Zooplankton Taxa Research Articles

Qualidade da água e comunidade planctônica do reservatório Owalla, Estado de Osun, sudoeste da Nigéria

Abstract Aim Owalla Reservoir, one of the largest and oldest man-made lakes in Osun State supplies potable water to many towns in the state including the state capital, Osogbo. Active fishing activities also takes place in the lake. Inspite of the importance of the reservoir, information on the planktonic community and physico-chemical water quality are scarce. Therefore, this study investigated the water quality and plankton composition of Owalla Reservoir, Osun State, Nigeria, from October 2012 to November 2013 with a view to providing baseline information on limnology of the reservoir. Methods Seven sampling stations (designated Stations 1-7) were established as representatives of the zones and regions of the reservoir and sampling was conducted quarterly. At Stations 1 and 3, only surface water samples were collected while water samples were collected from the surface, mid-depth and close to the bottom at other stations. Samples for total plankton and physico-chemical water quality were analyzed using standard methods. Results The result of the study showed that mean dissolved oxygen (P<0.001), biochemical oxygen demand, conductivity, pH (P<0.001), and alkalinity were higher at the surface of the reservoir. As regards seasonal variation, alkalinity, biochemical oxygen demand had the higher mean values during the rainy season. Also, acidity, dissolved oxygen, and pH showed significantly (P<0.001) higher values during the rainy season. One hundred and thirty-seven (137) taxa of phytoplankton and 39 taxa of zooplankton were recorded from the reservoir. The horizontal pattern of variation showed an increase in the mean abundance of most of phytoplankton groups from inflow to the dam area while vertical variation showed a decrease in mean abundance from surface to the bottom of the reservoir. Most of the phytoplankton and zooplankton taxa were more abundant during the dry season than in the rainy season. Conclusions The study concluded that all the monitored physico-chemical water quality parameters were within the guide level range as of the World Health Organisation (WHO) for drinking water, Owalla Reservoir is qualitatively rich in both phytoplankton and zooplankton and the reservoir can support a viable aquatic community and sustainable fishery production.

Hybridization Dynamics and Extensive Introgression in the Daphnia longispina Species Complex: New Insights from a High-Quality Daphnia galeata Reference Genome.

Hybridization and introgression are recognized as an important source of variation that influence adaptive processes; both phenomena are frequent in the genus Daphnia, a keystone zooplankton taxon in freshwater ecosystems that comprises several species complexes. To investigate genome-wide consequences of introgression between species, we provide here the first high-quality genome assembly for a member of the Daphnia longispina species complex, Daphnia galeata. We further resequenced 49 whole genomes of three species of the complex and their interspecific hybrids both from genotypes sampled in the water column and from single resting eggs extracted from sediment cores. Populations from habitats with diverse ecological conditions offered an opportunity to study the dynamics of hybridization linked to ecological changes and revealed a high prevalence of hybrids. Using phylogenetic and population genomic approaches, we provide first insights into the intra- and interspecific genome-wide variability in this species complex and identify regions of high divergence. Finally, we assess the length of ancestry tracts in hybrids to characterize introgression patterns across the genome. Our analyses uncover a complex history of hybridization and introgression reflecting multiple generations of hybridization and backcrossing in the Daphnia longispina species complex. Overall, this study and the new resources presented here pave the way for a better understanding of ancient and contemporary gene flow in the species complex and facilitate future studies on resting egg banks accumulating in lake sediment.

Density and Diversity of Zooplankton in Palu Bay after the Tsunami Disaster 28 September 2018

One of the marine areas in Central Sulawesi is Palu Bay. Research on the Density and Diversity of Zooplankton Species in the Palu Bay area of Central Sulawesi after the Tsunami Disaster 28 September 2018. This study aims to determine: Density and Diversity Index of Zooplankton Species. Sampling is carried out at the beginning of the month by considering the state of the neighbours, namely the transition between the first and second full tides when the tidal currents are weak. The research design used a completely randomized design model with seasons, stations, and depths as treatments. Community analysis based on species identification, number of individuals, density, diversity index,. The results showed that the composition of the zooplankton community in the Palu bay area after the Tsunami Disaster of 28 September 2018 consisted of 23 types of zooplankton, which were dominated by: the Copepoda group. The values of the Density and Diversity Index are influenced by habitat, time, and sea depth. The conclusion is that habitat or station, season, and depth are the 3 main factors that affect the density and diversity of zooplankton taxon species in the Palu Bay area.

Multi‐scale biodiversity analyses identify the importance of continental watersheds in shaping lake zooplankton biogeography

AbstractAimWe examined variation in crustacean zooplankton composition and diversity across Canada, the most lake‐rich country in the world. In addition to α‐diversity patterns, we explore mechanisms behind β‐diversity spatial variation, using taxonomic and functional metrics. Our goal was to explore geographical gradients and related mechanisms shaping zooplankton distribution across different spatial scales.LocationCanada.TaxonCrustacean zooplankton.MethodsPelagic zooplankton was sampled in and characterized for 624 lakes across Canada, spanning 12 ecozones (defined by climatic, vegetation and geological differences) or 6 continental drainage basins as part of the NSERC Canadian Lake Pulse Network project. We compared taxon and trait distributions, as well as spatial (longitudinal and latitudinal) patterns of community composition and diversity. We computed taxonomic and functional spatial β‐diversity indices, decomposing these into taxon replacement and richness differences. Finally, species (or traits) and lake uniqueness (contributions) to β‐diversity (SCBD and LCBD) were estimated by ecozone and continental basin.ResultsIn all, 90 crustacean zooplankton species were identified across the country. Differences in zooplankton taxonomic and functional composition were more distinct when considered by continental basin than by ecozone. α‐diversity varied greatly across space, with greatest diversity in eastern Canada. β‐diversity was greatest when based on taxonomy and was driven by richness differences across all spatial and biodiversity dimensions.Main conclusionsStructuring factors influencing zooplankton taxon and trait assemblages vary across spatial scales, being more important at the broadest scale considering continental hydrodynamics. Our results point to the combined effects of physical barriers to longitudinal dispersal and climate change in shaping zooplankton taxonomic and functional biogeography across Canadian lakes.

Reconciling Behavioural, Bioenergetic, and Oceanographic Views of Bowhead Whale Predation on Overwintering Copepods at an Arctic Hotspot (Disko Bay, Greenland)

Bowhead whales (Balaena mysticetus) visit Disko Bay, West Greenland in winter and early spring to feed onCalanusspp., at a time of year when the copepods are still mostly in diapause and concentrated in near-bottom patches. Combining past observations of copepod abundance and distribution with detailed observations of bowhead whale foraging behaviour from telemetry suggests that if the whales target the highest-density patches, they likely consume 26–75% of theCalanusstanding stock annually. A parallel bioenergetic calculation further suggests that the whales' patch selection must be close to optimally efficient at finding hotspots of high density copepods near the sea floor in order for foraging in Disko Bay to be a net energetic gain. AnnualCalanusconsumption by bowhead whales is similar to median estimates of consumption by each of three zooplankton taxa (jellies, chaetognaths, and predatory copepods), and much greater than the median estimate of consumption by fish larvae, as derived from seasonal abundance and specific ingestion rates from the literature. The copepods' self-concentration during diapause, far from providing a refuge from predation, is the behaviour that makes this strong trophic link possible. Because the grazing impact of the whales comes 6–10 months later than the annual peak in primary production, and because Disko Bay sits at the end of rapid advective pathways (here delineated by a simple numerical particle-tracking experiment), it is likely that theseCalanuspopulations act in part as a long-distance energetic bridge between the whales and primary production hundreds or thousands of km away.

Limnological Characterization of Three Tropical Crater Lakes in the Archipelago of Samoa (Lanoto‘o, Olomaga, Mataulano)1

We present a first limnological study of three humic crater lakes in the archipelago of Samoa. The basins of Lakes Lanoto‘o (17.5 m deep) and Olomaga (12.2 m) on Upolu Island and of Lake Mataulano (5.6 m) on Savai‘i Island developed during consecutive periods of volcanic activity ranging from the middle Pleistocene to the late Holocene. Lake Olomaga may be a permanently stratified meromictic lake, while stratified lakes Lanoto‘o and Mataulano contained oxygen down to the bottom. Forty-seven phytoplankton and 8 zooplankton taxa were identified in the pelagic zones of the three lakes. The Samoan endemic Diaphanosoma samoaensis, the cyclopoid Mesocyclops roberti originally described from neighboring archipelagos, and a hitherto undescribed species of Microcyclops were recorded. Lake Lanoto‘o is the only lake with introduced fish: goldfish (Carassius auratus) and tilapias (Oreochromis niloticus) were stocked and it harbored more than four times more phytobiomass (8 mg L-1) than the smaller, unstocked lakes (1.2–1.6 mg L-1). Fish introduction poses a threat to unstocked lakes in Samoa. Measures should be taken to protect them from any alterations.

Can the use of zooplankton dormant stages from natural wetlands contribute to restoration of mined wetlands?

Wetlands are among the most diverse environments on the planet and are strongly threatened by human activities. Their restoration and/or mitigation of human impacts, therefore, relies on information that can aid to the management of impacted wetlands so that they return to a (semi-) natural state. We investigate in this study the relationship between dormant stages of zooplankton and clay removal in areas subjected to mining. We evaluate whether a gradual increase in topsoil addition from donor natural wetlands to the sediment of mined wetlands influenced the zooplankton community. Eight wetlands were sampled in the Sinos River floodplain, four natural and four mined. In the laboratory, four field sediment samples were incubated for zooplankton hatching in five treatments comprising sediments from: mined wetlands, natural wetlands, and three treatments containing mined sediments added with low (5%), medium (20%) and high (40%) quantities of sediment from natural wetlands. Hatching consisted of 61 individuals distributed across eight zooplankton taxa. Copepod nauplii were the most abundant (31.1%) followed by Epiphanes sp. (29.5%) and Ovalona glabra (16.4%). While natural wetlands provided 42.6% of the hatched zooplankton, mined wetlands had just 6.5%. Zooplankton richness and abundance were higher in natural wetland sediments compared with mined and added sediment wetlands. To some degree, the sediment soil donation from natural to mined wetlands was considered viable. As long as prior studies are performed to test the size and quality of the dormant banks present in the sediment of candidate donor wetlands, sediment from donor wetlands may aid in the establishment of a more diverse community in disturbed systems.

Diversity and Abundance of Zooplankton in River Aswa in Uganda

Zooplankton community constitutes one of the keystone organisms that are crucial in understanding aquatic ecosystem responses to environmental distresses. The objective of this study was to contribute to the understanding of zooplankton ecological conservation status and assessment of potential impacts of the proposed Hydropower plant on the zooplankton community in River Aswa, Nwoya District, in Uganda. Baseline information on aquatic micro-invertebrate diversity, abundance and distribution along the affected river section was generated. Two copepods and four species of rotifers were recorded. The Intake site had the highest diversity (six species) while Powerhouse hadfour species. Of the species encountered, Keratella tropica registered the highest abundance—1,025 and 732 individuals m-2 at the Powerhouse and Intake sites, respectively. Total zooplankton densities were comparable with Intake (2,773 individuals m-2) and Powerhouse (2,311 individuals m-2). The zooplankton taxa do not appear in the IUCN Red List in the Catalogue of Life. Therefore, the proposed construction of a hydropower plant may not pose zooplankton conservation problems.
 Keywords: Biodiversity, Zooplankton, invertebrates, hydropower, River Aswa.

Zooplankton influences on phytoplankton, water clarity, and nutrients in Lake Tahoe

The grazing effects of zooplankton communities are predicted to be strongest in mesotrophic lakes relative to eutrophic and oligotrophic lakes, an idea known as the Mesotrophic Maximum Hypothesis. We tested if the predictions of this hypothesis depend on the community of zooplankton present by evaluating whether the community of zooplankton, in addition to lake trophic state, interact to determine the magnitude of grazing effects. We conducted mesocosm experiments to evaluate the effects of Daphnia spp., Epischura nevadensis, and juvenile and adult Mysis diluviana on ecosystem function in oligotrophic Lake Tahoe and its more productive embayment, Emerald Bay. In the Lake Tahoe experiment, the Daphnia and the Adult Mysid treatments produced lower dissolved organic carbon concentrations, and the Epischura treatment yielded lower soluble reactive phosphorus concentrations compared to a Control treatment that lacked macrozooplankton. In the Emerald Bay experiment, the Daphnia treatment lowered chlorophyll a concentrations, the Daphnia and Juvenile Mysid treatments reduced small particle (diameter 0.5 – < 5 µm) concentrations, and each of the species treatments produced higher ammonium concentrations and DIN/SRP ratios compared to the Control. Analyses of similarities (ANOSIM) indicated that these taxa differed from one another in their overall effects on Emerald Bay water, but not on Lake Tahoe water. This finding supports the Mesotrophic Maximum Hypothesis, but also shows that grazing effects are dependent on the taxonomic makeup of the zooplankton community in addition to lake trophic state. As ongoing cultural eutrophication continues to elevate Lake Tahoe's productivity, the roles and importance of the lake’s zooplankton taxa may diverge.

Trophic Diversity of a Fish Community Associated with a Caulerpa prolifera (Forsskål) Meadow in a Shallow Semi-Enclosed Embayment

This study investigates the trophic diversity of fishes living in a meadow of Caulerpa prolifera on a bimonthly basis between May 2006 and April 2007 in a semi-enclosed coastal marine ecosystem of the Mediterranean Sea (Elounda Bay, Crete Island). The study area is shallow and protected from waves, and it is covered by a C. prolifera bed, characterized by high organic input and a highly diverse macrobenthic community. Feeding patterns of the fish, investigated on the basis of stomach content analyses, were described in terms of numerical abundance and frequency of occurrence of prey taxa. A total of 1642 fish individuals, belonging to 17 species, were examined. In total, 45,674 prey individuals were identified belonging to 110 prey taxa, most of which were Malacostraca including their larvae and Copepoda (41,175 individuals identified to 71 taxa). Four different trophic groups were identified: herbivorous, pelagic, benthic (hyperbenthic) and piscivorous. Trophic diversity patterns of the fish species studied were also compared to the relative availability of macrobenthic and zooplanktonic taxa during the same period in the study area. The coexistence of many different, mostly benthic but also pelagic, fishes and their juveniles implies their high trophic flexibility, which is probably important for their survival in this particular habitat. Results of the present study provide basic knowledge on trophic diversity and interactions in the marine ecosystem and, therefore, some evidence as to the protection value of this particular habitat, which is essential for the implementation of a multispecies approach to decision-makers and managers of fisheries sources of the region.

Zooplankton variability in the Strait of Georgia, Canada, and relationships with the marine survivals of Chinook and Coho salmon.

The Strait of Georgia, Canada, has complex interactions among natural and human pressures that confound understanding of changes in this system. We report on the interannual variability in biomass of 12 zooplankton taxonomic groups in the deep (bottom depths greater than 50 m) central and northern Strait of Georgia from 1996 to 2018, and their relationships with 10 physical variables. Total zooplankton biomass was dominated (76%) by large-sized crustaceans (euphausiids, large and medium size calanoid copepods, amphipods). The annual anomaly of total zooplankton biomass was highest in the late 1990s, lowest in the mid-2000s, and generally above its climatological (1996-2010) average after 2011, although many individual groups had different patterns. Two latent trends (derived from dynamic factor analyses) described the variability of annual biomass anomalies underlying all zooplankton groups: a U-shaped trend with its minimum in the mid-2000s, and a declining trend from 2001 to 2011. Two latent trends also described the physical variables. The variability represented by these four latent trends clustered into two periods: 1996-2006, with generally declining zooplankton biomass and increasing salinities, and 2007-2018, with increasing zooplankton biomass and decreasing salinities. ARIMA modelling showed sea surface salinity at Entrance Island in the middle Strait of Georgia, the Pacific Decadal Oscillation, and the peak date of the spring phytoplankton bloom were significantly related to the two latent zooplankton trends. ARIMA models comparing zooplankton and physical variables with the marine survivals of four salmon populations which enter the Strait as juveniles (Chinook: Cowichan River, Puntledge River, Harrison River; Coho: Big Qualicum River) all included zooplankton groups consistent with known salmon prey; prominent among the physical variables were sea surface salinity and variables representing the flow from the Fraser River. These regressions explained (adjR2) 38 to 85% of the annual variability in marine survival rates of these salmon populations over the study time period. Although sea temperature was important in some relationships between zooplankton biomass and salmon marine survival, salinity was a more frequent and more important variable, consistent with its influence on the hydrodynamics of the Strait of Georgia system.

Seasonal Variation of Zooplankton Density and Physicochemical Parameters of A Perennial Freshwater Body, Samudrabundh of Joypur, Bankura, West Bengal, India

Water is the most essential and vital component required for the survival of all organisms in this earth. The physico-chemical and biological characteristics of a water body determine its efficacy for the production of plankton especially the zooplankton. Zooplankton are the most important primary consumer of aquatic food chain which in turn influence the productivity of finfishes in an aquatic body .The present study is primarily based on assessment of seasonal density and diversity as well as the physico-chemical condition of Samudrabundh, of Joypur block of Bankura district, West Bengal. Such type of assessment on this water body has not been done before this.. The study was carried during March.2019 to February, 2020. The water quality parameters which were used for study were temperature, PH, Dissolved Oxygen (DO), Free carbon dioxide (CO2),Chloride, salinity, alkalinity and total hardness. A total of 26 taxa of zooplankton were recorded. Out of which 8 sp ecies comprises of Rotifera, 05 species of Copepoda, 10 species of Cladocera and 03 species of Ostracoda. The total zooplankton density ranges from 756 (Ind/L) to 957 (Ind/L) which is quiet lower than the desired value required for good fish culture. The study concludes that the water body is of soft water type and medium productive in nature.

Characteristics of Eukaryotic Plankton Communities in the Cold Water Masses and Nearshore Waters of the South Yellow Sea

Eukaryotic plankton are important parts of the marine biome and play an important role in maintaining the stability of marine ecosystems. In order to characterize the eukaryotic plankton communities in the South Yellow Sea Cold Water Mass (CWM) and the South Yellow Sea nearshore waters (NW) in October 2019, Illumina high–throughput sequencing was performed using the 18S rDNA V9 region as the target gene. Environmental factors (depth, pH, salinity, temperature, Chl a, nitrate, nitrite, ammonium, silicate, phosphate) in two sea areas were measured, and their correlations with abundance and diversity of eukaryotic plankton were analyzed. A total of 807 species of plankton were identified, of which 663 species in 24 categories were from the CWM area, and 614 species in 26 categories were from NW. The total phytoplankton abundance in CWM waters was higher than that in NW. Dinophyta and Bacillariophyta were the most abundant phyla of phytoplankton in the two areas. Arthropoda and Cnidaria were the major zooplankton taxa. The dominant fungal population was mainly Basidiomycota. Both the CWM and NW have effects on dissolved inorganic nutrient concentrations and plankton abundance. Environmental factor correlation analysis showed that the concentration of dissolved inorganic nutrients within the CWM increased with water depth and the abundance of plankton gradually increased. Ammonium salts, nitrates, phosphates, silicates and water depth were important factors affecting phytoplankton growth. Phytoplankton abundance increased with increasing concentrations of inorganic nutrients. Bacillariophyta showed a strong positive correlation with silicates and depth. Depth and microscopic phytoplankton abundance were important factors influencing the structure of the zooplankton community.

Assessing size-based exposure to microplastic particles and ingestion pathways in zooplankton and herring in a coastal pelagic ecosystem of British Columbia, Canada

Microplastic particles (hereafter 'microplastics') are a widespread class of pollutants in marine environments that can become embedded in food webs. Due to their diverse composition and size, microplastics can enter food webs both directly through consumption and indirectly via trophic transfer. In this study, we investigated potential ingestion pathways of microplastics in an important pelagic food web in coastal British Columbia, Canada. Between March and September 2019, we completed repeat surveys of water, zooplankton, and larval Pacific herring Clupea pallasii at 11 locations in Baynes Sound, Strait of Georgia. Five zooplankton taxa were isolated from each zooplankton sample for specific analysis. Juvenile herring were sampled once in September. Samples were cold-digested with KOH or H2O2 and suspected microplastics isolated. Suspected microplastics were confirmed using μ-Raman spectroscopy and were subsequently identified from the collected samples. The average microplastic concentration in surface waters was 0.59 microplastic particles l-1, and no clear spatial pattern was evident. Average microplastic particle loads were 0.0007 ind.-1 in zooplankton, 0.0017 ind.-1 in larval herring, and 0.089 ind.-1 in juvenile herring. There was a clear difference in the biological:microplastic particle ratio across size fractions (125-250, 250-500, 500-1000, 1000-2000, 2000-4000 µm) in the water column. In size classes &lt;1000 µm, biological particles outnumbered microplastic particles by up to 4 orders of magnitude, whereas for size classes &gt;1000 µm, the ratio decreased to nearly 1. Zooplanktivorous consumers like juvenile herring are more likely to consume microplastics than prey since the ratio of microplastic particles &gt;1000 µm to potential food, and therefore encounter rate, is higher.

Large daphniids are keystone species that link fish predation and phytoplankton in trophic cascades

Daphniids act as keystone species in lake ecosystems by controlling phytoplankton biomass and experiencingintense fish predation. However, the importance of single daphniid species as trophic links betweenphytoplankton and fish remains unclear, especially compared with other zooplankton taxa. To disentangle the roleof individual zooplankton taxa in the food web of a large lake, we performed an in-situ mesocosm experiment withnatural phytoplankton and zooplankton communities in three treatments with native, invasive or no fish predators,respectively. A large daphniid, Daphnia longispina, was the zooplankter most strongly predated by both fish species,and also had the highest top-down effects on phytoplankton. All other zooplankton taxa, including a smalldaphniid species, had minor roles in terms of both predation by fish and grazing on phytoplankton. We suggest thatdaphniid species with large body sizes can strongly link higher and lower trophic

Phenology of alpine zooplankton populations and the importance of lake ice-out

AbstractThe prolonged ice cover inherent to alpine lakes incurs unique challenges for aquatic life, which are compounded by recent shifts in the timing and duration of ice cover. To understand the responses of alpine zooplankton, we analyzed a decade (2009–2019) of open-water samples of Daphnia pulicaria and Hesperodiaptomus shoshone for growth, reproduction and ultraviolet radiation tolerance. Due to reproductive differences between taxa, we expected clonal cladocerans to exhibit a more rapid response to ice-cover changes relative to copepods dependent on sexual reproduction. For D. pulicaria, biomass and melanization were lowest after ice clearance and increased through summer, whereas fecundity was highest shortly after ice-off. For H. shoshone, biomass and fecundity peaked later but were generally less variable through time. Among years, ice clearance date varied by 49 days; years with earlier ice-out and a longer growing season supported higher D. pulicaria biomass and clutch sizes along with greater H. shoshone fecundity. While these large-bodied, stress tolerant zooplankton taxa were relatively resilient to phenological shifts during the observation period, continued losses of ice cover may create unfavorably warm conditions and facilitate invasion by montane species, emphasizing the value of long-term data in assessing future changes to these sensitive ecosystems.

Relative strength of top-down effects of an invasive fish and bottom-up effects of nutrient addition in a simple aquatic food web.

Introduction of exotic predators or runoff of fertilizers can alter aquatic food webs, in particular zooplankton communities, through top-down and bottom-up effects. In a mesocosm experiment, we manipulated the density of Western Mosquitofish (Gambusia affinis) and nutrient levels (nitrate and phosphate independently) and observed effects on zooplankton and phytoplankton in a fall, temperate zone system. If top-down regulation were important, we expected mosquitofish predation to reduce zooplankton abundance, which would indirectly benefit phytoplankton. If bottom-up regulation were important, we expected nutrient addition to increase both primary producers and zooplankton. Western Mosquitofish predation significantly decreased the abundance of several zooplankton taxa, resulting in a trophic cascade with increased chlorophyll a (i.e., primary productivity). This effect did not differ between mesocosms with 5 or 10 fish. Nutrient addition had no significant effects on zooplankton; however, chlorophyll a was positively affected by both nitrogen addition and phosphorus addition. Our results suggest weak bottom-up regulation in our experimental community, but strong top-down regulation, emphasizing the potential consequences of introducing non-native Western Mosquitofish to native aquatic ecosystems.

Patterns of Seasonal Stability of Lake Phytoplankton Mediated by Resource and Grazer Control During Two Decades of Re-oligotrophication

Human-induced changes in external nutrient loading affect the phytoplankton community and abundance directly by changing the amount of nutrients available, but also indirectly through changes in the zooplankton (that is, grazer) community structure, mediated in part by changes in the fish community structure and biomass. Such shifts affect the species dynamics and community succession of lake phytoplankton communities, and they may ultimately influence community stability. However, the relative importance of different biotic mechanisms influencing the community stability of phytoplankton along nutrient and associated zooplankton grazing pressure gradients remains unclear. Here, we evaluated the importance of four potential stabilizing biotic metrics—taxon richness, synchrony, community dominance and biomass of phytoplankton to the seasonal stability over two decades of re-oligotrophication in 20 Danish lakes. We found no clear temporal patterns in seasonal stability across lakes but considerable variations in the individual lakes. Total phosphorus (TP) affected the seasonal stability of the phytoplankton communities either directly or indirectly through changes in community dominance. Total nitrogen (TN) influenced the seasonal stability indirectly via changes in phytoplankton taxon richness, synchrony, and community dominance. Grazer richness (that is, zooplankton taxa richness) impacted the seasonal stability indirectly through changes in phytoplankton taxon richness and synchrony. Grazing pressure, using the biomass ratio of zooplankton:phytoplankton as a proxy, had an indirect effect on seasonal stability via changes in synchrony and community dominance. Compensatory dynamics (as indicated by the synchrony of phytoplankton) exerted dominant control of phytoplankton seasonal stability at high TN and high grazer richness and pressure, while the portfolio effect (as indicated by taxon richness) contributed to phytoplankton seasonal stability at low TN and high grazer richness. However, a strongly negative selection effect (as indicated by community dominance of phytoplankton) was observed at high nutrient levels and low grazer richness. Grazer richness and grazing pressure had stronger stabilizing effects on the seasonal succession of the phytoplankton communities than did TP and TN. Our results highlight how various biotic mechanisms (for example, compensatory dynamics and portfolio effect) can change in their importance in maintaining the seasonal stability of phytoplankton communities subjected to nutrient and grazer control.

Seasonal variability of near-surface zooplankton community structure in the southern Gulf of Mexico

The zooplankton taxonomic group composition was analyzed in a known spawning area for snooks of the family Centropomidae during March 2011-February 2012 near the González River's mouth, a tributary of the Grijalva-Usumacinta River system, discharging into the southern Gulf of Mexico. Zooplankton was collected near the surface using three distinct zooplankton nets (20, 64, and 120 μm). Sixteen zooplankton taxonomic groups were collected between the three nets. Copepoda (76.9%), Trematoda (6.7%), Bivalvia (4.6%), and Chaetognatha (Sagittoidea 4.3%) numerically dominated zooplankton community structure. The 120 and 64 μm nets collected the highest diversity of zooplankton (15 taxa). Zooplankton was more abundant during June-October (summer storm season). They associated with lower salinities (due to the increase in the discharge volume of the Grijalva-Usumacinta River system) and higher regional primary productivity than observed during the rest of the year (March-May, dry season, and November-February, winter storm season). The highest peak of zooplankton abundance was found in November during the beginning of winter storms. Nine taxonomic groups were observed frequently and abundantly during the summer storm season, while only five taxonomic groups were abundant during the dry season.

Evaluation of water quality in the swamp river border using water quality index

As a source of minerals, water must be continuously maintained, including in term of its quality. Meanwhile, swamps are wetlands that have the potential to experience a decline in water quality. The presence of river borders in swamps has been known to maintain their water quality. Vegetation cover of the river border is established through restoration activities in which it is expected, directly and indirectly, to improve water quality. This study aimed to investigate the water quality in swamp using the Water Quality Index (WQI). Surveys were carried out and samples were collected to determine the effect of restoration on river border in swamps. Samples were collected severally, namely prior to restoration (T0), first year (T1), third year (T3) and fourth year (T4) after restoration. The parameters for water quality of T0 and T1 include pH, DO, BOD, TDS, turbidity and nitrate, while for T3 and T4 include: pH, DO, BOD, TDS, temperature, phosphate, E. coli and nitrate. The findings indicated that the WQI of the swamp prior to restoration was greater than that at the first year of restoration due to the process of land clearing. Meanwhile, the WQI at the third year has improved compared to before the restoration and land clearing phase. It suggests that the presence of vegetation on river border is able to improve the water quality. At the fourth year, a fire in the upstream reached the area adjacent to the study site. It led to a decline in surface water quality and affected the water quality index. Furthermore, the abundance of aquatic biota was indicated by two taxa of zooplankton in the third year of restoration while none of them was identified in the fourth year. In overall, restoration activities on the river border improve the quality of water in swamps in a sustainable manner.