit Bay (the northeastern Marmara Sea) were studied from October 2001 to September 2002. Most species within the zooplankton community displayed a clear pattern of succession throughout the year. Generally copepods and cladocerans were the most abundant groups, while the contribution of meroplankton increased at inner-most stations and dominated the zooplankton. Both species number (S) and diversity (H′) were positively influenced by the increase in salinity of upper layers (r = 0.30 and r = 0.31, p < 0.001, respectively), while chlorophyll a was negatively affected (r = −0.36, p < 0.001). Even though Noctiluca scintillans had a significant seasonality (F_11,120 = 8.45, p < 0.001, ANOVA), abundance was not related to fluctuations in temperature and only chlorophyll a was adversely correlated (r = −0.35, p < 0.001). In general, there are some minor differences in zooplankton assemblages of upper and lower layers. A comparison of the species composition and abundance of Izmit Bay with other Black Sea bays reveals a high similarity between them.     

A Numerical Simulation on the Mesoscale Dynamics of the Spring Bloom in the Sea of Japan

The northward migration of spring bloom was observed in the Sea of Japan from April to May 1997 by the Ocean Color and Temperature Scanner (OCTS) on board the Advanced Earth Observing Satellite (ADEOS). This phenomenon is well simulated with a numerical ecosystem model coupled with a hydrodynamic model. The hydrodynamic model is the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model (MOM). The ecosystem model consists of five components: dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), phytoplankton, zooplankton and detritus. Results of the numerical ecosystem model suggest that the mesoscale development of the spring bloom in the Sea of Japan is related to that of sea water temperature, and that the bloom is limited by the depletion of DIN. This revised version was published online in August 2006 with corrections to the Cover Date.