Southern Waters Research Articles

Distribution Characteristics of Trichiurus japonicus and Their Relationships with Environmental Factors in the East China Sea and South-Central Yellow Sea

The largehead hairtail (Trichiurus japonicus) is the most productive fish caught in China. In order to understand the seasonal distribution of T. japonicus in the East China Sea and the central and southern parts of the Yellow Sea, three species distribution models were used in this study, namely the random-forest model, K-nearest-neighbor algorithm, and gradient-ascending decision-tree model, based on the data of trawling surveys in the East China Sea and central and southern parts of the Yellow Sea from 2008 to 2009. Combined with a variance inflation factor and cross-check, a distribution model of T. japonicus was screened and constructed to analyze the influence of environmental factors on the distribution of T. japonicus in the East China Sea and central and southern parts of the Yellow Sea. The results showed that the random-forest model had the advantages of fitting effect and prediction ability among the three models. The analysis of this model showed that the water depth, bottom water temperature, and surface salinity had a great influence on the habitat distribution of T. japonicus. The relative resources of T. japonicus increased with the increase of bottom water temperature, reached the maximum at 23.8 °C, and first increased and then decreased with the increase of water depth and surface salinity, reaching the maximum when water depth is 72 m and surface salinity is 31.2%. This study also used the random-forest model to predict the spatial distribution of T. japonicus in the central and southern waters of the East China Sea and south-central Yellow Sea from 2008 to 2009, and the results showed that the predicted results were close to the actual situation. The research results can provide a reference for the exploitation and protection of T. japonicus resources in the East China Sea and the south-central Yellow Sea.

Catch and characteristics of Decapterus sp. fishing areas in The Southern Waters of East Java - Bali

Abstract One of the essential potential resources of small pelagic fish to the livelihood of fishermen is Decapterus sp. The purpose of this study was to examine the catch and features of the Decapterus sp fishing region in Indian Ocean waters from East Java to Bali. The fisheries data for Decapterus sp during 2019 - 2021 were provided by Ministry of Maritime Affairs and Fisheries, Republic of Indonesia. The chl-a, and SST data were downloaded from Copernicus Marine Environment Monitoring Service (https://marine.copernicus.eu/). The fisheries and environmental data were then grouped by season. The results showed that the highest catch per unit efforts (CPUE) value occurred during transition 2 season with value of 2.89 followed by west season with value of 2.65. The smallest value of CPUE occurred during transition 1 (1.98). In general, most of Decapterus sp were caught in SST range between 27 – 29°C and chl-a range between 0.1 – 0.3 mg/m3. These results can be used as a basis for management of Decapterus sp especially in southern waters of East Java - Bali.

Australia’s jurisdiction and law enforcement in combating IUU fishing in the Southern Ocean

Australia used to be an active law enforcer in the Southern Ocean in the 2000s and manifested its fulfillment of multiple roles and duties in exercising jurisdictions effectively to deter the Illegal, Unreported and Unregulated (IUU) fishing in this region. This paper provides an updated review of Australia’s maritime enforcement against IUU fishing. Australia’s approach to combating IUU fishing in the Southern waters has been reflected in its legislation, institutional arrangements, as well as judicial cases. This paper examines international and national laws relevant to Australia’s jurisdictions in the Southern Ocean, as well as critically reviews Australia’s institutional arrangements and availability of military resources in maritime enforcement. A analysis of enforcement programs and judicial practices is also provided by this paper.

Effect of environmental drivers on the spatiotemporal distribution of mackerel at age in the Nordic Seas during 2010−20

Abstract A joint spatio–temporal distribution model of mackerel (ages 3–10) was developed to investigate the age-based responses of mackerel to three environmental drivers: sea surface temperature (SST), mixed layer depth, and chlorophyll-a concentration during the summer months 2010–20 in the Nordic Seas. The study showed that SST was the most important variable amongst the ones tested and had the strongest impact on the distribution of the younger age classes (3–5), which had a narrower range of favourable SST and a stronger aversion to cold temperatures than older individuals. Consequently, the impact of SST differed regionally; in the polar front regions, SST explained up to 61% of the variability in the observed density of young individuals, where Arctic water masses likely acted as a barrier to these young individuals. That said, part of it could be confounded with the limited migration capability of young mackerels, which could not reach the furthest frontal regions. In warmer southern waters, the same environmental variables had less explanatory power for mackerel of all ages. Individuals in the south were likely not constrained by temperature and perhaps more influenced by other variables, such as food availability or ocean current (throughout their migration path), for which appropriate data are lacking. Moreover, the model showed that older mackerel were distributed more to the north and west, and their migration pattern changed when the 2013 year-class no longer migrated to the west compared to previous year-classes. Additionally, all-year classes started migrating more eastward from summer 2018.

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.

Similarities and differences in gastrointestinal microbiomes between wild and human-cared spotted dolphins (Stenella attenuata) in natural waters

Despite the growing awareness on the importance of gut microbiomes, understanding marine mammal gut microbiomes remains limited due to difficulties in sampling. Spotted dolphins (Stenella attenuata) are widely spread oceanic cetaceans, and there is a gap in knowledge regarding their gut microbiology. In this study, we opportunistically collected samples from both wild and human-cared spotted dolphins in the southern waters of Hainan Island, China. This provided the opportunity to examine the composition and diversity of the gut microbial communities of this cetacean species. Since these dolphins inhabit a similar water environment, different food sources might be the primary factor distinguishing the gut microbiomes of wild and human-cared populations, offering valuable experimental material to investigate potential differences in gut microbial community structure among marine mammals in similar environments but with varying food sources. We found that the gastrointestinal microbial community structure of wild and human-cared dolphins demonstrated significant differences, both overall and at specific locations. However, no significant difference was observed in the microbial diversity of their gastrointestinal tracts, indicating that the disparities primarily lie in microbiota composition. Additionally, we detected numerous potentially pathogenic bacteria, suggesting a comprehensive future study of marine mammal gut microbiology. Such a study might involve determining health indicator factors associated with these microbiomes. Our study not only supplements information on the gut microbiology of spotted dolphins but also delves into the similarities and differences in gastrointestinal microbial communities within the same marine mammal species when food source variations play a significant role in their lives.

Early Investigation of Tropical Cyclones Blake-Claudia’s Effect on Seasonal Downwelling in Southern Indonesia Waters

Abstract Indonesia southern waters area is one of the places where tropical storms form and develop into tropical cyclones. Apart from cyclones, southern Indonesia waters also experienced other oceanographic phenomena, the seasonal upwelling and downwelling. This study aims to investigate the physical conditions in southern Indonesia waters during the TC Blake-Claudia which occurred during seasonal downwelling period. Historical data shows that tropical cyclones in southern Indonesia generally occur in DFJ and almost never occur in JJA. Meanwhile, the downwelling period occurs during the DJF season. The results show TC Blake-Claudia has weaken or disrupted seasonal downwelling by decreasing SSHA and increasing chlorophyll concentration. This change in oceanographic parameter expected to be occur not only as the result of cyclonic activity which creates a void of water on the coast, but also supported by the initial conditions of the study area which tend to remain unstable just after upwelling event ends.

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.

Migratory movements of fin whales from the Gulf of St. Lawrence challenge our understanding of the Northwest Atlantic stock structure

Fin whales, Balenoptera physalus, are capital breeders, having the potential to separate breeding and feeding both spatially and temporally. Fin whales occur throughout the Northwest Atlantic, but stock structure and seasonal movements remain unclear. By deploying satellite transmitters on 28 individuals, we examine movement patterns within and beyond the Gulf of St. Lawrence (GSL), Canada, and challenge the current understanding of stock structure. Eight individuals left the GSL in autumn, with five tags persisting into January. Migration patterns of these whales showed considerable variation in timing and trajectory, with movements extending south to 24°N, and thus beyond the assumed distribution limit of the species in the Northwest Atlantic. A rapid return to the Scotian Shelf or Gulf of Maine was observed from several whales after incursions in southern waters, suggesting that fin whales in the Northwest Atlantic may not have a common winter destination that fits the definition of a breeding ground. Area-restricted search (ARS) behavior dominated fin whale activities during summer (92%) and fall (72%), with persistence into the winter (56%); ARS occurred at multiple locations in the GSL, Scotian Shelf and Shelf edge, and near seamounts of the North Atlantic, having characteristics consistent with foraging areas.

Spatiotemporal Patterns and Environmental Drivers of Particulate Inorganic Carbon (PIC) Variability in the Southern Waters of Sumatra‐Java Islands

AbstractThe southern waters of the Sumatra‐Java Islands, within the Indo‐Pacific Warm Pool, are highly susceptible to global climate change impacts. Understanding particulate inorganic carbon (PIC) dynamics and environmental responses in this region is critical for assessing climate change effects on marine ecosystems. Utilizing two decades of remote sensing PIC data (2003–2022), we identified five sub‐regions via K‐means clustering: the Sunda Strait, southern coastal/offshore waters of Sumatra Island, and southern coastal/offshore waters of Java Island. Self‐Organizing Map explored interannual PIC variations, while Generalized Additive Models delineated driving factors. In the Sunda Strait, PIC dynamics are influenced by water exchanges between the Indonesian Seas (ISs) and eastern Indian Ocean (EIO). Seasonally, PIC concentrations peak during the east monsoon (boreal summer); decreasing during positive Indian Ocean Dipole (+IOD) and El Niño events. Along the southern Sumatra, PIC variations positively correlate with rainfall and photosynthetically active radiation (PAR). Along the southern Sumatra, upwelling drives PIC variations, with higher concentrations during mature summer monsoon induced upwelling periods. PIC increases during +IOD and decreases during El Niño. Our study highlights the nexus between nutrients, physical factors (e.g., rainfall), and climatic events (e.g., El Niño) on PIC concentrations. Climate‐induced changes in oceanic physical processes modulate nutrient concentrations, thereby governing PIC variations. We propose a mechanistic model to elucidate PIC variations in upwelling areas. Findings suggest that prospective climate variability, encompassing alterations in climate events, rainfall, and temperature, may escalate PIC concentrations within the study area, advocating PIC as a forward‐looking climate change indicator.

Influence of river structure and hydrodynamics on water quality in the upper Taihu Basin, China

The Taihu Basin constitutes a complex river network and variable hydrodynamic forces, which contributing to alterations in regional water quality within the Yangtze River Delta. In this study, to explore the underlying mechanism of these dual factors on water quality in the upper Taihu Basin, a combination of graphical analysis, the water quality index (WQI) method, and the partial least square-structural equation model (PLS-SEM) were employed to quantitatively investigate the river structure indices (water surface ratio, WP; river system fractal, Δα; river network connectivity, γ) and hydrodynamic force indices (the flow index, FI), and their influence on water quality. Negative correlations were found between both WP and Δα with FI and a positive correlation between γ and FI. The southern water network had a higher water body area and greater difference in river network density, while the northern river network had enhanced connectivity and stronger water flow, thus exhibiting superior water quality. Regarding the influence of these factors on water quality, the impact of river structure on WQI was statistically insignificant (P > 0.05), while hydrodynamic force was significantly positively correlated with the WQI (P < 0.05). Moreover, in comparison to the path coefficient of 0.657 for the river structure's influence on the WQI, the hydrodynamic force exerted an even more significant impact on water quality with a path coefficient of 0.715. This study suggested that water quality improvements depend on optimizing the structural integrity of river systems and promoting favorable hydrodynamic conditions, with the latter having greater influence. This research provided theoretical underpinning for optimizing river structure and advancing river and lake water environments within the Taihu Basin.

The effect of pollutants on the ichthyofauna of Lake Ladoga and preventive measures

Lake Ladoga is the largest body of water in Europe with huge reserves of drinking water, and has a particularly important sanitary and hygienic significance for the Northwestern region of Russia. The lake has significant fishery importance – annual catches reached 6000 tons. per year. However, over the past few decades, the fishery status of the reservoir has changed significantly. Stocks and catches of the most valuable fish species have sharply decreased as a result of anthropogenic impact – pollution and eutrophication.Chemical-analytical studies of samples of water, bottom sediments, atmospheric precipitation and fish for metals were carried out in the laboratory of fishery ecology of the St. Petersburg branch of the Federal State Budgetary Institution "VNIRO" ("GosNIORH" named after L.S. Berg) on an atomic absorption spectrophotometer AA - 7000 (Shimadzu) according to approved methods (PNDF., 2010; M02-2406., 2013 and M02-902-125, 2005), and in the research laboratory of food and natural objects "ANALECT" of the Institute of the Ministry of Health of the Russian Federation, using the method of atomic absorption spectrometry according to approved methods. Hydrochemical and hydrological parameters were determined using an automatic multiparameter probe Aqua TROLL 500.The southern water area of the lake, which is the most valuable in terms of fisheries, turned out to be the most vulnerable to toxicological effects. Pollution of spawning grounds, toxicosis of fish, violation of natural reproduction in combination with the hydrological features of the reservoir have led to irreversible transformations in the structure of the ichthyofauna as a whole for the entire lake. Pronounced consequences for the ichthyofauna of the reservoir are associated with the sensitivity of fish to pollutants, their ability to accumulate pathological information over a long-life cycle. The hydrological features of the southern water area of Lake Ladoga, combined with the location of pollution sources and the routes of pollutants, make it difficult to carry out preventive measures in this most important fishery area.

Ocean Wave Energy Potential in Southern Waters of Malang

Ocean or marine energy has immense renewable energy capability, able to provide more than double the world’s current electricity consumption. Ocean energy is considered a non-polluting, renewable source of energy. The research was conducted in the waters of South Malang, East Java Province. This research utilizes wave modeling data that has been picture confirmed and processed within one year, in 2022. This procedure will yield the monthly height, period, and direction of wave arrival. The data used to create a map of the location of wave energy in South Malang comes from previously created wave energy maps. This location map is the result of an overlay of multiple prior maps in order to create a site that can be developed for the usage of wave energy. According to the results, the southern locations of Donomulyo, Bantur, and Sumbermanjing have the most potential for using wave energy for buoy planting. Point 29 is the closest point following point 30 to point 34. However, point 29 is the area covered by the turtle migratory route. Point 34 is the farthest away from the other two places if the distance from the coastline to the potential point is calculated perpendicularly. Despite its distance from the coast, this site experiences the least disturbance when compared to others.

The Central South Atlantic: The origin of its waters, its evolution and effects beyond

The primitive sea that occupied the Central South Atlantic (CSA), part of the intra-Gondwana rift during the Early Cretaceous, allowed precipitation of an extensive and thick layer of evaporites, the Ibura Salt, followed by the deposition of a prominent Albian carbonate package. Although the shallow platform facies do not contain classical benthic Tethys markers, the pelagic open sea carbonates are essentially dominated by planktonic elements coming from the Tethys Realm. This condition led some researchers to think that Tethys waters also contributed to salt formation, an idea that clashes with the geotectonic model of northward separation of Africa and South America and ingression of predominantly Austral marine waters. Now, a new controversy arises as to the age of this salt layer when trying to position bio-events and lithological and chemostratigraphic markers from these rocks with respect to established data for the Global Boundary Stratotype Section and Point for the Aptian/Albian boundary (GSSP-Alb). Biochronostratigraphic information on planktonic foraminifera points to an Aptian age as opposed to the earliest Albian traditionally accepted for the carbonate section that overlies the giant salt layer. On the other hand, stratigraphic and geochronological data suggest an age of 113 Ma for the base of the salt, very near to the 113.2 ± 0.1 Ma arbitrated for the GSSP-Alb. In this study, we adopt the base of the evaporite bed as the Aptian/Albian boundary in the CSA, Equatorial South Atlantic (ESA), and northeastern Brazilian interior basins (BNE) as well. Based on these criteria, a broad review and the integration of available information have led to new interpretations regarding the earliest phase of these segments of the South Atlantic and adjacent areas. Initially, during the Aptian-Albian transition, an ephemeral interior sea within Brazil, drawing its waters from the north, would have contributed to salt deposition in the intra-Gondwana rift (evaporitic stage of the CSA). Afterward, but still within the earliest Albian, the evaporitic system evolved into a carbonate gulf when the northern barrier, the Exception Zone (EZ), disappeared. The lagoonal circulation pattern that then formed in the CSA created a hypersaline and warm outflow plume that swept across the marine bottom of the ESA and part of the Tethys Sea. Paleoceanographic events registered at Site 545, Mazagan Plateau, support this new hypothesis and illustrate the potential complexity of correlation of organic-rich deposits in which local influences have been greater than global ones. This long, narrow, and continuous carbonate gulf disappeared at the end of the Albian with the arrival of southern waters from the Meridional South Atlantic (MSA), and the South Atlantic became consolidated as a proto-ocean.

Feeding habits of Pacific anchovy, Engraulis japonicus (Actinopterygii: Clupeiformes: Engraulidae), captured off the southern coasts of Korea

Understanding the feeding ecology of anchovies in the southern waters of Korea is crucial for improving ecosystem management. However, to date, few studies have examined seasonal changes in the diet of Pacific anchovy, Engraulis japonicus Temminck et Schlegel, 1846, in Korean waters, with the majority of these focusing on the larval and adult stages. The presently reported study provides updates on the feeding habits of E. japonicus off the southern coast of Korea. We analyzed 347 individuals. One-way analysis of similarity was performed to evaluate the differences in diet composition among size classes and seasons of E. japonicus, and correspondence analysis was conducted using the matrix of the percentage by number (%N) data for prey with occurrence of less than 10% to determine the distribution of prey across all size classes and each season. The diet of E. japonicus was investigated according to season and four size classes. The fork length of these specimens ranged from 5.4 to 14.1 cm. A total of 55 prey taxa of varying sizes between 0.33 mm (diatom Coscinodiscus spp.) and 5.8 mm (fish larvae) were recorded. Anchovies were exclusively planktivorous, and copepods were the most common prey, comprising 82.1% of the identified food items and 84.3% of anchovy stomach contents analyzed. However, their occurrence and abundance varied according to season and Pacific anchovy size class. According to the percentage of the index of relative importance (%IRI), the most important prey items were the copepods Calanus sinicus (48.0%), Paracalanus orientalis (31.7%), bivalve larvae (5.8%), Ditrichocorycaeus affinis (4.2%), and calanoid copepods (2.4%). Analysis of similarities and similarity percentage analysis indicated that a distinct diet of Pacific anchovy in the southern waters of Korea is potentially driven by differences in hydrological conditions. Correspondence analysis revealed that anchovies had the most significant impact on the differences between size classes. The results deepen our understanding of prey species diversity and intraspecific food competition off the southern coast of Korea.

Cestodes of the genus Anthobothrium van Beneden, 1850 in five carcharhinid shark species from the southern waters of Iran, with the description of three new species, new host and locality records, and a key to the species of the genus.

Examining the intestinal cestode fauna of the shark species Carcharhinus dussumieri (Müller and Henle), C. sorrah (Müller and Henle), C. leucas (Müller and Henle), and Rhizoprionodon acutus (Rüppell) from the Persian Gulf and C. macloti (Müller and Henle) from the Gulf of Oman resulted in the description of three new species of the tetraphyllidean genus Anthobothrium van Beneden, 1850, along with the establishment of new host and locality records. Anthobothrium afsanae sp. nov. and A. barsami sp. nov. were found in C. dussumieri and C. sorrah. Carcharhinus macloti was the additional host of A. barsami and new host record for A. parimae Sadeghi Kamachali and Haseli, 2022, for which a new locality record was established in the Gulf of Oman. Carcharhinus leucas is the type host of A. elenae sp. nov. and a new host record for A. lesteri Williams, Burt and Caira, 2004. A new locality record for A. lesteri is the Persian Gulf, which is far away from the type locality, Australia. Rhizoprionodon acutus is new host record for A. samae Sadeghi Kamachali and Haseli, 2022 and A. shayani Sadeghi Kamachali and Haseli, 2022. With 14 valid species of Anthobothrium and given the relatively uniform morphology of members of this genus, a key to the species of Anthobothrium is presented. The biogeographical distribution and host specificity are also discussed for the species of Anthobothrium.

Stock Assessment of Kawakawa (Euthynnus affinis Cantor, 1849) in the Persian Gulf and Oman Sea (Iranian Southern Waters), Using Data Limited Approach

Stock Assessment of Kawakawa (Euthynnus affinis Cantor, 1849) in the Persian Gulf and Oman Sea (Iranian Southern Waters), Using Data Limited Approach

Characterization of solitary internal waves in the northern Bali waters

Internal solitary wave (ISW) is an underwater wave, formed due to the evolution of internal tides. The presence of breaking ISWs in coastal areas can potentially influence coastal ecosystems through cross-shelf exchange mechanisms. The southern waters of the Kangean Island and the eastern waters of the Madura Island, known also as part of the northern Bali waters, have been an active habitat for ISW propagation. This study aims to identify and characterize ISW which potentially breaking onshore the Southern Kangean Waters (SKW) and the Eastern Madura Waters (EMW) using Sentinel 1 SAR (Synthetic Aperture Radar) imagery. ISW characterization was carried out using the Korteweg-de Vries (KdV) model. The ISW amplitudes which propagate to EMW varies from 1 - 28 m with a propagation speed of 1.60 - 1.98 m/s, while the ISW which propagate to the SKW has an amplitude of 1 - 60 m with a propagation speed of 0.83 to 2.17 m/s. The results show that the ISW propagating to the SKW has stronger amplitude, phase velocity, and horizontal-vertical velocities than the ISW propagating to the EMW. The maximum speed of the horizontal current triggered by ISW leading to the EMW is 0.03 - 0.17 m/s and the vertical velocity 0.11 - 4.53 cm/s; the maximum speed of horizontal velocity leading to the SKW is 0.02 - 1.29 m/s and the maximum speed of the vertical velocity 0.04 - 19.03 cm/s.

Annual changes in zooplankton biodiversity in the southern waters of Changdao

Annual changes in zooplankton biodiversity in the southern waters of Changdao

Unprecedented phytoplankton blooms in autumn/winter in the southern Bohai Sea (China) due to high Yellow River discharge: Implications of extreme rainfall events

The occurrence of abnormal phytoplankton blooms is one of the significant changes in coastal ecosystems due to climate change. However, the underlying mechanism of such blooms remains poorly understood due to the complexity of the system. In this study, the data from numerous observations was used to elucidate the unprecedented phytoplankton blooms in the autumn and winter of 2021 in Laizhou Bay, a typical aquaculture bay in the southern Bohai Sea of China. The abundance of phytoplankton cells increased by more than tenfold in the southern waters compared to that in the same period from 2019 to 2020. The phytoplankton bloom was first observed in winter in the Bohai Sea, with the cell abundance in the southern bay exceeding 108 cells L−1 in December 2021. The diversity and evenness of phytoplankton communities decreased in the southern area. Cerataulina pelagica was the dominant algae, comprising 69 % of the total phytoplankton in October and 99 % in December. In autumn 2021, the largest flood of the Yellow River in recent decades occurred. This was attributed to extreme rainfall events within the river basin. The input of substantial riverine nutrients played a significant role in promoting phytoplankton blooms. Correlation analysis indicated the important cumulative impact of the Yellow River on phytoplankton blooms rather than a direct short-term effect. Numerical modeling results indicated that exceptionally high Yellow River discharge in autumn could significantly affect the entire bay from autumn to the following spring. This study may contribute to understanding the abnormal phytoplankton blooms in coastal waters and provide valuable insights for environmental management in river basins and coastal waters.