Plankton Net Research Articles

Charismatic Krill? Size and Conservation in the Ocean

ABSTRACTThe open ocean is an alien place for human beings and for most of history it has been studied using very indirect means. A great deal of what we know about animals that live on land, from ants to elephants, is based on centuries of direct natural history observations of animals alive and in situ. There is no such body of observation of marine animals. Most of what we know about animals in the ocean comes from studying dead animals, collected in nets towed through ocean depths that we can rarely observe. Marine biological knowledge is flavored by the material we have to work with and this, in turn, is affected by the terminology that early scientists used in an attempt to describe the strange world that their nets revealed. Despite the recent development of more sophisticated ways of investigating the ocean, many marine scientists continue to adopt nineteenth-century terminology and approaches (such as the use of the term zooplankton and the use of plankton nets), and this colors interpretation of the results of oceanographic studies. Using Antarctic krill Euphausia superba as an example, we suggest that the perception amongst both scientists and the general public of krill's small size, passivity, and lack of individuality has led to their being treated less like animals themselves than as background habitat for other animals. Because krill have such a central role in the Antarctic ecosystem and are the subject of a large fishery, these assumptions may have serious consequences for krill themselves and the conservation of the Antarctic region as a whole.

Zooplankton diversity of Loktak Lake, Manipur, India

Zooplankton communities of Loktak Lake showed rich and speciose biocoenosis (162 and 142 species), high monthly richness (91 plus or minus 13 and 80 plus or minus 10 species) and by higher similarities (51.1-82.0 and 51.8-78.3 %) and peak richness during winter and autumn over two years of study. Zooplankton (267 plus or minus 41 n/l) formed a significant quantitative component (56.0 plus or minus 6.3 %) of net plankton and showed annual peak abundance during winter. Rotifera and Cladocera are dominant quantitative groups while Copepoda and Rhizopoda are sub-dominant groups. We observed significant annual and monthly variations of zooplankton richness and abundance. This study showed limited influence of individual abiotic factors on zooplankton, with richness showing a significant inverse correlation with water hardness and chloride, and abundance inversely correlated with nitrate. Multiple regressions indicated higher cumulative effects of 15 abiotic factors on richness and abundance. Our results exhibited no definite periodicity of richness and abundance of zooplankton and their constituent groups during two annual cycles. Zooplankton is characterized by highest species diversity (4.172 plus or minus 0.237), higher evenness and lower dominance.

Nucleopolyhedrovirus Detection and Distribution in Terrestrial, Freshwater, and Marine Habitats of Appledore Island, Gulf of Maine

Viruses in aquatic ecosystems comprise those produced by both autochthonous and allochthonous host taxa. However, there is little information on the diversity and abundance of viruses of allochthonous origin, particularly from non-anthropogenic sources, in freshwater and marine ecosystems. We investigated the presence of nucleopolyhedroviruses (NPV) (Baculovirus), which commonly infect terrestrial lepidopteran taxa, across the landscape of Appledore Island, Gulf of Maine. PCR and qPCR primers were developed around a 294-bp fragment of the polyhedrin (polH) gene, which is the major constituent protein of NPV multivirion polyhedral occlusion bodies. polH was successfully amplified from several aquatic habitats, and recovered polH sequences were most similar to known lepidopteran NPV. Using quantitative PCR designed around a cluster of detected sequences, we detected polH in Appledore Island soils, supratidal freshwater ponds, nearshore sediments, near- and offshore plankton, and in floatsam. This diverse set of locations suggests that NPVs are widely dispersed along the terrestrial--marine continuum and that free polyhedra may be washed into ponds and eventually to sea. The putative hosts of detected NPVs were webworms (Hyphantria sp.) which form dense nests in late summer on the dominant Appledore Island vegetation (Prunus virginiana). Our data indicate that viruses of terrestrial origin (i.e., allochthonous viruses) may be dispersed widely in coastal marine habitats. The dispersal of NPV polH and detection within offshore net plankton (>64 μm) demonstrates that terrestrial viruses may interact with larger particles and plankton of coastal marine ecosystem, which further suggests that viral genomic information may be transported between biomes.

Plankton dynamics associated with the convergence zone of a shear front in the permanently open Kowie Estuary, South Africa

Estuarine frontal systems are thought to play an important role in plankton accumulations in estuaries. However, knowledge surrounding these estuarine circulation patterns is not clear, and consensus regarding the importance of fronts has yet to be reached. A full appraisal of the plankton in frontal systems in the estuary was undertaken. Ichthyoplankton, zooplankton and phytoplankton were collected from in and out of the frontal systems in the Kowie Estuary, using two WP2 plankton nets. Plankton was identified and abundance calculated. Various water quality parameters were also recorded in and out of the front and make up an important part of determining the physical difference between the separated water masses. Values for in and out of the frontal region were determined in order to make comparisons between the different areas. All data was tested for normality and homogeneity of variance. Differences between in and out of the frontal region were determined using ANOVA or Kruskal-Wallis tests. Multiple linear regression was used to determine the relationships between water quality variables and plankton abundances. Community analysis was also run on the data in order to determine community dynamics associated with frontal system convergence and downwelling.

Distribution of polycystine Radiolaria, Phaeodaria and Acantharia in the Kuroshio Current off Shikoku Island and Tosa Bay during Cruise KT07-19 in August 2007

The occurrences of polycystine Radiolaria, Phaeodaria, and Acantharia are reported from plankton net samples, which were obtained in the transect covering from the Kuroshio Current off Shikoku Island to Tosa Bay during Cruise KT07-19 in August 2007. We employed 100 μm as the mesh size of the plankton nets, which was coarser than the mesh size of many recent radiolarian studies (e.g., 44 or 63 μm). The obtained specimens in the samples were categorized into 130 polycystine radiolarian, and 17 phaeodarian, and 3 acantharian taxa. The marked similarity of the polycystine radiolarian assemblages encountered in this study to those reported from the tropical and subtropical oceans in the literature clearly indicates the significant influence by the warm Kuroshio Current. Furthermore, the observed polycystine radiolarian assemblages are similar to those of the previous result from the same specific study area. However, the vertical distribution patterns of some of the major polycystine radiolarian and phaeodarian taxa are different from the previous results from the same region. The differences in vertical distribution may be primarily due to the differences in vertical water mass conditions due to different sampling seasons. In spite of the lengthy sample storage for seven months after the sampling in the shore laboratory, many acantharian specimens were still preserved and encountered in the laboratory census, representing the acantharian presence in the summer sea surface waters in the Kuroshio Current area.

Summer blooms of diatom-diazotroph assemblages and surface chlorophyll in the North Pacific gyre: A disconnect

[1] The discovery of large summer chlorophyll blooms in oligotrophic regions of the ocean has led to questions about the relationship between these blooms and the frequently cooccurring outburst of nitrogen‐fixing phytoplankton. We compared diatom‐diazotroph assemblage (DDA) abundance to size‐fractionated chlorophyll (chl) and satellite ocean color chlorophyll estimates to evaluate how DDAs affected ocean color estimates in the eastern and central North Pacific gyre at 28–30°N. DDA blooms were dominated by either Hemiaulus hauckii (in the central Pacific in 2003 and the eastern Pacific in 2002) or by Rhizosolenia (eastern Pacific in 2002), both with nitrogen‐fixing Richelia symbionts. The 2002 DDA bloom was measured a week prior to the development of a satellite‐ observed chlorophyll bloom at the same location. In contrast, the 2003 Hemiaulus bloom was not within a clearly defined satellite feature. Although DDA abundance increased 10 4 –10 5 ‐fold relative to the background and they dominated the net plankton (≥5 m mo r >10 mm chl size) fraction, the in situ chl (maximum ≤0.11 mg m −3 ) never reached the 0.15 mg m −3 threshold used to define satellite‐observed chlorophyll blooms in oligotrophic waters. The DDA blooms were not evident in the in situ fluorometer data; however, the blooms occurred within high beam attenuation features observed in the transmissometer data. Trichodesmium was not a component of either diatom bloom although elevated levels of Trichodesmium were observed at two stations where DDAs were not abundant. While DDA blooms and satellite ocean chlorophyll blooms are sometimes coincident, our data do not support that DDAs are the sole source of the satellite‐observed chlorophyll in summertime blooms. DDA blooms are likely underreported in the North Pacific, particularly in the waters west of Hawaii, due to their frequent lack of distinctive ocean color, fluorescence, and chlorophyll signatures. The source of the ocean color signature in the blooms remains elusive, but scattered literature observations suggest that cooccurring members of the near‐surface flora such as the small pennate diatom Mastogloia may play an important role.

Early juvenile development of Armases rubripes (Rathbun 1897) (Crustacea, Brachyura, Sesarmidae) and comments on the morphology of the megalopa and first crab

This article provides a description of the early juvenile stages of Armases rubripes and indicates some differences and additional details found in the megalopa and first juvenile crab stage compared with previous descriptions. The main characters that permit identification of the subsequent juvenile stages were assessed, as well as the moult interval and increment during successive moults and the beginning of development of the secondary sexual features. Megalopae of A. rubripes were collected from the Ubatuba region, São Paulo, Brazil using plankton and neuston nets. Morphological changes in body parts have been recorded for each stage and sex, as well as the duration of the intermoult period was noted. Possible effects of laboratory holding time on growth were checked by means of analysis of covariance. The importance of standardization of the terminology of setae is emphasized.

Zooplankton partitioning in a tropical alkaline–saline endorheic Lake Nakuru, Kenya: Spatial and temporal trends in relation to the environment

Spatial and temporal zooplankton variations were studied for 1 year in tropical alkaline–saline Lake Nakuru to determine how they partition in the habitat, relative to environmental variables. Monthly samples were collected at 10 sampling sites, with subsurface tows, using 33.5-μm mesh plankton nets. Physicochemical parameters displayed clear seasonal variations associated with precipitation patterns. Nine species, belonging to two main zooplankton taxonomic groups (ciliates; rotifers), were identified in the samples. Brachionus dimidiatus dominated the samples, accounting for 80% of the total zooplankton abundance. Kruskall–Wallis tests indicated significant (P < 0.05) temporal and spatial variations among all taxonomic groups. Different zooplankton species displayed a clear succession throughout the year. The total abundance of the rotifers and ciliates peaked at sampling sites near inlets during the long rainy seasons, while those in the inshore sites displayed variable succession patterns. Spatiotemporal structure of the zooplankton assemblages, and its correlation with environmental variables, indicated each species displayed distinct niche-based partitioning. The ciliates niche was associated with increasing soluble reactive phosphorus, total phosphorus and nitrite–nitrogen (NO2–N) concentrations. Niche partitioning in rotifers was associated with nitrate–nitrogen (NO3–N), conductivity and pH. These results indicate physical niche separation, even in a small, relatively homogenous lake among species of rotifers and ciliates, providing information from which future changes in their abundance and spatial distributions can be predicted, given continuous water quality changes.

Can different mesh sizes affect the results of copepod community studies?

Although mesozooplankton are important components of aquatic food webs and biogeochemical cycling, this plankton fraction is inadequately described and quantified. Standardized sampling procedures for its worldwide characterization are lacking as yet, affecting meaningful comparisons between regional situations. Mesh sizes in use vary greatly among studies, raising the possibility that sampling method bias results for size-related phenomena of the plankton, such as abundance and diversity in space and time. We tested the effects of different mesh sizes for sampling on the resulting size-frequency distributions of mesozooplankton by collecting copepod assemblages in the northern South China Sea. Sample retrieval by different mesh-size plankton nets were compared, using the abundance and distribution patterns of mesozooplankton collected with NORPAC zooplankton nets of 333, 200, and 100-μm mesh size. One-way ANOVA results for species number and richness indices of all samples showed significant differences between these three mesh size nets. In contrast, total copepod abundance of the 100-μm net was significantly higher than that from the 200-μm net (p=0.001) and of the 333-μm net (p<0.001). Index values of evenness and diversity were significantly different among the copepod assemblages obtained from the three mesh size nets. The evenness index values of the 100-μm net were significantly lower than those recorded from the 200-μm net (p=0.007) and the 333-μm net (p<0.001). The Shannon–Wiener diversity index of the 333-μm net was significantly higher than for the 200-μm net (p=0.016) and for the 100-μm net (p=0.006). In addition, the dominant species proportion in each copepod assemblage obtained in the three mesh size nets differed significantly. Densities of smaller mesozooplanktons such as copepodites were highly underestimated by larger meshed nets that were commonly used in previous studies in the waters of the North Pacific Ocean. Samples collected with a 100-μm mesh net demonstrated the numerical importance of smaller mesozooplankton in the northern South China Sea. Present results, therefore, suggest a striking selectivity of plankton net mesh sizes that significantly affected qualitative and quantitative aspects of copepod assemblages.

Comparison of two plankton net mesh sizes for ichthyoplankton collection in the northern Gulf of Mexico

Comparisons were made between ichthyoplankton samples collected in the northern Gulf of Mexico using a Bedford Institute of Oceanography Net Environmental Sampling System (BIONESS) fitted with 0.202 mm and 0.333 mm mesh plankton nets. Tow duration, tow speed, filtration efficiency and filtration rate were monitored in real time during paired oblique (1–18 m) tows. General tow characteristics and larval assemblages were compared for samples characterized by filtering efficiencies >85%. Plankton tows characterized by relatively short durations (approximately 4.5 min) and low filtered volumes (approximately 70 m 3) were largely overlapping in fish egg densities, larval densities, and length frequency distributions. Higher taxonomic richness (number of families) and diversity (exponential of Shannon Entropy) were observed in the 0.333 mm mesh net. No significant differences in larval fish densities were observed between mesh sizes for seven families of fishes; only unidentified clupeiform fishes were more common in the 0.333 mm mesh net. Mean lengths for total fish larvae, total non-clupeiform fish larvae, sciaenids and unidentified larvae were significantly larger in the 0.333 mm collections. However no significant differences were noted in the length frequencies for these groups. We conclude that under controlled tow conditions, ichthyoplankton samples collected in our region with these two mesh sizes are largely comparable.

Does the Mesh Size of the Plankton Net Affect the Result of Statistical Analyses of the Relationship Between the Copepod Community and Water Masses?

AbstractWe examined if the results of statistical analyses of the relationship between copepod communities and water masses would be affected by the mesh size of the plankton net, by comparing abundance and species composition of copepods in plankton samples collected by plankton nets of different mesh sizes. Our samples were collected during the summer of 2006 in the East China Sea (ECS) by plankton nets with mesh sizes of 100 and 330 μm. The abundance of copepods collected by the 100 μm-mesh plankton net was about two orders of magnitude higher than that collected by the 330 μm-mesh plankton net. The difference in abundance was mainly due to the loss of small-sized copepods in the samples collected by the plankton net with the larger mesh. Species richness was higher in samples collected by the 100 μm-mesh net and Piélou's evenness was generally higher in samples collected by the 330 μm-mesh net. Although species composition of copepods varied in samples collected by plankton nets with different mesh sizes, the statistical analysis of the relationship between the copepod community and the water masses in these samples appeared not to be affected.

A comparison of phytoplankton assemblages generated by two sampling protocols in a German lowland catchment

Research in the phytoplankton community has become an important part of the overall water-quality monitoring. However, to date studies in small rivers and streams were still scarce and sampling methods were also diverse and not as well developed as in lakes or large rivers. We investigated whether two sampling protocols collected different phytoplankton assemblages within a lowland catchment and, conse- quently, influenced the outcome of bio-assessment. Data collected from 77 sites by plankton net (PLNET) collection and sedimentation (SEDIM) protocols were analyzed. Median Bray-Curtis (BC) similarity between phytoplankton assemblages generated by the two protocols was 48.5% (range: 7.5-82.0%), and sites with the lowest BC similarities tended to have lower chlorophyll a (Chl a), water temperature (WT), total suspended solid (TSS) and volatile suspended solid (VSS), but higher channel width and water depth, than other sites with higher BC similarities. Reduced total algal density and biomass, but higher species richness, were observed by the PLNET protocol. However, overall phytoplankton assemblages generated by the two protocols were similar, as indicated by dominant species (paired t-test, P> 0.05) and non-metric multi- dimensional scaling (NMDS) ordination. Nevertheless, from the phytoplankton-based bio-assessment point of view, PLNET protocol was a better method compared with SEDIM protocol because algal data collected by PLNET protocol had higher relationship with environmental variables as indicated by 'Correlation Index' (CoI), Cumulative_R 2 and canonical correspondence analysis (CCA).

Sidewinder: Description of a New Block Winch for Deploying Instruments at Sea

AbstractWe describe a new electric winch design and its functionality for conducting research operations off different‐sized vessels. Currently, several small oceanographic winches are available for deploying research instruments and nets, but they are typically heavy, noisy, semipermanently mounted to the deck, hydraulically operated, and not readily transferable between vessels. The limitation of winch portability between vessels, in particular, has been exacerbated by the increasing use of a variety of chartered vessels to conduct state and federal agency and university research. To address these challenges, we developed a relatively lightweight (70 kg), portable block‐design winch that is spooled with 400 m of plasma line, powered by two 12‐V marine batteries, and operated by a remote control box on a pendant equipped with a joystick. The 2.2‐kW drive produces 100 kg of line pull at speeds of 0 to 2.0 m/s. The pendant includes digital displays for line speed, scope, and angle as well as an emergency stop. Nicknamed the “Sidewinder,” this winch is quiet, can be operated by one person, and is suspended outboard from a davit or crane boom, increasing available deck space and relocating all lines safely away from vessel personnel. On vessels 7 to 50 m in length the Sidewinder has been successfully tested for deploying small gear such as conductivity–temperature–depth profilers and large BONGO plankton nets that require specific deployment and retrieval speeds and line angles. To ensure safe operation, vessel support features such as the power system and davit working load capacity should be considered when the Sidewinder is custom‐built.

Plankton Dynamics Associated with the Convergence Zone of a Shear Front in the Permanently Open Kowie Estuary, South Africa

Estuarine frontal systems are thought to play an important role in plankton accumulations in estuaries. However, knowledge surrounding these estuarine circulation patterns is not clear, and consensus regarding the importance of fronts has yet to be reached. A full appraisal of the plankton in frontal systems in the estuary was undertaken. Ichthyoplankton, zooplankton and phytoplankton were collected from in and out of the frontal systems in the Kowie Estuary, using two WP2 plankton nets. Plankton was identified and abundance calculated. Various water quality parameters were also recorded in and out of the front and make up an important part of determining the physical difference between the separated water masses. Values for in and out of the frontal region were determined in order to make comparisons between the different areas. All data was tested for normality and homogeneity of variance. Differences between in and out of the frontal region were determined using ANOVA or Kruskal-Wallis tests. Multiple linear regression was used to determine the relationships between water quality variables and plankton abundances. Community analysis was also run on the data in order to determine community dynamics associated with frontal system convergence and downwelling.

Phytoplankton diversity of two floodplain lakes (pats) of Manipur, northeastern India

Phytoplankton communities of Utra and Waithou pats (floodplain lakes) of Manipur, studied during November 2002 - October 2004, revealed 62 and 61 species, and indicated monthly richness between 27-45 (38 � plus or minus 4) and 32-46 (39 � plus or minus 4) species respectively with distinct qualitative importance of Chlorophyta (29 � plus or minus 4 and 28 � plus or minus 3 species). Phytoplankton (154 � plus or minus 31 n/l and 164 � plus or minus 34 n/l) comprised between 43.8 � plus or minus 3.0 % and 41.5 � plus or minus 3.0 % of net plankton abundance respectively of these two lakes. Chlorophyta (115 � plus or minus 23 n/l and 113 � plus or minus 21 n/l), the dominant quantitative component (74.4 � plus or minus 4.1% and 67.5 � plus or minus 4.8%), indicated importance of the demids. Bacillariophyta (33 � plus or minus 9 n/l and 37 � plus or minus 12 n/l) formed sub-dominant group, and Dinophyta > Euglenophyta > Chrysophyta showed very low densities. Various abiotic factors registered relatively limited influence on richness and abundance of phytoplankton as well as on abundance of individual groups in Utra Pat than in Waithou Pat. Multiple regression depicted higher cumulative influence of fifteen abiotic factors on the stated biotic parameters in these pats. Both richness and abundance of Phytoplankton recorded significant monthly variations, showed insignificant temporal variations between two lakes and followed indefinite annual patterns in each pat. Phytoplankton communities of the sampled pats are characterized by higher species diversity, higher evenness and lower dominance.

Larval body size–mass relationships of barnacles common to the English Channel coast of the UK

The study presents dry mass and body measurements of the larval stages of five common barnacle species occurring in mesozooplankton catches of Southampton Water and the central Solent area of the south coast of the UK. Quantitative samples were collected with conventional 120-μm mesh plankton nets. Species-specific regression equations relating carapace width and total length with dry mass were obtained for stage II to stage VI nauplii and cyprids of Austrominius modestus, Amphibalanus improvisus, Balanus crenatus, Semibalanus balanoides and Verruca stroemia. Width–dry mass and length–dry mass regressions obtained in the present study accounted for more than 98% of the variability for naupliar stages, and length–dry mass for 80% of the variability for cyprids. The dry mass of barnacle larvae predicted from carapace width equations determined here differed by only –6% from the measured dry masses of an independent data set, suggesting these first-reported equations of barnacle larvae are useful additions to zooplankton production studies.

Dinophysiales (Dinophyceae) no extremo Sul do Brasil (inverno de 2005, verão de 2007)

Os dinoflagelados da ordem Dinophysiales representam um grupo morfologicamente diverso e ecologicamente heterogêneo, incluindo espécies autotróficas, mixotróficas e heterotróficas, outras contendo endossimbiontes ou ainda produtoras de ficotoxinas. No presente trabalho, foram identificadas as espécies de Dinophysis, Ornithocercus, Histioneis e Amphisolenia em águas costeira e oceânica na região Sul do Brasil, ao largo do Cabo de Santa Marta Grande, SC e Albardão-Chuí, RS. Arrastos verticais foram realizados com rede de plâncton (20 µm) à bordo do N. O. Atlântico Sul em 33 estações oceanográficas visitadas em agosto/setembro de 2005 (inverno) e fevereiro de 2007 (verão). As amostras de plâncton foram fixadas com formol (4%) e analisadas com o auxílio de microscópio invertido. Ao todo, 43 espécies de Dinophysiales foram identificadas, a maioria com ampla distribuição nas regiões costeira, de plataforma continental e oceânica, como Dinophysis acuminata, D. exigua, D. ovata e Histioneis hyalina no verão de 2007, e D. acuminata, D. caudata, D. fortii e D. schroederi no inverno de 2005. Algumas espécies apresentaram distribuição restrita à região oceânica, sob influência da Corrente do Brasil, como Dinophysis dubia, D. exigua, D. schuetti, Histioneis para, Ornithocercus thumii e O. splendidus no inverno de 2005, e D. similis, D. rapa, H. megalocopa, H. milneri, O. heteroporus e O. splendidus no verão de 2007. Seis espécies potencialmente tóxicas foram encontradas, Dinophysis acuminata, D. caudata, D. fortii, D. mitra, D. tripos e D. rotundata.

Selectivity of plankton nets over mesozooplankton taxa: implications for abundance, biomass and diversity estimation

The importance of the smaller copepod species is often underestimated as a result of the use of standard 200 μm mesh size nets, even though the small copepods probably represent the dominant component of the mesozooplankton community. Although the inadequacy of relatively coarse nets in providing reliable descriptions of the mesozooplankton assemblage is increasingly welldocumented, such nets continue to be commonly used. A major reason for this unwillingness to break with tradition is the belief that samples remain comparable even though the absolute values are biased. A one-year study of the abundance and size distribution of zooplankton collected in the Venice Lagoon using an 80 μm mesh size net showed an overwhelming abundance of small taxa. These data were used to derive estimates of the mesh selection effects of standard WP-2 nets on zooplankton abundance and biomass. Only 11% of numbers and 54% of biomass of lagoon zooplankton are likely to be caught with standard WP-2 nets. A comparison of seasonal changes in diversity, estimated from the fine and coarse datasets, confirmed that retention efficiency is seasonally dependent, which results in serious implications when extrapolating temporal patterns in community structure from WP-2 mesozooplankton counts.

Zooplankton of lakes in the spurs of the Putorana Plateau and adjacent territories (North of Krasnoyarsk Krai)

Species composition and parameters of biomass of net plankton were analyzed for four large and 35 small lakes from 10 areas located between 69.5° and 67.5°N and 87° and 92°E that were examined in July–August, 2001 and 2003–2004. In the composition of the first (dominant) and/or second (subdominant) species in the ranged row of the average biomass, the lakes were copepod in 78.8% of cases, in 67.3%, calanoid. The share of biomass of cladocerans in the total biomass of zooplankton exceeded 50% only in 31% of cases. By the frequency of occurrence as dominant or subdominant by biomass the first place is occupied by copepodites calanoid (34.6% of cases), the second, by sexually mature Heterocope appendiculata (26.9%), the third, by copepodites cyclopoid (17.3%), the fourth, by Polyphemus pediculus (15.4%), the fifth, by Acanthodiaptomus denticornis (13.5%), the sixth, by Bosmina cf. longispina (11.5%), the seventh, by Heterocope borealis (9.6%), the eighth, by Daphnia cf. longispina (7.7% of cases). For the first time in the region 14 species of crustacean zooplankton are given. The known range of some species and subspecies (for example, Chydorus biovatus, Camptocercus fennicus, Ophyoxus gracilis kolymensis, Arctodiaptomus acutilobatus, Acanthrodiaptomus tibetanus) is widened owing to the findings in the studied region. The groups of the areas are more similar in terms of zooplankton north to south than east to west; the number of the cladoceran species and the number of cladoceran lakes grew north to south and east to west, which corresponded to the general change of climate towards more mild north to south for similar altitudes and east to west for different altitudes from mountain areas to the low lands. The comparison of the species lists from different northern regions showed that the species diversity (total number of species) of cladocerans and copepods does not change significantly west to east. Distribution of species and changes in the zooplankton structure are discussed from the point of view of possible influence of the global warming.

Monsoon-forced distribution and assemblages of appendicularians in the northwestern coastal waters of South China Sea

This study examines species composition and abundance of appendicularians in the northwestern coastal waters of South China Sea based on in situ data obtained by 169 μm planktonic nets during summer and winter, and discusses the influence of environmental factors on their distribution and assemblages. A total of 19 appendicularian species (including one unidentified species) was collected. Species richness is higher in summer than in winter, and it increases from inshore to offshore waters. Average abundance of appendicularians is 103.1 (±198.1) and 54.6 (±111.1) ind. m −3 in summer and winter, respectively. The abundance distribution of appendicularians is generally high around inshore waters during summer and winter, and with a higher abundance assemblage along the eastern coast from Leizhou Peninsula to Hainan Island, especially at the eastern mouth of Qiongzhou Strait in summer. Oikopleurids accounted for 97.5% and 99.6% of total appendicularians abundance in summer and winter, and the region of high values was the same to that of total appendicularians abundance. Oikopleura longicauda, Oikopleura rufescens, and Oikopleura fusiformis are dominant species during summer and winter. Results showed that spatial distribution of species richness of appendicularians is considered to be the result of physical factors such as temperature and salinity in summer and winter, while variations in abundance of appendicularians are affected by the combination of physical and biological factors. In particular, variations of appendicularians abundance are affected by food availability in summer.