Number Of Zooplankton Species Research Articles

Zooplankton Composition in Super-Intensive Whiteleg Shrimp, Litopenaeus vannamei (Boone, 1931) Culture Tanks

This study aimed to determine the zooplankton species composition in super-intensive whiteleg shrimp, Litopenaeus vannamei (Boone, 1931) tanks. The research was conducted from January to May 2021 in Bac Lieu City, Bac Lieu province, Vietnam. Eleven sampling times were divided into two periods, the nursery phase (six times) and the grow-out phase (five times) of shrimp culture. The results showed that water quality parameters fluctuated dramatically during the culture period, in which some nutrient concentrations tended to increase at the end of the shrimp culture period. Nine zooplankton species were recorded, of which five species belonged to Protozoa, three Rotifera species, and one Copepoda species. The number of zooplankton species did not differ significantly among the sampling periods. Protozoa had the highest species composition and density during most of the shrimp culture period. Copepoda was only identified in the nursery stage of shrimp culture. The species component of zooplankton had a close positive correlation with temperature, but their abundance did not have a significant relationship with water quality parameters because each species was affected by the different water quality parameters. Zoothamnium sp. had significantly positive correlations with total ammonia nitrogen (TAN), nitrate (NO3)-, total phosphorus (TP), and total nitrogen (TN) concentrations. The rotifer Brachionus plicatilis had a strong relationship with TP content, whereas Dartintinnus alderae had a strong relationship with alkalinity. Protozoa dominance in shrimp tanks could affect shrimp growth, decreasing the economic efficiency of shrimp farming. Therefore, the results of this study contribute to water quality and natural food management to improve shrimp productivity.

How Do Specific Environmental Conditions in Canals Affect the Structure and Variability of the Zooplankton Community?

The present study investigates the responses of zooplankton (including changes in their structure and diversity) to physicochemical and biological parameters in two artificial waterways. Water samples were collected monthly from the Bydgoszcz Canal, the Noteć Canal, and the Brda River during the growing season of April–October 2019. We analyzed how selected parameters (including water temperature, Secchi disk visibility, oxygen concentration, conductivity, and pH, as well as nitrate, phosphate, and chl-a concentrations) affected seasonal variations in zooplankton diversity (T) and density (N). In total, we recorded 98 species, and average zooplankton density was 320 ind/L. At all sites, the same zooplankton species were dominant: Keratella cochlearis among rotifers and the Cladocera Bosmina longirostris among crustaceans. Rotifers dominated qualitatively and quantitatively over crustaceans. Zooplankton density and biomass, as well as the number of zooplankton species, were higher in the Bydgoszcz Canal than in the Brda River or the Noteć Canal. This may be connected to the locks on the Bydgoszcz Canal slowing down water flow, thereby increasing macrophyte vegetation, which creates ecological niches supporting zooplankton development.

Zooplankton community structure and influencing factors in Weihe River mainstem and its tributaries from the northern foot of Qinling Mountains

浮游动物作为食物链中重要的初级消费者，其群落结构特征是水生态系统健康评价的重要指标之一. 本研究于2017年秋季和2018年春季对渭河干流及秦岭北麓五条典型支流开展了系统的水环境及浮游动物群落调查. 结果表明，渭河干流营养盐浓度整体高于秦岭北麓支流，干流浊度远高于支流. 两次调查共鉴定出浮游动物种类数136种(原生动物65种，轮虫44种，枝角类15种，桡足类12种)，其中2017年秋季渭河干流浮游动物种类数、密度和生物量分别为14种、9.02 ind./L和0.0051 mg/L，秦岭北麓支流为37种、42.78 ind./L和0.0229 mg/L；2018年春季渭河干流浮游动物种类数、密度和生物量分别为52种、292.89 ind./L和0.1734 mg/L，秦岭北麓支流为68种、70.15 ind./L和0.0508 mg/L. 秋季渭河干流下游浮游动物种类数、密度和生物量最低，而春季随上、中、下游三者均依次增大；秋季秦岭支流中罗敷河浮游动物密度和生物量最高，而春季灞河最高. 春、秋两季干支流间浮游动物优势种差异较小，但秋季优势种种类数少于春季. 秋季渭河干流中游Shannon-Wiener指数、物种丰富度指数和物种均匀度指数最高，而春季下游最高；秋季秦岭北麓支流石堤河3个指数均最高，而春季灞河Shannon-Wiener指数和物种均匀度指数最高，石堤河物种丰富度指数最高. 典范对应分析表明渭河干流与秦岭北麓支流浮游动物群落结构主导因素均存在季节差异. 本研究揭示了渭河干流与秦岭北麓典型支流的浮游动物群落特征及其影响因素，可为渭河流域环境监测和生态保护提供数据支撑.;Zooplankton is an important primary consumer in the food chain, and its community structure is one of the important indicators for the health evaluation of aquatic ecosystems. A systematic survey of water environment and zooplankton was carried out in the Weihe River mainstem and its five tributaries from the northern Qinling Mountains during autumn 2017 and spring 2018. The nutrient concentrations of the Weihe River mainstem were higher than those of the five tributaries, while turbidity of the mainstem was 10-100 times higher than those of the tributaries. A total of 136 species of zooplankton (65 species of protozoa, 44 species of rotifers, 15 species of cladocerans, and 12 species of copepods) were identified in the two surveys. Among them, the number, density and biomass of zooplankton in the mainstem of the Weihe River mainstem in autumn 2017 were 14 species, 9.02 ind./L and 0.0051 mg/L, while tributaries were 37 species, 42.78 ind./L and 0.0229 mg/L, respectively. The number of species, density and biomass of zooplankton in the Weihe River mainstem in spring 2018 were 52 species, 292.89 ind./L and 0.1734 mg/L, while tributaries were 68 species, 70.15 ind./L and 0.0508 mg/L, respectively. In autumn, the number of zooplankton species, density and biomass in the lower reaches of the Weihe River mainstem were the lowest, while those increasing in the rank from upper, middle, to lower reaches of the Weihe River mainstem in spring. The density and biomass of zooplankton in the Luofu River were the highest in autumn, and those in the Bahe River highest in spring. The difference in dominant species of zooplankton between the trunk and tributaries of spring and autumn is relatively small, but the number of dominant species in autumn is less than that in spring. Canonical correspondence analysis revealed seasonal variance in the dominant factors of the zooplankton community structure in the Weihe River mainstem and the five tributaries. This study not only revealed the correlation between zooplankton community structure and environmental factors in the Weihe River mainstem and its five tributaries, but also provided key data for environmental monitoring and ecological protection in the Weihe River Basin.

Short Communication: Zooplankton as indicator of trophic status of lakes in Ilmen State Reserve, Russia

Abstract. Mashkova IV, Kostryukova AM, Shchelkanova EE, Trofimenko VV. 2021. Short Communication: Zooplankton as indicator of trophic status of lakes in Ilmen State Reserve, Russia. Biodiversitas 22: 1448-1455. Zooplankton is a potentially powerful tool for assessing the trophic state of aquatic ecosystems. The current paper studied taxonomic composition and biomass of zooplankton communities in ten lakes within Ilmen State Reserve, Chelyabinsk region, Russia and identified the influence of trophic status on its formation. Integrated samples were taken from epilimnion in the summer of 2016-2019. Several criteria were used to determine trophic status: the taxonomic structure and biomass of zooplankton; some hydroecological indicators some hydroecological indicators and the Carlson index. The trophic status of the studied lakes, determined based on the zooplankton biomass, revealed that most of the lakes were in the status of mesotrophic. The number of zooplankton species in the lakes was 44 with Pleuroxus laevis, Bosmina longirostris, Simocephalus vetulus were the most numerous species in mesotrophic lakes; while Chaetonotus ploenensis, Keratella quadrata frenzeli, Leptodora kindti are rare. Zooplankton communities of Bolshoye Miassovo and Maloye Miassovo Lakes were characterized by high species diversity and considered as one of the most significant among the foothill lakes of the eastern slope of South Ural. The study reveals that hydroecological assessment of the ecological status is not exactly precise, as values are not stable and can change not only under the anthropogenic influence but also due to many natural abiotic environmental factors. The research shows that species composition and biomass of zooplankton communities could provide a more accurate assessment of the trophic status of water-bodies.

Influence of trophic status on zooplankton structure in Chelyabinsk region lakes (Russia)

Eutrophication of water-bodies, as well as lakes, is currently one of the crucial problems of both theoretical and applied ecology. Zooplankton is sensitive to changes in the ecological state of different types of reservoirs. The article analyses differences and similarities of zooplankton communities in 10 lakes of Kisegach - Miassovo hydrological system of Chelyabinsk region (Russia). The current research aims at identifying taxonomic structure of zooplankton communities of the lakes in Chelyabinsk region (Russia) and stating the influence of some abiotic factors on its formation. Integrated samples were gathered in summer 2015 - 2019. The given paper studied the correlation of the main taxonomic groups of zooplankton, marked a regular decrease in the number of zooplankton species under adverse environment. When the trophic level of water in natural fresh lakes changes in the direction of oligotrophic-mesotrophic-eutrophic, the total number of zooplankton decreases from 400.90 individuals per L−1 to 106.06 individuals per L−1. In the same direction, the number of Cladocera representatives decreases (from 362.03 individuals per L−1 to 66.34 individuals per L−1) and the number of Copepoda representatives decreases (from 34.01 individuals per L 12.67 individuals per L−1), and the number of Rotifera representatives increases (from 6.97 individuals per L−1 to 26.60 individuals per L−1).

Fisheries research of the Pyasina river basin

At the end of April 2020, the largest man — made disaster in the Russian Arctic occurred-a diesel fuel spill in Norilsk. Oil products on the Ambarnaya river got to the lake. Pyasino (source of the river of the same name). To determine the extent of damage to the aquatic ecosystem of the Pyasina basin, it is necessary to know the nature and direction of previous research in the fisheries field. The aim of the work is to analyze the available open source publications in the field of fisheries research in the Pyasina basin. The history of ichthyological and hydrobiological studies of the Pyasina river basin (a large watercourse on the Taimyr Peninsula) is considered. Information is provided that the basin of this river is poorly studied in terms of fisheries due to its location beyond the Arctic circle. The chronology of fisheries research from the Foundation of the Yenisei ichthyological laboratory (Krasnoyarsk) in 1908 to 2020 is given. It is noted that the greatest interest in studying the basin of this river is shown in connection with the development of the Norilsk mining and metallurgical combine and the organization of the Federal state budgetary institution «United Directorate of Taimyr reserves». The role of individual scientific organizations in the study of water ecosystems of the Pyasina river basin is shown. The most significant contribution to the fisheries survey of the river basin was made by the Siberian scientific fisheries station (now the Krasnoyarsk branch of the all-Russian research Institute of fisheries and Oceanography), MSU, TSU. The publications of employees of these organizations contain materials on the study of phytoplankton and zooplankton, zoobenthos, their production characteristics, the biology of a number of species, the Stingray of larvae, features of the development of semi-passable ichthyofauna, materials on the genetic features of individual populations of whitefish, biological and morphological features of whitefish and char fauna, fish Parasitology, the content of polyunsaturated fatty acids, and others. Information is provided on the number of zooplankton species and forms, including 28 forms. It is shown that the composition of the ichthyofauna of the river basin to date, 38 species of fish are known.

Thành phần động vật phù du ở sông Cái Lớn huyện U Minh Thượng, tỉnh Kiên Giang

The objective of this study is to determine the diversity of zooplankton on Cai Lon river of U Minh Thuong district, Kien Giang province. The study was conducted in the period from February, 2017 to August, 2017. Zooplankton samples were collected at 6 times, of which 3 times were in the dry season, and 3 times were in the rainy season at six sites along the main river. The results showed that recorded 105 zooplankton species. The number of zooplankton species was highly variable according to the sampling season, from 71 in the rainy season to 95 in the dry season. Among them, Rotifera was the most abundant group with 47 species (44.8 %), followed by Copepoda with 23 species (21.9 %). In the study period, zooplankton density in Cai Lon river was at high levels, ranging from 14,167 to 62,000 individuals/m3.

Aquatic AQUATIC INVERTEBRATE FAUNA OF SONG THANH NATURE RESERVE IN QUANG NAM PROVINCE, VIETNAM

The study analyzed the composition of the aquatic invertebrate fauna of Song Thanh Nature Reserve in Quang Nam province of Vietnam. There were 48 qualitatively and 48 qualitative samples were collected at 12 sitesby plankton net for the zooplankton (plankton net No 52 for qualitative samples and plankton net No 57 for quantative samples), but with zoobenthos, using PondNet for the qualitative samples and Subber Net (50 cm x 50 cm, mesh size 0,2mm) for quantative samples. This investigation was realized in March and September 2015. As a result, a total of 166 species belonging to two groups, the zooplankton group has 12 species, 11 genera, 9 families, 3 ordes, 2 classes and the zoobenthos group has 154 species, 120 genera, 59 families, 13 orders,4classes. The most richness class is insecta with 141 species, 109 genera, 52 families, 9 orders. Moreover, pH is the environmental parameter that has more effective than others on zoobenthos group both in dry and rainy seasons; whereas, turbidity and total dissolved solids are two factors that effectmore strongly than others on zooplankton group. The number of zooplankton species in dry season is lower than in rainy season and in contrast with zoobenthos species. The species of Crustacea and Bivalvia classes are invisible in the dry season, they only appear the species that belong to insecta and Gastropoda classes.
 Keyword: aquatic invertebrate, fauna, Song Thanh, Nature Reserve, Vietnam

Optimal Monitoring Frequency Estimation Using Confidence Intervals for the Temporal Model of a Zooplankton Species Number Based on Operational Taxonomic Units at the Tongyoung Marine Science Station

Temporal changes in the number of zooplankton species are important information for understanding basic characteristics and species diversity in marine ecosystems. The aim of the present study was to estimate the optimal monitoring frequency (OMF) to guarantee and predict the minimum number of species occurrences for studies concerning marine ecosystems. The OMF is estimated using the temporal number of zooplankton species through bi-weekly monitoring of zooplankton species data according to operational taxonomic units in the Tongyoung coastal sea. The optimal model comprises two terms, a constant (optimal mean) and a cosine function with a one-year period. The confidence interval (CI) range of the model with monitoring frequency was estimated using a bootstrap method. The CI range was used as a reference to estimate the optimal monitoring frequency. In general, the minimum monitoring frequency (numbers per year) directly depends on the target (acceptable) estimation error. When the acceptable error (range of the CI) increases, the monitoring frequency decreases because the large acceptable error signals a rough estimation. If the acceptable error (unit: number value) of the number of the zooplankton species is set to 3, the minimum monitoring frequency (times per year) is 24. The residual distribution of the model followed a normal distribution. This model can be applied for the estimation of the minimal monitoring frequency that satisfies the target error bounds, as this model provides an estimation of the error of the zooplankton species numbers with monitoring frequencies.

Community structure of zooplankton and trophic status of some inland reservoirs in the low country intermediate zone of Sri Lanka

Diversity and abundance of zooplankton in relation to nitrate–N and total phosphorus levels of 20 minor and medium scale reservoirs in the low country intermediate zone of Sri Lanka were studied in June-October 2013. Total phosphorus content ranged from 0.029 mg L -1 recorded in Wendaruwewa reservoir to 0.529 mg L -1 recorded in Karangamuwa reservoir and Nitrate-N content varied from 1.186 mg L -1 recorded in Adukkane reservoir to 5.625 mg L -1 recorded in Anukkane reservoir indicating that all reservoirs studied are eutrophic. During the present study, a total of 43 species of zooplankton, comprising 31 species of rotifers, 9 species of cladocerans and 3 species of copepods were recorded. Number of zooplankton species in any one reservoir, which ranged from 4 to 13, was significantly correlated with the nitrate-N content (p Diacyclops nanus, which was present in 15 reservoirs. Abundance of zooplankton ranged from 4 individuals L -1 recorded for Alona monocantha and Chydorus parvus in Wendaruwewa and Metiyagane reservoirs respectively to 1017 individuals L -1 recorded for Filinia terminalis in Galewela reservoir. Margalef index which ranged from 0.532 in Adukkane reservoir to 2.096 in Dewahuwa reservoir, was significantly correlated with nitrate-N content of water (p 0.05). Keratella quadrata was present only in Anukkane reservoir where the nitrate-N content was the highest and therefore it may be considered as a bio-indicator of high levels of nitrate-N. Eutrophic conditions of theses reservoirs may possibly be due to runoff of nutrients from agricultural fields as these are located in an intense agricultural area. Therefore, it is necessary to take immediate action to control the overuse of inorganic fertilizer in this area so that contamination of water bodies with nutrients can be minimized.

Rotifer Invasion? On Appearance and Abundance of Tropical Species in Lakes of North-Eastern Poland

ABSTRACT: Trichocerca simoneae De Smet described in 1989 has since been found in tropical and subtropical areas, but was not recorded in Poland before World War II. A bibliography of Polish rotifers by Wiszniewski (1953), although very comprehensive, does not refer to T. simoneae. However, in the studies of plankton of the dystrophic lake, i.e. humic one with water rich in humic acids, acidic pH and brown coloured, carried out in the years 1998–2000, the species dominated. Here, studies in 39 small, inter-forest lakes of north-eastern Poland revealed T. simoneae in 15 of them, often at high densities, up to ca 6000 ind L-1. The possible reasons for this ‘invasion’ are: (1) zooplankton communities in dystrophic lakes are unsaturated with biotic interactions too weak to exclude invaders; CCA and RDA analyses showed that T. simoneae preferred habitats with low number of zooplankton species of low density and dystrophic lakes seem to offer such habitats; (2) long-term deposition of rotifer resting eggs is pro...

Community characteristics and of zooplankton in Qinzhou Bay

Qinzhou Bay, the biggest bay in Guangxi Province, is very species-rich and is developing a robust marine economy. In recent years, as human impact has increased, problems associated with the environment have become more complicated. Measuring zooplankton diversity and abundance is a way to monitor environmental conditions. According to the data from four ecological surveys of the zooplankton in Qinzhou Bay during 2008 and 2009, a total of 134 species of zooplankton were identified, including 52 Copepoda species, 27 Medusa species, 14 Planktonic larvae, 9 Chaetognatha species, 8 Pteropoda species, 5 Amphipoda species, 4 Cladocera species, 4 Ostracoda species, 3 Thaliacea species, 2 Appendiculata species, 2 Sergestdae species, 2 Protlsta species, 1 Rotiera species and 1 Cumacea species. The fauna was clearly characterized as tropical population. The total species number was highest in autumn, followed by spring, winter and summer. Zooplankton species diversity in Qinzhou Bay has increased compared with the results obtained in 1983–1985 (83 species). However, compared with other bays, the number of zooplankton species in Qinzhou Bay is close to Daya Bay (128), higher than in Zhilin Bay (60), Jiaozhou Bay (81) and Luoyuan Bay (70), and far lower than in the north South Sea (709). We adopted the dominant index Y>0.02 as the distinguishing standard of dominant species. The number of dominant species in spring, summer, autumn and winter were six, nine, eight and five. There was only one common dominant species (Penilia avirostris) appeared in different seasons, For summer and autumn, the shared dominant species numbered about four. Between other seasons, the shared dominant species varied between two and three. The number of uniquely dominant species was four in summer, three in autumn and one in both spring and winter. The dominant species in different seasons have some overlaps and some differences. The average biomass of zooplankton was 378mg/m3 at all times of year. The average biomass was largest in autumn, followed by winter, and was the least in spring and summer. The average density of zooplankton for the entire year was 805.11ind/m3. The average density was largest in summer, followed by winter, and was least in autumn and spring. Copepoda and Planktonic larvae were the major components of zooplankton in spring and summer at Qinzhou Bay, with the other species’ densities under 10%. In autumn, Copepoda, Planktonic larvae and Chaetognatha were the major components of the biomass, and in winter, the major species were Copepoda and Cladocera, with the others species’ density under 10%. The average value of the Shannon–Wiener diversity index (H′) was 3.84 and the evenness index (J′) was 0.77. The zooplankton diversity index and community evenness overall were good and the community organization had a complete and stable state, but the status of the community was relatively weak. The relationship between biomass/density of zooplankton and environmental factors is remarkable. Biomass and density are positively correlated with temperature and nutrient concentration, and are negatively correlated with salinity.

Long-Term Quantitative and Qualitative Changes in the Zooplankton Community of the Vistula Lagoon

ABSTRACT Paturej, E.; Gutkowska, A., and Mierzejewska, J., 2014. Long-term quantitative and qualitative changes in the zooplankton community of the Vistula Lagoon. Changes in environmental conditions, observed over time, exert a significant effect on the structure of ecosystems. The objective of this study was to determine long-term transformations in the qualitative and quantitative composition of the zooplankton community and changes in zooplankton biological diversity in the Vistula Lagoon over 30 years. Samples collected by standard methods in 2007 and 2009 were compared with those collected in 1977 and 1978 by Adamkiewicz-Chojnacka. The changes in the qualitative and quantitative structure in zooplankton were found to be statistically significant. The number of zooplankton species, abundance, and biomass were higher in studies conducted by Adamkiewicz-Chojnacka. Changes in zooplankton structure may provide a basis for estimating zooplankton biodiversity. A statistical analysis of the experimental mat...

Zooplankton of Koporskaya Bay of the Gulf of Finland in the Zone of the Influence of the Leningrad NPS

In the littoral zone of Koporskaya Bay adjacent to the discharge canals of the Leningrad NPS, the number of zooplankton species, and also their numbers and biomass, decreases, whereas the trophic structure of the community simplifies. Mainly eurythermic and euryhalinic species dominate in zooplankton. In this case, stenothermic and stenohalinic species either eliminate from the community, or their abundance essentially decreases. The structure of zooplankton changes in space.

Zooplankton composition and community structure in Lake Tiga, Kano, Nigeria

Zooplankton in Lake Tiga was identified and its community structure assessed between March 2009 and March 2011. A total of 54 species of zooplankton was recorded, comprising two species of Protozoa, 26 species of Rotifera, eight species of Copepoda, 11 species of Cladocera, four species of Ostracoda and three species of insect larvae. Species occurrence and abundance were both higher in the dry season than in the rainy season. Occurrence showed an increasing trend from the upper basin towards the lower basin (dam site) in the surface waters and a decreasing trend from the surface down to the bottom of the lake. Zooplankton abundance showed no definite pattern in its surface horizontal variation but showed a decreasing trend from the surface down to the bottom of the lake. In terms of species diversity, Rotifera had the highest number of zooplankton species, followed by Cladocera, Copepoda, Ostracoda, insect larvae and Protozoa. In terms of abundance, Rotifera again had the highest abundance value, followed by Cladocera, Copepoda, Protozoa, Ostracoda and insect larvae. Species diversity and evenness indices indicated that Lake Tiga, although not pristine, was not polluted.

Abundance and diversity of zooplankton in semi intensive prawn (Macrobrachium rosenbergii) farm.

The present study was carried out on the seasonal abundance and diversity of zooplankton in a semi- intensive prawn farm of Bagerhat district from July to December, 2008. Plankton samples were collected by conical shaped monofilament nylon net (Plankton net) and Lugol’s solution was used for preservation. The zooplankton abundance was influenced by physico-chemical factors. During the study period 11 genera of zooplankton under 5 orders were recorded from the study ponds namely Copepoda, Rotifera, Cladocera, Ostracoda and Crustacean Larvae. Among all groups copepod was the dominant order. The percentages of Copepoda, Rotifera, Cladocera, Ostracoda and Crustacean Larvae in semi-intensive culture system were 54%, 28%, 12%, 4% and 2% respectively. But the genera Brachionus under the order of Rotifer was dominant among all other genera. Cyclops and Helidiaptomus under the order of Copepod were the 2nd dominant genera. Numbers of zooplankton species were recorded to be the highest in summer season and minimum at early winter season. Highest number of zooplankton found at the month of October. Total zooplankton shows significant positive relationship with water temperature ((r = +0.384), Dissolve Oxygen(r = +0.113), pH(r = +0.320), Free CO2 (r = +0.319), Alkalinity(r = +0.269), Hardness (r = +0.402) and negative relationship with Salinity(r = -0.486), Transparency(r = -0.693). The findings of the present study will help to improve the management strategies of shrimp culture system.

Is the mass emergence of Themisto libellula in the northern Bering Sea an invasion or a bloom?

The mass occurrence of the large hyperiid Themisto libellula was recorded in both the western and the eastern Bering Sea within 2007–2011. Those were the years of a relatively long 6-year period of cold, which was caused mainly by the inflow of cold waters from the north; this is confirmed by the distribution of bottom and surface temperatures and also by the ice-cover values. This hyperiid became dominant in the diet of salmon, walleye pollock, herring, and several other nekton fish species. T. libellula periodically spreads southward with cold northern waters, finding favorable conditions in “new” areas. Being a rapidly growing species with a short life cycle, within 1 or 2 years it reaches a high abundance, which then gradually declines and remains at a mean or low level, as usually occurs with species that were introduced into a new habitat. After the environmental conditions deteriorate, as a “warm” period arrives with changes in the general circulation and a growing inflow of warmed Pacific waters, the southern boundary of the species range moves back far northward and it completely disappears in the areas where it prevailed in the plankton and was a main forage item in the diet of many fish species. Taking into account the durations of warm and cold periods from 1980 until 2010, an event like this in the Bering Sea can be expected within 1 or 2 years. In the eastern Bering Sea, the abundance and dominance of a number of zooplankton species may vary simultaneously. This effect is more pronounced in T. libellula and for this reason the species is considered as a biological indicator of the described climatic changes in the Bering Sea.

Effect of repeated partial cropping on population dynamics and yield of Oreochromis niloticus (L.) during polyculture with Heterobranchus longifilis (Val.)

The effect of repeated cropping of half the number of young and large adults on productivity and dynamics of Oreochromis niloticus was investigated during polyculture with Heterobranchus longifilis. Mixed-sex, large-sized and young adult tilapia of 841±0.3 g and 841±0.23 g were cultured with 40 catfish fingerlings in triplicate 36 m2 earthen ponds in 1 and 2 treatments respectively. At the 4th, 6th, 12th, 26th and 32nd week, cropping was done in treatment 2 and the weights of the crop were used to enrich supplementary feed, by displacing an equal weight of ingredients in treatment 1. Realized supplementary feed crude protein level was 12.9 and 18.3±5% in treatments 1 and 2 respectively. Feeding was at 1% body weight thrice daily. Weight data were analyzed with ANOVA and t-test. Surplus production of O. niloticus from treatment 2, calculated as sum of periodic harvest + final harvest minus final harvest in treatment 1, was 249±25 g per week. Treatment 2 had significantly higher H. longifilis harvest mean weight and growth rate (percentage per day) (p<0.01), with densities (p<0.05). It also has higher numbers of zooplankton and phytoplankton species, cyanophyceae and diatoms, as well as O. niloticus size susceptible to catfish predation. Chlorophyceae dominated the phytoplankton in both treatments. The implication of tilapia surplus production for catfish-tilapia polyculture is thus discussed. Key words: Oreochromis niloticus, partial harvest, population dynamics, compensatory growth, standing crop, surplus production, food availability, earthen pond.

Zooplankton community emerging from fresh and saline wetlands

Salinity is a significant factor affecting aquatic species distribution and diversity. To quantify the impact of increasing salinity on the zooplankton community structure, the emergence of zooplankton community from fresh and saline wetlands under different salinity was examined. Sediments from three wetlands from the Upper South East of South Australia were exposed to salinity levels of 300mg dm-3, 5000mg dm-3 and 15 000mg dm-3 for 21 days. After 21 days, more taxa had emerged from fresher wetland sediment than emerged from more saline wetlands. A reduction in the number of zooplankton species and their abundance was evident in the freshwater wetland sediment once salinity was increased from 300mg dm-3 to 5000mg dm-3. Species that emerged from freshwater sediment were mainly freshwater species and their number was significantly reduced as salinity increased. Saline wetlands were colonised by more salt tolerant species such as Brachionus plicatilis, Trichocerca sp. and calanoid copepods. The results indicate that increasing salinity will potentially reduce freshwater zooplankton richness and the community will be shifted from freshwater species to more salt tolerant species.

On Turbulence Production by Swimming Marine Organisms in the Open Ocean and Coastal Waters

Abstract Microstructure and acoustic profile time series were collected near Ocean Station P in the eastern subarctic North Pacific and in Saanich Inlet at the south end of Vancouver Island, British Columbia, Canada, to examine production of turbulent dissipation by swimming marine organisms. At Ocean Station P, although a number of zooplankton species are large enough to generate turbulence with Reynolds numbers Re &amp;gt; 1000, biomass densities are typically less than 103 individuals per cubic meter (&amp;lt;0.01% by volume), and turbulent kinetic energy dissipation rates ɛ were better correlated with 16-m vertical shear than acoustic backscatter layers. In Saanich Inlet, where krill densities are up to 104 individuals per cubic meter (0.1% by volume), no dramatic elevation of dissipation rates ɛ was associated with dusk and dawn vertical migrations of the acoustic backscatter layer. Dissipation rates are a factor of 2 higher [〈ɛ〉 = 1.4 × 10−8 W kg−1, corresponding to buoyancy Re = 〈ɛ〉/(νN 2) ∼ 140] in acoustic backscatter layers than in acoustically quiet waters, regardless of whether they are vertically migrating. The O(1 m) thick turbulence patches have vertical wavenumber spectra for microscale shear commensurate with the Nasmyth model turbulence spectrum. However, the turbulence bursts of O(10−5 W kg−1) proposed to occur in such dense swarms appear to be rare. Thus far, intense turbulent bursts have been found infrequently, even in very dense aggregations O(104 individuals per cubic meter) characteristic of coastal and high-latitude environs. Based on sampling to date, this corresponds to a frequency of occurrence of less than 4%, suggesting that turbulence production by the marine biosphere is not efficient.