Revision of the 'Acanthephyra purpurea' species complex (Crustacea: Decapoda), with an emphasis on species diversification in the Atlantic.

We inventoried all nine species of the 'Acanthephyra purpurea' complex, one of the most abundant and cosmopolitan group of mesopelagic shrimps. We used 119 specimens at hand and genetic data for 124 specimens from GenBank and BOLD. Phylogenetic analysis of four genes (COI, 16S, NaK, and enolase) showed that the 'Acanthephyra purpurea' complex is polyphyletic and encompasses two species groups, 'A. purpurea' (mostly Atlantic) and 'A. smithi' (Indo-West Pacific). The 'A. purpurea' species group consists of two major molecular clades A. pelagica and A. kingsleyi - A. purpurea - A. quadrispinosa. Molecular data suggest that hitherto accepted species A. acanthitelsonis, A. pelagica, and A. sica should be considered as synonyms. The Atlantic is inhabited by at least two cryptic genetic lineages of A. pelagica and A. quadrispinosa. Morphological analyses of qualitative and quantitative (900 measurements) characters resulted in a tabular key to species and in a finding of four evolutionary traits. Atlantic species showed various scenarios of diversification visible on mitochondrial gene level, nuclear gene level, and morphological level. We recorded and discussed similar phylogeographic trends in diversification and in distribution of genetic lineages within two different clades: A. pelagica and A. kingsleyi - A. purpurea - A. quadrispinosa.

Zooplankton communities in the Drake Passage through environmental boundaries: a snapshot of 2010, early spring.

BACKGROUND: Spatial distribution of zooplankton communities influenced by various environmental factors is always important for understanding pelagic ecosystems. The area of the Drake Passage (Southern Ocean) is of particular interest owing to the high spatial and temporal variability of hydrological parameters affecting marine fauna. This study provides a survey of zooplankton composition and spatial distribution along a transect in the Drake Passage sampled during the 31th Cruise of RV "Akademik Sergey Vavilov" in November, 2010. The main aim was to trace the main regularities in spatial zooplankton structure and its relationships with the environmental parameters. METHODOLOGY: A total of 43 vertical hauls from the surface to 1,000 m depth were made at 13 stations using the Juday plankton net. 60 taxa were recorded, abundance and biomass of each were assessed. Environmental parameters including temperature, salinity, depth, horizontal distance between stations and surface chlorophyll concentration were tested as environmental factors possibly explaining plankton distribution. RESULTS: Higher zooplankton abundance and biomass with lower diversity were observed near the Polar Front. Cluster analysis revealed five different groups of zooplankton samples, four of which were arranged mostly by depth. Along the transect within the 1,000 m depth range, the qualitative taxonomical composition differed significantly with depth and to some extent differed also among horizontal hydrological regimes, while the quantitative structure of the communities (abundance of taxa) was mainly determined by depth. Plankton assemblages within the upper 300-m layer depended on hydrological fronts. Abundance of dominant taxa as well as total zooplankton abundance showed a clear correlation with depth, salinity and surface chlorophyll concentration. Some taxa also showed correlations with temperature and latitude. Between the stations the similarity in zooplankton structure was clearly dependent on the distance among them which indicates an importance of latitudinal gradient. Surface chlorophyll concentration was not correlated with zooplankton biomass, which can be explained by the uncompleted seasonal migrations of zooplankton from deeper waters in early spring.

Long-term studies reveal major environmental factors driving zooplankton dynamics and periodicities in the Black Sea coastal zooplankton.

BACKGROUND: The development and management of shelf-sea ecosystems require a holistic understanding of the factors that influence the zooplankton structure and ecosystem functions. The Black Sea is an example of such areas influenced by eutrophication, overfishing, climate variability, invasions of the ctenophores Mnemiopsis leidyi followed by Beroe ovata. Thus, there is a set of principal factors which may influence and explain periodicities in the Black Sea ecosystem. METHODS: We analysed a total of 918 samples taken from 1991 to 2017 with intervals of 10 days. Taxa were identified to species, their abundance and biomass were calculated. We tested 12 environmental factors, which may explain zooplankton distribution: temperature, productivity-linked factors (surface chlorophyll as a proxi), wind, turbidity, lowest winter temperature, and concentration of the ctenophore M. leidyi. We used canonical correspondence analyses to find the dominant environmental factors and further regression analyses to retrieve dependences of plankton biomass on the major factors. Periodicities were assessed with the use of the Continuous wavelet transform and tested with use of One-way ANOSIM and PERMANOVA. The distances between ecosystem states in different years were assessed using non-metric multidimensional scaling. RESULTS: Currently, temperature and productivity are the major environmental factors driving zooplankton dynamics. Not long ago, before 1999, abundance of M. leidyi was one of the major factors explaining the zooplankton variance. Spectral analysis of species abundances revealed a 4-year transitional period in 1999-2002 (not reported before) when ecosystem adapted to a new invader B. ovata. Statistically robust 2- and 3-year periodicities were retrieved for most plankton taxa and some benthic larvae. We found robust correlations between temperature and surface chlorophyll concentration on one side and plankton abundances and biomass on the other, and retrieved multivariate regressions, which may have a prognostic value.

Assessing Deep-Pelagic Shrimp Biomass to 3000 m in The Atlantic Ocean and Ramifications of Upscaled Global Biomass.

We assess the biomass of deep-pelagic shrimps in the Atlantic Ocean using data collected between 40°N and 40°S. Forty-eight stations were sampled in discrete-depth fashion, including epi- (0-200 m), meso- (200-800/1000 m), upper bathy- (800/1000-1500 m), and lower bathypelagic (1500-3000 m) strata. We compared samples collected from the same area on the same night using obliquely towed trawls and large vertically towed nets and found that shrimp catches from the latter were significantly higher. This suggests that vertical nets are more efficient for biomass assessments, and we report these values here. We further compared day and night samples from the same site and found that biomass estimates differed only in the epi- and mesopelagic strata, while estimates from the bathypelagic strata and the total water column were independent of time of day. Maximal shrimp standing stocks occurred in the upper bathypelagic (52-54% of total biomass) and in the mesopelagic (42-43%). We assessed shrimp biomass in three major regions of the Atlantic between 40°N and 40°S, and the first-order extrapolation of these data suggests that the global low-latitude deep-pelagic shrimp biomass (1700 million tons) may lie within the range reported for mesopelagic fishes (estimations between 1000 and 15000 million tons). These data, along with previous fish-biomass estimates, call for the reassessment of the quantity and distribution of nektonic carbon in the deep ocean.

A phylogenetic study of krill (Crustacea: Euphausiacea) reveals new taxa and co-evolution of morphological characters.

The first comprehensive phylogenetic study of Euphausiacea (all 86 valid species) is presented. It is based on four molecular markers and 168 morphological characters (including 58 characters of the petasma). Phylogenetic analyses support the monophyly and robustness of the families Bentheuphausidae and Euphausiidae and reveal three major clades for which we erect three new subfamilies: Thysanopodinae, Euphausiinae and Nematoscelinae. All genus-level clades are statistically supported (except Thysanopoda in molecular analyses), deeply nested within the subfamily-level clades, and encompass 14 new species groups. Copulatory structures have a major impact on tree topology in the morphological analysis, the removal of which resulted in only half the number of supported clades and genera. We revealed three groups of morphological characters, which are probably coupled with the same biological role and thus interlinked evolutionarily: (i) antennular peduncle and petasma (copulation); (ii) eyes and anterior thoracopods (feeding); and (iii) shape of carapace and pleon (defence). We analysed the evolutionary pathways of the clades into main oceanic biotopes and compared them with morphological adaptations most likely to be coupled with this process.

The genus Gennadas (Benthesicymidae: Decapoda): morphology of copulatory characters, phylogeny and coevolution of genital structures.

Species within Gennadas differ from each other largely only in male (petasma) and female (thelycum) copulatory characters, which were restudied in scanning electron microscopy and used as a basis for phylogenetic analyses. Twenty-six petasma characters and 49 thelycum characters were identified. All 16 recognized species of Gennadas and Aristaeomorpha foliacea (outgroup) were included as terminals. Four robust monophyletic clades were retrieved, described and diagnosed as new species groups. The thelycum characters had greater impact on tree topology and supported deeper nodes than did the petasma characters. We hypothesize that features of the thelycum evolved first followed by aspects of the petasma. Relatively more conservative characters include parts of the sternites of the thelycum and of the petasma, while the scuti and protuberances on the thelycum and the shape and subdivisions of the petasma lobes are evolutionarily plastic. We identified two groups of copulatory characters, which are likely coupled functionally and interlinked evolutionarily: (i) the external part of the petasma and the posterior part of the thelycum and (ii) the internal part of the petasma and anterior part of the thelycum. We reconstruct possible mating position during copulation for each of the new species groups presented here. We also present an updated key to genera of Benthesicymidae and key to species of Gennadas.

Phylogeny and New Classification of Hydrothermal Vent and Seep Shrimps of the Family Alvinocarididae (Decapoda).

The paper addresses the phylogeny and classification of the hydrothermal vent shrimp family Alvinocarididae. Two morphological cladistic analyses were carried out, which use all 31 recognized species of Alvinocarididae as terminal taxa. As outgroups, two species were included, both representing major caridean clades: Acanthephyra purpurea (Acanthephyridae) and Alpheus echiurophilus (Alpheidae). For additional support of the clades we utilised available data on mitochondrial Cytochrome c Oxidase I gene (CO1) and 16S ribosomal markers. Both morphological and molecular methods resulted in similar tree topologies and nearly identical clades. We consider these clades as evolutionary units and thus erect two new subfamilies: Rimicaridinae (Alvinocaridinides, Manuscaris, Opaepele, Shinkaicaris, Rimicaris), Alvinocaridinae (Alvinocaris), whilst recognising Mirocaridinae (with genera Mirocaris and Nautilocaris) at subfamily level. One genus, Keldyshicaris could not be assigned to any subfamily and is thus left as incertae sedis. The monophyly of Alvinocardinae was supported by morphological data, but not supported by molecular data (two analyses); the monophyly of all subfamilies was supported both by morphological and molecular data. Chorocaris is herein synonymized with Rimicaris, whilst Opaepele vavilovi is herein transferred to a new genus Keldyshicaris. Morphological trends within Alvinocarididae are discussed and short biogeographical remarks are given. We provide emended diagnoses for all subfamilies and genera along with keys to all recognized species.

Global diversity and phylogeny of pelagic shrimps of the former genera Sergestes and Sergia (Crustacea, Dendrobranchiata, Sergestidae), with definition of eight new genera.

We revise the global diversity of the former genera Sergia and Sergestes which include 71 valid species. The revision is based on examination of more than 37,000 specimens from collections in the Natural History Museum of Denmark and the Museum of Natural History, Paris. We used 72 morphological characters (61 binary, 11 multistate) and Sicyonella antennata as an outgroup for cladistic analysis. There is no support for the genera Sergia and Sergestes as they have been defined until now. We define and diagnose eight genera of the former genus Sergia (Sergia and new genera Gardinerosergia, Phorcosergia, Prehensilosergia, Robustosergia, Scintillosergia, Challengerosergia, and Lucensosergia) and seven genera of the former genus Sergestes (Sergestes, Deosergestes, Eusergestes, Allosergestes, Parasergestes, Neosergestes, and a new genus Cornutosergestes). An identification key is presented for all genera of the family Sergestidae. The phylogeny of Sergestidae is mainly based on three categories of characters related to: (1) general decapod morphology, (2) male copulatory organs, and (3) photophores. Only simultaneous use of all three character types resulted in a resolved tree with minimal Bootstrap support 75 for each clade. Most genera are interzonal mesopelagic migrants, some are benthopelagic (Scintillosergia, Lucensosergia), bathypelagic (Sergia), or epipelagic (Cornutosergestes). Within each of meso- and benthopelagic genera there is one species with panoceanic distribution, while most species ranges are restricted to a single ocean. The genera demonstrate two different strategies expressed both in morphology and behavior: protective (Eusergestes, Sergestes, Cornutosergestes, Prehensilosergia, Scintillosergia, Lucensosergia, Challengerosergia, Gardinerosergia, Robustosergia, Phorcosergia, Sergia) and offensive (Neosergestes, Parasergestes, Allosergestes, Deosergestes).

Composition and dynamics of the Black Sea benthopelagic plankton and its contribution to the near-shore plankton communities.

At a shallow (7 m) near-shore sampling site in the Black Sea we analyzed composition, abundance, and biomass of benthopelagic organisms and the contribution these animals make to the total plankton. The site was monitored across several years (1996-2001; 2006-2007) whilst for 1999-2000 the seasonal variations were analysed. A total of 321 samples from Golubaja Bay near Novorossiysk (44°34'31.04″ N, 37°58'45.11″ E) in 1996-2007 were taken with a Judey net. The benthopelagic fauna was represented by 69 taxa, a diversity comparable to similar shelf areas. The benthopelagic component played an important role in near-shore plankton communities in the Black Sea accounting for 50% of the total zooplankton biomass at night during all seasons. Abundance and biomass of the benthopelagic animals showed seasonal fluctuations, the highest biomass being recorded during winter (>75% of the total zooplankton biomass) and early spring due to large amphipods, whilst the highest abundances occur during late summer because of numerous young stages of various taxa. Amphipods, mysids, and decapods are the main contributors to the plankton biomass and abundances. Both night and daytime samples are strongly recommended for the adequate description of the near-shore plankton communities.