Acartia Longiremis Research Articles

Food Selectivity in Juvenile Three-Spined Stickleback Gasterosteus aculeatus L. (Gasterosteidae) at Nursery Grounds in the White Sea

The spatial and temporal variability in the dietary preferences of juvenile three-spined stickleback Gasterosteus aculeatus were studied across the typical coastal habitats of Keret Archipelago, Kandalaksha Bay(the White Sea). The sampling of fish using a beach seine was conducted in the late July–early August period and in late August. Additionally, zooplankton samples were collected to conduct a quantitative assessment of the abundance of potential prey items. The similarity percentage (SIMPER) analysis was applied to the data obtained from the stomach content and revealed the five planktonic taxa most prominently contributing to the diet of juvenile sticklebacks. Among these, the copepod Temora longicornis was the most important prey item at marine sites, while Acartia longiremis dominated the diet of fish in the marine lagoon. The calculation of the selectivity index revealed that some taxa (such as A. longiremis) were always avoided by juvenile fish, whereas the selectivity of some taxa increased in late August. In general, juvenile sticklebacks demonstrated a pronounced individual variation in their selectivity, even when a particular prey item was selected positively during the whole period of study. Our data highlight that despite the predominant consumption of easily available prey by juvenile sticklebacks, they demonstrate taxonomic- and size-specific prey selectivity.

Kanningar av gongdini hjá fjarðarsild í Føroyum gjøgnum samdøgrið

In october 1968 investigations on plankton and 1, 2 and 3 years old herring were carried out during 24 hours in Funningsfjørður, Faroe Islands. Plankton as well as herring showed vertical migration.
 In daytime the main part of the herring and the plankton stayed from the bottom up to a level of 10 m below the surface, in the night they moved up from bottom coming to íhe surface entirely.
 The echograms showing the movements of the herring form a picture corresponding with Ball's (1951) three step movement described for middle depths in the North Sea. The only factor which the day and night migrations could be correlated with was the light intensity.
 Stomach contents was found in the afternoon, whereas a sample of herring taken at 730 GMT, at sunrise, had empty stomachs only. The herring feed was composed of Acartia sp. besides some few Temora longicornis. Acartia longiremis and Acartia Clausii were dominating in the plankton samples, ohiefly females with egg sacks.

Differential response of distinct copepod life history types to spring environmental forcing in Rivers Inlet, British Columbia, Canada.

The temporal dynamics of five copepod species common to coastal waters of the Pacific Northwest were examined in relation to variability in spring temperature and phytoplankton dynamics in 2008, 2009, and 2010 in Rivers Inlet, British Columbia, Canada. The five species were differentiated by life history strategies. Acartia longiremis, Metridia pacifica, and Paraeuchaeta elongata remained active over most of the year. By contrast, the reproductive effort of Eucalanus bungii and Calanus marshallae was concentrated over the spring period and they spent most of the year in diapause as C5 copepodites. A delay in the timing of the spring bloom was associated with a shift in the phenology of all species. However, following the delay in spring bloom timing, recruitment to the G1 cohort was reduced only for E. bungii and C. marshallae. Recruitment successes of E. bungii and C. marshallae was also drastically reduced in 2010, an El Niño year, when spring temperatures were highest. Reasons for the observed differential response to spring environmental forcing, and its effect on upper trophic levels, are discussed.

Reduced pH increases mortality and genotoxicity in an Arctic coastal copepod, Acartia longiremis.

This study investigates DNA damage and mortality in an Arctic marine copepod after long-term exposure to lowered pH. Acartia longiremis were collected from northern Norway and incubated in ambient pH 8.1, and reduced pH 7.6 and 7.2 over 3-4 weeks. Cumulative mortality was significantly elevated in the lowered pH treatments in all exposures. The fluorescence-based fast micromethod for analysis of DNA strand breaks and alkali-labile sites was modified for use on crustaceous zooplankton. DNA damage initially increased in the lowered pH treatments, decreasing after >14 days, and DNA damage was significantly higher in lowered pH conditions. This method is ideal for investigating oxidative stress and genotoxicity response to low pH in Arctic marine copepods exposed to future ocean acidification conditions.

Seasonal Variability in the Zooplankton Community Structure in a Sub-Arctic Fjord as Revealed by Morphological and Molecular Approaches

Phyto- and zooplankton in Arctic and sub-Arctic seas show very strong seasonal changes in diversity and biomass. Here we document the seasonal variability in the mesozooplankton community structure in a sub-Arctic fjord in Northern Norway based on monthly sampling between November 2018 and February 2020. We combined traditional morphological zooplankton identification with DNA metabarcoding of a 313 base pair fragment of the COI gene. This approach allowed us to provide the most detailed mesozooplankton species list known for this region across an entire year, including both holo- and meroplankton. The zooplankton community was dominated by small copepods throughout the sampling period both in terms of abundance and relative sequence counts. However, meroplankton was the most diverse group, especially within the phylum polychaeta. We identified four distinct periods based on the seasonal analysis of the zooplankton community composition. The pre-spring bloom period (February–March) was characterized by low abundance and biomass of zooplankton. The spring bloom (April) was characterized by the presence of Calanus young stages, cirripedia and krill eggs. The spring-summer period (May–August) was characterized by a succession of meroplankton and a relatively high abundance of copepods of the genus Calanus spp. Finally, the autumn-winter period (September–December) was characterized by a high copepod diversity and a peak in abundance of small copepods (e.g., Oithona similis, Acartia longiremis, Pseudocalanus acuspes, Pseudocalanus elongatus, Pseudocalanus moultoni, Pseudocalanus minutus). During this period, we also observed an influx of boreal warm-water species which were notably absent during the rest of the year. Both the traditional community analysis and metabarcoding were highly complementary and with a few exceptions showed similar trends in the seasonal changes of the zooplankton community structure.

Capturing copepod dynamics in the Northern California Current using sentinel stations

Ecosystem indicators track information about states and trends in ocean systems and are a valuable tool for ecosystem assessment and management. To ensure that indicators are used appropriately in both science and management contexts, it is important to understand the extent to which they represent broader spatial patterns. In the Northern California Current (NCC) off the Oregon and Washington state coasts in the USA, copepod metrics derived from data collected at a well-sampled station on the Newport Hydrographic (NH) Line (‘NH05’, five nmi offshore from Newport, OR, USA) are commonly used as indicators of the region’s general ocean conditions. Using correlation analyses, we examined the utility of NH05 as a sentinel station (i.e. representative of a broader region) with respect to the abundance and biomass of warm-water and cold-water copepods in the NCC. Copepod correlations between NH05 and other locations in the NCC were higher for the warm-water copepods than the cold-water group, with correlations being slightly higher for abundance than biomass. Paracalanus parvus had the highest NH05 correlations among the warm-water copepod species, and Acartia longiremis had the highest NH05 correlations among the cold-water copepod species. We also broadened our analysis to evaluate other sampling sites as sentinel stations and found that some sites were equally or more representative of copepod dynamics in the NCC than NH05, though none of these sites tend to be sampled as often as NH05. This analysis emphasized that the warm-water copepods tend to be more similarly distributed in the NCC than the cold-water copepods, and thus their changes through time are better captured by most stations. In contrast, correlations among the cold-water copepods in the NCC vary by location and appear to be strongly related to depth, with the highest correlations at mid-shelf stations.

Features of plankton community in the Chukchi Sea in August-September, 2017

Zooplankton in the eastern Chukchi Sea is described on the data of summer observa­tions in 2017. The northern part of the surveyed area was occupied by the cold water masses from the Arctic Ocean and Beaufort Sea. Large-sized zooplankton dominated here, including copepods Calanus glacialis , C. hyperboreus (this species is an indicator of Atlantic waters) and cold-water hyperiids Themisto libellula. In the southern part of the surveyed area, small-sized zooplankton dominated by biomass and abundance and species belonged to the Bering Sea community, as copepods Calanus glacialis + Calanus marshallae , Eucalanus bungii , and Metridia pacifica , were presented in the large-sized fraction. In the western part of the sur­veyed area and in the coastal waters, small-sized copepods Pseudocalanus spp. and Oithona similis prevailed, and biomass and abundance of neritic species as Centropages abdominalis and Acartia longiremis were high, too. Besides, some species typical for desalinated water were observed here ( Eurytemora herdmani , Podon sp., and Epilabidocera amphitrites ), as well as larval forms of benthic invertebrates (larvae of polychaetes, bivalves, gastropods, and echinoderms). Arrowworms Sagitta elegans were abundant everywhere that was caused by this species reproduction. The observed structure of plankton community corresponded to feeding demands of arctic cod juveniles, but the zooplankton biomass was rather low. These features of community could be interpreted as early summer state, when its biomass does not reach the maximum yet, as it was observed, for example, in September 2007.

New data on the diet of juvenile fish in the eastern Chukchi Sea

Data on feeding of underyearlings of arctic cod Boreogadus saida , pacific cod Gadus mac­rocephalus , saffron cod Eleginus gracilis , sand lance Ammodytes hexapterus , capelin Mallotus villosus , and other fish species were collected in the Chukchi Sea in August-September, 2017 in the framework of Arctic Integrated Ecosystem Survey (Arctic IES). In the time of survey, the eastern Chukchi Sea was free of the sea ice to 72о30′ N. Large aggregations of arctic cod were observed in the surveyed area. The diet of arctic cod juveniles and youngsters of other investi­gated species included both pelagic and near-bottom zooplankton, mainly copepods, euphausiids, oikoplevres, and juvenile decapods. The copepods Calanus glacialis and Calanus. hyperboreus dominated in the northern part of the surveyed area, being typical for the Arctic Ocean and Beau­fort Sea, and the species usual for the Bering Sea, as the copepods Calanus glacialis + Calanus marshallae , Eucalanus bungii , and Neocalanus cristatus , were in predominance in its southern part. Besides of these large-sized species, the species typical for the Alaska coastal waters were presented in the diet of juveniles, as the copepods Pseudocalanus spp., Centropages abdominalis , Acartia longiremis , Podon sp., Tortanus discaudatus , Epilabidocera amphitrites , and Eurytemora herdmani , as well as larvae of Polychaeta, Echinodermata, Cirripedia and veligers of Bivalvia. The arctic cod juveniles used the whole spectrum of prey but consumed mainly smalland medium-sized zooplankton, which biomass was relatively low in 2017: 21.8–243.5 mg/m3 in the southern part of the surveyed area and 5.1–83.0 mg/m3 in its northern part. Correspondingly, their feeding intensity was higher in the south: their stomach fullness was 98.7–67.5 ‱ in the south and 76.9–46.9 ‱ in the north; the mean daily ration was 4.2 % of the body weight in the south and 3.4 % in the north. These values are considered as low or medium, possibly the stock of arctic cod was too high for the feeding base, particularly in the northern area. From the other hand, the diets of arctic cod, saffron cod and sand lance were very similar in the areas of joint habitation, so competitive relations between these species could be assumed.

Broad plasticity in the salinity tolerance of a marine copepod species, Acartia longiremis, in the Baltic Sea

Broad plasticity in the salinity tolerance of a marine copepod species, Acartia longiremis, in the Baltic Sea

Seasonal variation of zooplankton abundance and community structure in Prince William Sound, Alaska, 2009–2016

Large calanoid copepods and other zooplankters comprise the prey field for ecologically and economically important predators such as juvenile pink salmon, herring, and seabirds in Prince William Sound (PWS).​ From 2009–2016, the Gulf Watch Alaska program collected zooplankton 5–10 times each year at 12 stations in PWS to establish annual patterns. Surveys collected 188 species of zooplankton with Oithona similis, Limacina helicina, Pseudocalanus spp., and Acartia longiremis as the most common species present in 519 samples. Generalized additive models assessed seasonal abundance and showed peak abundance in July (mean: 9826 no. m−3 [95% CI: 7990–12,084]) and lowest abundance in January (503 no. m−3 [373 to 678]). Significantly higher zooplankton abundance occurred in 2010 (542 no. m−3 ± 55 SE) and lowest in 2013 (149 no. m−3 ± 13). The species composition of communities, determined via hierarchical cluster analysis and indicator species analysis, produced six distinct communities based on season and location. The winter community, characterized by warm-water indicator species including Mesocalanus tenuicornis, Calanus pacificus, and Corycaeus anglicus, diverged into four communities throughout the spring and summer. The first spring community, characterized by copepods with affinities for lower salinities, occurred sound-wide. The second spring community, comprised of planktonic larvae, appeared sporadically in PWS bays in 2011–2013. Spring and summer open water stations were defined by the presence of large calanoid copepods. A summer community including the most abundant taxa was common in 2010 and 2011, absent in 2013, then sporadically appeared in 2014 and 2015 suggesting interannual variability of zooplankton assemblages. The zooplankton community shifted to a uniform assemblage characterized by cnidarians in the early autumn. Community assemblages showed significant correlations to a set of environmental variables including SST, mixed layer depth, location, depth of chlorophyll-a max, mixed layer average salinity, chlorophyll-a maximum, and bottom depth (ρ = 0.24, p < 0.05). The disappearance of the summer community coincided with the appearance of the Gulf of Alaska warm water anomaly known as “The Blob”. A shift in zooplankton community composition during critical grazing periods for predators such as juvenile Pacific herring (Clupea pallasi) could have energetic consequences for overwintering success.

Seasonal dynamics of mesozooplankton in the Arctic Kongsfjord (Svalbard) during year-round observations from August 1998 to July 1999

We conducted a year-round mesozooplankton study in the Arctic Kongsfjord from August 1998 until July 1999 to investigate seasonal abundance and vertical as well as stage distributions of the prevalent taxa. It is the first investigation in Kongsfjord that covers the Arctic winter season and provides reasonable estimates also of small-sized copepod species. Abundant smaller copepods comprised Oithona similis, Pseudocalanus minutus, Microcalanus spp., Triconia borealis and Acartia longiremis. Among the larger copepods, Calanus finmarchicus, C. glacialis, C. hyperboreus and Metridia longa dominated. The thecosome pteropod Limacina helicina was also an important component. Abundance maxima occurred in November (988,669 ind. m−2) with one to two orders of magnitude higher numbers as compared to all other months (39,832–200,067 ind. m−2). The summers of 1998 and 1999 were characterized by intrusions of Atlantic water, but the community was not entirely dominated by advected boreal species. During winter, the majority of the mesozooplankton occurred below 100 m. Advection is the most likely reason for the accumulation of zooplankton at depth in winter, but local production may also contribute to high overwintering numbers. Much lower abundances of most species in spring suggest high winter mortality and emphasize the importance of sufficient reproductive success during the previous summer to ensure enough winter survivors as seed stock for the coming reproductive season. This study was conducted prior to the recent warming trend in the Arctic. Therefore, it provides valuable baseline data and allows comparing present and future states of the zooplankton community in Kongsfjord.

Temporal variation in copepod abundance and composition in a strong, persistent coastal upwelling zone

Zooplankton abundance and species composition provide information on environmental variability in the ocean. While zooplankton time series span the west coast of North America, less data exist off north-central California. Here, we investigated a zooplankton time series, focusing specifically on copepods, collected within the Gulf of the Farallones–Cordell Bank area (37.5° to 38.5°N) from 2004 to 2009. Impacted by seasonally strong, persistent upwelling, this study area is located downstream of a major upwelling center (Point Arena). We found copepod abundance and species composition differed significantly, particularly between the first three years (2004–2006) and the latter three years (2007–2009) of the study. These changes were mainly observed as changes in abundance of boreal copepod species, Pseudocalanus mimus and Acartia longiremis. These taxa showed increasing abundances for the latter three years of the study (2007–2009). During the first three years of the time series, environmental measurements in the region showed lower alongshore wind stress, weaker upwelling, minimal surface alongshore flow, and warmer surface ocean temperatures. Temporal variations in copepod abundance and species composition correlated with several of these environmental measurements (e.g., surface cross-shore and alongshore flows, upwelling, and alongshore wind stress), indicating environmental forcing of primary consumers and ecosystem productivity in this strong, persistent upwelling zone.

Stable Associations Masked by Temporal Variability in the Marine Copepod Microbiome.

Copepod-bacteria interactions include permanent and transient epi- and endobiotic associations that may play roles in copepod health, transfer of elements in the food web, and biogeochemical cycling. Microbiomes of three temperate copepod species (Acartia longiremis, Centropages hamatus, and Calanus finmarchicus) from the Gulf of Maine were investigated during the early summer season using high throughput amplicon sequencing. The most prominent stable component of the microbiome included several taxa within Gammaproteobacteria, with Pseudoalteromonas spp. especially abundant across copepod species. These Gammaproteobacteria appear to be promoted by the copepod association, likely benefitting from nutrient enriched microenvironments on copepods, and forming a more important part of the copepod-associated community than Vibrio spp. during the cold-water season in this temperate system. Taxon-specific associations included an elevated relative abundance of Piscirickettsiaceae and Colwelliaceae on Calanus, and Marinomonas sp. in Centropages. The communities in full and voided gut copepods had distinct characteristics, thus the presence of a food-associated microbiome was evident, including higher abundance of Rhodobacteraceae and chloroplast sequences in the transient communities. The observed variability was partially explained by collection date that may be linked to factors such as variable time since molting, gender differences, and changes in food availability and type over the study period. While some taxon-specific and stable associations were identified, temporal changes in environmental conditions, including food type, appear to be key in controlling the composition of bacterial communities associated with copepods in this temperate coastal system during the early summer.

Egg production rates of two common copepods in the Barents Sea in summer

Small copepod species play important roles in the pelagic food webs of the Arctic Ocean, linking primary producers to higher trophic levels. The egg production rates (EPs) and weight-specific egg production rates (SEPs) of two common copepods, Acartia longiremis and Temora longicornis, were studied under experimental conditions in Dalnezelenetskaya Bay (southern Barents Sea) during summer. The average EP and SEP at 5–10 °C were 4.7 ± 0.4 eggs female−1 day−1 and 0.025 ± 0.002 day−1, respectively, for A. longiremis and 13.1 ± 0.9 eggs female−1 day−1 and 0.075 ± 0.006 day−1, respectively, for T. longicornis. EP and SEP were significantly higher at 10°C than at 5°C for both species. The mean egg diameter correlated positively and significantly with female prosome length (PL) in each species. SEP of T. longicornis correlated negatively and significantly with PL. Daily EP and SEP were similar to rates recorded for other Acartia and Temora species in temperate and warm regions. The influence of environmental factors (temperature, salinity, and phytoplankton concentration) on EP of both species is discussed. We conclude that temperature is the main factor determining the reproduction rate and timing in A. longiremis and T. longicornis in the Barents Sea.

Variability in the vertical distribution and advective transport of eight mesozooplankton taxa in spring in Rivers Inlet, British Columbia, Canada

Zooplankton vertical distribution data and velocity estimates from a hydrodynamicmodel were employed to determine zooplankton daily exchange during four cruisesconducted from March to June 2010 in Rivers Inlet, a fjord in central BritishColumbia, Canada. Zooplankton transport rates varied temporally, being fastest inMarch when water velocities were highest. The active vertical movement of thezooplankton interacted with the vertically sheared flow field to influence zooplanktonadvection. Surface dwelling plankton such as Acartia longiremis and larvaceans experi-enced the highest advection losses of 20.4 and 20.5 day

Mesozooplankton community development at elevated CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentrations: results from a mesocosm experiment in an Arctic fjord

Abstract. The increasing CO2 concentration in the atmosphere caused by burning fossil fuels leads to increasing pCO2 and decreasing pH in the world ocean. These changes may have severe consequences for marine biota, especially in cold-water ecosystems due to higher solubility of CO2. However, studies on the response of mesozooplankton communities to elevated CO2 are still lacking. In order to test whether abundance and taxonomic composition change with pCO2, we have sampled nine mesocosms, which were deployed in Kongsfjorden, an Arctic fjord at Svalbard, and were adjusted to eight CO2 concentrations, initially ranging from 185 μatm to 1420 μatm. Vertical net hauls were taken weekly over about one month with an Apstein net (55 μm mesh size) in all mesocosms and the surrounding fjord. In addition, sediment trap samples, taken every second day in the mesocosms, were analysed to account for losses due to vertical migration and mortality. The taxonomic analysis revealed that meroplanktonic larvae (Cirripedia, Polychaeta, Bivalvia, Gastropoda, and Decapoda) dominated in the mesocosms while copepods (Calanus spp., Oithona similis, Acartia longiremis and Microsetella norvegica) were found in lower abundances. In the fjord copepods prevailed for most of our study. With time, abundance and taxonomic composition developed similarly in all mesocosms and the pCO2 had no significant effect on the overall community structure. Also, we did not find significant relationships between the pCO2 level and the abundance of single taxa. Changes in heterogeneous communities are, however, difficult to detect, and the exposure to elevated pCO2 was relatively short. We therefore suggest that future mesocosm experiments should be run for longer periods.

Every species is good in its season: Do the shifts in the annual temperature dynamics affect the phenology of the zooplankton species in the White Sea?

We hypothesize that shifts in the annual pattern of the environmental parameters may affect the phenology of the zooplankton especially in temperate and polar areas. Five species (cold-water: Calanus glacialis, warm-water: Centropages hamatus, Temora longicornis, Acartia longiremis, and Evadne nordmanni) were tested with regard to the annual pattern of the water temperature using the dataset of 50-year-long monitoring in the White Sea (1961–2010). The hydrological summer duration increased by 20 days during the last 50 years, as it has been tracked by an earlier warming up of 0–10-m water layer in spring. Calanus glacialis responded to these changes by the appearance of CI copepodites earlier in the season. We suggest that the earlier start and longer period of ice melt may cause a longer phytoplankton bloom and thus may promote better trophic conditions during the period of Calanus reproduction and its early development. In contrast to cold-water C. glacialis, the phenology and abundance of warm-water copepods have not changed significantly. Both the timings of autumn cooling and average summer temperature remained relatively stable since the beginning of observations resulting in steady conditions during the reproductive period of warm-water species. Prolongation of summer had no effect on their reproduction.

The results of zooplankton studies in the Bering Sea under the NPAFC Program (BASIS expedition). Part 1. Eastern areas

Data on zooplankton in the eastern Bering Sea are presented. Samples were collected and processed by the planktonologists of the Pacific Fisheries Research Center (TINRO Center) aboard American vessels in the summer and fall from 2003 through 2011. Based on the analysis of the averaged values of bottom temperature, surface temperature, ice cover index, and also on maps of temperature distribution on the surface and near the bottom, the years 2003–2006 are referred to as “warm” and 2007–2011 as “cold.” A comparison of these two periods showed that with the advent of the “cold” period, the overall stock of zooplankton in the eastern part of the sea grew, particularly in the shelf zone, where it increased more than three times exclusively at the expense of the large fraction. Chaetognaths and copepods constituted the major proportion of this increase; stocks of euphausiids, mysids, hyperiids, and pteropods also grew, while a loss was observed in decapods (larval crabs and shrimps) and coelenterates. In the southern part of the shelf zone, a vast area with a higher biomass of the large fraction occurred, which was mainly due to copepods and chaetognaths. At the same time, areas with denser concentrations were formed by euphausiids and amphipods. The horizontal distribution of small and medium-sized zooplankton almost did not change; meanwhile, the main species of the small fraction, viz., Pseudocalanus newmani and Oithona similis, exchanged their significance and the neritic species Centropages abdominalis, Eurytemora herdmani, and Acartia longiremis, as well as cladocerans and meroplankton (larval Cirripedia, Bivalvia, and Polychaeta) almost completely vanished from the plankton by 2011. In most of cases, the mean biomass of the profiling species of the large fraction (Calanus marshallae, Neocalanus flemingeri, N. cristatus, Eucalanus bungii, Thysanoessa raschii, Themisto libellula, Limacina helicina, and Sagitta elegans) grew during the cold period. In the large fraction, S. elegans constituted half of the biomass (52% in the warm period and 49% in the cold one); the following two species were the copepods E. bungii and C. marshallae (both amounted to 26% and 39%, respectively), while Th. raschii, which is usually predominant among euphausiids, was only the last in the top five species. According to the example of the eastern areas of the sea, it becomes evident that the hyperiid Themisto libellula is brought into the studied area with cold waters from the north and disappears when their inflow stops. This species responds later to cooling and earlier to warming as compared to other species or groups. It appears that the end of the “cold” period can be expected in 2012.

Late-summer zooplankton community structure, abundance, and distribution in the Hudson Bay system (Canada) and their relationships with environmental conditions, 2003–2006

Zooplankton communities were examined for the first time in three different hydrographic regions of the Hudson Bay system (HBS) in early August to early September from 2003 to 2006. Sampling was conducted at 50 stations distributed along different transects located in Hudson Bay (HB), Hudson Strait (HS), and Foxe Basin (FB). Variations in zooplankton biomass, abundance, taxonomic composition, and diversity in relation to environmental variables were studied using multivariate techniques. During all sampling years, the total zooplankton biomass was on average four times lower in HB than in HS and FB. Clustering samples by their relative species compositions revealed no interannual variation in zooplankton community but showed a marked interregional variability between the three regions. Water column stratification explained the greatest proportion (25%) of this spatial variability. According to redundancy analysis (RDA), the zooplankton taxa that contribute most to the separation of the three regions are Microcalanus spp., Oithona similis, Oncaea borealis, Aeginopsis laurentii, Sagitta elegans, Fritillaria sp., and larvae of cnidaria, chaetognatha, and pteropoda in HB; hyperiid amphipods in FB; and Pseudocalanus spp. CI–CV, Calanus glacialis CI–CVI, Calanus finmarchicus CI–CVI, Calanus hyperboreus CV–CVI, Acartia longiremis CI–CV, Metridia longa N3-N6 CI-CIII CVIf, Eukrohnia hamata, larvae of echinodermata, mollusca, cirripedia, appendicularia, and polychaeta in the northwestern and southeastern HS transects. For the HB transect, the RDA analyzed allowed us to distinguish three regions (HB west, central, and east) with different environmental gradients and zooplankton assemblages, in particular higher concentration of Pseudocalanus spp. nauplii and CI–CVI, as well as benthic macrozooplankton and meroplankton larvae in western HB. In HS, Calanoid species (mainly C. finmarchicus and C. glacialis) were mostly observed at the north shore stations associated with the weakly stratified Arctic–North Atlantic waters coming from southwestern Davis Strait (inflow). In general, the RDA models tested among the HBS regions were very consistent with its general surface circulation pattern for summer conditions in terms of environmental variables and distinct zooplankton assemblages. Overall, zooplankton biomass and diversity indices (H′, J′, and S) were lower in the most stratified environment (i.e., HB) than in the deeper (FB) and more dynamic (HS) regions. The results of this work clearly show that the spatial differentiation and structure of the zooplankton communities are strongly influenced by the hydrodynamic conditions in the HBS that, trough their actions on temperature, salinity, stratification, mixing conditions and depth strata, lead to the spatial differentiation of these communities.

Transport and coastal zooplankton communities in the northern California Current system

[1] Alongshore transport was estimated from the gridded AVISO altimeter data and water level data from NOAA tide gauges (1993–2010) for the northern California Current (NCC) system. The biomass of the cold neritic copepods including Calanus marshallae, Pseudocalanus mimus and Acartia longiremis (dominants in the eastern Bering Sea, coastal Gulf of Alaska, and NCC) was estimated from a 15 year time series of zooplankton samples (1996–2010) collected biweekly at a coastal station 9 km off Newport Oregon U.S.A. The alongshore currents and the biomass of the cold neritic copepods exhibit a strong seasonal pattern and fluctuate in opposite phase: positive alongshore current (from south) leads to low biomass in winter and negative alongshore current (from north) leads to high biomass in summer. When the Pacific Decadal Oscillation (PDO) is positive, i.e., warm conditions around the northeast Pacific, there is more movement of water from the south in the NCC during winter. When the PDO is negative, there is more movement of water from the north during summer. The mean biomass of cold neritic copepods was positively correlated with the survival rate of juvenile coho salmon and cumulative transport was negatively correlated with coho salmon survival, i.e., in years when a greater portion of the source waters feeding the NCC enters from the north, the greater the salmon survival. We conclude that alongshore transport manifests PDO signals and serves as a linkage between large scale forcing to local ecosystem dynamics.