Finding of the Hydromedusa Hydractinia minima (Trinci, 1903) (Cnidaria: Hydrozoa: Hydractiniidae) in Peter the Great Bay, Sea of Japan

The first finding of the hydromedusa Hydractinia minima (Trinci, 1903) in plankton of Peter the Great Bay (Sea of Japan) is reported. The hydromedusae are 0.24–0.51 mm in bell diameter and 0.25–0.53 mm in height. The size characteristics of the nematocysts of this species (desmonemes and microbasic euryteles) are given. H. minima is present in the plankton of Peter the Great Bay from June through October at water temperatures of 16.4 to 22°C with the highest mean monthly density of 151 ind./m³. The finding of H. minima in Peter the Great Bay extends the area of this species in the North Pacific to the low-boreal subzone.Original Russian Text Copyright © 2005 by Biologiya Morya, Chaplygina, Dautova.     

Peculiarities of reproductive biology and larval development of the red king crab <Emphasis Type="Italic">Paralithodes camtschaticus</Emphasis> in Peter the Great Bay,Sea of Japan

Based on materials from trawling (2002–2005) and plankton (2004–2006) surveys, some problems of the reproduction biology of the red king crab Paralithodes camtschaticus (Tilesius, 1815) population from Peter the Great Bay are considered. It was shown that the width of the carapace varied from 105 to 190 mm in female red king crabs with eggs; 50% of the females reached maturity with a carapace width of 112.8 mm. The average individual absolute fecundity of females was 200000 (114000–296000) eggs. A direct linear correlation between fecundity and female carapace width was recorded. The zoeas I–IV of the red king crab occurred in the plankton from the middle of April up to the end of the second decade of May at water temperatures from 2.8 up to 9.3°C. The periods of larval occurrence in plankton in various years correlated with the water temperature, with a temperature decrease, the duration of the pelagic period increased. No direct correlation was revealed between the phytoplankton bloom and larval release. The density of red king crab larvae in Peter the Great Bay did not exceed 0.02–13.3 spec./m³. The maximum concentration of zoeas was recorded in the central part of Ussuriysky Bay.     

Seasonal and interannual dynamics of larval abundance of <Emphasis Type="Italic">Mytilus coruscus</Emphasis> Gould, 1861 (Bivalvia: Mytilidae) in Amursky Bay (Peter the Great Bay,Sea of Japan)

Based on an analysis of the gonads, as well as the size composition and abundance of larvae in plankton, we determined the seasonal and long-term dynamics of the reproduction of the mussel Mytilus coruscus in Amursky Bay (Peter the Great Bay, Sea of Japan). Mussel gonads were in a mature condition in late July-early August; the spawning season continued from mid-August to mid-September. The larvae of this species occurred in plankton from June to September, under surface water temperatures of 14.5–23.5°C. The density of larvae in different years varied from 350 to 4500 ind/m³. Two peaks of larval abundance were observed annually, in June and September. The first peak was apparently provided by allochthonous larvae, the second, by larvae of the local population. The high density of larvae of M. coruscus in the plankton of Peter the Great Bay enabled us to consider this species as a potential object for mariculture.     

Composition of the zooplankton community, with emphasis in copepods, in Punta Morales, Golfo De Nicoya, Costa Rica

The composition of the mesozooplanktonic community was studied in the Punta Morales estuary, Gulf of Nicoya, Pacific coast of Costa Rica, during 1997. Oblique plankton hauls were performed during high and low tide using a 280 microm mesh screen net equipped with a flowmeter. The community was characterized by holoplanktonic and meroplanktonic organisms. For the holoplanktonic community, the main groups were copepods (80%) and chaetognaths (16%). The most abundant species were the copepods Acartia lilljeborgii and Paracalanus parvus. A. lilljeborgii is a typical estuarine species that maintains high populations in estuarine systems. Meroplankton was represented mainly by crustacean larvae (66%), and icthyoplankton (18%). The dominance of crustacean larvae and icthyoplankton is an evidence of the ecological importance of the Punta Morales zone.     

春季长江口邻近外海网采浮游生物的生物量谱

对2005年春季黄海南部、东海北部近江口外海水域网采的浮游生物个体大小的粒径分布进行研究,确定各粒级大小的功能群组成,建立此季该调查水域网采浮游生物的生物量谱.样品是用小、中、大型浮游生物网(网孔径为77、160、 505μm)采集所得.三网具采集浮游生物个体大小粒径是连续的,其中浮游植物,其等效粒径(ESD)和含碳量范围分别为5～250μm、15pg～146ng;浮游动物,含碳量范围为115ng～7.5mg,ESD分别为120μm～5.8mm、200μm～2cm.所得网采浮游生物的标准生物量谱,总测区的斜率为-0.607±0.059、截距为19.45±0.46;各站位的生物量谱斜率为-0.889～-0.455、截距为12.866～16.863,两特征参数分布规律为南高北低,且具有显著的站位间差异.相关性分析表明截距和回归系数与粒级多样性有关.     

Stomach contents of the Antarctic Silverfish Pleuragramma antarcticum from the southern and eastern Weddell Sea (Antarctica)

Summary The stomach contents of 142 Pleuragramma antarcticum from the southernmost part of the Weddell Sea (Gould Bay: 77°19S) and from the eastern coast (72°–74°S) were analyzed. The fish were collected in February 1983 and stored frozen. Size range of the investigated specimens was from 6.4 cm SL (7.3 cm TL) to 21.9 cm SL (24.1 cm TL). The fish were caught by bottom trawl (Gould Bay) and Agassiz Trawl and pelagic RMT-m net in the upper 300 m layer at the eastern coast, respectively. Thirty-six stomachs were empty or contained sand only. The most important prey in terms of biomass were euphausiids, which occurred in 49 stomachs at a mean number of 2. Their dry weight was estimated to be 15–50 times that of the next important food items, which were copepods, gastropods and gammarids. Krill (Euphausia superba) constituted up to 14% of the euphausiids in the diet of fish caught in the eastern Weddell Sea. The rest was usually made up by Euphausia crystallorophias. This species was taken with preference even when the abundance of E. superba in accompanying plankton catches was 16 times higher. In the Gould Bay, gastropods were frequently eaten despite high numbers of copepods in the plankton, whereas in the eastern Weddell Sea, copepods were abundant both in plankton and in the stomach content. The almost complete absence of the early stages of fish in the diet of Pleuragramma antarcticum in the southern and eastern Weddell Sea is due to a pronounced vertical segregation of fish of different sizes. This distribution pattern is thought to be an adaptive mechanism to avoid intraspecific predation, as 90% of the ichthyoplankton in that area is Pleuragramma antarcticum.     

Density Dynamics and Size Composition of Bivalve Mollusk Larvae of the Genus Mya in Peter the Great Bay (Sea of Japan)

The seasonal population size of planktonic larvae of mollusks of the soft-shell clam genus Mya were studied in Vostok Bay. The larvae occurred in plankton from the first third of June to early September. The highest density of larvae (279.7 ± 98.7 specimens/m³) was found in late June. In early July, larval numbers decreased sharply, and at the end of the first third of July, only single Mya larvae were found in the plankton. Another increase in larval population was observed in early and late August. The larvae varied in length from 175 to 325 m in June–July and from 150 to 250 m in August. It is likely that the larvae of two species of Mya, M. arenaria and M. uzenensis, are present in the plankton of Vostok Bay.     

Pelagic larvae of the bivalves of Ussuriysky Bay, Sea of Japan

Based on materials of plankton surveying carried out in May–October 2008, the species composition, distribution, and density of pelagic larvae of bivalves of the Ussuriysky Bay (Peter the Great Bay, Sea of Japan) were studied. Larvae of 66 taxa were revealed and identified. The Bivalvia larvae occurred in the plankton during the entire period of study. Two areas, the inner and open part of the bay, which vary in the composition, concentration, and terms of larva occurrence in the plankton were distinguished. The larvae of Mytilus coruscus, Mactra chinensis, Modiolus kurilensis, Ruditapes philippinarum, Mya uzenensis and Teredo navalis were the most numerous and widespread. It was shown that despite high taxonomic diversity, the density of Bivalvia larvae in the Ussuriysky Bay was an order of magnitude lower, even in terms of their maximum number, than in other studied areas of the Peter the Great Bay.     

A comparison of marine planktonic and sediment core diatoms in Hong Kong with emphasis on Pseudo-nitzschia

Potentially toxic diatoms belonging to the genus Pseudo-nitzschia were observed for the first time in plankton samples from Hong Kong collected in 1996. To determine whether potentially toxic diatoms had become more common during the last six decades, three gravity cores were taken from the anaerobic sediments of Kowloon Bay in Victoria Harbour. Anaerobic sediments are thought to be ideal for palaeoecological reconstructions because their vertical stratigraphy is undisturbed by bioturbidation. Analysis of the Kowloon Bay sediment cores indicated that very few individual diatoms belonged to the genus Pseudo-nitzschia, even though Pseudo-nitzschia was found in abundance in many of the plankton samples taken from a nearby site. The relative absence of Pseudo-nitzschia frustules was interpreted as indicating that these thin walled, poorly silicified, planktonic diatoms failed to preserve in the saline (32–34‰), slightly alkaline (pH 7.6–7.8), anaerobic sediments of Kowloon Bay. Dissolution of thinly silicified diatoms rather than predation was believed to be the reason for their virtual absence in the core. The anaerobic conditions near the bottom of Kowloon Bay and the shallowness of the Bay, 12 m, makes predation an unlikely explanation. Diatom abundance declined in the sediment cores below a depth of 15 cm (ca 1955). This was attributed to the decrease in nutrient loading to Victoria Harbour prior to 1955 rather than enhance diatom dissolution in the deeper sediments. Benthic diatoms became proportionately more abundant below the15 cm core depth. This revised version was published online in August 2006 with corrections to the Cover Date.     

Long-term study of zooplankton in the estuarine system of Ribeira Bay,near a power plant (Rio de Janeiro,Brazil)

The structure of the zooplankton community in an estuary adjacent to the Admiral álvaro Alberto Nuclear Power Plant at Angra dos Reis, state of Rio de Janeiro, Brazil was studied from 2001 through 2005. At that time, the power plant had been operating for 20 years. The results were compared with a previous study in 1991–1993. The zooplankton was sampled 4 times a year, in vertical hauls using a 150 μm net, at two fixed points near the plant’s intake and discharge sites. Temperature, salinity, and chlorophyll a were measured. The water of Ribeira Bay is warm, with salinities typical of Coastal Water and more saline waters. Zooplankton density at the discharge site (Mean: 245,434 ind m⁻³, SD: 335,358 ind m⁻³) was higher than that at the intake site (Mean: 84,634 ind m⁻³, SD: 101,409 ind m⁻³). A total of 121 mesozooplankton taxa were recorded from 2001 to 2005. Copepoda constituted the most common taxon and comprised more than 57% of the total zooplankton, followed by cladocers and gastropod larvae. A seasonal zooplankton cycle was observed only during 2004; in other years, the plankton varied only between years. Overall mesozooplankton abundance at the discharge site was similar to levels reported from the inner zone of this estuary in 1991–1993. Surface temperature was the important factor structuring the zooplankton community at the discharge site. No effect on the mesozooplankton by passage through the condensers could be discerned, and no permanent negative influence on the plankton populations could be detected. Guest editors: U. M. Azeiteiro, I. Jenkinson & M. J. Pereira Plankton Studies     

Zooplankton in the Vychegda River

The species composition of plankton invertebrates was studied in the middle Vychegda River (the main tributary of the Northern Dvina River) in 2003–2005. A list of planktonic rotifers and lower crustaceans was made. The dominating complexes of zooplankton organisms were found. The quantitative characteristics of plankton communities in the river were described.     

Seasonal changes of macrozooplankton and Benthic Boundary Layer macrofauna from the Bay of Saint-Brieuc (western English Channel)

The macrozooplankton and Benthic Boundary Layer (BBL) macrofauna over a coarse sand and pebble community in the Bay of Saint-Brieuc (western English Channel) were sampled with a WP2 zooplankton net and with a modified MACER-GIROQ suprabenthic sledge, respectively, from February 1994 to November 1995. One hundred and sixty-four species were collected in 44 suprabenthic sledge hauls and 19 taxa in 30 zooplankton net hauls. In the water column, appendicularians and cnidarians dominated, while, in the BBL, holoplanktonic amphipods, chaetognaths, amphipods and mysids dominated the fauna; among them Apherusa spp., Sagitta setosa Muller, Anchialina agilis (Sars), Sirella clausii Sars and Eusirus longipes Boeck were the dominant species. The density and biomass of the BBL macrozooplankton were lower than those of the macrozooplankton in the water column. The density and biomass of suprabenthos remained a low throughout the year. In the water column, density and biomass of macrozooplankton showed a maximum in spring and remained low from autumn to winter; conversely, in the BBL, the density and biomass of both macrozooplankton and suprabenthos were higher from summer to autumn. The change in abundance of both BBL and pelagic taxa was seasonal. Some species were primarily sampled in the water column (appendicularians, cladocerans and cnidarians), while others were preferentially found at the BBL (suprabenthic species, holoplanktonic amphipods and cephalopods). A third group was collected throughout the water column (chaetognaths and fish larvae).      

The abundance cycle and influence factors on red tide phenomena of Noctiluca scintillans (Dinophyceae) in Dapeng Bay, the South China Sea

The seasonal occurrence of Noctiluca scintillans and the causativemechanisms of red tide phenomena were investigated in the northwesternpart of Dapeng Bay, the South China Sea, from March 1990 toJune 1992. It occurred in the plankton usually from Januarythrough May/June with peak abundance from March to early May.At least eight red tides of this organism, when the surfacewater was covered with the pink patches and slicks, were observedduring the investigation period, and all of them took placebetween March and early May. Noctiluca occurred at temperaturesfrom 15.8 to 2.8.6°C, and the population density was thehighest at temperatures between 19 and 25°C. It disappearedfrom the plankton in summer and fall when the temperature warmedto lethal level of     

Carbon isotope ratio and photosynthetic activity of phytoplankton in the eutrophic Mikawa Bay,Japan

Primary production by phytoplankton in the eutrophic Mikawa Bay, Japan, was studied by simultaneous measurements of natural carbon isotope ratio (δ ¹³C) and short-term carbon uptake rates (¹³C tracer study) of size-fractionated nannoplankton (<10 μm) and net plankton (>10 μm) samples. Short-term photosynthetic rates, which represent the physiological state of algae, were variable regardless of standing stock sizes. Theδ ¹³C values of particulate organic carbon (POC) in June and July displayed horizontal variations for both the net plankton fraction (−19.8 to −12.7‰) and the nannoplankton fraction (−22.0 to −12.8‰). For both fractions, low concentrations of POC had more negativeδ ¹³C values (−22 to −18‰). Highδ ¹³C values for the net plankton were found when POC concentrations were much higher, due to red tide. This suggests that the increase in algal standing crop for the net plankton fraction resulted from accelerated photosynthetic activity. However the nannoplankton fractions with higher POC values have relatively lowδ ¹³C values.     

Labelling patterns of carbon-14 in net plankton during a winter-spring bloom

Weekly surface samples were collected in lower Narragansett Bay, Rhode Island, during the 1975 winter-spring bloom and fractionated by nets to nannoplankton (<20 μm) and total (< 158 μm) size fractions. Each size fraction was assayed for paniculate carbon, nitrogen, carbohydrate, protein, chlorophyll a, and cell counts. The <20 μm values were subtracted from the <158 μm values to estimate the composition of the 20 μm to 158 μm fraction (termed net plankton). As nutrients (primarily nitrogen) decreased to undetectable levels with the culmination of the diatom bloom, the ratios of protein/carbohydrate, carbohydrate/carbon, and carbon/chlorophyll a in the net plankton indicated the diatom population was increasingly nutrient-limited. Each size fraction was also incubated at a saturating light intensity with carbon-14; following filtration, the cells were extracted with solvents to obtain labelled polysaccharide and protein. The daily rates of polysaccharide and protein synthesis in the net plankton declined as the bloom entered the stationary phase. When the diatom population was at its maximum density the majority of the carbon-14 was found in the ethanol-soluble fraction; this may be due to high light intensities or nutrient effects.     

Assessment of the Neva Estuary ecosystem state on the basis of structural characteristics of benthic animal communities in 1994–2005

In the years 1994–2005, the values of the integrated index IP’ at some stations of the Neva Bay changed from 38.1 to 81.9%, water quality changed from class 3 to class 5, and the states of some areas of the ecosystem that were evaluated as “tense” went to “catastrophic.” The integrated mean assessment of water quality according to the IP’ index over the entire Neva Bay throughout 12 years (1994–2005) remained relatively stable, waters were assessed as “polluted” (fourth class), and the state of the ecosystem was considered “critical.” The state of the eastern part of the Gulf of Finland in 1994–2005 was less favorable. The species diversity of zoobenthos in the resort zone of the eastern part of the Gulf of Finland is considerably lower than in the Neva Bay. Waters of the resort zone of the eastern part of the Gulf of Finland in 1994–2005 were assessed as one class lower than in the Neva Bay, i.e., as “polluted-dirty” (fourth-fifth class), and the state of the ecosystem was assessed as being in a “crisis.” In the resort zone, there was a decline in species diversity and abundance and biomass of benthic animals; i.e., all characteristics of the degradation of benthic animal communities were observed.