Zooplankton Samples Research Articles

Advancements in DNA Metabarcoding Protocols for Monitoring Zooplankton in Marine and Brackish Environments

Over the past century, numerous studies have proposed various organisms for the biomonitoring of aquatic systems, but only recently has zooplankton emerged as a promising indicator of water quality. The traditional identification methods, however, can be inefficient in the context of monitoring efforts, as they are often time consuming and costly. DNA metabarcoding offers a powerful alternative, providing a more efficient and reliable approach to monitor zooplankton communities. In this review, we assess the current state-of-the-art methodologies used to evaluate marine and brackish zooplankton communities through the DNA metabarcoding workflow. While several emerging approaches have been reported, no standardization has been achieved so far. The DNA extraction step has gained the most consensus, with the widespread use of commercial kits (DNeasy Blood & Tissue kit employed in ca. 25% of the studies), though there is still a significant variation in kit selection. Additionally, 18S and COI were the main molecular markers employed (ca. 61% and 54%, respectively) though the target region varied in the former. Moreover, many methodologies, particularly those used for processing zooplankton samples, lack practical validation. Some studies also fail to provide sufficient detail in their methodology descriptions hindering reproducibility. Overall, DNA metabarcoding shows great potential for the efficient monitoring of zooplankton communities, but further effort is needed to establish standardized practices and optimize the current approaches across the entire methodological pipeline.

Ecological interactions between marine RNA viruses and planktonic copepods

The interactions between zooplankton and viruses, which have been overlooked despite their crucial roles in marine ecosystems, are investigated in the copepod Pseudocalanus newmani. Copepod transcriptome data reveal four novel RNA viruses and weekly zooplankton samplings detect all viruses with different prevalence peaks during low-abundance periods of P. newmani. In addition to water temperature and food quality, our results suggest that marine virus is one of the factors controlling copepod population dynamics. Gene expression analysis indicates possible increased viral replication and decreased copepod movement in P. newmani with the Picorna-like virus, which is closely related to phytoplankton viruses, and metabarcoding diet analysis detects diatoms as P. newmani’s major prey. Viral-like particles are observed in the gut contents of copepods during the high prevalence of this virus, suggesting infected copepod prey may affect copepod physiology. These results show that investigating zooplankton–virus interactions can provide a better understanding of marine ecosystems.

Latitudinal variation in zooplankton over the Emperor Seamounts (34°–44° N, 170°–171° E) during the summer of 2019

The horizontal and vertical distributions of zooplankton over the Emperor Seamounts (Koko, Jingu, Nintoku, and Suiko guyots) were analyzed. The zooplankton was represented by four genera of amphipods, seven genera of pteropods, 39 genera of copepods, and larvae of benthic invertebrates and fish. The abundance and biomass of zooplankton increased towards higher latitudes along the series Koko < Jingu < Nintoku < Suiko guyots. The highest index of diversity was recorded over the Koko and Jingu guyots; the highest species richness occurred over the Jingu and Nintoku guyots. Small-sized copepods, appendicularians, chaetognaths, euphausiids, and fish eggs and larvae concentrated in the epipelagic; large copepods and ostracods were concentrated in the mesopelagic. We identified three types of zooplankton assemblages: a Subtropical assemblage between 34°–35°N characterized by tropical/subtropical forms; a Transition assemblage characterized by subtropical, subarctic, and widespread species between 38°–41°N; and a Subarctic assemblage characterized by subarctic and widespread species between 43°–44°N. The spatial distribution of zooplankton was a function of environmental variables such as surface salinity, temperature at 200 m, and, to a certain extent, by surface Chl-a concentrations.

Ecological impact of artificial barrage on calanoid copepods in the Vembanad Lake, Southwest Coast of India

The Vembanad Lake (VL) is a brackish water lagoon, an integral part of Ramsar site, Vembanad Kol Wetland ecosystem on the southwestern coast of India. VL faces escalating anthropogenic impact, notably worsened by the establishment of the Thanneermukkom barrage (TMB) in 1976. This study hypothesizes that the TMB has led to significant ecological changes in VL, specifically altering the distribution and abundance of calanoid copepods, which are vital as a food source for higher trophic levels, particularly fish. To test this hypothesis, zooplankton samples were collected from various sites along the lake, and environmental parameters such as salinity and chlorophyll-a concentration were measured. This investigation reveals a distinct limnetic zone in the southern region, in contrast to the oligo-mesohaline zone in the north, attributed to the TMB. The study identifies the prevalence of calanoid copepod species such as Heliodiaptomus cinctus, Allodiaptomus mirabilipes, and Acartiella gravelyi in the TMB-South region, reflecting a freshwater-dominated ecosystem. The low salinity and high chlorophyll-a content in this area create an optimal environment for these species. In contrast, the dominance of Acartia (Odontacartia) spinicauda, Pseudodiaptomus serricadatus, and Paracalanus sp. in the TMB-North indicates higher salinity levels, with species in this region adapting to a different ecological niche. Thus, the installation of the TMB has significantly altered the ecological balance of VL by dividing the water body into two distinct salinity zones. This separation has led to changes in the distribution and abundance of calanoid copepods, which are essential for energy transfer to higher trophic levels in the VL food web, consequently affecting fish populations and overall biodiversity.

Interannual differences vs small-scale spatiotemporal variability of spring zooplankton in the Crimean marine hypersaline lake

Ecosystems in the shallow marine hypersaline environment, such as marine lakes, are among the most changeable and have significantly lower species richness than freshwater and marine. It could be assumed that the intricate interconnections in hypersaline water ecosystems are easier to understand than in other aquatic ecosystems. Interannual differences vs small-scale spatiotemporal variabilities were studied in the spring zooplankton of hypersaline Lake Moynaki from 2019 to 2023. Salinity, water temperature, wind speed and direction were measured along with zooplankton sampling. The average spring wind speed and water temperature varied significantly from year to year, seemingly with a certain cyclicity. In total, 17 species were noted in zooplankton. The copepods Acanthocyclops vernalis and Arctodiaptomus salinus were not previously recorded in the lake. Bottom species were found in the plankton, among which the oligochaete Nais pseudobtusa, the gastropod Bittium reticulatum, and dragonfly larvae Gomphus sp. had not previously been found in the lake. Only four species, Gammarus aequicauda, Eucypris mareotica, Moina salina, and Cletocamptus retrogressus were regularly observed en masse. On average, the total zooplankton abundance near the windward shore was 2 times higher than that near the leeward shore and the abundance of individual species was from 2 to 5 times higher. If the values near only one coast were used, then the range of interannual differences would be underestimated or overestimated by approximately 2–4 times. Based on the zooplankton similarity in different years, all years except 2019, are grouped into a single cluster. Various changes are occurring in the lake, which are difficult to present as a complete picture of the cause-and-effect relationships that determine them.

The Origin of the Chionoecetes Opilio Snow Crab Larvae in the Kara Sea

Most likely, the non-indigenous snow crab opilio, Chionoecetes opilio, entered the Kara Sea from the Barents Sea, both due to the migration of adults and with currents at the larval stage. At the moment, all bottom stages, including mature individuals and a large number of pelagic larvae are present in the Kara Sea. However, the origin of the larvae has not yet been clarified. The larvae that hatched in the Kara Sea should be at an earlier stage of development compared to the Barents Sea larvae that got here due, to later development of phytoplankton and, accordingly, later hatching. The larvae of the snow crab Chionoecetes opilio and the spider crab H. araneus were collected in the central and southwestern parts of the Kara Sea in July — early August 2019 by the Bongo zooplankton net 60 cm in diameter. It was established that the larvae were unevenly distributed across the Kara Sea. The main concentrations were found on the border with the Barents Sea in the St. Anna Trough (up to 860 ind./m2), and relatively high concentrations of larvae were noted in the southwestern part, where their abundance at the stations varied from 18 to 302 ind./m2. In the zone of the Ob-Yenisei plume, crab larvae were absent or their abundance was minimal. Using molecular genetic methods, the species identity of 361 larvae (344 C. opilio and 17 H. araneus) was reliably determined, and measurements of a number of morphological structures were made for 401 larvae. Significant differences in size at the zoea stage II between C. opilio and H. araneus were established. In most of the Kara Sea in July 2019, in zooplankton samples, crab larvae were represented by zoea I C. opilio with rare specimens of zoea I H. araneus of the Kara Sea origin. Only in the southwestern part, on the border with the Barents Sea, the presence of zoea II C. opilio and H. araneus was observed in samples with an increase in the proportion of the latter species in catches, which probably originate from the Barents Sea.

Zooplankton vertical stratification in the East-pacific and Indian sectors of the Southern Ocean

IntroductionIn the Southern Ocean, the large-scale distribution of zooplankton, including their abundance and community composition from the epipelagic to the upper bathypelagic layers, remains poorly understood. This gap in knowledge limits our comprehension of their ecological and biogeochemical roles.MethodsTo better understand their community structure, depth-stratified zooplankton samples were collected from 0 to 1500 m during four summers in the East-Pacific and Indian sectors of the Southern Ocean. In addition, analysis of environmental drivers including temperature, salinity, dissolved oxygen, and chlorophyll a concentration, as well as water masses was conducted.ResultsOur study indicates that zooplankton diversity may be similar between the two sectors, while zooplankton abundance was higher in the East-Pacific sector during different sampling months and years. Moreover, zooplankton abundance decreased with depth in both sectors. Based on cluster analysis, zooplankton communities were generally divided by either the epipelagic or the deeper layers’ communities. In both sectors, the epipelagic layer was dominated by cyclopoid copepods, such as Oithona similis and Oncaea curvata, as well as calanoid copepods including Calanoides acutus, Rhincalanus gigas, and Ctenocalanus citer, while copepods and other taxa including Chaetognatha, Amphipoda, and Ostracoda, were important contributors to the deep layer communities.DiscussionOur analysis revealed that water masses, combined with their physical characteristics such as specific temperature and salinity ranges and depth, along with biological factors such as chlorophyll a concentration, might be the most important drivers for structuring zooplankton communities from epipelagic to upper bathypelagic layer.

Species composition and structural organization of the littoral zooplankton communities in the Oleksandrivka Reservoir (Ukraine)

Today, the issue of researching reservoirs, which are an important source of human water supply and are significantly affected by anthropogenic factors, is gaining more and more relevance. Research on the Oleksandrivka Reservoir is highly important since the safety of operation of the South-Ukrainian NPP depends on the functioning of this reservoir. The research material was samples of littoral zooplankton, which is a bioindicator of changes in the aquatic environment. During the research, both classical methods and the original method of standardizing the number and localization of zooplankton sampling stations within different types of reservoir were used. As a result of original research, the species composition and structural organization of littoral zooplankton communities in different parts of the Oleksandrivka Reservoir were analyzed for the first time. A total of 126 species of zooplankton were registered, of which 96 were observed in this reservoir for the first time. The rotifer Euchlanis dapidula was discovered for the first time in the fauna of Ukraine. The peculiarities of the formation of the faunal spectrum, trophic groups, complex of dominant species, distribution of biotopes, distribution in different parts of the reservoir, density, biomass, as well as seasonal and daily dynamics of littoral zooplankton groups were also clarified. It was established that the biomass of phytoplankton has a statistically significant effect on the density and biomass of zooplankton.

Characteristics of the fish food supply of the Uglich reservoir

The work on assessing the feed base of the Uglich Reservoir was carried out within the framework of annual monitoring studies by the Branch for Freshwater Fisheries of the Federal State Budgetary Scientific Institution “VNIRO” (VNIIPRH). Samples were taken in July 2021 and 2022 on three sections. During the year, 10 samples of zooplankton and benthic invertebrate communities were collected and processed. The purpose of the study is to evaluate the fish food supply of the Uglich Reservoir according to the indicators of zooplankton and benthic invertebrate communities in the period 2021–2022. The tasks of the study: to determine the number and biomass of zooplankton of the Uglich Reservoir in 2021–2022; to determine the number and biomass of benthic invertebrate communities of the Uglich Reservoir in 2021–2022. The Uglich Reservoir belongs to the Upper Volga cascade of hydro nodes. Located in the territory of two regions and having a length of more than a hundred kilometers, it has differences in water temperature and oxygen content in the water by reaches. Oxygen conditions in 2021 in the bottom layers, and in 2022 — both in the surface and in the bottom horizons, were unfavorable: deviations from the water quality standard were observed. The studies showed that the productivity of the Uglich Reservoir also varies by reaches. The maximum indicators of zooplankton development were observed in the channel part of the Upper reach of the reservoir. During the observation period (with incomplete determination), 21 taxa of planktonic organisms were recorded, including: Rotifera — 5, Cladocera — 12, Copepoda — 3 and Bivalvia — 1 species. In the composition of the plankton fauna, Cladocera dominated in number and biomass. The benthic invertebrate communities of the Uglich Reservoir is mainly represented by oligochaetes, chironomid larvae and bivalve molluscs. By the magnitude of the summer biomass of zooplankton and benthic invertebrate communities, in accordance with the generally accepted classification of Pidgayko (1968), the Uglich Reservoir in 2021 can be assessed as a high-feed reservoir, and in 2022 — as a medium-feed reservoir.

Studies on the conservation and sustainability challenges of the wetland resources of the Baro-Akobo River Basin in Gambella and Benishangul-Gumuz regions, Ethiopia

In this study, the water quality of the Baro-Akobo River Basin in Ethiopia was comprehensively assessed. Key parameters including temperature (°C), pH, dissolved oxygen (DO), electrical conductivity, total dissolved solids (TDS), and ion concentrations such as K+, Ca2+, Na+, NO3−, NO2−, PO43−, CO32−, HCO3−, and NH4+were measured using standard methods, alongside sampling of phytoplankton, zooplankton, macroinvertebrates, macrophytes, and fish. Phytoplankton and zooplankton were sampled using Hydrobios nets with mesh sizes of 30 μm and 55 μm, respectively, while macroinvertebrates were collected via the kicking method. Results indicated generally alkaline pH levels and elevated turbidity, but acceptable levels of dissolved oxygen and ion concentrations according to WHO and FAO guidelines. Moreover, the study suggests that the wetlands in Gambella and Benishangul-Gumz regions are currently in good condition, providing valuable insights for the conservation and sustainable management of Ethiopia's water resources, ensuring their conservation for both present and future generations. Local authorities can use the study's findings to implement remedial measures to protect water quality and biodiversity in the regions.

Status of the transfer state of 137Cs in zooplankton and surface water fish off Fukushima during 2018–2021

Radiocaesium introduced to coastal waters by the accident at the Fukushima Dai-ichi Nuclear Power Station (F1NPS) elevated the radioactivity level in biota. The radionuclide level in zooplankton, concentration of 137Cs radioactivity in surface water fish decreased rapidly, which was the primary food source for planktivorous fish, was recognized as not to be depurated at the same level prior to the accident. To evaluate the possible cause of this phenomenon, zooplankton and surface water fish were collected off Fukushima during 2018–2021, and the presence of radioactive particles was also examined. The concentrations of stable Cs and 137Cs radioactivity were analysed along with aluminium which was an indicator element of Cs that originated from suspended particles which were attached to or ingested by zooplankton. As a result, radioactive particles were often found in coastal zooplankton samples, and stable Cs and 137Cs of this inorganic fraction were identified. After removal of this excess radioactivity, the 137Cs radioactivity in whole-body tissue of zooplankton was derived. However, the level in the soft part of zooplankton during 2018–2020 was still greater than the levels which existed before 2010. Since habitat seawater was understood to not be a substantial source of 137Cs, then 137Cs transfer along the food chain, possibly from phytoplankton or detritus of enhanced radioactivity were suggested as important sources of 137Cs. In addition, enhanced 137Cs radioactivity in zooplankton was considered consequently elevate radioactivity levels in surface-dwelling water fish off Fukushima. Although the radioactivity level was not radiologically significant in relation to seafood safety limit, enhanced 137Cs radioactivity levels in biota was demonstrated in southern waters off Fukushima. In contrast, derived 137Cs/133Cs atom ratios of fish and seawater south of 37°E and west from 142°E indicated that radiocaesium transfer between fish and the environment was in an equilibrium state, showing the environment beyond these geographical coordinates had returned to the pre-accident state.

Small pelagic fish in the shallow Wadden Sea show opportunistic feeding with a strong benthic link

Abstract Small pelagic fish (SPF) are crucial in marine food webs, transferring energy from plankton to higher trophic levels. This study focuses on herring (Clupea harengus) and sprat (Sprattus sprattus), addressing knowledge gaps in their feeding ecology in a nursery area, the Dutch Wadden Sea. We conducted a year-long, monthly survey, and used DNA metabarcoding to analyse zooplankton samples and stomach contents of two size classes of herring and sprat. Intra-, interspecific, and seasonal variations in fish condition, stomach fullness, and diet composition, along with selective feeding, were studied. Our study showed that condition and diet composition of herring and sprat, along with zooplankton density, exhibited a clear seasonal pattern. Juvenile herring and sprat displayed opportunistic feeding behaviour, rather than showing distinct prey selection. Besides copepods, we regularly observed (larvae of) benthic invertebrates in their diet. This emphasizes the crucial role of SPF as energy transfer agents, not solely between trophic levels, but also from benthic to pelagic habitats. Furthermore, fish post-larvae were part of the diet of larger herring (10–15 cm). Because of its unprecedented temporal and taxonomical detail, this study advances the understanding of seasonal dynamics of dominant components at the base of the Wadden Sea food web.

Seasonal and Spatial Distribution of Zooplankton Communities with Relation to some Physico-Chemical Parameters in the South East Coast of Bangladesh

Seasonal and spatial distribution of zooplankton communities in relation with some physico-chemical parameters in the south eastern coastal waters of Bangladesh was carried out from January 2016 to November 2016. Zooplankton samples were collected from seven different selected stations covering various ecosystems, viz.: Riverine (Bhola, Barishal &amp; Chandpur), Offshore Island water (Sandwip &amp; Hatia) and Nearshore (Cox’s bazar &amp; Naf River) regions. In total 33 genera were recorded during sampling periods and the highest abundance of zooplankton were recorded at Naf River (331.318 ind/m3) and the lowest at Chandpur (22.6414ind/m3) during post-monsoon. In pre-monsoon the highest abundance was recorded at Sandwip (31.49435ind/m3) and the lowest at Bhola (8.239854ind/m3). During monsoon the highest abundance was recorded at Cox’s Bazar (51.64085ind/m3) and the lowest at Barishal (4.389972ind/m3). A total of 24, 22 and 32 individuals (genera) of zooplankton identified during monsoon, pre-monsoon and post-monsoon respectively from all sampling stations. Calanoida, Cyclopoida, Fish larvae, Lucifer and Shrimp Zoea were common in every sampling station. Dictoyptera was the only species found in marine water. The statistical analysis of water quality parameters as temperature, pH, salinity, transparency, DO, TDS and TSS indicated the substantial relationship with seasonal and spatial distribution, diversity and abundance of zooplankton. Diversity index also indicated seasonal and spatial variation of zooplankton communities in the south eastern coastal waters of Bangladesh. The Chittagong Univ. J. B. Sci.,Vol. 10(1 &amp;2):95-119, 2020

Foraging dives of southern right whales (Eubalaena australis) in relation to larger zooplankton size prey availability in Golfo Nuevo, Península Valdés, Argentina

Southern right whales (SRWs, Eubalaena australis) have been observed feeding both at and below the surface (< 10 m) in Golfo Nuevo (42°42′ S, 64°30′ W), Península Valdés, Argentina, an area traditionally recognized as calving ground. In addition, we documented diving feeding behavior in SRWs during their stay in this gulf, which has not been previously described. We assessed this behavior using suction-cup-attached video-imaging tags (CRITTERCAMs) on individual whales. A total of eight CRITTERCAM deployments were successful, and feeding events were documented in all SRWs successfully equipped with CRITTERCAMs. The highest speeds occurred during the ascent phase, and the average diving time was 6 min 45 s ± 3 min 41 s for SRWs. Concurrently, zooplankton samples were collected from the subsurface and bottom of the water in areas where tagged whales dived to assess differences in composition, abundance, and biomass. Copepods dominated the upper layer, while euphausiids were more abundant in the deeper sample. Furthermore, zooplankton total biomass was five times higher at depth (2515.93 mg/m3) compared to the subsurface (500.35 mg/m3). Differences in zooplankton characteristics between depths, combined with CRITTERCAM videos, indicated that SRWs exploit high concentrations of organisms near the seafloor during daytime feeding dives. This study provides baseline insights into how SRWs utilize Península Valdés during their stay in the area.

Mortality of mesozooplankton in an acidified ocean: Investigating the impact of shallow hydrothermal vents across multiple monsoonal periods

The shallow hydrothermal vents (HVs) of Kueishan Island are considered as a template for studying the extremes of sulfide-polluted and acidified water. The present study examined the biological and spatiotemporal aspects of mesozooplankton mortality in waters around this extreme HV environment. Zooplankton sample collection was carried out in three monsoonal periods and the results revealed that there was a significant decrease in the mortality of total mesozooplankton with increasing distance from the HVs. The overall mortality of mesozooplankton showed a significant negative correlation with sea surface temperature and pH. Particularly, mortality of copepods showed a significant negative correlation with pH, whereas it was significantly positive correlated with sea surface temperature in the southwest monsoon prevailing period. Overall, the results may imply a situation that zooplankton will encounter in the more acidified environment of a future ocean.

Spatio-temporal variation in the zooplankton community of the Zahara-El Gastor Reservoir (Cádiz, Spain)

Reservoirs play a crucial role in providing essential social and economic services at different scales. However, in recent years, anthropogenic impacts such as climate change and pollution have increased, affecting this type of ecosystem. Zooplankton communities are fundamental for regulating the biological balance in these environments, so it is essential to understand the processes that affect their dynamics. This study investigated the seasonal and spatial variation in species abundance of the zooplankton community of the Zahara- El Gastor Reservoir, Cádiz, Spain. This reservoir it is located in the Guadalete-Barbate River basin and is included in the Sierra de Grazalema Natural Park, the area with the highest rainfall in the Iberian Peninsula. Water and zooplankton samples were collected monthly over a year at four sampling sites located along the reservoir’s long-axis to determine its physicochemical characteristics and zooplankton species composition. The reservoir presented a mesotrophic state and a monomictic thermal cycle, with the mixing period occurring in winter. Temperature, water depth and volume, phosphates, carbonates, pH, and conductivity were the main environmental variables that affected the seasonal and spatial patterns of the zooplankton community. Rotifers presented the highest number of species and were predominant at the tail of the reservoir, especially in autumn, where Polyarthra spp. reached high densities. Relatively low densities of copepods were found throughout the year. Small branchiopods and cyclopoids were predominant in summer, while Daphnia longispina was linked to the colder seasons. The zooplankton community of the Zahara-El Gastor Reservoir reflected changes in the trophic state of the reservoir both in space and time.

Estimating ethanol correction factors for δ13C and δ15N isotopic signatures of freshwater zooplankton from multiple lakes

AbstractIn freshwater systems, δ13C and δ15N stable isotopes can be used to differentiate between pelagic and littoral energy sources and to quantify trophic position. In these ecosystems, crustacean zooplankton are frequently used to characterize the pelagic baseline. Zooplankton samples are often preserved prior to processing and analysis, which can affect isotopic signatures. Variability in preservation effects across studies make it difficult to determine if and how to correct for preservation effects. Here, we develop a correction factor for ethanol preservation and present a flexible statistical method that can be updated with additional data to increase its applicability. We collected zooplankton from five lakes in Minnesota, USA encompassing wide isotopic ranges (δ13C from −37.23‰ to −23.96‰; δ15N from 3.07‰ to 14.44‰). Changes in zooplankton δ13C and δ15N signatures were quantified using a Bayesian hierarchical model predicting fresh values from ethanol‐preserved values. Ethanol preservation increased δ13C by a factor of 1.158 (95% CI 0.866–1.441) and had a negligible effect on δ15N (slope = 1.077; 95% CI 0.833–1.359). Lake‐specific values did not differ from the overall relationship. K‐fold and leave‐one‐out cross validation tests verified that both models were accurate; RMSE of predicted δ13C = 0.701 and RMSE of predicted δ15N = 0.590. Our correction factors could be applied to other systems in which baseline δ13C and δ15N values fall within the range of our study, and this approach also enables the inclusion of data from additional lakes to estimate new corrections.

Fatty acid composition of whale shark (Rhincodon typus), and zooplankton in two aggregation sites in the Gulf of California

The whale shark Rhincodon typus (Smith, 1828) is a filter-feeding species that feeds on zooplankton. There are whale shark aggregation sites in the Gulf of California, Bahia de La Paz in Baja California Sur, and Bahía de Los Angeles in Baja California. Whale shark ecotourism is an important and economically profitable activity for the coastal communities surrounding their habitat areas. Fatty acid (FA) profiles, including arachidonic acid (ARA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), are used as trophic tracers in marine food webs because they are essential for marine fish and provide information on the nutritional quality of zooplankton. In the present study, we analyzed the FA profile of zooplankton to trace them in the stomach contents, blood, liver, and muscle of stranded male whale sharks and the subdermal tissue of live whale sharks. Total lipids were extracted to calculate the energy density. Then lipids were methylated to obtain FA methyl esters (FAMEs) and analyzed in a gas chromatograph with a flame ionization detector. Permutational multivariate analysis of variance was applied to compare FA profiles. Zooplankton of both aggregation sites had 70 % similarity in their FA profiles. The FA profile found in the liver of whale sharks was similar to that of zooplankton in both aggregation sites (DHA > EPA > ARA). However, muscle and subdermal tissue had FA profiles significantly different from zooplankton, and there was preferential ARA assimilation in the subdermal tissue of stranded and live whale sharks. Therefore, FA profiles reflected just 50–60 % of the diet, suggesting that whale shark tissues retain FA according to their metabolic requirements or that surficial zooplankton do not provide ARA detected in subdermal tissue. Future studies should consider night sampling and FA analysis of demersal zooplankton in each aggregation site.

How Do Zooplankton Communities Respond to Environmental Factors across the Subsidence Wetlands Created by Underground Coal Mining in the North China Plain?

The degradation and loss of natural wetlands has caused severe crises for wetland taxa. Meanwhile, constructed wetlands are expanding significantly and facing dramatic environmental changes. Exploring the responses of wetland organisms, particularly zooplankton, may have important implications for the management of wetlands. Environmental and zooplankton samples were collected from 34 subsidence wetlands created by underground coal mining across the North China Plain in August 2021. We used generalized linear models and redundancy analysis to test zooplankton responses to environmental variables, with the relative importance quantified by variation partitioning. We identified 91 species, divided into 7 functional groups, with the highest density of rotifer filter feeders (RF, 2243.4 ± 499.4 ind./L). Zooplankton species richness was negatively correlated with electrical conductivity (EC), chlorophyll-a, total phosphorus, and pH. The Shannon–Weiner and Pielou evenness indices were positively correlated with transparency and negatively correlated with the photovoltaic panel area (AS). Rotifer predators (RCs) and RF densities were positively correlated with cropland area and dissolved oxygen, but negatively correlated with AS. Small crustacean filter feeders positively correlated with AS, whereas medium crustacean feeders (MCFs) positively correlated with EC. AS was the most critical variable affecting the zooplankton community. Our study showed that the spatial pattern of zooplankton communities was shaped by environmental heterogeneity across the subsidence wetlands, providing implications for the management and conservation of these constructed wetlands.

Dynamic oceanographic influences on zooplankton communities over the northern Gulf of Mexico continental shelf

Dynamic influences of ocean processes on distribution, abundance, and diversity of zooplankton communities were studied over the continental shelf in the northern Gulf of Mexico (GoM) from 2015 to 2017. Zooplankton sampling was conducted on four summer cruises in the northcentral GoM. Sampling was designed in waters potentially influenced by the Loop Current (LC) and/or Mississippi River discharge to assess the impacts of these two mesoscale features on the abundance and diversity of zooplankton. During the three-year study, the LC displayed distinct spatial-temporal variations in penetration and occurrence in the northern GoM. Environmental conditions (i.e., sea surface temperature, salinity, and dissolved oxygen) varied between months and years sampled, and were significantly different among cruises (ANOVA, p < 0.001). The majority of zooplankton consisted of calanoid copepods (65% ± 7.2%, mean ± SD), while non-copepod taxa were primarily chaetognaths, polychaetes, tunicates, and ostracods (23 ± 9.2%). Species abundance and diversity of zooplankton were significantly correlated with sea surface temperature, salinity, and dissolved oxygen (p < 0.05). Canonical correspondence analysis displayed significant associations between mesoscale features and dominant zooplankton groups among cruises and by taxa (Monte Carlo Permutation Test, p < 0.001). In addition, non-metric multidimensional scaling indicated that zooplankton assemblages were distinct, likely caused by Mississippi River plumes during the study period. As one of the few efforts to examine zooplankton dynamics at a low taxon level over the GoM continental shelf regarding the impact of mesoscale features, this study revealed seasonal (i.e. summer) and spatial patterns in distribution, abundance, and diversity of zooplankton communities subjected to the dynamic physicochemical conditions in the northern GoM, which will continue in a changing climate.