Large Algae Research Articles

Peculiarities of seasonal dynamics of net primary production and its microzooplankton grazing in the coastal waters of the Black Sea (Sevastopol region)

The studies of net primary production (NPP) seasonal dynamics, its microzooplankton grazing were conducted at two stations in the western Black Sea coastal waters near Sevastopol during a period from January 2020 to December 2022. Each year, one maximum of the phytoplankton NPP (280–820 mg C·m-3·day-1) was observed in July, when the water temperature ranged from 22 to 25 °C, and solar radiation intensity was 48–50 E·m-2·day-1. Large diatoms and dinoflagellates played a key role in its formation. At this time, the values of the net phytoplankton growth rate were 0.3–1.0 day-1, and the relative share of primary production consumed by microzooplankton (g/m) did not exceed 26%. In December – February, when the water temperature was 8.0–13.5 °C and the intensity of solar radiation was 10–15 E·m-2·day-1, the NPP decreased to a minimum (4–38 mg C·m-3·day-1). Under these conditions, the net phytoplankton growth rate decreased to 0–0.40 day-1, and g/m was 15–100%. For three years at station 2, the contribution of large algae with cell volumes from 4000 to 18000 µm3 in the NPP was significantly higher than at station 1. It was 61.1 % in 2020, 69.7 % in 2021 and 23% in 2022. The consumed NPP for this size group of algae was 54 % in 2020, 68.4 % in 2021 and 47.8 % in 2022.

The culture of Chlorella with livestock wastewater and the application of its oligosaccharides in promoting rice seed germination under high salinity conditions

Algal oligosaccharides, derived from polysaccharides in algal biomass, exhibit bioactive properties that enhance plant antioxidant enzyme activity and free radical scavenging. Currently, algal oligosaccharides are mainly produced from large algae, while studies on preparing algal oligosaccharides from microalgae are relatively insufficient. This study focuses on utilizing Chlorella cultivated under controlled conditions using diluted livestock wastewater to produce algal oligosaccharides and investigates their impact on rice seed germination under salt stress. Results show that culturing Chlorella with diluted livestock wastewater not only stimulated algal growth but also efficiently removed nitrogen, phosphorus, and other nutrients. Algal oligosaccharides demonstrated significant improvements in rice seed germination, vigor indices, biomass accumulation, and nitrogen absorption under salt stress. Physiological indicators revealed elevated osmotic adjustment substances, increased chlorophyll content, and alleviated oxidative damage in rice seedlings treated with algal oligosaccharides. The study introduces an innovative method of using livestock wastewater for algal oligosaccharides production, emphasizing its dual benefits including efficient resource utilization and significant cost reduction. The findings also support the theoretical application of Chlorella-derived algal oligosaccharides in enhancing rice cultivation under salt stress.

Anisotropic Green Tide Patch Information Extraction Based on Deformable Convolution

Green tides are marine disasters caused by the explosive proliferation or high concentration of certain large algae in seawater, which causes discoloration of the water body. Accurate monitoring of its distribution area is highly important for early warning and the protection of marine ecology. However, existing deep learning methods have difficulty in effectively identifying green tides with anisotropic characteristics due to the complex and variable shapes of the patches and the wide range of scales. To address this issue, this paper presents an anisotropic green tide patch extraction network (AGE-Net) based on deformable convolution. The main structure of AGE-Net consists of stacked anisotropic feature extraction (AFEB) modules. Each AFEB module contains two branches for extracting green tide patches. The first branch consists of multiple connected dense blocks. The second branch introduces a deformable convolution module and a depth residual module based on a multiresolution feature extraction network for extracting anisotropic features of green tide patches. Finally, an irregular green tide patch feature enhancement module is used to fuse the high-level semantic features extracted from the two branches. To verify the effectiveness of the AGE-Net model, experiments were conducted on the MODIS Green Tide dataset. The results show that AGE-Net has better recognition performance, with F1-scores and IoUs reaching 0.8317 and 71.19% on multi-view test images, outperforming other comparison methods.

The Dynamics of Floating Macroalgae in the East China Sea and Its Vicinity Waters: A Comparison between 2017 and 2023

Ulva prolifera and Sargassum are two common floating macroalgae in China’s coastal algal bloom events. Ulva prolifera frequently emerges concomitantly with Sargassum outbreaks, thereby presenting challenges to the monitoring of algal blooms, thereby presenting challenges to the monitoring of algae. To tackle the challenge of differentiating between Ulva prolifera and Sargassum, this study employs Sentinel-2 MSI data for spectral analysis. Notably, significant disparities in the Remote Top of Atmosphere Reflectance (Rtoa) between Ulva prolifera and Sargassum are observed. This study proposes a random forest-based algorithm for discriminating between Ulva prolifera and Sargassum in the regions of the Yellow Sea and East China Sea. The algorithm introduced in this study attains remarkable accuracy in distinguishing Ulva prolifera and Sargassum within Sentinel-2 MSI data, achieving identical F1 scores of 99.1% for both. Moreover, when tested with GF-1 WFV data, the algorithm showcases outstanding performance; this demonstrates the algorithm’s robustness and its ability to mitigate the uncertainty linked to threshold selection. Simultaneously, a comparative analysis of algae distribution was conducted for both 2017 and the period from January to May 2023. Experimental results indicate that the algorithm exhibits high accuracy in distinguishing between Ulva prolifera and Sargassum. This capability will significantly enhance the monitoring of large algae in maritime regions; this holds crucial theoretical significance and offers substantial practical value in the realm of marine ecological conservation.

Characteristics of Carbonate Facies and Depositional Environment of Tapak Formation in the Ajibarang Area, Central Java, Indonesia

The limestone of Tapak Formation is well exposed in the Ajibarang area and its surroundings, Central Java, Indonesia. Very intensive mining activity is a very serious threat to this limestone. Hitherto, the geological study on this limestone is still very limited. The objective of this study was to investigate the characteristics of these limestone facies and their sedimentation. This research consists of field and laboratory (petrography and micropaleontology) analysis. The results showed that the limestone of the Tapak Formation consisted of three facies: planktonic packstone, algal foraminifera packstone, and foraminifera algal packstone. Planktonic packstone facies are composed of bioclastic fragments in a micro matrix. The fragments were dominated by planktonic foraminifera consisting of a genus of Globigerina, Globigerinoides, Globorotalia, and Orbulina. Benthic foraminifera and radiolarians were also identified. Sedimentation from planktonic packstone facies was estimated to occur in the deep marine environment. Algal foraminiferal packstone facies are composed of bioclastic fragments in a micro matrix. Large algae and large foraminifera dominated the fragments. Algae were from the type of red algae, consisting of Lithophyllum, Corallina, and Rhodolite. Foraminiferal algal packstone and algal foraminiferal packstone that were observed in the studied area were characterized by the abundance of large foraminifera and interpreted to be deposited in the upper reef slope. We interpreted that the limestone in the study area was deposited in the upper reef slope to the lower reef slope environments. We hope that the information we provided here is useful for petroleum system study in Central Java, Indonesia.

Footprint of the plastisphere on freshwater zooplankton

Changes in the functional groups of zooplankton were studied in autumn in a temperate floodplain lake (Lake Sakadaš, Kopački Rit Nature Park, Croatia) and in the Drava River (in the Croatian part of the river). Various abiotic parameters as well as available food sources (phytoplankton and microphytes (algae and cyanobacteria) developing on epixylon, epilithon and artificially introduced microplastics called “plastisphere”) were also studied. The lake was hydrologically isolated from the main river during the study, while the water level of the Drava River fluctuated, resulting in larger variations in limnological parameters. Due to stable conditions in the lake, zooplankton abundance, biomass, and species richness were higher than in the Drava River. In both environments, zooplankton species feeding on bacteria, detrital suspensions, and small algae were most abundant, with predators and microfilter-feeders being more abundant in the lake. Microphytes were diverse and mostly small and medium-sized in phytoplankton and all substrate types. Stable lake conditions promoted higher abundance of the zooplankton group, which effectively uses larger algae as a food source. The lower abundance of zooplankton feeding on larger algae and predatory species in the river suggests that the epilithon and plastisphere community was a less mature community compared to the lake, and the heterotrophic component with ciliates and/or other small heterotrophs was not well developed. The importance of plastispheres was particularly evident under the turbid hydrologic conditions that prevailed in the river at the end of the study, when phytoplankton biomass decreased and zooplankton abundance steadily increased, suggesting that microphytes colonised on microplastics were an additional food source for higher trophic levels.

Seaweed Beds and Community Structure in the East and South Coast of Korea

This study conducted a community investigation via scuba-diving excursions into the subtidal regions of seven sea areas on the eastern coasts and three sea areas on the southern coasts, from October to December 2017, to determine the characteristics of seaweed communities and the current status of barren ground in natural seaweed beds in Korea. The results showed that species composition and average biomass in the sea area were 5–48 species and an average of 114.42 g/m2 (0.29–273.60 g/m2) in the eastern coasts, where red algae—an annual opportunity species—were dominant, and 21–48 species and an average of 1056.84 g/m2 (53.03–2683.02 g/m2) in the southern coasts, where perennial large brown algae were dominant. Using Orfanidis’ EEI-c model, evaluations of the community states showed they varied significantly depending on the inclusion of melobesidean algae, and this model was determined to be inappropriate for direct application in sea areas with a low coverage of all macroalgae. A comprehensive review of the seaweed community characteristics of seaweed beds, the marine environment, the coverage of melobesidean algae, and the analysis results regarding the density of grazers showed that a decrease in the seaweed community, according to the barren ground phenomenon, was more severe in the eastern than southern coasts. Furthermore, there were also significant differences in seaweed community characteristics according to sea area and barren ground. Therefore, suitable countermeasures corresponding to the characteristics of each sea area are necessary; for example, the creation of growth substrates for the colonization of macroalgae in Deoksin and Saido Is., the transplantation of large brown algae in Gangyang and Daedurado Is., action plans for marine forest monitoring in Geomundo Is., and an improvement in substrates in Yeongjin, Mangsang, Daejin, Chogok, and Geundeok are possible countermeasures.

Isolation and Identification of a Large Green Alga Virus (Chlorella Virus XW01) of Mimiviridae and Its Virophage (Chlorella Virus Virophage SW01) by Using Unicellular Green Algal Cultures.

Virophages are a group of small double-stranded DNA viruses that infect protist hosts and parasitize the viral factory of host giant/large viruses to propagate. Here, we discover a novel cell-virus-virophage (CVv) tripartite interaction system by using unicellular micro-green algae (Chlorella sp.) as eukaryotic hosts for the first time. Viral particles, resembling known virophages and large alga viruses, are detected in culture supernatants and inside algal cells. Complete genomic sequences of the virophage (Chlorella virus virophage SW01 [CVv-SW01]; 24,744 bp) and large virus (Chlorella virus XW01 [CV-XW01]; 407,612 bp) are obtained from the cocultures. Both genomic and phylogenetic analyses show that CVv-SW01 is closely related to virophages previously found in Dishui Lake. CV-XW01 shares the greatest number of homologous genes (n = 82) with Cafeteria roenbergensis virus (CroV) and phylogenetically represents the closest relative to CroV. This is the first report of a large green alga virus being affiliated with a heterotrophic zooplankton-infecting Cafeteriavirus of the family Mimiviridae. Moreover, the codon usage preferences of CV-XW01 and CVv-SW01 are highly similar to those of CroV and its virophage Mavirus, respectively. The discovery of such a novel CVv system with the green alga Chlorella sp. as the single cellular eukaryotic host paves a way to further investigate the potential interaction mechanism of CVv and its significance in the ecology of green algae and the evolution of large/giant viruses and their parasitic viruses. IMPORTANCE Parasitic virophages are small unicellular eukaryotic dsDNA viruses that rely on the viral factories of coinfecting giant/large dsDNA viruses for propagation. Presently, the identified eukaryotic hosts of isolated virophages were restricted to a free-living amoeba, Acanthamoeba polyphaga, and a widespread marine heterotrophic flagellate, Cafeteria roenbergensis. In this study, we successfully discovered and identified a novel tripartite interaction system comprised of a micro-green alga (Chlorella sp.), Mimiviridae large green alga virus, and virophage at the coculture level, with Chlorella sp. as the eukaryotic host, based on combination analysis of infection, morphotype, genome, and phylogeny. The large green alga virus CV-XW01 represents the closest relative to the Mimiviridae giant virus Cafeteria roenbergensis virus, host virus of the virophage Mavirus, as well as a novel large virus of Mimiviridae that infects a non-protozoan protist host. The virophage CVv-SW01 highly resembles Mavirus in its codon usage frequency and preference, although they are phylogenetically distantly related. These findings give novel insights into the diversity of large/giant viruses and their virophages.

High abundance of a single taxon (amphipods) predicts aquatic macrophyte biodiversity in prairie wetlands

Conservation programs often aim to protect the abundance of individual species and biodiversity simultaneously. We quantified relations between amphipod densities and aquatic macrophyte (large plants and algae) diversity to test a hypothesis that biodiversity can support high abundance of a single taxonomic group. Amphipods (Gammarus lacustris and Hyalella azteca) are key forage for waterfowl and are declining in the Prairie Pothole Region of North America. We sampled a large gradient of amphipod densities (0–7050 amphipods/m3) in 49 semi-permanent wetlands, and 50% of the study wetlands had high amphipod densities (> 500 amphipods/m3). Generalized linear models revealed G. lacustris and H. azteca densities increased exponentially with macrophyte diversity indices. Further, H. azteca densities were greatest at moderate levels of submersed vegetation biomass. Community analyses showed both amphipod species were positively associated with diverse macrophyte assemblages and negatively associated with high coverage of cattails (Typha spp.), a taxon that creates monotypic stands, as well as bladderwort (Utricularia spp.), a carnivorous plant. Our results indicate that amphipods could be used as an umbrella species for protecting diverse macrophyte communities in semi-permanent and permanent wetlands of North America’s Prairie Pothole Region.

Phytoplankton Growth Rate and Microzooplankton Grazing under Conditions of Climatic Changes and Anthropogenic Pollution in the Coastal Waters of the Black Sea (Sevastopol Region)

In the coastal waters of the Black Sea near Sevastopol, a gradual temperature elevation and an increase in anthropogenic pressure since the early 2000s have caused significant structural and functional changes in phytoplankton. Currently, there is a significant decrease in the contribution of small diatom species (Skeletonema sp. and Chaetoceros socialis H.S.Lauder as well as coccolithophorids Emiliania huxleyi (Lohmann) W.W.Hay and H.P.Mohler) to the total phytoplankton biomass in these waters. Previously these species caused regular weak blooms. In the warm periods (from May to October), during which the main phytoplankton biomass is formed, large diatom species Pseudosolenia calcar-avis (Schultze) B.G.Sundström, 1986, Proboscia alata (Brightwell) Sundström and dinoflagellates predominate. Therefore, the maximum values of the phytoplankton community’s specific growth rate are about two times lower than in the preceding periods and do not exceed 1.10–1.40 day−1. There was also a decrease observed in the microzooplankton grazing rate, which, during the year, was no higher than 0.70–1.20 day−1. This is primarily conditioned by the increased role of large algae in phytoplankton, which means a decline in nutrition quality for microzooplankton. As a result of the joint influence of nutrition quality and water pollution, the relative share of net primary production consumed by microzooplankton in the warm periods of the year averaged only 32%, which is two times lower than the average values generally accepted for marine ecosystems. This means that the transfer of matter and energy from phytoplankton to higher trophic levels is significantly decreased.

Production of Carotenoids from Cultivated Seaweed.

Cladosiphon (C.) okamuranus, a brown alga endemic to the Nansei Islands, Japan, has been conventionally ingested as food. Nowadays, it is a major aquatic product of the Okinawa Prefecture with an annual production of around 20,000 tons. The life cycle of C. okamuranus comprises the macroscopic sporophyte (algal body) generation and the microscopic gametophyte generation. The germlings in the latter generation can proliferate when floating in seawater. This floating form has been exploited in techniques involved in the commercial production of C. okamuranus seedlings.Brown algae contain fucoxanthin, a carbonyl carotenoid known to have anticancer, anti-obesity, and antidiabetic effect in addition to the anti-oxidation effect. We found that the fucoxanthin content of cultivated floating form of C. okamuranus discoid germlings becomes up to 50 times that of the mature alga. Since the discoid germlings repeatedly grow like microorganisms, although they are large algae, they are utilized to produce fucoxanthin. We optimize the culture conditions by changing the temperature, light intensity, photoperiod, light wavelength, and nutrient salt conditions for optimal fucoxanthin productivity. The cultivation has been successful to industrial plant scale, culminating in the use of 1 ton of cultivating medium.In brown algal cells, fucoxanthin is primarily found bound to the photosynthetic pigment-protein complexes known as fucoxanthin-chlorophyll protein (FCP). Consequently cultivated floating form of C. okamuranus also shows high content of FCP. Isolation and characterization of pigments bound to the FCP were determined precisely, and ultrafast spectroscopies were applied to elucidate the photosynthetic function of fucoxanthin bound to the pigment-protein complexes. This cultivation method has also been applied to the other edible brown algae. We found that the optimal cultivation conditions as well as the yields of fucoxanthin and FCP highly depend on the species.The floating form cultivation was also applied to a large-sized edible green alga, Codium intricatum, which is uniquely producing a carbonyl carotenoid, siphonaxanthin. This has several anti-disease effects and is also a primal photosynthetic pigment which is found bound to photosynthetic antenna complex usually called siphonaxanthin-chlorophyll protein (SCP). We are working on the improvement of productivity, scale-up of production, and development of cultivation technology of new macro algae.

Effects of zebra mussels (Dreissena polymorpha) on phytoplankton under eutrophic conditions

We conducted two mesocosm experiments (2014 and 2017) to determine how invasive zebra mussels affected abundance and structure of phytoplankton community. Algae reaction was different for the introduction of D. polymorpha in 2014 and 2017. There was no influence of zebra mussels on the phytoplankton total abundance; however, it changed the biomass of individual taxa. Cyanoprokaryota reaction as a result the zebra mussels introduction was influenced by the initial phytoplankton structure and initial nitrogen and phosphorus concentrations in water. The biomass of Сyanoprokaryotа decreased at low N:P ratios and increased at high N:P ratios. Dreissena increased the biomass of large green filamentous algae, which is a poor food resource for zooplankton.

涠洲岛造礁石珊瑚群落变化特征及其环境影响因子

以涠洲岛造礁石珊瑚群落为研究对象，分析其群落物种组成、多样性、Raunkiaer频度和种间Spearman轶相关，探讨群落组成与水环境因子的相关性，并结合近10年来涠洲岛造礁石珊瑚变化情况，找出涠洲岛造礁石珊瑚群落的主导影响因素。结果表明：（1）近10年来涠洲岛造礁石珊瑚覆盖率显著降低，珊瑚形态组成趋于块状化，尽管珊瑚群落多样性较高，但群落分布较松散，群落结构较不稳定，部分优势种种间竞争较激烈。（2）悬浮物含量是影响石珊瑚群落最显著的环境因子。石珊瑚优势种群在不同水深中分布差异显著，泥沙覆盖率、营养盐对不同石珊瑚种群影响差异较大，大型海藻覆盖率在局部区域对优势珊瑚形成较强的竞争关系。（3）营养盐和泥沙沉积物的增加与涠洲岛近海养殖业及生活排污、海岸工程及海岸侵蚀密切相关。;For the Weizhou Island, which is geographically independent, the human-induced influence is more significant to the rapid degradation of its coral reef ecosystems. the identification of dominant influencing factors on different temporal scales remains a challenge for the local aquatic environment. It is, therefore, essential to explore the ecological status of the coral reefs and the potential threats in Weizhou Island. The primary aim of this study is to explore the dominant influencing factors for the degradation of the scleractinian coral community in Weizhou Island within the 10 years of 2009-2019. To this end, the species composition, diversity, Raunkiaer frequency and Spearman correlation of the community were analyzed. The correlations between the community composition and environmental variations of water were further discussed. The identification of the dominant factors was performed through analyzing the ecological changes of scleractinian coral community in Weizhou Island over 10 years. Results demonstrated that, the coverage of scleractinian coral in the study area significantly decreased, with the changes of the coral reef in morphology, e.g., block. It was noted that, the diversity of the scleractinian coral community was relatively high, but scarred distribution in space of the coral community was observed. Furthermore, the ecological structure was unstable due to the intense competition among some dominant species. It was believed that the high loads of suspended sediments were the most important factor to affect the ecological characteristics of the scleractiniane coral community in Weizhou Island. The spatial distribution of the dominant species was highly related to the water depths, whilst the sediment coverages and nutrient sources significantly affected the diversity of coral populations. Further, relatively strong competition between local large algae and the dominant species of coral reefs was observed. We also observed that the environmental factors, nutrients and sediments, were closely correlated with the aquaculture, human sewage, coastal engineering, coastal erosion, etc.

Photosynthetic Pigments Changes of Three Phenotypes of Picocyanobacteria Synechococcus sp. under Different Light and Temperature Conditions

It is estimated that the genus Synechococcus is responsible for about 17% of net primary production in the Global Ocean. Blooms of these organisms are observed in tropical, subtropical and even temperate zones, and they have been recorded recently even beyond the polar circle. The long-term scenarios forecast a growing expansion of Synechococcus sp. and its area of dominance. This is, among others, due to their high physiological plasticity in relation to changing environmental conditions. Three phenotypes of the genus Synechococcus sp. (Type 1, Type 2, and Type 3a) were tested in controlled laboratory conditions in order to identify their response to various irradiance (10, 55, 100 and 145 µmol photons m−2 s−1) and temperature (15, 22.5 and 30 °C) conditions. The highest total pigment content per cell was recorded at 10 μmol photons m−2 s−1 at all temperature variants with the clear dominance of phycobilins among all the pigments. In almost every variant the highest growth rate was recorded for the Type 1. The lowest growth rates were observed, in general, for the Type 3a. However, it was recognized to be less temperature sensitive in comparison to the other two types and rather light-driven with the highest plasticity and adaptation potential. The highest amounts of carotenoids were produced by Type 2 which also showed signs of the cell stress even around 55 μmol photons m−2 s−1 at 15 °C and 22.5 °C. This may imply that the Type 2 is the most susceptible to higher irradiances. Picocyanobacteria Synechococcus sp. require less light intensity to achieve the maximum rate of photosynthesis than larger algae. They also tolerate a wide range of temperatures which combined together make them gain a powerful competitive advantage. Our results will provide key information for the ecohydrodynamical model development. Thus, this work would be an important link in forecasting future changes in the occurrence of these organisms in the context of global warming.

Low-cost and versatile sensor based on multi-wavelengths for real-time estimation of microalgal biomass concentration in open and closed cultivation systems

Microalgae show great potential as a bioresource for modern agriculture since its farming can be performed in lands with soil, water, or climate that are not suitable for conventional crops. A current challenge in algae farming is the real-time monitoring of biomass production to control parameters which are important to sustain a fast microalgae growth and high biomass productivity. Laboratory-scale methods developed for the determination microalgal biomass concentration lack the scalability required for monitoring large algae farms. Thus, this study proposes a low-cost and versatile sensor for real-time monitoring of the optical density of microalgae cultures in open and closed cultivation systems. The optical density unit of the sensor was based in ultraviolet and near-infrared wavelengths, and the validation of sensor measurements was performed correlating its response with a spectrophotometer. The sensor showed strong linearity and precisely measured the biomass concentration in dry weight basis (DW) in the range of 40–800 mg L−1. The sensor-based on multi-wavelengths was conceived with an automatic sampling unit that works continuously and neither requires manual intervention nor sample dilution. The proposed system is cheaper than usual devices used for microalgae biomass quantification and compatible with the Internet of Things concept, data loggers with RS-232, universal serial bus, and analog inputs.

Novel Cell-Virus-Virophage Tripartite Infection Systems Discovered in the Freshwater Lake Dishui Lake in Shanghai, China.

Virophages are small parasitic double-stranded DNA (dsDNA) viruses of giant dsDNA viruses infecting unicellular eukaryotes. Except for a few isolated virophages characterized by parasitization mechanisms, features of virophages discovered in metagenomic data sets remain largely unknown. Here, the complete genomes of seven virophages (26.6 to 31.5 kbp) and four large DNA viruses (190.4 to 392.5 kbp) that coexist in the freshwater lake Dishui Lake, Shanghai, China, have been identified based on environmental metagenomic investigation. Both genomic and phylogenetic analyses indicate that Dishui Lake virophages (DSLVs) are closely related to each other and to other lake virophages, and Dishui Lake large DNA viruses are affiliated with the micro-green alga-infecting Prasinovirus of the Phycodnaviridae (named Dishui Lake phycodnaviruses [DSLPVs]) and protist (protozoan and alga)-infecting Mimiviridae (named Dishui Lake large alga virus [DSLLAV]). The DSLVs possess more genes with closer homology to that of large alga viruses than to that of giant protozoan viruses. Furthermore, the DSLVs are strongly associated with large green alga viruses, including DSLPV4 and DSLLAV1, based on codon usage as well as oligonucleotide frequency and correlation analyses. Surprisingly, a nonhomologous CRISPR-Cas like system is found in DSLLAV1, which appears to protect DSLLAV1 from the parasitization of DSLV5 and DSLV8. These results suggest that novel cell-virus-virophage (CVv) tripartite infection systems of green algae, large green alga virus (Phycodnaviridae- and Mimiviridae-related), and virophage exist in Dishui Lake, which will contribute to further deep investigations of the evolutionary interaction of virophages and large alga viruses as well as of the essential roles that the CVv plays in the ecology of algae.IMPORTANCE Virophages are small parasitizing viruses of large/giant viruses. To our knowledge, the few isolated virophages all parasitize giant protozoan viruses (Mimiviridae) for propagation and form a tripartite infection system with hosts, here named the cell-virus-virophage (CVv) system. However, the CVv system remains largely unknown in environmental metagenomic data sets. In this study, we systematically investigated the metagenomic data set from the freshwater lake Dishui Lake, Shanghai, China. Consequently, four novel large alga viruses and seven virophages were discovered to coexist in Dishui Lake. Surprisingly, a novel CVv tripartite infection system comprising green algae, large green alga viruses (Phycodnaviridae- and Mimiviridae-related), and virophages was identified based on genetic link, genomic signature, and CRISPR system analyses. Meanwhile, a nonhomologous CRISPR-like system was found in Dishui Lake large alga viruses, which appears to protect the virus host from the infection of Dishui Lake virophages (DSLVs). These findings are critical to give insight into the potential significance of CVv in global evolution and ecology.

Pediludiella daitoensis gen. et sp. nov. (Scenedesmaceae, Chlorophyceae), a large coccoid green alga isolated from a Loxodes ciliate

Freshwater protists often harbor unicellular green algae within their cells. In ciliates, possibly because of large host cell sizes and the small size of algal coccoids, a single host cell typically contains more than a hundred algal cells. While surveying such algae-bearing protists on Minami Daito Jima Island in Japan, we found a green Loxodes ciliate (Loxodida, Karyorelictea) that contained one or two dozens of very large coccoid algae. We isolated one of these algae and analyzed its characteristics in detail. A small subunit (SSU) rDNA phylogeny indicated Pseudodidymocystis species (Scenedesmaceae, Chlorophyceae) to be the taxon closest to the alga, although it was clearly separated from this by 39 or more different sites (inclusive of gaps). SSU rRNA structure analyses indicated that these displacements included eight compensatory base changes (CBCs) and seven hemi-CBCs. We therefore concluded that this alga belongs to a separate genus, and described it as Pediludiella daitoensis gen. et sp. nov. The shape of the isolated and cultured P. daitoensis was nearly spherical and reached up to 30 µm in diameter. Chloroplasts were arranged peripherally and often split and elongated. Cells were often vacuolated and possessed a net-like cytoplasm that resembled a football (soccer ball) in appearance, which was reflected in the genus name.

Differences in size distribution of marine phytoplankton in presence versus absence of jellyfish support theoretical predictions on top-down control patterns along alternative energy pathways

While theoretical food web studies highlight the importance of alternative energy pathways in shaping community response to bottom-up and top-down forcing, empirical insight on the relevance of the predicted patterns is largely lacking. In marine plankton food webs differences in food size spectra between ciliates and copepods lead to alternative energy pathways, one expanding from small phytoplankton over ciliates to copepods, the other from large edible phytoplankton directly to copepods. Correspondingly, predation pressure by copepods leads to an increase of small phytoplankton through top-down control of copepods on ciliates, but to a decrease of large phytoplankton through direct predation by copepods. Hence, food web theory predicts a shift from the dominance of large to small algae along an enrichment gradient. This prediction clearly deviates from the general assumption of a shift from small fast growing to larger slow-growing phytoplankton taxa with increasing nutrient availability. However, if copepods themselves are under top-down control by strong predation through planktivores such as fish or jellyfish, dominance of large algae is expected throughout the enrichment gradient. We tested these predictions by analyzing the phytoplankton composition from numerous marine lakes and lagoon sites located on the archipelago of Palau covering a wide range of nutrient levels, comparing sites lacking large numbers of higher trophic levels with sites harboring high densities of jellyfish. The observed patterns strongly support that higher trophic levels influence the phytoplankton size distribution along a nutrient enrichment gradient, highlighting the importance of alternate energy pathways in food webs for community responses.

Dynamics of Species and Size Structures of Phytoplankton at Different Levels of Bottom-Up and Top-Down Effects in Experimental Conditions

An experimental study of the impacts of trophic conditions and the activity of zooplankton and fish on the phytoplankton structure has shown that, at the beginning of the experiment, the species and size structures of algae were dependent on the N : P ratio. This parameter causes the differences in phytoplankton structures between mesotrophic and eutrophic conditions so that, in mesotrophic conditions, the dominant taxa are diatoms, dinoflagellates and chrysophytes while, in eutrophic mesocosms, cyanobacteria are most abundant. Later on, the differences in N : P ratio in the treatments are smoothed out and the dominance shifts to large filamentous green algae. Fish reduce zooplankton control over phytoplankton, thus promoting the development of edible diatoms; this is most clearly manifested in eutrophic conditions.

Research on Comparison of Artificial Alga Reef Site Selection Scheme in Beidaihe Sea Area

Artificial algae reefs can effectively improve the ecological environment of the sea areas, restore submarine vegetation, and provide habitats for fish and avoid enemies. The study area is located in Beidaihe sea area. According to the regional characteristics, this paper uses ecological model to predict the floating trajectory of large algae debris, and obtains the impact of large algae on the landscape of Beidaihe bathing field. At the same time, through the marine physical environment(water depth, water flow, subsoil type, seabed topography), offshore distance, economic benefits and other factors, selected the most suitable location for artificial reefs in the Beidaihe sea area.