Planktonic Species Research Articles

Shifting phenology as a key driver of shelf zooplankton population variability

AbstractThe timing of biological events, known as phenology, plays a key role in shaping ecosystem dynamics, and climate change can significantly alter these timings. The Gulf of Maine on the Northeast U.S. Shelf is vulnerable to warming temperatures and other climate impacts, which could affect the distribution and production of plankton species sensitive to phenological shifts. In this study, we apply a novel data‐driven modeling approach to long‐term datasets to understand the population variability of Calanus finmarchicus, a lipid‐rich copepod that is fundamental to the Gulf of Maine food web. Our results reveal how phenology impacts the complex intermingling of top‐down and bottom‐up controls. We find that early initiation of the annual phytoplankton bloom prompts an early start to the reproductive season for populations of C. finmarchicus in the inner Gulf of Maine, resulting in high spring abundance. This spring condition appears to be conducive to enhanced predation pressure later in the season, consequently resulting in overall low C. finmarchicus abundance in the fall. These biologically controlled dynamics are less pronounced in the outer Gulf of Maine, where water exchanges near the boundary have a greater influence. Our analysis augments existing hypotheses in fisheries oceanography and classical ecological theory by considering unique plankton life‐history characteristics and shelf sea dynamics, offering new insights into the biological factors driving C. finmarchicus variability.

Diagenetic impacts on calcium isotopes and Mg/Ca ratios of Globigerinoides ruber shells in the eastern Mediterranean

The presence of Mg-rich calcite in foraminifera shells has impeded traditional calcite-based paleothermometry in the eastern Mediterranean, complicating our understanding of the region's past climate. This study analysed the calcium isotopic composition ( δ 44/40 Ca) in the shells of the planktonic foraminifera species Globigerinoides ruber (white), collected from 12 core top sediment samples spanning the Aegean and Levantine Seas in the eastern Mediterranean. The shells exhibited varying degrees of early diagenetic Mg-rich authigenic calcite coatings, which complicates traditional calcite-based paleothermometry in the region. Our findings demonstrate a significant correlation between the δ 44/40 Ca data and the Mg/Ca ratios of the shells and suggest that the inorganic calcite overgrowth originates from seawater. Moreover, the calcium isotopic composition increases with the amount of calcite overgrowth. This relationship allowed us to quantify the maximum potential inorganic endmember. The highest amount of post-depositional calcite precipitation was observed in the warm, shallow basins of the South Aegean Sea. The diagenetic alteration of the primary biogenic δ 44/40 Ca geochemical signal is linked to the quantity of secondary calcite present. By combining Ca isotope and Mg/Ca measurements on isolated foraminifera tests, we provide novel insights into the early diagenetic history of carbonate-bound geochemical proxies.

Species of the thecate dinoflagellate genus Heterocapsa (Dinophyceae; Heterocapsaceae) from the tropical Mexican Pacific, with special reference to two new records in the area and the ultrastructure of Heterocapsa borneoensis

Background: The thecate dinoflagellate genus Heterocapsa encompasses marine planktonic species, which have been poorly studied in the Mexican Pacific coasts. Question: Is it possible to extend the knowledge of the genus Heterocapsa in the Mexican Pacific by means of different study techniques? Study sites: Acapulco Bay, Guerrero, Mexico During November 2021 and March 2024. Methods: Establishment of cultures, morphological analysis by light microscopy and molecular identification using the region D1-D2 (LSU rDNA) Results: Five strains belonging to species of the genus Heterocapsa were established. The strains were identified as H. borneoensis, H. iwatakii and Heterocapsa sp., respectively. Each strain was morphologically characterized by light microscopy, highlighting characters such as the overall shape of the cell, proportion of the episome and hyposome, shape and position of the nucleus and number and position of the pyrenoids. Additionally, the morphology of the body scales and the ultrastructure of H. borneoensis were studied. Molecular identification of two species was confirmed by analysing the D1-D2 region (LSU rDNA). The phylogeny showed that sequences obtained in this study clustered with previous sequences of H. borneoensis and H. iwatakii. Conclusion: This study confirmed the first record of H. borneoensis and H. iwatakii from the eastern Pacific Ocean.

The Contribution of Siliceous Plankton to Vertical Export Flux in the Eastern Mediterranean: A Comparative Study of the North Aegean, Cretan, and Ionian Seas

This study investigates the intricate dynamics of siliceous plankton species within the open marine regions of the Greek Seas, focusing on their seasonal and spatial variability. For this purpose, vertical export fluxes of diatoms (DtF), silicoflagellates (SF), and radiolaria (RF) were analyzed in three sediment trap time series obtained from the North Aegean, Cretan, and Ionian Seas. Special attention was given to diatom assemblages, resulting in the estimation of the DtF community structure and diversity for each studied site. Diatom flux values reached 353.9 × 103 valves m−2 day−1, 77.7 × 103 valves m−2 day−1, and 42.4 × 103 valves m−2 day−1 in the North Aegean, Ionian, and Cretan Seas, respectively. SF maxima were 1309.8 × 103 skeletons m−2 day−1 in the North Aegean Sea, 35.2 × 103 skeletons m−2 day−1 in the Ionian Sea, and 11.9 × 103 skeletons m−2 day−1 in the Cretan Sea (South Aegean Sea). RF values reached 13.9 × 103 radiolaria m−2 day−1, 11.9 × 103 radiolaria m−2 day−1, and 5.4 × 103 radiolaria m−2 day−1 in the North Aegean, Ionian, and Cretan Seas, respectively. The North Aegean Sea exhibited significantly higher mean total fluxes, particularly for diatoms, driven by the north-to-south oligotrophy gradient, which was influenced by riverine inflows and the nutrient-rich Black Sea water. In the Cretan and Ionian Seas, convective mixing and atmospheric deposition, especially during increased rainfall (precipitation) events, were identified as primary drivers for the increased siliceous plankton fluxes recorded in the late winter–spring months. Diatom communities were dominated by Naviculales and Fragilariales; the prevalence of the former in the North Aegean Sea is likely linked to the higher nutrient levels in its upper photic zone, as Naviculales includes species with a high affiliation to nutrient enrichment.

Epiplastic Algal Communities on Different Types of Polymers in Freshwater Bodies: A Short-Term Experiment in Karst Lakes

The increasing amount of plastic debris in water ecosystems provides a new substrate (epiplastic microhabitats) for aquatic organisms. The majority of research about epiplastic communities has focused on seawater environments, while research is still quite limited and scattered concerning freshwater systems. In this study, we analyze the first stages of colonization on different types of plastic by a periphytic algae community (its composition and dominant species complex) in freshwater bodies located in a nature reserve (within the Middle Volga Basin). A four-week-long incubation experiment on common plastic polymers (PET, LDPE, PP, and PS), both floating and dipped (~1 m), was conducted in two hydrologically connected karst water bodies in July 2023. The composition of periphytic algae was more diverse (due to the presence of planktonic, benthic, and periphytic species) than the phytoplankton composition found in the water column, being weakly similar to it (less than 30%). Significant taxonomic diversity and the dominant role of periphytic algae were noted for diatoms (up to 60% of the total composition), cyanobacteria (up to 35%), and green (including Charophyta) algae (up to 25%). The composition and structure of periphytic algae communities were distinct between habitats (biotope specificity) but not between the types of plastic, determined primarily by a local combination of factors. Statistically significant higher values of abundance and biomass were demonstrated for some species, particularly for Oedogonium on PP and Nitzschia on LDPE (p-value ≤ 0.05). As colonization progressed, the number of species, abundance, and dominance of individual taxa increased. In hydrologically connected habitats, different starts of colonization are possible, as well as different types of primary succession (initiated by potentially toxic planktonic cyanobacteria or benthic cyanobacteria and mobile raphid diatoms). Within the transparency zone, colonization was more active on the surface (for example, in relation to green algae on PP (p-value ≤ 0.05)). These results indicate a tendency for microalgae communities to colonize actively submerged plastic materials in freshwater, and they may be useful in assessing the ecological status of these aquatic ecosystems.

Deciphering microbial assembly and coexistence in rivers subjected to long-term reclaimed water replenishment

Reclaimed water recharge into rivers is an important supplementary approach to address water resource shortage in arid and semi-arid areas worldwide. However, the ecology impacts of reclaimed water recharge on the rivers are still unknown, especially for the microbial assemble and species coexistence in different seasons. Here, the evolution of microbiome and its response to different reasons in the Jialu River, which was subjected to long-term reclaimed water recharge, is investigated by using 16S rRNA gene sequencing and multivariate statistical methods. The results indicated that microbial communities exhibited significant temporal heterogeneity across different periods and were negatively correlated with river discharge. Their assembly was primarily influenced by stochastic processes such as dispersal limitation and drift. As the transition occurred from the dry season to the normal season, the role of drift diminished, while the deterministic effects of dispersal limitation and niche selection intensified. The relationships among planktonic bacterial species were primarily positive (cooperative), and the complexity and positive correlations within the ecological network showed a trend of first decreasing and then increasing with the change of seasons. Temperature, dissolved oxygen, and ammonia nitrogen were the main driving forces influencing the structure of microbial communities. In summary, these findings provided insights into the impact of seasonal variations on the microbial community patterns in reclaimed water-supplemented river ecosystems.

Water-surface photovoltaic systems have affected water physical and chemical properties and biodiversity

The implementation of water-surface photovoltaic systems as a source of renewable power has expanded rapidly worldwide in recent decades. Water-surface photovoltaic avoids negative impacts on terrestrial ecosystems, while the impacts on aquatic physical and chemical properties and biodiversity are unclear. To understand the ecological and environmental impacts of water-surface photovoltaic systems, here we conducted a field survey on water physical and chemical properties, plankton and bird communities of 26 water-surface photovoltaic systems in the Yangtze River basin in China during the winter and summer of 2022. We found that water-surface photovoltaic systems decreased water temperature, dissolved oxygen saturation and uncovered area of the water surface, which caused a reduction in plankton species and individual density, altering the community composition. Water-surface photovoltaic systems also caused an overall decrease in bird diversity and changed bird community compositions. These findings suggested that water-surface photovoltaic systems have impacts on the water environment and ecology. Since water-surface photovoltaic systems will continue to expand in the future, our results emphasize that rational planning is critical for the sustainable development of water-surface photovoltaic systems and the protection of the aquatic environment and biodiversity.

Mechanisms promoting biodiversity in ecosystems

AbstractExplaining biodiversity is the central focus in theoretical ecology. A significant obstacle arises from the competitive exclusion principle (CEP), which states that two species competing for the same type of resources cannot coexist at constant population densities, or more generally, the number of consumer species cannot exceed that of resource species at steady states. The conflict between CEP and biodiversity is exemplified by the paradox of the plankton, where a few types of limiting resources support a plethora of plankton species. In this review, we introduce mechanisms proposed over the years for promoting biodiversity in ecosystems, with a special focus on those that alleviate the constraints imposed by the CEP, including mechanisms that challenge the CEP in well‐mixed systems at a steady state or those that circumvent its limitations through contextual differences.

Insights into the plankton community seasonal variations in a finer scale of the Bohai Sea: biodiversity, trophic linkage, and biotic-abiotic interplay

Plankton play an indispensable role in the biogeochemical processes of marine ecosystem. However, unraveling the intricate interactions among biodiversity, trophic linkages, and biotic-abiotic interplay between phytoplankton-zooplankton remains a significant challenge. Here, we conducted field studies in the neritic area of the Bohai Sea during autumn 2023 and spring 2024 to explore seasonal variations of both phytoplankton and zooplankton through microscope. Our analysis revealed a sharp decline in trophic interactions across phytoplankton and zooplankton, with an abundance ratio in autumn 2023 being 5.5 times higher than in spring 2024. Additionally, dominant plankton species (Y ≥ 0.02) exhibited obvious differences between the two seasons, with higher species diversity observed in autumn. Moreover, each dominant zooplankton species had distinct preferred food items in both seasons, with Rhizosolenia setigera being favored by Noctiluca scintillans and Acartia pacifica. Furthermore, a multivariate biota-environment analysis indicated that each dominant plankton species had unique correlation with specific environmental parameters, highlighting how plankton can fully exploit external environmental conditions to survive in seasonal variations. Ultimately, our findings emphasize significant seasonal dynamics and provide a solid foundation for assessing the potential impacts of environmental changes on plankton in coastal marine realm.

Complementary roles of eDNA metabarcoding and microscopy in plankton monitoring across seven habitats

Abstract Plankton biodiversity in aquatic ecosystems is currently investigated by labor-intensive and time-consuming microscope identification. Environmental DNA (eDNA) metabarcoding is emerging as a highly effective and objective tool for assessing biodiversity. In this study, we compared the effectiveness of eDNA metabarcoding with conventional microscope identification for monitoring plankton biodiversity in seven habitats. The eDNA metabarcoding identified a rich diversity of 190 families, 410 genera and 871 species within the planktonic community across seven habitats. In contrast, traditional microscope identification only identified 51 families, 75 genera and 96 species. In addition, primer choice influenced the detected plankton community diversity, with the V4 primers performing poorly for detecting Cladocera and Euglenophyta taxa and the V9 primers revealing more eukaryotic plankton species. Despite primer-specific differences in species detection, there was substantial overlap between the species detected by eDNA metabarcoding strategies and microscope identification. These results suggest that eDNA metabarcoding can be used as a complementary method alongside microscope identification rather than replacing them entirely.

Зообентос и зоопланктон малых рек бассейна реки Кобры (национальный парк «Койгородский»)

The studies were carried out on two small rivers – tributaries of the Kobra River (the Volga River basin), located on the territory of Koygorodsky National Park. The structure, quantitative development of zoobenthos and fauna of benthic invertebrates were studied. Hydrobiological sampling was carried out in June – July 2021. Standard methods were used for sampling. 87 species and taxa of a higher rank of invertebrates were found in the benthic fauna. The most diverse were caddisflies (21), mayflies (21), stoneflies (13) and oligochaetes (12 species). Quantitative development of the zoobenthos of the Kobra River basin is comparable to the average for the rivers of the Vyatka River basin as a whole and was 19 thous. ind./m2 and 74.6 g/m2 in the Suran River, and 14.1 thous. ind./m2 and 19.2 g/m2 in the Mytets River. The chironomids played a leading role in benthic invertebrate communities, and accounted for an average of 26.3–33.4% of the total zoobenthos abundance. Mayfly larvae and leeches dominated in the Suran River by biomass, as well as molluscs and caddisflies – in the Mytets River. The maximum quantitative characteristics were noted on the reaches of both rivers. The development of benthos was much poorer on the riffles. Three rare species from the orders of mayflies, stoneflies and dragonflies were identified. Zooplankton in the small tributaries of the Kobra River was studied using standard methods: in the Suran River on the early June and in the Mytets River – on the end of the July 2021. Plankton fauna was represented by 28 taxa, rotifers and copepods prevailed. Plankton species diversity, abundance and biomass were lower in the Suran River (the beginning of the vegetation season), which indicated the processes of zooplankton formation. The above indicators were higher in the middle of the summer season in the Mytets River, and indicated the stability of plankton communities. The presented data significantly expand the understanding of the biodiversity of aquatic ecosystems in the southern taiga zone.

Identification of plankton habitats in the North Sea.

The definition of an ecological niche makes it possible to anticipate the responses of a species to changing environmental conditions. Broad tolerance limits and a paucity of readily observable niches in the pelagic zone make it difficult to anticipate responses of the plankton community related to anthropogenic or environmental changes. Plankton distributions are closely linked to climate change and shape the seascape for higher trophic levels, so monitoring plankton distributions and defining ecological niches will help to understand and predict ecosystem responses. Here we apply a machine learning autoencoder and a density-based clustering algorithm to high-frequency datasets sampled with a ROTV Triaxus in the North Sea. The results indicate that in this highly dynamic environment, local hydrography prevents niche-based separation of plankton species at the sub-mesoscale, despite the availability of different habitats. Plankton patches were associated with naturally occurring frontal systems and anthropogenically induced upwelling-downwelling dipoles in the vicinity of offshore wind farms (OWFs).

Effect of Rice–Carp Coculture on Phytoplankton and Microzooplankton Community Composition in Paddy Water during Different Rice Growth Stages

Integrated rice–fish farming, an agricultural practice that combines cultivating rice and breeding fish in the same field, has attracted widespread attention. However, there is limited research on how the rice–carp coculture impacts the community structure of phytoplankton and microzooplankton in paddy water. This study employed eDNA metabarcoding sequencing to analyze the composition of phytoplankton and microzooplankton in a rice monoculture system (RM) and a rice–carp coculture system (RF). Following annotation, we identified 9 phyla, 89 families, 275 genera, and 249 species of phytoplankton, along with 20 phyla (or subphyla and classes), 85 families, 222 genera, and 179 species of microzooplankton. The alpha diversity indices revealed significantly higher richness, diversity, and evenness in the RF group compared to the RM group during grain-filling stage. Principal coordinates analysis (PCoA) demonstrated notable differences in the phytoplankton and microzooplankton compositions between the two groups across various rice growth stages. Composition analysis showed that rice–carp coculture increased the relative abundance of dominant phytoplankton phyla such as Bacillariophyta, Chrysophyta, and Euglenophyta while decreasing that of Cryptophyta. In microzooplankton, the coculture resulted in an increased abundance of Intramacronucleata (subphylum) and a decrease in Conoidasida (class). In conclusion, the rice–carp coculture enhances the diversity of plankton, particularly during the grain-filling stage, and simultaneously alters the composition and abundance of dominant plankton species in the paddy water. These findings enhance understanding of the broader impacts of integrated rice–carp farming on agricultural ecosystems, emphasizing alterations in the diversity and composition of aquatic microorganisms

Depositional environment and stratigraphic framework of the NS- 1 well, Coastal Swamp Depobelt, Niger Delta Basin: a foraminiferal perspective

A comprehensive analysis of 102 ditch-cutting samples from the NS-1 well in Leuma Field, Coastal Swamp Depobelt, Niger Delta Basin, covering depths from 4730 ft to 7790 ft, is presented. Lithologic descriptions revealed eleven lithostratigraphic sub-units within the transitional-paralic sequence of the Agbada Formation, comprising alternating sandstone and shale. The foraminiferal analysis identified 58 species: 14 planktonic, 26 calcareous benthic and 18 agglutinated benthic. Key planktonic index species such as Globigerinoides sp. and Globorotaliacontinuosa indicates a Middle to Late Miocene age. The biozonation correlates with the Blow (1969) Scheme (N7- N9/N10/N11) placing the intervals within the Middle Miocene to Late Miocene epochs. The depositional environment transitioned from Coastal Deltaic to Inner Neritic and Middle Neritic, suggesting a shallow marine setting influenced by a warm, humid climate. The presence of calcareous foraminifera supports a shallow marine deposition above the carbonate compensation depth. This study provides valuable insights into the sedimentological, stratigraphic, and paleoenvironmental history of the NS-1 well during the Miocene.

Analysis of oil accumulation mechanisms in plasma induced mutant Scenedesmus strains compared to original Scenedesmus strains

Scenedesmus sp. is a species of the Scenedesmus genus within the phylum Chlorophyta, commonly found as a planktonic algal species in freshwater and known for its rapid growth rate. This study employs room-temperature, atmospheric-pressure plasma mutagenesis for the breeding of Scenedesmus sp., utilizing transcriptomic analysis to investigate the biosynthesis mechanism of triglycerides. Further analysis of differentially expressed genes in transcriptome by measuring the macroscopic biological indicators of mutant and original algal strains. The findings of the study suggest that the mutant strain's photosynthesis has been enhanced, leading to improved light energy utilization and CO2 fixation, thereby providing more carbon storage and energy for biomass and lipid production. The intensification of glycolysis and the TCA (tricarboxylic acid) cycle results in a greater shift in carbon flux towards lipid accumulation. An elevated expression level of related enzymes in starch and protein degradation pathways may enhance acetyl CoA accumulation, facilitating a larger substrate supply for fatty acid production and thereby increasing lipid yield.

Characterization of the Ecological Niche and Interspecific Connectivity of Plankton in Baiyangdian Lake by Combining Ecological Networks

To understand the structure of the plankton community and the ecological niche characteristics of their dominant species, sampling surveys of plankton were conducted in Baiyangdian Lake in the spring （March）, summer （July）, and autumn （September） of 2022. The changes in the plankton community during the three seasons were analyzed by constructing ecological network diagrams, non-metric multidimensional scaling analysis （NMDS）, and the ecological niche width. The niche overlap of zooplankton dominant species was evaluated by the improved Levins' formula and Petraitis' index. The interspecific connectivity of dominant species was judged using the chi-square test and interspecies connectivity coefficients. The results showed that the niche width of plankton in the whole area was low. Zooplankton was dominated by rotifers, and phytoplankton was dominated by diatoms, cyanobacteria, and green algae. There were significant seasonal changes in the community structures of plankton. Compared with that in summer and autumn, there were fewer species of plankton in spring and lower interspecies connectivity. The overlap of dominant species of zooplankton was high in summer, and the interspecific competition was intensified, whereas the interspecific overlap of phytoplankton was at a low level in all three seasons. There was a significant positive correlation （W > χ20.05） between phytoplankton in summer and autumn, and the community structure was stable. The interdomain ecological network of zooplankton and phytoplankton showed a high negative correlation ratio in autumn, especially between copepods and cladoceras of zooplankton and chlorophyta and cyanophyta of phytoplankton. The plankton species in Baiyangdian Lake were abundant, with obvious seasonal differences. The dominant species were mainly a narrow ecological niche. The plankton community was generally in a stable state, and there was a strong predation relationship between copepods and cladoceras and green algae and cyanobacteria.

Humans and climate in ritualized landscapes, the case of Lake Tota in the eastern highlands of Colombia

Tota is an Andean lake located in the Altiplano of the Eastern Andes of Colombia where socio-politically hierarchical societies of the Herrera and Muisca, flourished for millennia. To them, the lake and surrounding forest were places used for diverse of activities including religious rituals. In this study we produced a multi-proxy paleolimnological reconstruction using diatoms, isotopes, and geochemistry, to try to understand the lake’s pathways of change in response to natural climatic variations and anthropogenic activities. The diatom record is dominated by tychoplanktonic Staurosirella dubia and planktonic Aulacoseira species including species A. cf lirata, A. granulata, A. distans, and A. ambigua. Diatoms were grouped into functional groups and used to infer limnological changes that were further complemented with the geochemistry of the sediments to reconstruct the past environment. Results show three main periods in which the lake changed significantly, these are dated from ~800 to 1200, 1200 to 1500, and 1500 to 1900 CE. A correlation with the archeological record of the region, ethnohistoric accounts and climate suggests that these changes occurred simultaneously with changes in archeological stages, the Spanish arrival, and more recently by the industrial revolution, and the Little Ice Age.

Trophic Ecology of the Pyjama Shark Poroderma africanum (Gmelin, 1789) Elucidated by Stable Isotopes.

Sharks may occupy both intermediate and upper levels of marine food webs. They are overfished worldwide and constitute one of the largest portions of the bycatch. The removal of top-predator species has negative cascading effects on the entire food web, causing the "mesopredator release" phenomenon, which leads to an increase in mesopredators with consequent changes in the ecosystem's energetic balance. Despite their important ecological role, information on their trophic ecology is limited. This essential information can be obtained through the analysis of stomach contents and, more recently, by using less invasive techniques, such as the stable isotope analysis of muscle tissue, obtained through biopsies. Here, we analysed the trophic ecology of the pyjama shark or striped catshark Poroderma africanum, an endemic species of South Africa, by means of SIA. The results obtained from SIA were analysed using the R SIMMR and SIBER packages to estimate the contribution of potential food sources to the diet and to evaluate the extent of the trophic niches. The SIMMR outputs showed that adults select more benthic prey than juveniles, which consume more planktonic species, with juveniles being more generalist than adults, according to SIBER outputs. As assessed by IUCN, the population of P. africanum is increasing, and given its role as mesopredator, future monitoring efforts could be crucial to elucidating their potential effects in marine food webs.

Diatom dynamics during the last six centuries in Lake Odensjön: a new varved sediment record from southern Sweden

AbstractVarved lake sediments offer valuable insight into past environmental conditions with high temporal resolution and precise chronological control. A combination of diatom and geochemical analyses of the recently deposited sediments of Odensjön, a small dimictic lake in southern Sweden, shows alternating light and dark laminae composed of greater amounts of biogenic silica and organic matter, respectively. As confirmed by independent radiometric dating and Pb pollution data, and supported by scanning electron microscopy of individual laminae, these features represent ongoing deposition of biogenic varves. Corresponding diatom and geochemical data obtained from a 92-cm long freeze core provide evidence of substantial lake-ecosystem dynamics during the last six centuries, related mainly to variations in light penetration and wind shear driven by human-induced changes in catchment vegetation. The diatom assemblage of Odensjön’s varved sediments is dominated by planktonic species, primarily Asterionella formosa, Fragilaria saxoplanktonica and Discostella lacuskarluki during periods of forest cover, while increased catchment openness from the mid-1500s to the late 1800s led to increased abundance of Lindavia comensis. Long-term variations in climate and land use, mediated through changing length of the ice-cover season and nutrient input, respectively, probably contributed to the observed trends, as well as to variations in the appearance and visibility of the varve record across the sampled sediment sequence. Odensjön represents the southernmost varved sediment record in Fennoscandia documented to date, offering potential to study the effects of various types of external forcing on its sensitive lacustrine ecosystem since the Late Weichselian deglaciation. In the present study, we investigated the possibility of assessing the local impacts of two major, historically documented volcanic events, Laki 1783–84 and Tambora 1815, which are known to have affected European societies. Although the mildly alkaline waters of the lake are well buffered and hence relatively resilient to volcanic acid deposition, a minor response to the Laki eruption may be recorded in the diatom stratigraphy.

Influence of different stocking densities of pearlspot (Etroplus suratensis) on plankton diversity indices of biofilm-based rearing system

Aim: Biofilm-based aquaculture systems, proven cost-effective, reduce the need for expensive supplementary feed. The biofilm acts as a natural planktonic food source for reared organisms. Previous research highlighted the influence of fish stocking density and biomass on plankton diversity in different aquaculture settings, underscoring the significance of these factors in biofilm-based systems. Hence, the present study attempted to understand how varying stocking densities of pearlspot (Etroplus suratensis) influence plankton diversity indices in the biofilm-based aquaculture system. Methodology: The present experiment was designed in 5 Practical Salinity Unit (PSU) brackishwater with soil-bottomed FRP circular (500 L) tanks for 60 days. The sugarcane bagasse was used as a substrate forbiofilm production after fertilization with cow dung, urea, and lime. Fries of pearlspot (4.67 ± 0.04 mm 1.71 ± 0.03 g-1) were stocked at four different stocking densities in triplicates viz T1 (50 nos); T2 (100 nos), T3 (150 nos) and T4 (200 nos) fish fry m-3 in the biofilm-based rearing system. Plankton samples were collected from water and biofilm deposited on the substrate and analyzed for diversity indices. The Shannon Diversity Index, Simpson Diversity Index, Simpson Dominance Index, and Margalef Richness Index were used to compute the plankton diversity indices in different treatments using standard equations. Results: In the current investigation, lower stocking densities with lower fish biomass were associated with significantly higher (P≤0.05) Shannon Diversity Index, Simpson Diversity Index, and Margalef Richness Index in water. In contrast, the Simpson Dominance Index in water showed a significantly lower (P≤0.05) value for treatments with lower fish biomass than for treatments with higher biomass. Interpretation: The values obtained for various diversity indices indicated that a biofilm-rearing system with lower E. suratensis biomass produced more planktonic abundance, evenness, and species richness. Key words: Biofilm, Pearlspot, Plankton diversity, Stocking density