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The prevalence of endoparasites associated with chaetognath abundance in the coastal waters of the Mexican Central Pacific was studied fortnightly from November 2010 to December 2011. A total of 35 (0.21%) out of 16,407 chaetognaths were found to be parasitized. Five out of twelve chaetognath species (Flaccisagitta enflata, F. hexaptera, Parasagitta euneritica, Serratosagitta pacifica, Zonosagitta bedoti) were found to be parasitized by nine endoparasitic taxa: Protists (two morphotypes), digenean metacercariae [Didymozoidae, Hemiuridae, Parahemiurus sp., Lepocreadiidae, Prosorhynchus sp. (Bucephalidae)], and cestodes (metacestodes) [Tetraphyllidea (two morphotypes)]. Parasagitta. euneritica and Z. bedoti were the most abundant chaetognath species, and Protist sp. 2 and Tetraphyllidea sp. 1 were the most abundant parasites. The highest prevalence for most of the endoparasite species occurred in June, and the values varied according to three hydroclimatic periods: stratified (S), semi-mixed (SM), and mixed (M). Eight non-infected chaetognath species, two parasitized chaetognaths (F. enflata and S. pacifica), and two parasites (Protist sp. 1 and Tetraphyllidea sp. 2) were associated with warm temperatures (S and SM periods); in contrast, P. euneritica, Z. bedoti, parasitized F. hexaptera, and the parasite Tetraphyllidea sp. 1 showed a strong local preference for cooler temperatures, high productivity, and high biomass conditions (M periods). We discovered the occurrence of the digenean Prosorhynchus sp. (Bucephalidae) parasitizing the chaetognath P. euneritica, and this is the first report of Prosorhynchus parasitizing chaetognaths worldwide. We also confirmed the presence of Lepocrediidae (metacercariae larval stage) infecting F. hexaptera, a parasite that had only been recorded infecting other chaetognaths of the Atlantic Ocean. The parasite diversity affecting the chaetognath populations of the Central Mexican Pacific coast likely differs between the offshore, outer slope areas, and the surveyed coastal system.

The prevalence of endoparasites associated with chaetognath abundance in the coastal waters of the Mexican Central Pacific was studied fortnightly from November 2010 to December 2011. A total of 35 (0.21%) out of 16,407 chaetognaths were found to be parasitized. Five out of twelve chaetognath species (Flaccisagitta enflata, F. hexaptera, Parasagitta euneritica, Serratosagitta pacifica, Zonosagitta bedoti) were found to be parasitized by nine endoparasitic taxa: Protists (two morphotypes), digenean metacercariae [Didymozoidae, Hemiuridae, Parahemiurus sp., Lepocreadiidae, Prosorhynchus sp. (Bucephalidae)], and cestodes (metacestodes) [Tetraphyllidea (two morphotypes)]. Parasagitta. euneritica and Z. bedoti were the most abundant chaetognath species, and Protist sp. 2 and Tetraphyllidea sp. 1 were the most abundant parasites. The highest prevalence for most of the endoparasite species occurred in June, and the values varied according to three hydroclimatic periods: stratified (S), semi-mixed (SM), and mixed (M). Eight non-infected chaetognath species, two parasitized chaetognaths (F. enflata and S. pacifica), and two parasites (Protist sp. 1 and Tetraphyllidea sp. 2) were associated with warm temperatures (S and SM periods); in contrast, P. euneritica, Z. bedoti, parasitized F. hexaptera, and the parasite Tetraphyllidea sp. 1 showed a strong local preference for cooler temperatures, high productivity, and high biomass conditions (M periods). We discovered the occurrence of the digenean Prosorhynchus sp. (Bucephalidae) parasitizing the chaetognath P. euneritica, and this is the first report of Prosorhynchus parasitizing chaetognaths worldwide. We also confirmed the presence of Lepocrediidae (metacercariae larval stage) infecting F. hexaptera, a parasite that had only been recorded infecting other chaetognaths of the Atlantic Ocean. The parasite diversity affecting the chaetognath populations of the Central Mexican Pacific coast likely differs between the offshore, outer slope areas, and the surveyed coastal system. [ABSTRACT FROM AUTHOR]

Chaetognatha, the second-most abundant zooplankton in the marine ecosystem, is a connecting link between copepods and organisms of the higher trophic level. The present checklist provides detailed information on the morphology and distribution of chaetognaths in the eastern Arabian Sea (northeastern Arabian Sea, southeastern Arabian Sea, and Laccadive Sea). It includes five families under two orders with 34 species belonging to 15 genera and recorded from both shelf, oceanic and deep sea waters of the eastern Arabian Sea, creating a first line data on chaetognaths of the Arabian Sea. [ABSTRACT FROM AUTHOR]

The present work aims to evaluate the MP contamination of zooplankton and its impact on MP trophic transfers at the lower levels of the food web in a field study. During 1 year, seasonal surveys were conducted to collect zooplankton and water samples from different sites in two estuaries, the Douro and Lima estuaries (NW, Portugal). The zooplankton was quantified and identified into major zooplanktonic groups. Dedicated protocols that had been previously optimized were used to assess the MP presence in the water samples and in two of the most abundant zooplankton groups (copepods and chaetognaths). The results showed the presence of MPs in all water samples, with similar MP concentrations in both estuaries (Lima: 2.4 ± 2.0 MPs m−3; Douro: 2.3 ± 1.9 MPs m−3). In general, no temporal or spatial variations were observed. Fibres, blue and of a small size (<1 mm), were the most common characteristics of the MPs found in the water and zooplankton, indicating that water can be a source of MPs for zooplankton. Chaetognatha exhibited higher MP contamination in the Lima (2.9 ± 3.1 MPs ind−1) and Douro (2.0 ± 2.8 MPs ind−1) estuaries than Copepoda, which tended to have lower levels of MP contamination (Lima: 0.95 ± 1.12 MPs ind−1; Douro: 1.1 ± 1.2 MPs ind−1). Such differences in the MP concentrations between these two categories of zooplanktonic organisms indicate a possible MP trophic transfer at the lower levels of the food web. The results highlight the novel possibility of an MP trophic transfer in zooplankton and the need to fully assess the impacts of MPs in real scenarios. [ABSTRACT FROM AUTHOR]

In the oceans, Chaetognatha can contribute significantly to the total zooplankton biomass (up to 10–30%). The genus Eukrohnia, the dominant Chaetognath genus in the western subarctic Pacific, includes E. hamata and E. bathypelagica. Although it has been pointed out that there is no genetic difference between the two species, no study has been made that treats them as the same species group. In this study, we investigated vertical distribution based on the eight vertical stratification samplings down to 1000 m depths conducted day/night at four seasons covering one year, community structure, and population structure of the three dominant Chaetognath species: Parasagitta elegans, E. hamata, and E. bathypelagica in the western subarctic Pacific. The population densities of each species at 0–1000 m water column were 0.04–0.36 ind. m−3 for P. elegans, 0.14–1.60 ind. m−3 for E. hamata, 0.24–1.54 ind. m−3 for E. bathypelagica, and 1.37–2.62 ind. m−3 for Eukrohnia juveniles. The vertical distributions were consistent both day and night, and no diel changes were observed for all species throughout the seasons. The vertical distribution of Chaetognaths evaluated by the distribution center was 61–169 m for P. elegans, 143–206 m for Eukrohnia juveniles, 134–279 m for E. hamata, and 253–612 m for E. bathypelagica. The body length of P. elegans ranged from 4 to 34 mm, and one to three cohorts were identified at each sampling occasion. While the presence of the eight stages has been reported for Eukrohnia, only one to five stages occurred, and specimens belonging to six to eight stages were not observed in the samples throughout the year. The body length of the whole Eukrohnia species ranged from 2 to 14 mm. The body length histograms of the Eukrohnia species group, including E. hamata and E. bathypelagica, and their juveniles showed the presence of two to four cohorts at each sampling date. Within the Eukrohnia species group, vertical changes in body length were present, which were characterized by the smaller specimens occurring at shallower depths, followed by an increase in body length with increasing depths. From the vertical distribution and population structure of the Eukrohnia species group (Eukrohnia juvenile + E. hamata + E. bathypelagica) in this study, there was no difficulty in treating them as one species. It may suggest that E. hamata and E. bathypelagica in the western subarctic Pacific could be treated as one species group. To clarify this point, a detailed genetic analysis of the Eukrohnia species group will be needed for future studies.

In the oceans, Chaetognatha can contribute significantly to the total zooplankton biomass (up to 10–30%). The genus Eukrohnia, the dominant Chaetognath genus in the western subarctic Pacific, includes E. hamata and E. bathypelagica. Although it has been pointed out that there is no genetic difference between the two species, no study has been made that treats them as the same species group. In this study, we investigated vertical distribution based on the eight vertical stratification samplings down to 1000 m depths conducted day/night at four seasons covering one year, community structure, and population structure of the three dominant Chaetognath species: Parasagitta elegans, E. hamata, and E. bathypelagica in the western subarctic Pacific. The population densities of each species at 0–1000 m water column were 0.04–0.36 ind. m−3 for P. elegans, 0.14–1.60 ind. m−3 for E. hamata, 0.24–1.54 ind. m−3 for E. bathypelagica, and 1.37–2.62 ind. m−3 for Eukrohnia juveniles. The vertical distributions were consistent both day and night, and no diel changes were observed for all species throughout the seasons. The vertical distribution of Chaetognaths evaluated by the distribution center was 61–169 m for P. elegans, 143–206 m for Eukrohnia juveniles, 134–279 m for E. hamata, and 253–612 m for E. bathypelagica. The body length of P. elegans ranged from 4 to 34 mm, and one to three cohorts were identified at each sampling occasion. While the presence of the eight stages has been reported for Eukrohnia, only one to five stages occurred, and specimens belonging to six to eight stages were not observed in the samples throughout the year. The body length of the whole Eukrohnia species ranged from 2 to 14 mm. The body length histograms of the Eukrohnia species group, including E. hamata and E. bathypelagica, and their juveniles showed the presence of two to four cohorts at each sampling date. Within the Eukrohnia species group, vertical changes in body length were present, which were characterized by the smaller specimens occurring at shallower depths, followed by an increase in body length with increasing depths. From the vertical distribution and population structure of the Eukrohnia species group (Eukrohnia juvenile + E. hamata + E. bathypelagica) in this study, there was no difficulty in treating them as one species. It may suggest that E. hamata and E. bathypelagica in the western subarctic Pacific could be treated as one species group. To clarify this point, a detailed genetic analysis of the Eukrohnia species group will be needed for future studies. [ABSTRACT FROM AUTHOR]

El Archipiélago Cubano contiene una gran fracción de la diversidad regional pero no existen estudios recientes sobre el mesozooplancton. Nuestro objetivo fue caracterizar la fracción de tamaño grande (> 500 μm) del mesozooplancton a través de cuatro hábitats costeros (manglar, pasto marino, fondo sin vegetación y arrecife de coral) en tres cuencas (o golfos: Ana María, Batabanó y Guanahacabibes). Además, probar la hipótesis de que el golfo y el tipo de hábitat tienen un efecto significativo sobre la estructura del mesozooplancton en relación con la dispersión y la selección respectivamente. El muestreo incluyó 71 arrastres de plancton en 28 sitios con una red cónica de 500 μm de apertura de malla. En total, se identificaron 41049 organismos de 30 grupos taxonómicos y 3551 quetognatos de ocho especies. La estructura de la comunidad del mesozooplancton fue típica de regiones tropicales con diversidad alta, abundancia baja y dominancia de Copepoda y Chaetognatha. Larvas y huevos contribuyeron en gran proporción a la abundancia sugiriendo la importancia del mesozooplancton costero para los ciclos de vida de muchas especies y reafirmando la función de los arrecifes de coral como áreas de desove. La mayoría de los taxa del mesozooplancton tuvieron amplia distribución a través de los golfos y los hábitats probablemente asociado a un régimen oceanográfico complejo. El factor golfo tuvo efectos significativos sobre la estructura del mesozooplancton comparado con el tipo de hábitat, indicando la importante función de las barreras a la dispersión entre golfos y una selección débil por parte del tipo de hábitat costero. Se registraron ocho especies de quetognatos, con Parasagitta megalophthalma y Sagitta helenae siendo nuevos registros para el Archipiélago cubano. La relación débil entre los quetognatos y el tipo de hábitat probablemente reflejó la tolerancia ecológica amplia de las especies costeras.

Previously unidentified small (up to 1.3 mm in length), gently curved hollow spines composed of calcium phosphate and derived from the upper Famennian (Devonian) of the Holy Cross Mountains in central Poland are described. They are similar to the type species of Phakelodus, but show some distinct morphological differences, therefore, have been included into Phakeloides polonicus gen. et sp. nov. The studied specimens of that species show relatively massive mineral structure characterized by significant porosity with well-preserved major structural features. The outer layer of the spines is, in contrary, fragmentarily preserved, and exposes distinct mosaic-like ornamentation of the surface of the middle layer, which consists of obliquely arranged, shallow furrows. Geochemical analyses of the Devonian Phakeloides polonicus gen. et sp. nov. spines have revealed the presence of a weaker mineralized structure, compared to conodont apatite, composed of a diagenetic phosphate phase. It is characterized by moderate cathodoluminescence intensity, elevated concentrations of iron and sulphur as well as decreased concentrations of strontium, calcium, and phosphorus. The "Orsten" type, early diagenetic phosphatization of the outer layer of the spines is not observed in studied specimens of Phakeloides polonicus gen. et sp. nov., contrary to the previously investigated Furongian (Cambrian) material. This points to the low rate of diagenetic phosphatization, which was likely enabled by very slow sedimentation and long residence time of the spines close to sediment-water interface at varying redox conditions and significant flux of phosphate ions. [ABSTRACT FROM AUTHOR]

The present study was done to understand the abundance and species diversity of arrow worms, zooplankton in relation to hydrographical parameters and the spatial and temporal variations for a period of 16 months from October 2020 to March 2022. Monthly sampling was carried out at selected stations of coastal waters with an average depth of 8m. The qualitative analyses revealed the presence of seventeen different groups of zooplankton. copepods, cladocerans are the dominant group in zooplankton followed by chaetognaths, during the study period seven species of chaetognaths were recorded viz, Sagitta enflata, Sagitta robusta, Sagitta bedotii, Sagitta bipunctata, Sagitta ferox, Sagitta planktonis and Sagitta elegans. Among them, Sagitta enflata was the dominant species followed by S.bedotii and S. robusta. The richness, evenness and diversity of chaetognaths varied in the different stations and the maximum and minimum values also varied between stations, but in most of the stations the minimum values were observed in the post-monsoon season and the highest values ranged between January to March. In a comparison of the present abundance of chaetognaths with a previous study, it was observed that the density of chaetognaths decreased compared to previous studies. [ABSTRACT FROM AUTHOR]

A Zooplankton survey was carried out between August 2015 and July 2016 along the Egyptian Red Sea coast of Hurghada to describe the species distribution of the arrow worms, Chaetognatha, in relation to the biological and physical factors. Monthly samples were collected by plankton nets of 350 and 500µm mesh size and 100cm mouth opening from four transects along the coast for one year. The average spatial and temporal variations, as well as diversity indices, were calculated. The correlation between Chaetognatha and physical parameters from one side and the biological factors from the other side was also investigated. A total of 17 species belonging to 3 genera and 3 families of the arrow worms were identified. The total abundance of Chaetognatha was 760 individuals/L, with an average of 126 individuals/L. The highest abundance of Chaetognatha was recorded in spring with a peak in April (378). The highest number of species was found in December (16 species). The most abundant species was Sagitta neodecipinens, with an average abundance of 159 individuals/L. Chaetognatha recorded a strong negative correlation with temperature and a strong positive correlation with pH and dissolved oxygen. They had a significant positive correlation with Copepods, Hydromedusa, and Tintinnids and a negative correlation with fish larvae. [ABSTRACT FROM AUTHOR]

Zooplankton was sampled from the epipelagic layer (0–200 m) in the Bering Sea using Jedae net (mouth 0.1 m2, mesh size 0.168 mm) in 1986–2018. Arrowworms were the most numerous predators, represented with 3 species: Parasagitta elegans, Eukrohnia hamata, and Pseudosagitta maxima. Their summary biomass was 215.7 mg/m3, on average (26.3 % of the total zooplankton biomass), and varied seasonally from 105.9 mg/m3 in winter to 311.8 mg/m3 in autumn. Parasagitta elegans dominated absolutely (> 99 % WW). Mean stock of this species was 64.36. 106 t; its seasonal yield was estimated as 22.1. 106 t in winter, 78.5. 106 t in spring, 191.9. 106 t in summer, and 130.3. 106 t in autumn, so its mean production was 422.8. 106 t WW per year.

The mesopelagic zooplankton community plays an important role in the cycling and sequestration of carbon via the biological pump. However, little is known about the physiology and ecology of key taxa found within this region, hindering our understanding of their influence on the pathways of energy and organic matter cycling. We sampled the eight most abundant zooplankton (Calanoides acutus, Rhincalanus gigas, Paraeuchaeta spp., Chaetognatha , Euphausia triacantha, Thysanoessa spp., Themisto gaudichaudii and Salpa thompsoni) from within the mesopelagic zone in the Scotia Sea during a sinking diatom bloom and investigated their physiological ecology using lipid biomarkers and stable isotopic signatures of nitrogen. Data suggest that the large calanoid copepods, C. acutus and R. gigas , were in, or emerging from, a period of metabolic inactivity during the study period (November 15th – December 15th, 2017). Abundant, but decreasing lipid reserves in the predominantly herbivorous calanoid copepods, suggest these animals may have been metabolising previously stored lipids at the time of sampling, rather than deriving energy solely from the diatom bloom. This highlights the importance of understanding the timing of diapause of overwintering species as their feeding is likely to have an impact on the turnover of particulate organic matter (POM) in the upper mesopelagic. The δ15N signatures of POM became enriched with increasing depth, whereas all species of zooplankton except T. gaudichaudii did not. This suggests that animals were feeding on fresher, surface-derived POM, rather than reworked particles at depth, likely influencing the quantity and quality of organic matter leaving the upper mesopelagic. Our study highlights the complexity of mesopelagic food webs and suggests that the application of broad trophic functional types may lead to an incorrect understanding of ecosystem dynamics. • Calanoides acutus and Rhincalanus gigas use stored lipids for energy not ingestion. • Actively feeding zooplankton consumed fresh POM, not reworked particles at depth. • Decoupling between zooplankton feeding dynamics and ambient POM in the upper 500m. [ABSTRACT FROM AUTHOR]

The dramatic warming of the Arctic Ocean will impact pelagic ecosystems in complex ways, including shifting patterns of species distribution and abundance, and altering migration pathways and population connectivity. Species of the Phylum Chaetognatha (arrow worms) are abundant in the zooplankton assemblage and are highly effective predators, with key roles in pelagic food webs. They are useful indicator species for impacts of climate change on marine ecosystems. This study examined the population genetic diversity, structure and connectivity of the chaetognath, Eukrohnia hamata, based on sampling from six regions defined by geography, bathymetry, and major currents flowing through the Arctic Ocean. A 528-base pair sequenced region of mitochondrial cytochrome oxidase I (mtCOI) analyzed for 131 specimens resulted in 78 haplotypes and very high haplotype diversity. Analysis of mtCOI haplotype frequencies provided no evidence of population genetic structure. Genomic Single Nucleotide Polymorphisms (SNPs) detected from the same specimens by double-digest Restriction-site Associated Digestion (ddRAD) confirmed high levels of gene flow among the regions, but supported the genetic distinctiveness of two population clusters: Atlantic–Arctic versus Pacific–Arctic. Removal of SNPs subject to selection resulted in slightly higher probability of three clusters, and suggested the possibility of local adaptation of regional populations of E. hamata. Comparative analysis revealed evidence that random selection of subsets of SNPs, perhaps impacted by different ecological and (micro) evolutionary drivers, can result in marked differences in numbers and distributional patterns of clusters and associated variation in F-statistics. Analysis of population connectivity using SNPs supported the primary migration pathway via flow from the Atlantic to the Pacific Arctic regions.

Chaetognaths (arrow worms) are an enigmatic group of transparent planktonic invertebrates and play an important role in the marine food web. Their morphological and developmental features have raised extensive debates since the discovery of the phylum in the 18th century. Uncertainty in the phylogenetic placement of certain chaetognath species still exists and is puzzling many scientists who have tried to clarify this task. Studies using a portion of both small subunit ribosomal ribonucleic acid (SSU rRNA) and large subunit ribosomal ribonucleic acid (LSU rRNA) genes when integrated with conventional taxonomy were contributed to resolve taxonomical issues in this group. Here we present the first phylogenetic study of Chaetognatha based on a portion of mitochondrial cytochrome oxidase I (COI) gene and compare our results with the earlier morphological and molecular evolutionary hypotheses. This study includes 16 extant species, representing 8 genera and 6 of which are among the 9 extant families. We recommend the following clade structure for the phylum: Aphragmophora comprising Sagittidae with Pterosagittidae and Krohnittidae included in the Sagittidae and Phragmophora comprising Eukrohniidae, Spadellidae, and Heterokrohniidae. Phylogenetic analyses also supported the division of Phragmophora into two monophyletic groups: the Monophragmophora and Biphragmophora. Moreover, Ctenodontina/Flabellodontina and Syngonata/Chorismogonata suborders were not validated. Precise phylogenetic investigations using various molecular markers and specimens from diverse regions are definitely needed to provide an exact evolutionary concept on this phylum. [ABSTRACT FROM AUTHOR]

Chaetognaths are ubiquitous in the marine environment and are among the most abundant carnivorous plankton. Nevertheless, characterization of physiological parameters remains limited largely due to the difficulty in obtaining the data from pelagic chaetognaths in laboratory studies. This study therefore aimed to determine the feeding and growth rates of Zonosagitta nagae under laboratory rearing condition. A total of 54 field-collected chaetognaths with maturity Stage I and II ranging from 5 to 12 mm in body length collected in June, August and October were individually incubated at 20–22°C with excess copepod prey and growth parameters were obtained from 26 individuals that survived ~10–46 days. For Z. nagae , ingestion and growth rates increased with body dry weight, and both parameters were significantly related, indicating that gross growth efficiency was ~47%. Specific ingestion rates ranged from 0.03 to 0.43 d−1 and tended to decrease with an increase of size of the chaetognaths. Individual specific growth rate varied widely in small-sized individuals (~6 mm), ranging from −0.103 to 0.135, but became relatively constant (~0.032) with increasing size. Overall the study results suggest that Z. nagae is characterized by high gross growth efficiency, which is in striking contrast with previously studied inshore species. [ABSTRACT FROM AUTHOR]

Zooplankton predator–prey relations in northern Norwegian fjords are highly variable in time and space, and the mechanisms driving this variability are still poorly understood. Replicate Juday net sampling in October and February from 1983 to 2005, which included five repeated tows from bottom to surface, was conducted in Saltfjord and Mistfjord, northern Norway. The time-series provided evidence of in situ variability in species abundance, as well as seasonal and interannual changes in standing stock abundance. The shallow sill of one fjord caused accumulation of coastal water in the fjord’s basin, while the other fjord’s deeper sill selected denser water of Atlantic origin from the same open shelf habitat. The selective advection caused differences in the immigration of species recruiting to the fjords’ specific overwintering communities of zooplankton. Statistical analyses of the cumulated replicate data indicated significant in situ variability in the spatial density of species. Cases with an abundance of carnivores relating positively to other species probably resulted from the carnivores’ attraction to patches with concentrations of prey. Interspecific negative density relations likely indicated either predator avoidance or substantial trophic activity during the sampling. During years of high abundance, some wintering stocks of carnivores evidently reduced the local stocks of overwintering prey. We conclude that predator–prey interactions and stock variability in Subarctic fjords result from complex bio-geophysical interactions that occur on the scales of local habitats and basin-scale population systems. [ABSTRACT FROM AUTHOR]

Lophotrochozoa (also called Spiralia), the sister taxon of Ecdysozoa, includes animal taxa with disparate body plans such as the segmented annelids, the shell bearing molluscs and brachiopods, the colonial bryozoans, the endoparasitic acanthocephalans and the acoelomate platyhelminths. Phylogenetic relationships within Lophotrochozoa have been notoriously difficult to resolve leading to the point that they are often represented as polytomy. Recent studies focussing on phylogenomics, Hox genes and fossils provided new insights into the evolutionary history of this difficult group. New evidence supporting the inclusion of chaetognaths within gnathiferans, the phylogenetic position of Orthonectida and Dicyemida, as well as the general phylogeny of lophotrochozoans is reviewed. Several taxa formerly erected based on morphological synapomorphies (e.g. Lophophorata, Tetraneuralia, Parenchymia) seem (finally) to get additional support from phylogenomic analyses. [ABSTRACT FROM AUTHOR]

Cuban archipelago harbors a large fraction of regional diversity but lacks recent studies about diversity and distribution of mesozooplankton. We aimed to characterize the large-size fraction (> 500 µm) of the mesozooplankton across four coastal habitats (mangrove, seagrass bed, unvegetated bottom, and coral reef) in three basins (or gulfs: Ana María, Batabanó, and Guanahacabibes). Furthermore, we tested the hypothesis that gulf and habitat type have a significant effect on mesozooplankton structure in relation with dispersal and selection respectively. The sampling included 71 plankton tows in 28 sites with a conical net of 500 µm mesh size. In total, 41049 organisms of 30 major taxonomic groups were identified; while 3551 chaetognaths belonging to eight species were reported. The mesozooplankton community structure was typical of tropical regions with large diversity, low abundance and dominance of Copepoda and Chaetognatha. Larvae and eggs accounted for a large proportion of total abundance suggesting the importance of coastal mesozooplankton for life cycles of many species and supporting the role of coral reefs as spawning areas. Most of the mesozooplankton taxa had broad distribution across gulfs and habitats likely associated with a complex oceanographic regime. The factor gulf had significant effects on mesozooplankton structure compared to the habitat type, highlighting the influential role of barriers to dispersal among basins and a weak selection by the coastal habitat type. Eight chaetognatha species were recorded with Parasagitta megalophthalma and Sagitta helenae being new records for Cuban archipelago. The weak relationship between chaetognaths and habitat type likely reflected the broad ecological tolerance of coastal species. [ABSTRACT FROM AUTHOR]

Digestion time and feeding of the pelagic chaetognath Zonosagitta nagae, which occurs predominantly in warm waters around Japan, were investigated in the laboratory. Young individuals of Z. nagae ranging from 4.1-7.6 mm in body length were used for the experiments with adult females of the copepod Acartia steueri as prey. The mean digestion time of Z. nagae was 115±3 minutes at 20°C. Temporal change in individual's feeding intensity was observed every 1.5 h for 24 h to determine the diel feeding pattern, feeding interval, feeding rates and daily ration. Almost all individuals showed no clear diel rhythm within 24-h at 20°C under 12L:12D cycle; time interval between feeding was 4.5-6 h (mode) for individuals that ingested multiple copepods. The number of copepods ingested by a chaetognath ranged from 0 to 5 and on average 2.6 copepods were consumed a day per individual. Specific daily ration in most individuals corresponded to ca. 50% of its dry weight while some individuals showed the extremes of non-feeding or voracious feeding (>200% d-1), indicating that some of the young Z. nagae had an intermittent feeding mode, which would be adaptive to save energy expenditure at low prey densities and to reduce mortality by lowering the risk of predation. [ABSTRACT FROM AUTHOR]

Although chaetognaths inhabiting polar ecosystems are relatively well known, there are few reports on their functioning in the Antarctic coastal plankton community. The presented results provide the first comprehensive description of population structure of chaetognaths in the neritic zone west of the Antarctic Peninsula. The studies were performed on samples collected in Admiralty Bay, from December 1994 to June 1995. Following six chaetognath species were determined: Eukrohnia hamata, E. bathypelagica, E. fowleri, Pseudosagitta gazellae, P. maxima and Solidosagitta marri. The representatives of Eukrohnia were observed almost throughout the research period, whereas those of Pseudosagitta and Solidosagitta were found only during first four months of our investigation. Eukrohnia hamata showed a strong dominance in respect to abundance (max. 445 ind./1000 m3). The mean abundance of all taxa significantly fluctuated in the study period and across weeks. Generally, all species were represented by the first three maturity stages (I-III), individuals stage IV occurred sporadically, and mature specimens (stage V) were not recorded at all. Morphometric analysis of the most abundant species showed distinct differences in their total length and body proportions. Our findings may suggest that chaetognath populations in Admiralty Bay are migrant, dependent on the inflow of water from the Bransfield Strait, but to prove this statement further, round year study is necessary.

State of zooplankton, as the food base of walleye pollock, in the western Bering Sea in the early 21st century is considered. Warm period of the 2001-2006 changed to cold period of the 2007-2013 and, after the transitional year of 2014, a new warm period began in 2015 that could be seen on a number of parameters including the ice cover that was the lowest for the last 15 years. In the previous warm period, the walleye pollock food base wasn’t reduced in this area, in contrast to the eastern Bering Sea where the biomass of its favorite prey was lowered. The same is observed in the beginning of the new warm period. Data on zooplankton abundance are presented, including both dominant and minor groups, that allows to assess a real feeding conditions for six size classes of walleye pollock. Food supply of pollock is evaluated quantitatively as a number of its monthly rations in the zooplankton stock, taking into account age and regional properties of its diet. This index was high in the western Bering Sea for both warm and cold periods, any deficit of food for pollock was never observed there.

The paper is devoted to the Upper Cambrian and Tremadocian organophosphatic microfossils which were hitherto treated as conodonts and assigned mainly to the genera Coelocerodontus and Viirodus. Individual elements of the fossils, similarly to the elements of conodonts, belonged originally to the multi-element apparatuses. Present studies, based mainly on the collections from Sweden, Poland (core sections), Estonia and Kazakhstan, show that despite the similarities of their individual elements to conodonts, they significantly differ from them in the inner structure, as well as in the construction of the apparatuses composed of them. Elements of their apparatuses are matched in shape to each other and certainly functioned in conjunction, while those belonging to the euconodont apparatuses are usually differentiated in shape and usually functioned in separation. All fossils of this group are provisionally named coelocerodonts in this paper. Their individual elements, as well as the apparatuses composed of them, are similar in construction to those of the genus Phakelodus, which is an ancestor of chaetognaths.

The use of pots in the north Atlantic finfish fisheries is negligible because this fishing method typically has a low capture efficiency. Large numbers of individuals encounter baited pots, but the proportions of fish that enter the pot and become caught are low. Krill, which constitutes an important prey for cod (Gadus morhua), is attracted by light. The catching efficiency of baited cod pots with three light sources with different colours and intensities (white: 9744 mW m−2, white: 23 mW m−2, green: 8 mW m−2) were tested in coastal waters in northern Norway. Pots with the light source of highest intensity gave a 17 times higher catch rate of cod than that of control pots (with bait only). The light source of medium intensity gave about a five times higher catch rate, whereas the weakest light did not influence the catch. Cod caught in pots with light had more krill and arrowworms in their stomach and were observed feeding on these preys inside the pot. We concluded that light sources of increasing intensity attract more krill, and that cod were attracted into the pot by the dense swarms of prey and not the light per se. [ABSTRACT FROM AUTHOR]

Although Serratosagitta tasmanica is widely distributed, there is little information on how hydrology affects its distribution, abundance and demography. In this study we analyzed the distribution, carbon content and population structure of S. tasmanica in the Southwestern Atlantic Ocean. Samples were collected at 34°-39°S (Northern Argentine Continental Shelf in winters of 1999 and 2000) and at 47°-55°S (Southern Argentine Continental Shelf in spring 2005, summer 2006 and winter 2006). The analysis of more than 8500 individuals showed that its dominance decreased spatially from south to north, whereas biomass (mgC/m2) increased temporally by three orders of magnitude between spring (4.06) and summer (12.7). In the southern area the presence of all maturity stages in all seasons suggests year-round reproduction, with maximum reproductive activity in winter. Body length increased with increasing latitude and decreased with temperature. We detected differences in the morphology of seminal vesicles and ovary length between mature specimens. In the northern area all individuals exhibited short-type ovaries whereas in the southern area individuals had either short or long ovaries, suggesting that some individuals of the latter area had been advected from the Southern Pacific Ocean through the water discharged from the Magellan Strait. [ABSTRACT FROM AUTHOR]

An attempt was made out to study the distribution and diversity of gelatinous zooplankton in the South Eastern Arabian Sea in the region Kanyakumari to off Kollam. A total of 19 species belonging to 8 groups such as chaetognaths, siphonophores, Hydrozoa and Scyphozoa of the phylum Cnidaria, ctenophores, appendicularians, doliolids and salps were recorded. Chaetognaths were not only predominant group, but also the most numerous. Sagitta enflata was the most widely distributed chaetognath species from most of the stations studied. The siphonophores were the second most abundant group. Shannon-Weaver species diversity index (H'), Margalef's species diversity index (D) and Pielou's species evenness (J') of gelatinous zooplankton were found to be higher from the off shore, Kollam (Station 10) and minimum from the inshore, the Kanyakumari (Cape) West (Station 1). Diversity of gelatinous zooplankton was found to be positively correlated with atmospheric temperature, sea surface temperature and pH. A continuous seasonal study should be conducted to understand the clear impact of physical and chemical factors on the distribution and diversity of gelatinous zooplankton along this region. [ABSTRACT FROM AUTHOR]

Abstract Microplastic ingestion by mesozooplankton may be an important pathway for the microplastics to enter the food web. To determine microplastic abundance in Guanabara Bay, samples were collected by neustonic haul with a 64-μm-net and oblique hauls using 64- and 200-μm nets. Microplastic size and abundance as well as copepod, fish-larvae, and chaetognath sizes, densities, and preferential prey sizes were determined. Microplastic abundance was higher in samples collected with fine nets (average 4.8 microplastics m−3, maximum 11 microplastics m−3) than in those collected with coarse net. Microplastic abundance in Guanabara Bay was higher than that in other marine ecosystems. Microplastics >100 μm were too large to be ingested by copepods. However, for fish larvae and chaetognaths, the abundance of microplastics, at the corresponding prey size range, were, respectively, ~9000- and 14,400-folds lower than the preferential copepod prey, in the same size range. Thus, in Guanabara Bay, microplastics were available, but too diluted to be frequently ingested by fish larvae and chaetognaths. Highlights • Higher microplastic abundances determined by using fine mesh nets • The relevance of sampling microplastic over the whole water column • High microplastic abundance, but high zooplankton:microplastic ratios • Estimates of potential microplastic ingestion by fish larvae and chaetognaths [ABSTRACT FROM AUTHOR]

Most known giant viruses, i.e., viruses producing giant virions, parasitize amoebae and other unicellular eukaryotes. Although they vary in the level of dependence on host nuclear functions, their virions self-assemble in the host cell’s cytoplasm. Here we report the discovery of a new prototype of giant virus infecting epidermal cells of the marine arrow worm Adhesisagitta hispida. Its 1.25 μm-long virions self-assemble and accumulate in the host cell’s nucleus. Conventional transmission electron microscopy reveals that the virions have a unique bipartite structure. An ovoid nucleocapsid, situated in a broad “head” end of the virion is surrounded by a thin envelope. The latter extends away from the head to form a voluminous conical “tail” filled with electron-dense extracapsidular material. The 31nm-thick capsid wall has a distinctive substructure resulting from a patterned arrangement of subunits; it bears no ultrastructural resemblance to the virion walls of other known giant viruses. The envelope self-assembles coincident with the capsid and remotely from all host membranes. We postulate that transmission to new hosts occurs by rupture of protruding virion-filled nuclei when infected arrow worms mate. Future genomic work is needed to determine the phylogenetic position of this new virus, which we have provisionally named Meelsvirus. [ABSTRACT FROM AUTHOR]

Zooplankton in shelf waters is dominated by a highly diverse assemblage of copepods, followed by a variety of organisms sorted according to the environmental conditions. Epipelagic copepod, chaetognath and cladoceran species assemblages in the upper 100 m layer, together with mesozooplankton major groups were characterized in relation to dynamics of the water masses in the subtropical domain of the Brazilian shelf. Water samples for nutrients and chlorophyll, measurements of temperature, salinity and fluorescence (Rosette/CTD) and zooplankton samples were collected in four transects (26°S to 29°S), ~ 250 km long, across the shelf, during early summer. Intrusions of the cold South Atlantic Central Water (~ 15 m) was evidenced by the large abundance (> 3000 ind.m -3 ) of the small copepod Oncaea venusta , highlighting the role of small omnivorous copepods in the coastal upwelling at ~ 26°S. Low-salinity waters (< 34.5) were observed up to 120 km off the bay area at ~ 29°S, together with a high abundance of Temora turbinata . At the slope, the dominance of the Tropical Water increased the prevalence of Clausocalanus furcatus . The chaetognath Flaccisagitta enflata and the cladoceran Penilia avirostris in the inner shelf and the cladoceran Evadne spinifera in the outer shelf were also dominant species in the area. Zooplankton assemblages were related to different oceanographic scenarios, associated with coastal upwelling, coastal and estuarine plumes, shelf and slope areas. These assemblages were mainly comprised of epipelagic and tropical species; however, the recurrent presence of copepod, cladoceran and chaetognath cold-water species reinforced the transitional character of the area. In addition, there was a clear cross-shelf gradient, with an increasing contribution of large copepods, siphonophores, salps and euphausiids toward the ocean. The characteristic tropical species assemblages emphasise the dominant role of small metazoans in the pelagic food webs driven by the dynamics of the water masses. The species assemblages also established the species distribution baseline in the subtropical Brazilian shelf. [ABSTRACT FROM AUTHOR]

Continental slope canyons off the United States Atlantic coast remain poorly studied, and in particular, the distributions of pelagic organisms in waters overlying these unique environments are not well documented. During the Early Career Scientist Deep Submergence Training cruise, AT36-EAGER, the distribution of organisms in the water column overlying Hydrographer Canyon, which cuts through the northwestern Atlantic continental margin, was investigated through daytime midwater observations using HOV Alvin (AD4831) at three depths. Mixed swarms of krill and Themisto sp. amphipods were observed at all depths surveyed. Observations centered at 250 m were also dominated by chaetognaths, copepods, and Phronima sp. amphipods, while at 500 and 750 m, the assemblages were dominated by the fishes in the families Paralepididae, Nemichthyidae, and Mytophidae. Additionally, measurements of methane, nitrous oxide, optical properties (absorbance and fluorescence), dissolved organic carbon, and base-extracted particulate organic carbon were made to better characterize the hydrography and biogeochemistry over Hydrographer Canyon. This study was aided by the use of telepresence to communicate between ship and shore-based researchers, and the expedition marks the first use of SMS messaging to communicate between the submersible and the ship. This study demonstrates the capabilities and utility of using Alvin for conducting water column science. [ABSTRACT FROM AUTHOR]

The corona ciliata of Chaetognatha (arrow worms) is a circular or elliptical groove lined by a rim from which multiple lines of cilia emanate, located dorsally on the head and/or trunk. Mechanoreception, chemosensation, excretion, respiration, and support of reproduction have been suggested to be its main functions. Here we provide the first experimental evidence that the cilia produce significant water flow, and the first visualisation and quantification of this flow. In Spadella cephaloptera , water is accelerated toward the corona ciliata from dorsal and anterior of the body in a funnel-shaped pattern, and expelled laterally and caudally from the corona, with part of the water being recirculated. Maximal flow speeds were approximately 140 μm s −1 in adult specimens. Volumetric flow rate was Q = 0.0026 μl s −1 . The funnel-shaped directional flow can possibly enable directional chemosensation. The flow measurements demonstrate that the corona ciliata is well suited as a multifunctional organ. [ABSTRACT FROM AUTHOR]

Chaetognaths (arrow-worms) are enigmatic in terms of their phylogenetic position, while the existence of Protosagitta spinosa from the Chengjiang Lagerstätte suggests minimal change in their unique bodyplan since at least the early Cambrian. Apart from rare (and sometimes controversial) soft-bodied remains, the fossil record of chaetognaths is otherwise almost entirely dependent on early Palaeozoic phosphatic microfossils, some of which are placed amongst so-called protoconodonts. Fused spine clusters are strikingly similar to the cephalic grasping apparatus of extant forms and are assumed to have had a comparable configuration. Here we report a new chaetognath, Ankalodous sericus gen. et sp. nov., coeval with Protosagitta but with a complex feeding apparatus consisting of multiple bundles of recurved spines whose principal function appears to have been grasping. Like all other chaetognaths a predatory mode of life is likely, but its position relative to the sediment-water interface is less certain. Reduction of the feeding apparatus, from the multi-jawed arrangement of A. sericus to the grasping spines and associated smaller teeth seen in other chaetognaths, was probably a subsequent development and conceivably was linked with a shift to a pelagic mode of life. We also report a new specimen of Protosagitta. This confirms earlier observations but it possesses hitherto unrecognized features, including a cephalic tentacle and fin rays. [ABSTRACT FROM AUTHOR]

In Arctic seas, primary production and the availability of food for zooplankton are strongly pulsed over the short productive summer. We tested the hypothesis that Eukrohnia hamata and Parasagitta elegans, two similar and sympatric arctic chaetognaths, partition resources through different reproductive strategies. The two species had similar natural longevities of around 2 years. Eukrohnia hamata, which occurred at epi- and meso-pelagic depths, spawned two distinct broods in autumn and spring. Offspring production coincided with drops in the frequency of E. hamata with visible lipid reserves, characteristic of capital breeders. Growth was positive from April to January and negative in February and March. Growth and maturation were similar for the two broods. Storage reserves contained in an oil vacuole may allow E. hamata to reproduce and grow outside the short production season. Parasagitta elegans produced one brood in summer-autumn during peak production in near-surface waters, characteristic of income breeders. In winter, P. elegans co-inhabited meso-pelagic waters with E. hamata, where it neither grew nor reproduced. As the Arctic warms, the development of an autumn phytoplankton bloom could favour the summer-autumn brood of P. elegans. [ABSTRACT FROM AUTHOR]

Until recently many oceanic zooplankton species have been considered as cosmopolitan organisms. At present it became evident that some of them comprise many distinct molecular operational taxonomic units (MOTUs) that often are regarded as cryptic species. As they can significantly change our perceptions of large-scale biogeographic patterns, it is important to characterize the true diversity within common and ecologically important groups. We have analysed the molecular and morphological diversity of the cosmopolitan mesopelagic chaetognath Pseudosagitta maxima throughout the Atlantic Ocean from 60° S to 85° N and its position within the genus Pseudosagitta. Three distinct mitochondrial clades within P. maxima were revealed with phylogenetic analyses (Maximum Likelihood, Bayesian Inference) and were geographically separated. The subsequent analyses of nuclear markers (H3, ITS1) have shown that P. maxima most likely comprises two distinct MOTUs, tropical and bipolar, that also have some morphological differences. The latter MOTU consists of two genetically slightly divergent populations: southern and northern. The morphological examination allowed the determination of a character (type of hook coloration) that accurately distinguishes juveniles of the P. maxima complex from the other congeneric species. Molecular data have shown that evolutionary P. lyra and P. gazellae are more closely related to each other than to P. maxima. Number of hooks, number of anterior and posterior teeth and the arrangement of ova in the ovary were proposed to be the most useful morphological characters to distinguish between tropical and bipolar MOTUs within the P. maxima complex. The first three characters should be determined for each maturity stage separately. [ABSTRACT FROM AUTHOR]

The extentofwithin-species genetic variation across thediversityof animal life is an underexplored problem in ecology and evolution. Although neutral genetic variation should scale positively with population size, mitochondrial diversity levels are believed to show little variation across animal species. Here, we report an unprecedented case of extreme mitochondrial diversity within natural populations of twomorphospecies of chaetognaths (arrowworms). We determine that this diversity is composed of deep sympatric mitochondrial lineages, which are in some cases as divergent as human and platypus. Additionally, based on 54 complete mitogenomes, we observed mitochondrial gene order differences between several of these lineages. We examined nuclear divergence patterns (18S, 28S, and an intron) to determine the possible origin of these lineages, but did not find congruent patterns between mitochondrial and nuclearmarkers. We also show that extrememitochondrial divergence in chaetognaths is not driven by positive selection. Hence, we propose that the extreme levels of mitochondrial variation could be the result of either a complex scenario of reproductive isolation, or a combination of large population size and accelerated mitochondrial mutation rate. These findings emphasize the importance of characterizing genome-wide levels of nuclear variation in these species and promote chaetognaths as a remarkable model to study mitochondrial evolution. [ABSTRACT FROM AUTHOR]

The Red Sea has been recognized as a unique region to study the effects of ecohydrographic gradients at a basin-wide scale. Its gradient of temperature and salinity relates to the Indian Ocean monsoon and associated wind-driven transport of fertile and plankton-rich water in winter from the Gulf of Aden into the Red Sea. Subsequent evaporation and thermohaline circulation increase the salinity and decrease water temperatures toward the North. Compared with other ocean systems, however, relatively little is known about the zooplankton biodiversity of the Red Sea and how this relates to Red Sea latitudinal gradients. Among the most abundant zooplankton taxa are Chaetognatha, which play an important role as secondary consumers in most marine food webs. Since Chaetognatha are sensitive to changes in temperature and salinity, we surmised latitudinal changes in their biodiversity, community structure and diel variability along the coast of Saudi Arabia. Samples were collected at nine coral reefs spanning approximately 1500 km, from the Gulf of Aqaba in the northern Red Sea to the Farasan Archipelago in the southern Red Sea. Thirteen Chaetognatha species belonging to two families (Sagittidae and Krohnittidae) were identified. Latitudinal environmental changes and availability of prey (i.e. Copepoda, Crustacea) altered Chaetognatha density and distribution. The cosmopolitan epiplanktonic Flaccisagitta enflata (38.1%) dominated the Chaetognatha community, and its abundance gradually decreased from South to North. Notable were two mesopelagic species (Decipisagitta decipiens and Caecosagitta macrocephala) in the near-reef surface mixed layers at some sites. This was related to wind-induced upwelling of deep water into the coral reefs providing evidence of trophic oceanic subsidies. Most Sagittidae occurred in higher abundances at night, whereas Krohnittidae were more present during the day. Chaetognatha with developing (stage II) or mature ovaries (stage III) were more active at night, demonstrating stage-specific diel vertical migration as a potential predator avoidance strategy. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to track the seasonal vertical distribution of zooplankton abundance in the epipelagic zone off Sharm El-Sheikh, Red Sea. Zooplankton samples were collected seasonally within the depth ranges of 0-25, 25-50, 50-75, 75-100 m at a single station off Sharm El-Sheikh City. The present study is a trial to expand knowledge about the structure as well as the vertical distribution of the epipelagic zooplankton community in the Gulf of Aqaba in general and in its southern part in particular. The results indicate the occurrence of 52 copepod species and several species of other planktonic groups in the study area; the zooplankton standing crop fluctuated between 1124 and 4952 organisms m-3. Copepods appeared to be the predominant component, forming an average of 86.5% of the total zooplankton count, and with other groups demonstrated a markedly different seasonal vertical distribution. Twelve bathypelagic copepod species were reported during the present study, and five species were new to the area, having migrated northwards from the main basin of the Red Sea.

The aim of this study was to describe the total density, densities of developmental stages and the reproduction period of Parasagitta friderici. Weekly samples were collected at one station in the channel of Guanabara Bay, Rio de Janeiro, during one year. Three vertical hauls were made for each sample, and P. friderici was separated, the developmental stages were identified, and body length (BL), ovary length (OL) and seminal vesicle width (SVW) were measured. Throughout the year P. friderici was the most abundant chaetognath species occurring in all four developmental stages, the densities of which varied from week to week. Higher densities of adults occurred in the spring, followed by peaks of juveniles in the summer. Although P. friderici seems to reproduce continuously in Guanabara Bay, a reproductive peak was apparent during the spring. The intensification of reproduction during the spring, with juveniles occurring in the summer, seems to be related to the period of higher food supply during the rainy season and intrusions of the South Atlantic Central Water.O objetivo deste estudo foi descrever a densidade total, densidades dos estágios de desenvolvimento e o período reprodutivo de Parasagitta friderici. As coletas foram realizadas semanalmente durante um ano em uma estação no canal da Baía de Guanabara, Rio de Janeiro. Foram realizados três arrastos verticais em cada amostragem e, P. friderici foi separada, os estágios de desenvolvimento identificados e o comprimento do corpo, comprimento dos ovários e a largura da vesícula seminal foram medidos. Ao longo do ano, P. friderici foi a espécie de Chaetognatha mais abundante, ocorrendo em todos os quatro estágios de desenvolvimento, dos quais as densidades variaram entre as semanas. As densidades mais altas de adultos ocorreram na primavera seguidas de picos de juvenis no verão. Embora, P. friderici se reproduza continuamente na baía de Guanabara, um pico reprodutivo foi aparente durante a primavera. A intensificação da reprodução durante a primavera com a ocorrência de juvenis no verão, parece estar relacionada ao aumento da oferta de alimento durante a estação chuvosa e intrusões da Água Central do Atlântico Sul.

Population dynamics of Ferosagittaferox (Chaetognatha) was carried out in coastal waters Of Khur-e-Mussa's Channel in Khuzestan Province, northwest Persian Gulf. Monthly samples were collected with 300 mm mesh size plankton net in oblique tow from near bottom to surface waters. In total, 7 species of Chaetognaths were identified belonging to I class (Sagittoidea), 1 order (Aphragmophora), 2 families (Sagittidae and Krohnittidae) and 4 genera (Aidanosagitta, Ferosagitta, Flaccisagitta and Krohnitta). The identified species included Aidanosagitta bedfordi, A. neglecta, Ferosagitta ferox, Flaccisagitta enflata, F. hexaptera, Krohnitta pacifica and one unknown species. Due to presence and excessive frequency of Ferosagitta ferox in all samples, we focused on its population variation as an indicator of Chaetognatha. We determined length groups for adult individuals in 4-21mm range with 1mm increments. The year round presence of juvenile and small individuals showed the continuous reproduction of F. ferox with two considerable peaks in March and July. The evaluated recruitment indicated that the species has a low growth rate and a long life cycle.