Abundance Of Fish Larvae Research Articles

Community structure of fish larvae associated with advections of the Kuroshio and its neighboring waters

The Kuroshio has been long thought to be disadvantageous as nursery grounds for larval fishes due to the low plankton standing stocks under the oligotrophic conditions. Despite of the potential risk for survival and growth, early life stages of various fishes appear abundantly in the Kuroshio and its neighboring waters. Here, we report what kind of taxonomic groups establish community structure of larval fishes in the Continental shelf waters (CW) and the Kuroshio (KW). 16 orders and 78 families were classified in the present study. Mesopelagic fishes more abundantly appeared in the KW than in the CW, while larval fish abundance was not different between the two areas. Multivariate analysis demonstrated the regional difference of the taxonomic compositions, represented by Callionymidae, Bothidae, Labridae and Bregmacerotidae for the CW and Gonostomatidae, Myctophidae and Notosudidae for the KW. Abundance of fish larvae to ambient salinity exhibited significantly positive correlations for Gonostomatidae, Sigmops gracilis and Myctophum orientale predominated in the KW and negative correlations for Labridae appeared abundantly in the CW. These results suggest that mixture of advected specimens from the coastal and Kuroshio waters also contribute to larval fish community with high biodiversity and comparable abundance between the Kuroshio and its neighboring waters.

Abundance and distribution of larval and early juvenile fish in Puck Lagoon and outer Puck Bay in the southern Baltic Sea

Puck Bay, regarded as a crucial region along the Polish coastline, has witnessed a decline in fish taxa diversity and abundance over the past several years. The objective of this study was to ascertain the abundance and geographical distribution of fish larvae in Puck Lagoon and outer Puck Bay over the period from April to the end of September. A neuston net with a 300-μm mesh was utilized at 10–15 stations situated in the shallow coastal waters of the study area. A total of 13 taxa were identified among the larvae captured. The majority of larvae observed during the entire study period were identified as Gobiidae. Furthermore, the most abundant taxa were three-spined stickleback, broad-nosed pipefish, straight-nosed pipefish, Ammodytidae, and sprat. The presence of larvae belonging to other taxa, including herring, flounder, cod, turbot, fourbeard rockling, and roach, was observed on a sporadic basis. Details such as Shanon’s diversity Index, the month of larval presence, geographical distribution, and differences in abundance and body size between Puck Lagoon and outer Puck Bay were recorded. The findings indicated that the study area was characterized by a limited diversity of fish taxa. Furthermore, the majority of these taxa (e.g., Gobiidae, broadnose and straight-nosed pipefishes) are not the subject of fishing activities. Nevertheless, they serve as a food source for other taxa and are integral to the ecological balance of the ecosystem. It can thus be concluded that Puck Lagoon and the outer Puck Bay constitute an important habitat for non-commercial and commercial fish taxa.

Variations in the Abundance, Biodiversity, and Assemblage Structure of Larval Fish in the Restricted Waters of the Wang-an Light Fishery off Penghu, Taiwan

This study examined the abundance, biodiversity, and assemblage structure of larval fish inside and outside the restricted fishing zone of the Wang-an light fishery, which is located off Penghu, Taiwan. A total of 97 taxa belonging to 48 families of larval fish were identified through plankton tows conducted during the present investigation. Upeneus japonicus from the Mullidae family emerged as the dominant species in the surveyed area. Diurnal variation in larval fish abundance was evident, with higher abundance observed at night-time than during daytime. However, no significant difference was observed between the larval fish abundance inside and outside the restricted zone. Moreover, fish egg abundance and larval fish biodiversity did not exhibit notable differences between sampling locations or times. Cluster analysis revealed the presence of two groups of seasonal species. The major species in the spring group were Abudefduf vaigiensis and Pomacentrus coelestis, which prefer a low-temperature environment. The major species in the summer group was U. japonicus, which prefers a high-temperature environment. The seasonal succession of water masses under the influence of monsoon activity likely contributed to the observed grouping patterns of larval fish assemblages in the study area. These patterns were closely linked to the marine environmental conditions in this area. The study outcomes provide scientific insights and recommendations regarding the importance and benefits of establishing a restricted fishing zone for sustaining fishery resources.

Ichthyoplankton Biodiversity in the Indonesian Fisheries Management Area-573 in 2015

Abstract Studying ichthyoplankton is crucial for understanding the impact of fish larvae mortality on the recruitment of adult fish and fishing resources. Fish larvae samples were collected in the southern waters of Java using the Baruna Jaya IV research vessel in September - October 2015. Fish larvae were collected using bongo-net and oceanographic data were collected using Conductivity Temperature Depth (CTD) are Temperature and salinity and chlorophyll-a using Aqua MODIS satellite L3 at 36 stations. The results showed the range of fish larvae abundance was 0 - 2,074 ind/1000 m3 with an average of 174 ind/1000 m3. The fish eggs were found with an abundance of 0 - 1,601 eggs/1000 m3. and an average of 213 eggs/1000 m3. The composition of fish larvae recorded 22 families, there were 5 dominant families namely Scombridae (28.60%), Bregmacerotidae (22.96%), Carangidae (7.93%), Blennidae (7.52%), and Gobiidae (7.52%). The diversity of fish larvae was most prevalent at station 28 (SST 26.7 0C; SSS 34.4 PSU; and CHL-a 0.43 mg/m3) and station 36 (SST 27.4 0C; SSS 34.4 PSU) each found 9 families. The abundance of fish larvae was mostly found at stasion 11 had SST 23.50 0C; SSS 34.56 PSU; and CHL-a 0.33 mg/m3 with the dominance of the family Bregmacerotidae. Scombridae was mostly found at stasion 22 with sea surface temperature (SST) 26.52 0C; sea surface salinity (SSS) 34.28 PSU; and sea surface chlorophyll-a (CHL-a) 0.41 mg/m3 which is in the southern waters of Lombok.

Seasonal fish larvae abundance and composition in seagrass habitats of coastal East Africa.

Seagrass habitats play a major role in fisheries productivity through nursery functions and feeding grounds for diverse fish species. However, little is known about the seasonal distribution of fish larvae at large spatial scales in coastal East Africa. We investigated drivers of the seasonal fish larvae abundance and composition in seagrass habitats in Kenya and Tanzania. We found a high diversity of fish larvae (54 families) inhabiting seagrass habitats that differed between sites and seasons. Fish larvae abundance were highest in Kenya, particularly during the northeast monsoon season. Overall, total larval abundances per site were low, reaching less than 190 individuals/100m3 in Kenya and less than 40 individuals/100m3 in Tanzania, likely related to the low productivity and strong hydrodynamic processes in this region. Our data suggests that most of the fish spawn year-round in these tropical waters as we did not find strong seasonal patterns. All sites had a high relative abundance of larvae from demersal spawning fishes, indicating that many fish species move to coastal sites for spawning. Primary productivity and dissolved oxygen, driven by hydrodynamics conditions are positively related to fish larvae productivity both in Kenya and Tanzania. These findings indicate that the occurrence of both resident and transient fish larvae in seagrass meadows is driven by strong hydrodynamic and tidal processes that transport fish larvae across adjacent habitats.

Larval Fish Assemblages in Coastal Waters of Bangladesh: Spatial and Seasonal Dynamics

The distribution of fish larvae in estuaries is crucial for comprehending the functioning of these ecosystems and their role as nursery grounds for marine fish species. Data regarding larval fish assemblages in the coastal waters of Bangladesh are currently scarce. This study examines the spatial and seasonal dynamics of larval fish communities in these waters using a two-year sampling effort with a bongo net. This study investigates the diversity, abundance, and distribution of larval fishes at four sites (Bakkhali River Estuary, Moheshkhalipara, Naf River Estuary, and Rezu Khal Estuary) on the southeastern coast of Bangladesh. A total of 10,387 fish larvae representing 25 families were identified. Clupeidae (42.9%), Engraulidae (35.5%), Ambassidae (10.1%), Myctophidae (2.1%), and Gobiidae (1.9%) were the five most dominant families based on the larval catch composition. Marked seasonal differences in the larval fish abundance were observed. However, these differences were not observed when comparing the four sampled sites. Additionally, the correlation between environmental variables and the larval abundance indicated that salinity negatively influences (p < 0.001) the larval fish abundance. This is the first comprehensive investigation of larval fish assemblages in the coastal waters of Bangladesh. The findings of this study enhance our understanding of the nursery habitat requirements for the early development stages of both migratory and resident species in subtropical coastal waters, providing valuable information for potential applications in management and conservation efforts.

Coupling and de-coupling of the El Niño Southern Oscillation to the supply of larval fishes to benthic populations in the Hawaiian Islands.

Several recent high intensity ENSO events have caused strong negative impacts on the adult phases of foundational species in coral reef ecosystems, but comparatively little is known about how climatic variables related to recent ENSOs are impacting the supply of larvae to benthic populations. In marine fishes and invertebrates, reproductive adults and planktonic larvae are generally more sensitive to environmental variability than older, non-reproductive adults. Further, the transport of larvae in ocean currents may also be strongly ENSO dependent. The interactions between the dynamics of larval survivorship and larval transport could lead to population bottlenecks as stronger ENSO events become more common. We tested the predictions of this hypothesis around the Main Hawaiian Islands (MHI) by constructing a correlation matrix of physical and biological time series variables that spanned 11 years (2007-2017) and multiple ENSO events. Our correlation matrix included four types of variables: i. published ENSO indices, ii. satellite-derived sea surface temperature (SST) and chlorophyll variables, iii. abundance and diversity of larval fishes sampled during the late winter spawning season off Oahu, and iv. abundance and diversity of coral reef fish recruits sampled on the western shore of the Big Island of Hawaii. We found that the abundance and diversity of larval fishes was negatively correlated with the Multivariate El Niño Index (MEI), and that larval variables were positively correlated with measures of fall recruitment (September & November), but not correlated with spring-summer recruitment (May & July). In the MHI, SST variables were not correlated with the MEI, but two successive El Niño events of 2014-15 and 2015-2016 were characterized by SST maxima approaching 30°C. Two large pulses of benthic recruitment occurred in the 2009 and 2014 recruitment seasons, with > 8000 recruits observed by divers over the summer and fall months. Both events were characterized by either neutral or negative MEI indices measured during the preceding winter months. These patterns suggest that La Niña and the neutral phases of the ENSO cycle are generally favorable for adult reproduction and larval development in the spring and summer, while El Niño phases may limit recruitment in the late summer and fall. We hypothesize that episodic recruitment during non-El Niño phases is related to favorable survivorship and transport dynamics that are associated with the formation of pairs of anticyclonic and cyclonic eddies on the leeward sides (western shores) of the Main Hawaiian Islands.

Comparison of Abundance and Structure of Larval Fish Assemblages between Autumn and Spring in the Waters Surrounding Taiwan Bank, Western North Pacific

The fluctuations in both time and space of larval fish assemblages in relation to hydrographic characteristics in the waters surrounding Taiwan Bank were studied in October 2021 (autumn) and March 2022 (spring). Throughout the study period, we identified a total of 149 taxa of fish larvae, encompassing 96 genera and 71 families. Engraulis japonicus, Diaphus slender type, unidentified Gobiidae, Apogon sp., unidentified Clupeidae, and Benthosema pterotum were the six dominant taxa and together constituted 47.39% of the total catch. There were no notable temporal variations observed in the abundance of fish larvae, but the species number of fish larvae was greater in spring than in autumn. Significant variations in species composition were observed between the different cruises, and the cluster analysis unveiled a distinct temporal structure of the assemblages of fish larvae. The dynamics of the prevailing currents induced by seasonal monsoons contribute significantly to the transportation of fish larvae. The distribution of fish larvae showed a good association with hydrographic characteristics, where seawater temperature and salinity emerged as the primary explanatory factors influencing the composition of larval fish assemblages in the waters surrounding Taiwan Bank. While the increased influx of nutrients from upwelling ensures abundant food availability, the hydrographic conditions may not be suitable for every fish larva.

Predictive performance from abundance distribution models of Vinciguerria lucetia larvae in the southern portion of the California current system using XGBOOST

Vinciguerria lucetia is a mesopelagic fish whose larvae show an almost permanent presence in the southern portion of the California Current System. Due to its sensitivity to environmental changes, the species has been considered an indicator of water masses and interannual variability. Fish larvae abundance registered from 1997 to 2015 by the program Investigaciones Mexicanas de la Corriente de California was used to predict the abundance distribution of V. lucetia larvae under two extreme thermal conditions (2000 La Niña and 2015 El Niño), utilizing the novel machine learning algorithm eXtreme Gradient Boosting (XGBOOST). The data were segmented into COLD and WARM groups based on the mean sea surface temperature recorded at each station and contrasted with an undivided TOTAL group. Models were generated using 12 environmental and biological predictor features. Root-mean-squared logarithm error (RMSLE) was used as a prediction performance metric for both internal and external validation. The COLD model showed the best performance for the internal validation with a lower RMSLE value, while the TOTAL model for both the coldest and warmest external validation presented the lowest RMSLE values. The external validation demonstrated models that accurately predicted the spatial distribution; however, none of the models were able to accurately predict the same abundance magnitude observed in both extreme thermal conditions. Nevertheless, XGBOOST shows promise for describing the future distribution traits of V. lucetia.

Declines in the Mekong’s Megadiverse Larval Fish Assemblages: Implications for Sustainable Development

Migratory fishes of the Mekong Basin are facing challenges from human-induced stressors. Quantifying the patterns of fish’s early life stages provides important information on spawning seasons, spawning and nursery habitats, reproductive strategies, migration and dispersal patterns, and stock status. However, the ecology of the Mekong larval fishes, including patterns and drivers of larval fish dispersal, is not well understood. Here, we investigate the temporal variability of drifting larval and juvenile fish assemblages in the Cambodian Mekong River and identify their environmental drivers using long-term (10 year) daily fish larval/juvenile data collections. We found that, in the Mekong main channel, the larval and juvenile assemblages were dominated by longitudinal migrants from the families Cyprinidae and Pangasiidae. Peak abundance and richness were found to occur in July and August, respectively. We detected a significant decline in larval and juvenile abundance and richness over the study period. Cross-wavelet analysis revealed that water levels always lead larval abundance, but lag richness. In addition, cross-correlation analysis observed that peak abundance and richness occurred eight weeks and one week, respectively, before the peak water level. We also discovered that species abundance and richness had a strongly positive relationship with maximum water levels. Variation in fish larval and juvenile abundance and richness was also related to total phosphorus, nitrate, alkalinity, and conductivity. Maximum water levels and the key water quality parameters (e.g., phosphorus, nitrate, alkalinity, and conductivity) significantly influence larval and juvenile fish abundance and richness patterns. Therefore, safeguarding natural seasonal flows, especially maximum flows associated with the peak flood pulse, as well as maintaining good water quality, are key to the reproductive success of many migratory fishes and effective dispersal of offspring to the lower floodplain for nursing, rearing, and growth. Clean and unregulated rivers support productive and diverse fisheries.

Vertical variability in the diversity and abundance of fish larvae in a shallow tropical estuary in Southern Gulf of Mexico

Vertical migration in ichthyoplankton is relevant for its survive and it has been documented in estuaries with more than 10 m depth. In shallow estuaries this process is unknow or not supposed since no environmental stratification is assumed. The objective of this research is to investigate the vertical variability of fish larvae assemblages in shallow tropical estuarine zones. The model study site was the estuarine area of the San Pedro y San Pablo River located east of the Centla Wetland Biosphere Reserve in the Gulf of Mexico. The experimental design includes depth (bottom-surface), habitat type (coast-low complexity and mangrove-high complexity), circadian cycle (sunrise–midday–sunset–night), and season (dry-rainy). The ichthyoplankton were collected using a supporting net (150 cm in length, 50 cm mouth diameter, 400μm mesh size) device for simultaneous collection on the surface and bottom. Circular tows (2.7–4 km/h) were carried out for 5 min. A total of 40,968 fish larvae were collected, belonging to 13 orders, 26 families, and 38 species. The highest larval abundance expressed as mean density (693 ± 916 ind/m3), richness (4.57 ± 3.46), Shannon-Wiener diversity (1.05 ± 48.48), and Pielou evenness (0.88 ± 0.3) were recorded in the bottom. The variance component analysis indicated that the most important factors to explain the larval abundance was the depth (15.55%), the period of the day (11.20 %) and the interaction between all factors (10.51 %). Fish larvae species as Achirus lineatus, Trinectes maculatus, Etropus crossotus, and Symphurus civitatium occupied only the bottom. Despite the low depth, a vertical stratification was observed in the physicochemical parameters, especially in the salinity, being greater in the bottom than in the surface during the two seasons and habitat type and it was related with higher values of abundance, richness, and diversity of ichthyoplankton.

Variation in Larval Fish Assemblage Dynamics Associated with Harmful Algal Blooms in a Temperate Estuary, South Africa

Eutrophication and concomitant harmful algal blooms (HABs) are on the rise globally and pose a threat to larval stages of fishes that rely on estuarine nursery habitats for growth and survival. The anthropogenically altered low inflow estuary (LIE), Sundays Estuary, South Africa, supports persistent and predictable HABs. This study investigated the effects of HABs on the environmental conditions and larval fish assemblage of this warm temperate nursery area. Sampling took place during the austral spring of 2016 and 2018 at three sites in the mesohaline zone where both larval fish abundance and HABs are known to reach maxima. Physico-chemical and phytoplankton data were collected during the day and night, while larval fishes were sampled after nightfall. Physico-chemical parameters and larval fish assemblages were compared by water column (surface and bottom) and sites within the mesohaline zone, years, and HAB intensity (hypereutrophic ≥ 2781 H. akashiwo cells•mL−1; standard ≥ 205 H. akashiwo cells•mL−1; none < 205 H. akashiwo cells•mL−1). A longer period of consecutive hypereutrophic bloom conditions was recorded during 2018 compared to 2016. Dissolved oxygen concentration was notably higher during hypereutrophic blooms (χ2 = 23.759, df = 2, P < 0.001) and reached a maximum of approximately 21 mg•L−1 during the day and 13 mg•L−1 at night. Density and similarity of estuarine resident larval assemblages were negatively correlated to supersaturated dissolved oxygen concentrations. Greater mean densities of estuarine resident larvae were recorded during hypereutrophic blooms compared to standard blooms and bloom absence and diversity was lower during 2018 when hypereutrophic bloom conditions were more persistent. These changes may have major implications for successful early development of fishes that rely on the Sundays Estuary and similar LIEs as a nursery.

Lagoon morphology as an overarching driver for perch breeding success

Fish spawning and nursery habitats are critically important for the maintenance and conservation of viable fish stocks. Understanding habitat use of breeding fish is therefore important. This study examines the spatial distribution of Eurasian perch (Perca fluviatilis) egg strand occurrence and larval density in 18 brackish water post-glacial land-uplift lagoons in the northern Baltic Sea. The aim of the study was to quantify spawning habitat characteristics and evaluate how geomorphological, hydrological, and biological parameters affect perch breeding. Egg strand occurrence was assessed by snorkeling whereas fish larvae and zooplankton were sampled using horizontal surface hauls. Egg strand and larval density increased with higher habitat isolation, i.e., bay morphology had a decisive role in determining early recruitment success. Moreover, egg strand occurrence and larval density correlated positively with water temperature, charophyte cover and negatively with salinity. The zooplankton community structure differed among lagoon types but neither zooplankton density nor diversity showed a clear association with egg strand or fish larvae abundance. However, cladocerans and copepods were abundant in the most enclosed bays, and their density correlated positively with perch larval density. Our findings comply with earlier studies highlighting the importance of bay isolation for fish recruitment strength. We call for a foreseeing coastal management planning, that apart from considering current status and trends, also integrates decadal long projections of isostatic land-uplift processes in conservation decisions to secure the long-term persistence of the best spawning and nursery areas.

From Staple Food to Scarce Resource: The Population Status of an Endangered Striped Catfish Pangasianodon hypothalamus in the Mekong River, Cambodia

Striped catfish Pangasianodon hypopthalmus (Sauvage, 1878) is a flagship catfish species of the Mekong River region, a commercially valuable food fish that is important in freshwater fisheries, and a popular aquaculture species in many Asian countries. The species was assessed as “Endangered” by the International Union for Conservation of Nature (IUCN) due to range contraction and declining abundance, though the status of the species’ wild population in Cambodia, a critical habitat for the species, is not well understood. Here, we assess the population status of the striped catfish in Cambodia using multiple sources, including time-series catch data and length frequency distribution data from a commercial fishery (stationary trawl bagnet or dai) operated in the Tonle Sap River from 1998/99 to 2017/18 and larval drift data monitored in the Mekong River in Phnom Penh from 2004 to 2018. We found that there was a significant decline (R2 = 0.54, p = 0.0002) in the catch (metric tonnes) of the striped catfish from the commercial dai fishery over the last two decades. Similarly, length-based indicator analysis indicates that striped catfish mean length and abundance have both declined over the study period, raising concerns about the sustainability of river catfish fisheries. Moreover, long-term larval drift monitoring in Mekong River shows that there was a marginally significant decline in the quantity of striped catfish larvae/juvenile drifting downstream to the lower floodplain over the last decade. Changes in flood index (extent and duration of flood) in the Tonle Sap floodplain affected by the Mekong’s flow are likely key factors driving the decline of the wild populations of the striped catfish. Both larval fish abundance and floodplain fish harvests have a significant positive relationship with Mekong flow and flood extent. Indiscriminate fishing exacerbates pressures on striped catfish stocks. Therefore, actions such as maintaining natural seasonal flows (flood timing, extent, and duration) to the Tonle Sap floodplain and protecting migratory fish stocks from overharvest and habitat fragmentation are essential to the persistence of stocks of striped catfish and other large-bodied migratory fishes that utilize both the Cambodian Mekong and Tonle Sap floodplains.

Fish functional biotic simplification in a Neotropical reservoir: An approach from the ichthyoplankton

AbstractEcosystem services provided by communities are related to the diversity of functional traits, and biotic functional simplification occurs when this diversity is reduced. Thus, we used the approach of functional indices, applied to the abundance of fish larvae and traits of the spawning stock, to evaluate the spatial and temporal variations in the functional diversity of the fish community of a Neotropical reservoir. The following hypotheses were tested: (i) different environmental conditions between reproductive periods lead to temporal variations in the functional diversity of the community, and (ii) the spatial heterogeneity (longitudinal and lateral) of the environmental conditions formed in the reservoir causes functional biotic simplification to occur from lotic towards lentic areas since the original community was formed by rheophilic species. Larval collections were carried out monthly, at night, between October and March, from 2009 to 2016, with plankton nets equipped with a flowmeter in nine sample areas categorised into three longitudinal zones (fluvial‐FLU, transition‐TRA and lacustrine‐LAC) and three sides (upper‐UPP, middle‐MID and lower‐LOW). Water samples were obtained to measure the temperature and turbidity. Precipitation and reservoir quotas were obtained from official agencies. After the identification of captured larvae, we determined which species were present and used the functional traits of the adults (parental stock), obtained from specialised literature, and functional richness (FRic) and its corresponding standardised effect size (SES.FRic) were computed. The spatiotemporal variations in these indices were evaluated through the two‐way block factorial MANOVA/ANOVA. Their association with environmental variables was inferred through multiple linear regression models. Altogether, 51,995 larvae were captured with the highest abundance in the period V, longitudinally in LAC and TRA and laterally in LOW. Among these, the functional indices were higher in periods IV and V. The highest values of FRic occurred longitudinally in FLU and laterally in LOW. Among the abiotic conditions, rainfall and water temperature were the most influential variables over functional indices and total larvae abundance. The results indicate that fish reproduction is linked to spatiotemporal variations in abiotic conditions confirming our first hypothesis. The second hypothesis was partially supported because functional biotic simplification was observed in the longitudinal gradient, with reductions in FRic in LAC. However, this reduction was not observed in the lateral gradient. We showed that the temporal variability of abiotic conditions is important for the high functional diversity of reservoirs.

Shifts in the composition and distribution of Pacific Arctic larval fish assemblages in response to rapid ecosystem change.

The Pacific Arctic marine ecosystem has undergone rapid changes in recent years due to ocean warming, sea ice loss, and increased northward transport of Pacific-origin waters into the Arctic. These climate-mediated changes have been linked to range shifts of juvenile and adult subarctic (boreal) and Arctic fish populations, though it is unclear whether distributional changes are also occurring during the early life stages. We analyzed larval fish abundance and distribution data sampled in late summer from 2010 to 2019 in two interconnected Pacific Arctic ecosystems: the northern Bering Sea and Chukchi Sea, to determine whether recent warming and loss of sea ice has restricted habitat for Arctic species and altered larval fish assemblage composition from Arctic- to boreal-associated taxa. Multivariate analyses revealed the presence of three distinct multi-species assemblages across all years: (1) a boreal assemblage dominated by yellowfin sole (Limanda aspera), capelin (Mallotus catervarius), and walleye pollock (Gadus chalcogrammus); (2) an Arctic assemblage composed of Arctic cod (Boreogadus saida) and other common Arctic species; and (3) a mixed assemblage composed of the dominant species from the other two assemblages. We found that the wind- and current-driven northward advection of warmer, subarctic waters and the unprecedented low-ice conditions observed in the northern Bering and Chukchi seas beginning in 2017 and persisting into 2018 and 2019 have precipitated community-wide shifts, with the boreal larval fish assemblage expanding northward and offshore and the Arctic assemblage retreating poleward. We conclude that Arctic warming is most significantly driving changes in abundance at the leading and trailing edges of the Chukchi Sea larval fish community as boreal species increase in abundance and Arctic species decline. Our analyses document how quickly larval fish assemblages respond to environmental change and reveal that the impacts of Arctic borealization on fish community composition spans multiple life stages over large spatial scales.

Acidification scenario of Cox’s Bazar coast of the Bay of Bengal, Bangladesh and its influence on fish larvae abundance

Ocean acidification is caused mainly by atmospheric carbon dioxide stored in the ocean. Ocean acidification is considered a major threat to aquatic life, and how it influences the abundance of marine fish larvae is still unclear. This research was designed to measure the current ocean acidification scenario of the Cox's Bazar coast of the Bay of Bengal, Bangladesh, and its probable influence on the abundance of fish larvae. Three research stations were selected: Bakkhali river estuary, Naf river estuary, and Rezu Khal. Monthly sampling was done, and larvae sample was collected from the surface water column (depth: 0.5 m) using a bongo net. Water parameters such as temperature, salinity, total alkalinity, and pH were determined using laboratory protocol. The seacarb package of the R programming language was used to determine ocean acidification factors. The Bakkhali river estuary showed the highest partial carbon dioxide (143.99 ± 102.27 μatm) and the lowest pH (8.27 ± 0.21). A total of 19 larvae families were identified, and the highest larval count was found in Rezu Khal (390 larvae/1000 m3), while the lowest was found in the Bakkhali river (3 larvae/1000 m3). Clupeidae, Myctophidae, and Engraulidae comprised more than 50% of the identified larvae. Blenniidae, Carangidae, Clupeidae, Engraulidae, and Gobiidae were found in all three seasons. Most of the larvae families showed the highest mean abundance under less pCO2. A negative correlation was observed between larvae and acidification factors such as pCO2, HCO3−, and dissolved inorganic carbon (DIC). The study revealed that acidification parameters of the Cox's Bazar coast were not in an acute state for the aquatic organisms' survival, but fish larvae abundance could be declined with raises in the partial carbon dioxide. The results of this study may aid in developing a management plan for conserving Bangladesh's marine and coastal fish.

Spatial distribution and seasonal variation of fish larvae in the upper 200 m of the Philippine Sea

The Philippine Sea, owing to its complicated circulation pattern and the presence of numerous seamounts, is considered to be a hotspot for biodiversity and an important fishing ground. However, to date, few studies on ichthyoplankton in the Philippine Sea have been conducted. During the summer, autumn, and winter of 2020–2021, a series of investigations were conducted to study the spatial and temporal structure of fish larvae in the Philippine Sea. A total of 65 samples were collected by vertical hauling from a depth of 200 m to the surface. A total of 882 fish larvae representing 81 distinct taxa, 49 genera, and 23 families were identified. A seasonal pattern was also observed based on the differences in abundance and dominant taxa. The abundance of fish larvae was 11.35 ± 12.46 ind./100 m3 (mean ± sd.) in summer, 5.83 ± 7.03 ind./100 m3 in autumn, and 2.57 ± 2.73 ind./100 m3 in winter. The dominant species were Vinciguerria nimbaria, Encrasicholina punctifer, and Cyclothone sp. in summer, V. nimbaria, and Ceratoscopelus warmingii in autumn, and Diaphus spp., D. garmani, and Sigmops sp. in winter. A significant latitudinal variation in fish larvae assemblages was found via cluster analysis, and two geographic groups were separated by the northern boundary of the North Equatorial Current. In addition, the fish larvae species diversity also showed a significant latitudinal gradient in autumn, which disappeared in summer. Canonical correspondence analysis indicated that the structure of fish larvae assemblages was affected by average temperature, salinity, and net primary productivity in the upper ocean and sea level anomaly. All dominant species were associated with specific niche environments. This study suggests that latitudinal zonation of fish larvae also occurs in the oligotrophic low latitude Pacific Ocean and is enhanced in autumn. These results provide multi-seasonal baseline data of fish larvae assemblage in the upper Philippine Sea, being an important reference for the planning of marine protected areas in the high seas.

Spatio-temporal relationships between larval fishes and zooplankton in cool-temperate estuaries of South Africa emphasizing the importance of mesohaline zone interactions

A conceptual model for cool-temperate South African estuaries has been proposed to explain the interactions between zooplankton and larval fishes based on small-scale biological processes. Larval fishes and zooplankton data from nine south and west coast South African estuaries were analyzed in terms of the cumulative density of all species and the density dynamics of the dominant taxa in each group. Larval fish and zooplankton density were positively correlated and varied across seasons, peaking simultaneously in summer, although zooplankton also peaked during the stable conditions of the closed phase of some estuaries. Plankton density was positively correlated with salinity and water temperature and negatively correlated with turbidity. The mesohaline zones of estuaries are highlighted as supporting plankton productivity maxima. These results were attributed to the summer peak in plankton productivity coinciding with the lower rainfall, higher temperatures, and clearer waters that are often typical of the dry summers on the south and west coasts of South Africa. Correlation between selected predator, competitor, and prey species supported the hypothesis that estuaries exhibit extensive reciprocal trophic relationships permitting an ideal feeding environment, which maintains a positive relationship between overall larval fish and zooplankton abundance.

Seasonal Changes in Abundance, Biomass, and Species Diversity of Zooplankton in Areas Offshore the Crimea (Black and Azov Seas)

New data are presented the seasonal changes in abundance, biomass of copepods and fodder zooplankton in areas offshore the Crimea. These investigations are based on the materials of five expeditions of the RV “Prof. Vodyanitsky” in the northern part of the Black Sea and the southern part of the Sea of Azov in different seasons of 2016. It was shown: 1) Seasonal differences in the taxonomic structure of the Copepoda taxocene from the shelf and deep waters were revealed. The warm-water invasive species Acartia (Acanthacartia) tonsa and Oithona davisae were relative numerous in the copepod assemblages on the shelf in summer and autumn. In the deep waters, with a low abundance of warm-water invaders, cold-water native species were dominating, and the structure of the Copepoda taxocene was more stable than on the shelf in these seasons. 2) Zooplankton abundance in 2016 was higher compared to 2010 and the 1990s. The data on zooplankton, supported by information about an increase in the species richness and abundance of fish larvae in recent years, make it possible to talk about the transition of the Black Sea ecosystem to a new, relatively stable state.