Zooplankton Biomass Research Articles

Chlorophyll shading reduces zooplankton diel migration depth in a high-resolution physical–biogeochemical model

Abstract. Zooplankton diel vertical migration (DVM) is critical to ocean ecosystem dynamics and biogeochemical cycles, by supplying food and injecting carbon into the mesopelagic ocean (200–800 m). The deeper the zooplankton migrate, the longer the carbon is sequestered away from the atmosphere and the deeper the ecosystems they feed. Sparse observations show variations in migration depths over a wide range of temporal and spatial scales. A major challenge, however, is to understand the biological and physical mechanisms controlling this variability, which is critical for assessing impacts on ecosystem and carbon dynamics. Here, we introduce a migrating zooplankton model for medium and large zooplankton that explicitly resolves diel migration trajectories and biogeochemical fluxes. This model is integrated into the MOM6-COBALTv2 ocean physical–biogeochemical model and is applied in an idealized high-resolution (9.4 km) configuration of the North Atlantic. The model skillfully reproduces observed North Atlantic migrating zooplankton biomass and DVM patterns. Evaluation of the mechanisms controlling zooplankton migration depth reveals that chlorophyll shading decreases zooplankton migration depths by 60 m in the subpolar gyre compared with the subtropical gyre, with pronounced seasonal variations linked to the spring bloom. Fine-scale spatial effects (<100 km) linked to eddy and frontal dynamics can either offset or reinforce the large-scale effect by up to 100 m. This could imply that, for phytoplankton-rich regions and filaments, which represent a major source of exportable carbon for migrating zooplankton, a high chlorophyll content contributes to reducing zooplankton migration depth and carbon sequestration time.

Primary production drives varied zooplankton migration strength and twilight‐zone particle dynamics across ecological gradients in the western North Pacific

AbstractDiel vertical migrations (DVM) of zooplankton play a crucial role in transferring organic matter efficiently to the deep ocean. However, the spatial regulatory determinants of DVM strength, including migrant biomass and migration amplitude, remain understudied. We conducted 34 stratified trawls and 85 Underwater Vision Profiler 5 casts across latitudes 12.5°N to 41.5°N in the western North Pacific and developed a structural equation model to explain DVM variability relative to measured and remotely sensed environmental data. Migrant biomass was mainly determined by net primary productivity (NPP), being two orders of magnitude greater in high NPP waters due to higher zooplankton biomass and larger migrating individuals. Migration amplitude was also larger at high NPP stations but was determined by a direct negative correlation to euphotic zone depth and an offsetting indirect positive interaction with water clarity. Migration patterns reflect the classic tradeoff between predation risk and reduced daytime feeding for regular DVM and likely avoidance of mesopelagic visual predators at night for reverse migrants. In high‐resolution profiles, particle abundances and large particle contributions increased in the twilight zone during the daytime, generally aligning with biomass distributions and respiratory fluxes of migratory zooplankton. Migrants likely contribute to mesopelagic particle dynamics with pulsed fecal matter delivery from the euphotic zone and direct interactions with deep particle fields. Mesopelagic particle dynamics might also be linked to deep migrant mortality, the least quantified component of the biological carbon pump.

Characteristics of productivity for the Academy Bay (Okhotsk Sea)

The data on parameters of biological productivity measured in the Academy Bay in September 2020, as chlorophyll a concentration in the euphotic layer, primary production, phytoplankton and zooplankton biomass, and results of echo sounding at 200 kHz are presented. The primary production estimated by Zvalinsky model varied from 300 to 6050 mgC per m2 per day. Diatoms with the biomass of 660–1220 mg/m3 dominated in phytoplankton, whereas Copepoda with the biomass ranged from 18 to 478 mg/m3 was the dominant zooplankton group. A discrepancy is noted between the measured net zooplankton biomass and thickness of the sound diffusion layer. The more productive area with the highest biomass of zooplankton was found in the northern Academy Bay enriched by nutrients transferred there from the Okhotsk Sea due to patterns of the estuarine circulation, but the thickest sound-diffusing layer was observed in the southern and central parts of the bay where it was presumably formed by shoals of juvenile fish rather than copepod aggregations. The feeding grounds of bowhead whales were located in the southern Academy Bay, too. This spatial misalignment of the feeding grounds with the highly productive area is explained by the hypothesis that juvenile fish may be important prey for whales, in addition to zooplankton.

Zooplankton biomass as a promising new agent for biomedical applications

Zooplankton biomass as a promising new agent for biomedical applications

Special delivery of proteinaceous matter to deep-sea microbes.

Earth's deep ocean holds a vast reservoir of dissolved organic carbon, traditionally considered old and resistant to microbial degradation. Radiocarbon analyses indicate the hidden occurrence of younger dissolved organic carbon components, assumed to be accessible to deep-sea microorganisms but not yet demonstrated. Using compound-class radiocarbon analysis, molecular characterization, and bioassay experiments, we provide direct evidence for rapid microbial utilization of young, labile, high-molecular weight proteinaceous material in bathypelagic waters. The abundance of labile proteinaceous material diminishes from epipelagic to mesopelagic waters but notably increases in bathypelagic waters, where it exhibits a short turnover time (days) and resembles surface plankton in molecular composition. This observation coincides with peak zooplankton biomass recorded over the year. The nonmonotonic depth trend suggests a deep-sea replenishment of organic particles from mesopelagic migrating zooplankton. Our results indicate the presence of labile organic molecules at bathypelagic depths and reveal a nonlinear supply of plankton-derived substrates that support microbial metabolism and carbon sequestration in the deep ocean.

Current state of zooplankton in Lake Valdayskoe (Valdaysky National Park)

Valdayskiy National Park is one of the largest protected natural areas in the European part of Russia. On the territory of this national park there are about 200 lakes, one of which is Lake Valdayskoe. The study of its zooplankton community started more than 100 years ago and was repeatedly carried out. The presence of a long series studies provides a rare opportunity to trace changes in the zooplankton community of this unique reservoir. Pelagic zooplankton (Rotifera, Cladocera and Copepoda) of this lake was studied in summers of 1999 and 2020. 39 invertebrate taxa were revealed. The majority of the zooplankton community was typical for the temperate zone of European Russia. The water quality in the lake during the study period can be estimated as oligosaprobic (clean). In areas of the lake located near settlements, an increase in the abundance and biomass of zooplankton, a decrease in the number of indicator species of oligosaprobic waters, and an increase in the proportion of copepods with morphopathology were observed. In general, in 1999 and 2020 zooplankton abundance has declined and biomass has increased compared to the 1970s.

Zooplankton communities in mountain reservoirs of the Eastern Alps.

Zooplankton communities in mountain reservoirs of the Eastern Alps.

Can Ecosystem Transformations by Non-Indigenous Mussel Introductions Inform Shellfish Reef Restoration?

Shellfish reefs were once common features in temperate coastal waters and estuaries. However, anthropogenic impacts have resulted in significant declines in these ecosystems globally. Whilst a growing body of scientific literature and restoration projects have demonstrated the success of restoration using oysters, at both local and ecosystem-wide scales, restoration initiatives using mussels are relatively new. Due to the lack of long-term data on the ecological impact of restored mussel reefs, information to assist restoration practitioners in identifying potential positive and negative outcomes is limited. However, introductions of mussels have occurred on every continent, and detailed documentation exists on their impacts on local ecosystems. Such information is thus invaluable as these long-term studies can contribute knowledge on predicting ecosystem changes following mussel introductions. Through compiling information derived from 318 published articles, unplanned mussel introductions were found to have both positive and negative impacts, and these were context- and species-specific. In eutrophic water bodies, the impacts were typically considered positive, particularly on shallow-water benthic communities. It was also found, however, that mussels can reduce zooplankton biomass, impact native mussels and were occasionally implicated in increasing cyanobacteria concentrations. Despite these instances, this review presented multiple lines of evidence that mussel introductions, when undertaken intentionally at suitable locations, would have a considerable positive impact at the ecosystem-wide scale.

Spatial–Temporal Pattern and Stability Analysis of Zooplankton Community Structure in the Lower Yellow River in China

In March (spring), June (summer), October (autumn), and December (winter) 2022, zooplankton were quantitatively investigated in the lower reaches of the Yellow River in China. A total of 29 sampling points that were separated by about 20 km were set up in the survey area. The purpose of this study is to investigate the seasonal dynamics and spatial distribution characteristics of the zooplankton community in the Yellow River, which has a high sediment content. The main results are as follows: A total of 119 species of zooplankton were found during the survey, including 70 species of rotifers, 29 species of cladocerans, and 20 species of copepods. Because the temperate continental monsoon climate has four distinct seasons, the zooplankton community in the Yellow River showed typical seasonal dynamics. There were significant differences in the richness of zooplankton and dominant species across the four seasons (p < 0.05). There were 15 common species in each of the four seasons. The density and biomass of zooplankton were significantly higher in spring (16.76 ind./L; 0.049 mg/L) and summer (26.17 ind./L; 0.249 mg/L) compared to autumn (5.65 ind./L; 0.042 mg/L) and winter (1.56 ind./L; 0.006 mg/L) (p < 0.05). Additionally, the density and biomass of zooplankton were significantly lower in estuarine areas compared to other areas. The results of multidimensional non-metric ranking (NMDS) based on zooplankton abundance showed four distinct communities: a spring community, a summer community, an autumn community, and a winter community. The spatial heterogeneity of zooplankton communities in spring, summer, and autumn was significantly different (p < 0.05). However, only the estuarine area had a special zooplankton community in winter. Monte Carlo test results showed that pH, water temperature, electrical conductivity, dissolved oxygen, total nitrogen, and total phosphorus were the main environmental factors affecting the community structure of zooplankton (p < 0.05). The areas of the Yellow River affected by human disturbances have lower zooplankton community stability. Overall, the standing stock of zooplankton was very low (less than 15 ind./L), but the species richness was higher (119 species) in the river, which had a high sediment content and a fast flow.

Zooplankton of Shatskoye reservoir in 2023

In 2023, a study was conducted on the quantitative and qualitative composition of zooplankton in the Shatsky reservoir of the Tula region. Samples were collected and analyzed by conventional methods at six stations during the growing season. In total, the zooplankton includes 14 species of rotifers, 2 species and representatives of 2 families of branchous crustaceans, as well as representatives of 2 orders of copepods. The taxonomic composition of zooplankton turned out to be similar for different reservoir stations. Among the rotifers, Brachionus angularis and B. calyciflorus, Asplanchna priodonta, Keratella quadrata and representatives of the genus Polyarthra, among branchiform crustaceans — representatives of the genus Bosmina, among copepods — representatives of the order Cyclopoida. The highest abundance values were recorded in autumn (on average 645.2 thousand specimens/m3) and spring (567.5 thousand specimens/m3), and biomass in autumn (2.7 g/m3) and summer (1.3 g/m3). In summer, zooplankton abundance was minimal (360.9 thousand specimens/m3), and in spring, biomass (0.5 g/m3). The average number of zooplankton during the growing season was 524.5 thousand. specimens/m3, biomass — 1.5 g/m3, their base is represented by rotifers — 61.8 and 46.7%, respectively. In terms of zooplankton biomass, the Shatsky reservoir in 2023 was characterized as a medium-sized reservoir, which should meet fisheries needs.

Characteristics of the Zooplankton Community Structure in Shengjin Lake and Its Response to the Restored Aquatic Vegetation

Macrophytes taxa composition determines microinvertebrates utilized as environmental indicators in freshwater ecosystems. This study was conducted in Shengjin Lake. In this lake, local communities have been practicing using sine fishing nets for fishing and this has a disrupting effect on macrophyte vegetation, even though it was the major for the disappearance of submerged vegetation before it was banned. As a result of this sine fishing net ban by the local authorities, the vegetation that had disappeared began to recover. Thus, this study investigated the role of architecturally differentiated macrophytes restoration effect on zooplankton communities’ diversity, abundance, and species composition; open water was used as a control. For this, the data were collected from different habitats via site 1 (open water) site 2, (free-floating), site 3 (emergent and submerged), site 4 (submerged), and site 5 (emergent) macrophytes. In the present study, the results demonstrated that the relative mean density of Rotifer was measured high which ranged from (219 ± 141–678 ± 401 ind L−1), mainly dominated by Keratella cochlearis and Lecane cornuta species. Following Rotifera, Cladocera population density was reported high and ranged within (36 ± 6.2–262.5 ± 49.4 ind L−1). The Cladocera group was dominated by Daphnia spp., Moina micura, Ceriodaphnia reticulata, and Chydorus latus species. Compared to Rotifer and Cladocera, Copepod community were recoded least with relative mean density ranged within (11.52 ± 2.22–85.5 ± 27 ind L−1) and dominated by Microcyclops javanus, Thermodiaptomus galebi, and Sinocalanus doerrii species. From environmental variables and the zooplankton density relationship analyzed, the redundancy analysis (RDA) results indicated that Water Temperature, Chlorophyll a, Dissolved Oxygen, Total Phosphorus, and Ammonium Nitrogen were found the most influential variables on zooplankton communities. Stepwise regression correlation showed that Copepod and Cladocera were found more dependent on environmental factors. For instance, Nitrate Nitrogen was negatively correlated with Cladocera, Copepod, and total zooplankton biomass but positively with Cladocera diversity. Water Temperature showed a positive relationship with Rotifer diversity; however, both Chlorophyll a and Electrical Conductivity were correlated positively with Cladocera biomass. Species diversity by the Shannon–Wiener index (H) illustrated a dynamic trend among the monitored sites which ranged between (0.65–4.25). From the three groups of zooplankton communities in contrast to Cladocera and Copepod, Rotifer species obtained more diversity across the studied sites. The Cladocera diversity (H′) index indicated a similar tendency in all sites. However, more Copepod diversity (H′) was observed in site 4. In conclusion, this study results can provide valuable insights into the health and dynamics of the aquatic ecosystem to understand factors deriving ecological imbalance and develop an integrated approach for effective strategies for management and conservation.

A mass occurrence of pteropods (Limacina spp.) drove a pronounced peak in zooplankton biomass in Atlantic water in the Barents Sea in 1994.

Zooplankton have been monitored on autumn cruises in the Barents Sea since the late 1980s. The time series shows a pronounced peak in zooplankton biomass in the inflow region of Atlantic water in 1994. The mean biomass was ~ 20g dry weight m-2, which is more than twice the long-term average, and showed an atypical composition with dominance of the small size fraction (<1mm). Analysis of stored samples revealed that the high biomass event in 1994 was due to a mass occurrence of two species of Limacina pteropods (Limacina retroversa and Limacina helicina) dominated by small juveniles < 1mm in diameter. High biomass in the Atlantic inflow region also in 1995 was due to a strong but delayed summer generation of the dominant copepod Calanus finmarchicus. Estimated biomass of copepods (from numbers and individual weight by species and stage) was strongly dominated by C. finmarchicus in both years (~90%). The average biomass of Limacina spp. in 1994 was ~ 7g dw m-2, estimated to be mainly in the small fraction, and contributed to the 1994 peak on top of a "typical" biomass of C. finmarchicus. The results contribute to a better understanding of the Barents Sea ecosystem.

Seasonal dynamics of zooplankton communities in a recent lava delta on an oceanic island in the Central East Atlantic Ocean

Abstract We examined the structure of the zooplankton community in a Special Area of Conservation affected by the recent formation of lava deltas caused by a volcanic eruption on the island of La Palma (Canary Islands) in the Central East Atlantic Ocean. Seasonal variability in biomass, abundance, and composition of the zooplankton community was analyzed, both in total and within different size ranges. The results showed higher biomass values in winter at 30 m and in spring–summer at 10 m depth, possibly related to seasonal changes in food availability and seawater temperature. Significant differences were observed in the biomass of the smaller size range compared to larger sizes. Similarly, organisms in the smaller size range were the most abundant, primarily due to the community being dominated by copepods, which represented 80.43% of the total abundance in winter, decreasing to 47.14% in spring–summer. At the same time, a significant increase was observed in decapod larvae, gastropods, invertebrate eggs, and cladocerans during the warmer season. An increase in gelatinous organisms, especially siphonophores, was also observed in spring–summer for the largest size range, suggesting potential seasonal changes in the zooplankton trophic structure. This study indicates a limited direct impact of volcanic activity on zooplankton biomass but highlights the importance of understanding seasonal variability in community structure for managing marine conservation. Continuous monitoring of zooplankton dynamics is crucial for detecting potential future impacts on the food web and developing targeted conservation management strategies.

Toward more robust net primary production projections in the North Atlantic Ocean

Abstract. Phytoplankton plays a crucial role in both climate regulation and marine biodiversity, yet it faces escalating threats due to climate change. Understanding future changes in phytoplankton biomass and productivity under climate change requires the utilization of Earth system models capable of resolving marine biogeochemistry. These models often differ significantly from one another, and most studies typically use the average response across an ensemble of models as the most reliable projection. However, in the North Atlantic, this straightforward method falls short of providing robust projections of phytoplankton net primary production (NPP) over the 21st century. A new inter-comparison approach was therefore developed and applied to eight models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) exhibiting substantial divergence in their NPP projections in the North Atlantic. The basin was first divided into three bioregions tailored to the characteristics of each model using a novel method based on a clustering procedure. The mechanisms controlling NPP projections were then identified in each model and in each bioregion, revealing two mechanisms responsible for a large part of model divergence: diazotrophy in the subtropical region and the presence of an ammonium pool in the subpolar region. This allowed for an informed selection of models in each region based on the way they represent these two mechanisms, resulting in reduced projection uncertainty, enhanced total NPP decrease in the subtropical region, and a strengthened increase in small phytoplankton NPP in the subpolar North Atlantic. These model selections enhanced the decreases in carbon export and phytoplankton biomass but had no impact on zooplankton biomass. This innovative approach has strong synergies with other widely used inter-comparison techniques, such as emergent constraints, and their combination would provide valuable insights into the future trajectory of the Earth's climate system.

Coarse-scale vertical distribution of pelagic amphipods in two contrasting seasons of the southern Gulf of Mexico

In the oceans, ecological analyses of pelagic amphipods have mainly focused on the epipelagic zone with few studies in the deep waters. In this study, a coarse-scale vertical analysis, between 0 and 1000 m depth, was performed in the southern Gulf of Mexico during summer and winter. We hypothesize greater differences between the epi-and mesopelagic zones during the summer, because of a stronger vertical gradient in environmental conditions, especially temperature. As well, we think that the zooplankton biomass (as a measure of food availability) will play a significant role in regulating the amphipod distribution and abundance. Zooplankton samples were obtained at five levels (0-200, 200-400, 400-600, 600-800, 800-1000 m) of the water column using a stratified net system during the winter of 2013 and summer of 2014 in the southern Gulf of Mexico. To probe vertical differences, the amphipod community was analyzed considering two assemblages defined a priori, the ‘epipelagic’ and the ‘mesopelagic’; and considering each of the five sampling levels as separate groups. Results indicated that assemblages were significantly different in both seasons (ANOSIM test, p &amp;lt; 0.05), but differences were stronger in winter, which contradicts the first hypothesis. The vertical hydrological structure during the summer was characterized by a deepening of 15-18°C temperature values towards the upper mesopelagic zone, resulting in less heterogeneity between the epi- and the mesopelagic zones. A BEST-BIOENV test was used to evaluate the degree of association between the environmental (temperature, salinity, zooplankton biomass) and biological (amphipod composition and density) matrices. As expected, the zooplankton biomass was the most important factor affecting the distribution of the amphipods, especially during the summer (rho = 0.319, p = 0.001). The dominant species was Lestrigonus bengalensis in winter and the juveniles of the genus Primno in summer. The SIMPER analysis also showed these taxa as responsible for the discrimination of the epi- and mesopelagic assemblages. In a finer analysis taking the sampling levels as a factor, results indicated that, during the summer, the 200-400 m level showed a differentiation from the other deep levels; again, the effect of the deepening of temperature values between 15 and 18°C, could be the responsible. Comparisons of day/night sampling time in the average amphipod abundance indicated that only the members of the infraorder Physosomata showed significant differences during the summer (ANOSIM test, p &amp;lt; 0.05), which could be indicative of a migratory process. The diversity of the assemblages in both seasons was analyzed using alpha diversity species accumulation curves and a completeness analysis, using the sampling coverage. Seasonally, the summer was more diverse, while in the vertical plane, the mesopelagic zone was more diverse than the epipelagic one. We suggest further studies in the poorly sampled mesopelagic zone of the ocean to better understand the ecology of the deep-sea pelagic amphipods.

Variability of plankton communities in relation to the lunar cycle in oceanic waters

The short-term variability of plankton communities in the oceanic realm is still poorly known due to the paucity of high-resolution time-series in the open ocean. Among these few studies, there is compelling evidence of a lunar cycle of epipelagic zooplankton biomass in subtropical waters during the late winter bloom. However, there is few information about lower trophic levels and zooplankton physiological changes related to this lunar cycle. Here, we studied the short-term variability of pico-, nano-, micro-, and mesoplankton in relation to the lunar cycle in subtropical waters. Weekly sampling was carried out at four stations located north of the Canary Islands from November 2010 to June 2011. Zooplankton abundance and biomass, gut fluorescence (GF), electron transfer system (ETS), and aminoacyl-tRNA synthetase (AARS) activities were measured before, during, and after the winter vertical mixing in these waters in a wide range of size classes. Chlorophyll a, primary production, and zooplankton biomass were low, showing a rather weak late winter bloom event due to the high temperature and stratification observed. Chlorophyll, nanoplankton, diatoms, and mesozooplankton proxies for grazing (GF), respiration (ETS), and growth (AARS) varied monthly denoting a lunar pattern. Chlorophyll a, nanoplankton, diatoms, and mesozooplankton proxies for grazing and respiration peaked between 4 and 6 days after the new moon, followed by an enhancement of the mesozooplankton index of growth between 8 to 9 days after the new moon. However, mesozooplankton biomass only increased during the productive period when supposedly growth exceeded mortality. Coupled with previous results in pico-, nano-, and microplankton, we suggest that the lunar cycle governs the development of planktonic communities in the high turnover warm subtropical ocean. This study provides further evidence of the match of plankton communities with the predatory cycle exerted by diel vertical migrants, adding essential information to understand the short-term functioning of the open ocean.

Environment-driven trends in larval abundance predict fishery recruitment in two saltwater basses

Abstract Environmental and biological factors influencing fish larvae can drive fishery cohort strength, yet larval abundance is typically a better indicator of spawning biomass. Under a changing ocean, studies that explore the relationships between environmental variables, larval abundance, and fishery recruitment remain valuable areas for ongoing research. We focus on a popular, recreational-only, multispecies saltwater bass fishery (genus Paralabrax) whose population status and recovery potential are uncertain. We resolved Paralabrax spp. larval data to species over a 54-year period (1963–2016) and used species distribution models to (i) generate and test species-specific standardized indices of larval abundance as indicators of adult stock status and fishery recruitment and (ii) evaluate long-term spatiotemporal trends in their population dynamics relative to environmental variables and climate forcing. Contrary to initial hypotheses, species-specific larval abundance predicted future catches, with higher recent larval abundances suggesting potential for fishery recovery. Temperature, zooplankton biomass, and isothermal depth were important predictors of bass larval abundance, indicating these variables could also be valuable for predicting fishery recruitment and anticipating population change. Our findings paint a path forward towards a more ecosystem-based fishery management approach for this important fishery and may serve as a template for data- or assessment-limited fisheries.

Production Trend of Hokkaido Chum Salmon Estimated by Multivariable Models Incorporating Environmental Factors and Biological Interactions in the North Pacific Ocean

Global warming continues unabated. The global annual mean of sea surface temperature (SST) is increasing at a rate of 0.6ºC per century, and was the highest on record in 2023. SST in the North Pacific Ocean has warmed by about 1ºC over the past 120 years. Pacific salmon (Oncorhynchus spp.) play an important role as a keystone species and provider of ecosystem services in North Pacific ecosystems. Their total catch has shown an increasing trend since the late 1970s. However, in this century, the abundance of Pacific salmon has decreased in southern areas and increased in northern areas due to the effects of global warming. In particular, the abundance of Hokkaido chum salmon (O. keta) has decreased since the 2000s (Kaeriyama 2023). On the other hand, in the Bering Sea, the marked increase in pink salmon abundance has negatively impacted trophic cascades through the top-down effect by reducing herbivorous zooplankton abundance sufficiently to increase phytoplankton densities (Ruggerone et al. 2023) and low growth of sockeye salmon (O. nerka) (Rand and Ruggerone 2024). Japanese chum salmon are a southernmost population, and they migrate widely, inhabiting different ecosystems in the North Pacific and adjacent seas, depending on their life stage and season (Urawa et al. 2018). This complicated life history makes it difficult to understand the mechanisms of their population dynamics. The objective of this study is to discuss how the marine life history of Hokkaido chum salmon is affected by marine environmental factors such as inter- and intraspecific interactions among Pacific salmon, SST, and zooplankton biomass using various models, and to predict their future production trends.

Fish Larval Assemblage Associated with an Eastern Tropical Pacific Coral Reef: Seasonal and Interannual Variability

The seasonal and interannual temporal variation in the composition, richness, diversity, and similarity of fish larval assemblages associated with an Eastern Tropical Pacific (ETP) coral reef system was studied in March (cold water) and September (warm water) during the years 2017, 2018, and 2019. Throughout the study period, we collected 4779 fish larvae and identified 88 taxa, encompassing 46 families. This increased the total number of recorded fish taxa for the region to 146. Fish larvae were collected by daytime and nighttime surface trawls, using a bongo net 30 cm in diameter and 180 cm in length, equipped with mesh sizes of 300 and 500 μm. The species diversity and abundance of ichthyoplankton over this ETP coral reef changed by intra-annual variation of the hydrological conditions of the upper layer of the sea. Six significant assemblages were identified (SIMPROF, p &lt; 0.05), each one associated with each sampling period (ANOSIM, R = 0.764); Cetengraulis mysticetus, Diaphus pacificus, Anchoa sp., Anisotremus sp., Bremaceros bathymaster, Oligoplites saurus, Caranx sp., Seriola sp., Gobiidae sp., Microgobius sp., and Synodus evermanni were the species that contributed to dissimilitude between groups. Canonical correspondence analysis revealed significant associations between specific larval fish taxa abundance and temperature, salinity, dissolved oxygen, and zooplankton biomass. Overall, the assemblage of ichthyoplankton in this ETP coral reef system is sensitive to seasonal changes in water column hydrographic conditions.

Long-term dynamics of the food base for nekton in Pacific waters at the Kuril Islands and Kamchatka in summer

Modern data on dynamics of structure and abundance of zooplankton communities in the epipelagial layer of Pacific waters at the Kuril Islands and Kamchatka are presented on the data collected in summer of 2004–2023. On the background of changing environmental conditions, the portion of small- and medium-sized zooplankton is increased recently, mainly due to increasing abundance of moderately cold-water copepod Oithona similis and hyperiid Themisto pacifica. Among the large-sized zooplankton, increasing abundance of warm-water copepod Eucalanus bungii and decreasing number of cold-water Neocalanus copepods (especially N. cristatus) is observed. Inter-annual fluctuations of the total zooplankton stock did not exceed 3 times, while the biomass of some taxonomic groups varied in 4–9 times. The total biomass of zooplankton, which forms the basis of food base for fish and squids, is assessed as (96 ± 6).106 t in the 0–50 m layer and (90 ± 6).106 t in the 50–200 m layer. In summer, nekton consumes a small part of zooplankton production in this season (1/27). The studies of fish and squids consumption of zooplankton in the North-West Pacific did not reveal its significant dependence on the changes in structure and abundance of zooplankton communities, possibly related with oceanographic regime changes.