Dominant Algae Research Articles

Elevated nutrients and herbivory negatively affect Dictyota growth dynamics

Caribbean coral reefs are experiencing a shift to algal dominance at the expense of stony corals. Determining the factors leading to algal phase shifts is crucial for assuring the survival of Caribbean coral reefs. In this study, factors controlling the growth of the abundant brown macroalgae Dictyota spp. were investigated by varying herbivory pressure (caging) and nutrients (fertilizer addition) on coral reefs near St. Thomas (US Virgin Islands). Experiment 1 measured Dictyota heights and percent cover at 3 sites (11-20 m depth) and showed no growth response to nutrient addition and a weak negative response to herbivory. To confirm results of Experiment 1, a caging and nutrient manipulation (Experiment 2) was conducted at one site (14 m depth) using the dependent variable Dictyota biomass. A strong negative response of growth to nutrient addition was shown, presumably because of nutrient inhibition, and an equally negative response to herbivory (loss of ~50% biomass over 21 d). The inhibitory effect of fertilization on growth was confirmed in a third experiment that showed increasing biomass loss over 4 treatment levels of increasing fertilizer addition (0 [ambient], 5, 10, 20 g). Overall, Dictyota was not nutrient limited at any sites, and was weakly controlled by herbivore populations. Factors responsible for Dictyota abundance on Caribbean reefs may reflect decreased herbivory caused by overfishing and reductions in coral cover and do not appear to be affected by recent changes in nitrogen or phosphorus load. This study reinforces the need for conservation and management of herbivores in coral reef ecosystems, to mitigate the effects from anthropogenic stressors.

High summer temperatures amplify functional differences between coral- and algae-dominated reef communities.

Shifts from coral to algal dominance are expected to increase in tropical coral reefs as a result of anthropogenic disturbances. The consequences for key ecosystem functions such as primary productivity, calcification, and nutrient recycling are poorly understood, particularly under changing environmental conditions. We used a novel in situ incubation approach to compare functions of coral‐ and algae‐dominated communities in the central Red Sea bimonthly over an entire year. In situ gross and net community primary productivity, calcification, dissolved organic carbon fluxes, dissolved inorganic nitrogen fluxes, and their respective activation energies were quantified to describe the effects of seasonal changes. Overall, coral‐dominated communities exhibited 30% lower net productivity and 10 times higher calcification than algae‐dominated communities. Estimated activation energies indicated a higher thermal sensitivity of coral‐dominated communities. In these communities, net productivity and calcification were negatively correlated with temperature (>40% and >65% reduction, respectively, with +5°C increase from winter to summer), whereas carbon losses via respiration and dissolved organic carbon release more than doubled at higher temperatures. In contrast, algae‐dominated communities doubled net productivity in summer, while calcification and dissolved organic carbon fluxes were unaffected. These results suggest pronounced changes in community functioning associated with coral‐algal phase shifts. Algae‐dominated communities may outcompete coral‐dominated communities because of their higher productivity and carbon retention to support fast biomass accumulation while compromising the formation of important reef framework structures. Higher temperatures likely amplify these functional differences, indicating a high vulnerability of ecosystem functions of coral‐dominated communities to temperatures even below coral bleaching thresholds. Our results suggest that ocean warming may not only cause but also amplify coral–algal phase shifts in coral reefs.

An integrated organic–inorganic geochemical characterization of Paleogene sediments in No.1 Structural Belt of the Nanpu Sag, Bohai Bay Basin, eastern China: implications for the origin of organic matter

Paleogene sediments, especially the third member of the Dongying Formation (Ed 3 ) and the first and third members of the Shahejie Formation (Es 1 and Es 3 ), have been regarded as the most important source rocks in the Nanpu Sag. Organic and inorganic analyses, including Rock-Eval pyrolysis, gas chromatography-mass spectrometry, and element geochemistry, in 91 mudstone samples, were used to reconstruct the palaeoenvironmental conditions, such as palaeoclimate, palaeo-salinity and palaeo-redox conditions, and to recognize the origin of organic matter. The results show that Es 3 has a higher TOC content than Es 1 and Ed 3 . Hydrocarbon genetic potential (S 1 + S 2 ) of the samples indicate fair to good hydrocarbon potential. The kerogen type of Ed 3 and Es 1 source rocks are Type II 1 –II 2 , while Es 3 source rocks are dominated by Type II 2 –III kerogens. Biomarkers and inorganic geochemical indicatives of source rocks, such as Pr/Ph, V/(V + Ni) and Cu/Zn, indicate a lacustrine environment with fresh to brackish water under suboxic to anoxic conditions during deposition. Ed 3 source rocks are characterized by low G/C 30 H (gamacerane/C 30 hopane) (<0.1), TT/C 30 H (tricyclic terpane/C 30 hopane) and S/H (serane/hopane), high Pr/Ph (pristane/phytane) and C 24 TeT/C 23 TT (C 24 tetracyclic terpane/C 23 tricyclic terpane), indicating mixed input of both algae and terrestrial higher plants, dominated by terrestrial higher plants. Es 1 source rocks display medium G/C 30 H, TT/C 30 H, S/H, Pr/Ph and C 24 TeT/C 23 TT, indicative of a mixed input of both algae and terrestrial higher plants. Es 3 source rocks are characterized by high G/C 30 H (>0.1), TT/C 30 H and S/H, low Pr/Ph and C 24 TeT/C 23 TT, typical of a mixed input of algae and terrestrial higher plants, with algal dominance. Ed 3 , Es 1 and Es 3 source rocks were mostly deposited in semi-arid to humid-warm climate conditions, with an average temperature higher than 15°C. This study suggests that suitable temperatures, a fresh to brackish lacustrine environment and suboxic to anoxic conditions could result in a high organic matter concentration and preservation, thus providing prerequisites for the formation of high-quality source rocks. Supplementary material : Tables S1–S3 are available at https://doi.org/10.6084/m9.figshare.c.5227684

Ecological Status of the Chusovaya River by Its Epilithon and Hydrochemical Indices (near the Chusovoy Town)

As a result of our study, data were obtained on the structure of the epilithon and the physicochemical parameters of the waters in the Chusovaya river near the town of Chusovoy for 2017–2018. The taxonomic structure, quantitative characteristics, dominant species, features of the distribution of the main groups of algae were studied. The algal flora includes 191 infrageneric algal taxa (168 species) from 6 divisions, 10 classes, 24 orders, 51 families and 86 genera. The taxonomic spectrum is based on diatoms (67.5% of the total numbers), green algae (21%), and cyanobacteria (9%). In the environmental and geographical aspects, the epilithon is mainly represented by widespread salinityindifferent benthic and plankton-benthic species, having an optimum in slightly alkaline or neutral waters. The epiliton of the Chusovaya river has reached a fairly high level of development. The values of the total biomass varied from 1.46 to 46.32 g/m2, and the abundance did from 1.5 to 31.7 billion cells/m2. The species diversity index (an average of 3.22±0.18) indicates species-rich and balanced algocenoses of the Chusovaya river, while in summer the indices are 1.9–2.2 times lower than in autumn. The dominant algae species differed in seasons, they were represented by diatoms or cyanobacteria in terms of their number, and by diatoms in terms of their biomass. In water samples with epilithon flushing, higher concentrations of chemical substances (NH4+, NO3-, PO43-, and Fetot) were noted than in river water, indicating the ability of the epilithon to accumulate substances. Significant changes in the biomass and/or abundance of epilithon as a function of the content of chemical substances in water and fouling washes were revealed. By the value of the saprobity index (from 1.34 to 2.27), the sanitary-biological state of the water in the Chusovaya river is assessed as satisfactorily pure (II–III water quality classes), the saprobity zone is ο-β-, β-mesosaprobic.

DNA metabarcoding unveils niche overlapping and competition among Caribbean sea urchins

Detailed information of trophic interactions among consumer–resources in food webs is usually limited due to the lack of accurate identification of eaten food resources. The use of DNA-metabarcoding has been proven useful for molecular identification of the numerous taxa present in stomach contents. Here, we characterize the diet and trophic behavior of four sea urchin species inhabiting shallow waters of Puerto Rico using this molecular technique. We extracted, sequenced, and analyzed DNA from the gut content of a total of 60 individuals collected at three sites at the northeastern coast of Puerto Rico. Our results demonstrated that seaweeds were the dominant food source for the four sea urchin species at all three sites, but also small protists, fungi and metazoans were important components of sea urchin’s diet. Interspecific differences in diet were also found among sites. PERMANOVA analysis detected significant differences among species (Pseudo-F = 1.755, p < 0.001), and among sites (Pseudo-F = 2.52, p < 0.001). A SIMPER analysis showed that in all cases the main taxa causing differences between species and sites were macroalgae (Rhodophyta, Chlorophyta and Ochrophyta) with some contribution of small eukaryotes (Apicomplexa and Bacillariophyta). This diet characterization in sea urchins revealed a generalist omnivore behavior, but with a clear dominance of algae as a main dietary component. Thus, we found a potential inter-specific competition due to niche overlapping, which seems to be more common than initially thought.

Effect of iron and phosphorus on the microalgae growth in co-culture.

Iron and phosphorus (P) are the important micro- and macro-nutrient for microalgae growth, respectively. However, the effect of iron and P on microalgae growth in co-culture associating with the formation of dominate algae has not been investigated before. In the current study, Anabaene flos-aquae, Chlorella vulgaris and Melosira sp. were co-cultivated under the addition of different initial iron and P to reveal the effect of iron and phosphorus on the growth of microalgae. The results showed that the mean growth rate of A. flos-aquae, C. vulgaris and Melosira was 0.270, 0.261 and 0.062, respectively, indicating that the A. flos-aquae and C. vulgaris algae are liable to be the dominant algae while the growth of Melosira was restrained when co-cultured. The ratio of Fe to P has a significant impact on the growth of microalgae and could be regarded as an indicator of algae growth. Microalgae showed a much more obvious uptake of iron compared to that of P. The information obtained in the current study was useful for the forecast of water quality and the control of microalgae bloom.

Trophic interactions will expand geographically but be less intense as oceans warm.

Interactions among species are likely to change geographically due to climate-driven species range shifts and in intensity due to physiological responses to increasing temperatures. Marine ectotherms experience temperatures closer to their upper thermal limits due to the paucity of temporary thermal refugia compared to those available to terrestrial organisms. Thermal limits of marine ectotherms also vary among species and trophic levels, making their trophic interactions more prone to changes as oceans warm. We assessed how temperature affects reef fish trophic interactions in the Western Atlantic and modeled projections of changes in fish occurrence, biomass, and feeding intensity across latitudes due to climate change. Under ocean warming, tropical reefs will experience diminished trophic interactions, particularly herbivory and invertivory, potentially reinforcing algal dominance in this region. Tropicalization events are more likely to occur in the northern hemisphere, where feeding by tropical herbivores is predicted to expand from the northern Caribbean to extratropical reefs. Conversely, feeding by omnivores is predicted to decrease in this area with minor increases in the Caribbean and southern Brazil. Feeding by invertivores declines across all latitudes in future predictions, jeopardizing a critical trophic link. Most changes are predicted to occur by 2050 and can significantly affect ecosystem functioning, causing dominance shifts and the rise of novel ecosystems.

Coral cover a stronger driver of reef fish trophic biomass than fishing.

An influential paradigm in coral reef ecology is that fishing causes trophic cascades through reef fish assemblages, resulting in reduced herbivory and thus benthic phase shifts from coral to algal dominance. Few long‐term field tests exist of how fishing affects the trophic structure of coral reef fish assemblages, and how such changes affect the benthos. Alternatively, benthic change itself may drive the trophic structure of reef fish assemblages. Reef fish trophic structure and benthic cover were quantified almost annually from 1983 to 2014 at two small Philippine islands (Apo, Sumilon). At each island a No‐Take Marine Reserve (NTMR) site and a site open to subsistence reef fishing were monitored. Thirteen trophic groups were identified. Large planktivores often accounted for >50% of assemblage biomass. Significant NTMR effects were detected at each island for total fish biomass, but for only 2 of 13 trophic components: generalist large predators and large planktivores. Fishing‐induced changes in biomass of these components had no effect on live hard coral (HC) cover. In contrast, HC cover affected biomass of 11 of 13 trophic components significantly. Positive associations with HC cover were detected for total fish biomass, generalist large predators, piscivores, obligate coral feeders, large planktivores, and small planktivores. Negative associations with HC cover were detected for large benthic foragers, detritivores, excavators, scrapers, and sand feeders. These associations of fish biomass to HC cover were most clear when environmental disturbances (e.g., coral bleaching, typhoons) reduced HC cover, often quickly (1–2 yr), and when HC recovered, often slowly (5–10 yr). As HC cover changed, the biomass of 11 trophic components of the fish assemblage changed. Benthic and fish assemblages were distinct at all sites from the outset, remaining so for 31 yr, despite differences in fishing pressure and disturbance history. HC cover alone explained ~30% of the variability in reef fish trophic structure, whereas fishing alone explained 24%. Furthermore, HC cover affected more trophic groups more strongly than fishing. Management of coral reefs must include measures to maintain coral reef habitats, not just measures to reduce fishing by NTMRs.

Food Spectrum and Habitat-Specific Diets of Benthic Foraminifera From the Wadden Sea – A Fatty Acid Biomarker Approach

Tidal coasts are characterized by natural disturbances, forming a broad variety of habitats, which provide different niches and varying food resources for benthic foraminifera. Foraminifera occupy different trophic levels and fill key trophic positions in benthic food webs, but detailed studies on their nutrition spectrum in inter- to supratidal environments are lacking. Further, it is unknown to what extent foraminifera can switch between different feeding modes depending on resource availability in different Wadden Sea habitats. In order to shed light on these questions, we investigated potential food resources in sediments as well as the food spectrum of two dominant benthic foraminifera, Trochammina inflata and Ammonia tepida, in four characteristic habitats of the Wadden Sea: salt marsh, mixed flat, oyster reef and mud flat, using fatty acid (FA) analysis. The sediments of the four habitats provide a broad range of food sources including green algae, brown algae, diatoms and bacteria for benthic foraminifera. The FA profile of T. inflata from the salt marsh and mixed flat was dominated by green algae and bacteria, whereas the brown algae biomarker was only found in specimens from the salt marsh. In comparison, FA profiles of A. tepida suggested dominant algae feeding (green algae and diatoms), whereas brown algae and bacterial FAs were only found in specimens from the oyster reef. The results suggest that foraminifera mainly feed at low trophic levels with selective food intake closely depending on their habitat. The diverse nutritional strategies may allow efficient exploitation of resources in dynamic tidal habitats. Presumably, foraminifera serve as an important link between lower and higher trophic levels and thus fill key trophic positions in the benthic food web of the Wadden Sea.

Fast behavioral feedbacks make ecosystems sensitive to pace and not just magnitude of anthropogenic environmental change

Anthropogenic environmental change is altering the behavior of animals in ecosystems around the world. Although behavior typically occurs on much faster timescales than demography, it can nevertheless influence demographic processes. Here, we use detailed data on behavior and empirical estimates of demography from a coral reef ecosystem to develop a coupled behavioral-demographic ecosystem model. Analysis of the model reveals that behavior and demography feed back on one another to determine how the ecosystem responds to anthropogenic forcing. In particular, an empirically observed feedback between the density and foraging behavior of herbivorous fish leads to alternative stable ecosystem states of coral population persistence or collapse (and complete algal dominance). This feedback makes the ecosystem more prone to coral collapse under fishing pressure but also more prone to recovery as fishing is reduced. Moreover, because of the behavioral feedback, the response of the ecosystem to changes in fishing pressure depends not only on the magnitude of changes in fishing but also on the pace at which changes are imposed. For example, quickly increasing fishing to a given level can collapse an ecosystem that would persist under more gradual change. Our results reveal conditions under which the pace and not just the magnitude of external forcing can dictate the response of ecosystems to environmental change. More generally, our multiscale behavioral-demographic framework demonstrates how high-resolution behavioral data can be incorporated into ecological models to better understand how ecosystems will respond to perturbations.

Negative trophic relationship between parrotfish biomass and algal cover on Philippine coral reefs

The importance of herbivory in preventing phase shifts to algal dominance on coral reefs is widely acknowledged. However, there is a paucity of information on which and how much herbivores are needed to effectively prevent an overgrowth of different algal types in natural environments. Our study showed the overall negative relationship between herbivorous fish biomass and benthic algal cover on Philippine coral reefs. The strongest negative relationships were between parrotfish biomass and both total algal and algal turf covers, and between total herbivore biomass and macroalgal cover. We further identified 4.0 mt/km2 and 2.0 mt/km2 for parrotfish, and 1.0 mt/km2 for all herbivores, as the potentially critical biomass levels needed to keep total algal, algal turf, and macroalgal covers, respectively, at low levels. The mean (±SE) cover of all algae was about 37.0 ± 0.7% in areas with ≥4.0 mt/km2 parrotfish biomass compared with 46.2 ± 0.8% and 44.0 ± 1.1% in areas with 2.0–3.9​ mt/km2 and <2.0 mt/km2 parrotfish biomass, respectively. Algal turf cover of 10.1 ± 0.7% in areas with <2.0 mt/km2 parrotfish biomass was almost twice as high as those with ≥2.0 mt/km2 parrotfish biomass. Macroalgal covers were only 4.7 ± 0.5% and 10.6 ± 1.1% in areas with 1.0–2.0 and >2.0 mt/km2 total herbivore biomass, respectively, compared with 39.8 ± 1.6% in those with <1.0 mt/km2 total herbivore biomass. Our findings support the hypothesis that phase shifts to algal dominance on coral reefs would not happen as long as there are no major losses of important herbivore species and herbivore biomass levels do not fall below critical levels.

Characteristics of Fluorescence Spectra, UV Spectra, and Specific Growth Rates during the Outbreak of Toxic Microcystis Aeruginosa FACHB-905 and Non-Toxic FACHB-469 under Different Nutrient Conditions in a Eutrophic Microcosmic Simulation Device

Microcystis aeruginosa is the dominant alga forming cyanobacteria blooms, the growth of which is limited by available nutrients. Thus, it is necessary to study cyanobacteria blooms and explore the growth of Microcystis aeruginosa under different nutrient conditions. In this paper, we take Microcystis aeruginosa, including toxic Freshwater Algae Culture of Hydrobiology Collection (FACHB)-905 and non-toxic FACHB-469 strains, into account. The strains were cultured using a simulation device under different nutrient conditions. Ultraviolet spectra, three-dimensional fluorescence spectra, and kinetic parameter indicators of the two species are studied. Compared to FACHB-469, the results show that the specific growth rate of FACHB-905 is much higher, in particular, FACHB-905 is the dominant species under low nutrient conditions. Furthermore, the UV spectral characteristics indicate that the molecular weight of dissolved organic matter in the culture tank of toxic FACHB-905 is greater than that of FACHB-469. Additionally, the humification index of toxic FACHB-905 is slightly higher as well, which suggests that it is more stable in the presence of dissolved organic matter during blooms. Therefore, the toxic Microcystis strain is more likely to become the dominant species in water blooms under lower eutrophic conditions and water blooms formed by the toxic Microcystis strain may be more difficult to recover from.

Change in fish and benthic communities in Belizean patch reefs in and outside of a marine reserve, across a parrotfish capture ban

The role of a marine reserve and fisheries regulations in restoring fish populations on reefs disturbed by climate impacts was evaluated. Eight patch reefs, divided equally between no-fishing and fished zones in the remote Glover’s Reef atoll lagoon, were studied for 22 yr: 13 yr before and 9 yr after a ban on parrotfish capture. Findings indicate that the main effect of the fisheries closure was the recovery of targeted carnivorous species, notably snappers, jacks, and groupers. Recovery continued for most of the time series, including the later period when parrotfish capture was banned. Parrotfish abundance slowly declined in both management zones and across the ban period. The loss occurred for both small non-fished species, such as the striped parrotfish Scarus iserti, and for larger fished species, such as the stoplight Sparisoma viride and red-band parrotfish Sparisoma aurofrenatum. Consequently, parrotfish abundance appeared to be controlled by the ecology of these patch reefs rather than fishing mortality. We suggest that the high and persistent cover of late-successional algae reduces the renewal rates of algae, which had negative consequences for all studied parrotfish populations. Low ocean currents and physical energy in the lagoon appeared to promote algal persistence. Thus, parrotfish bans may be more effective in promoting reef recovery in environments that promote rapid algal turnover. Fisheries regulations are unlikely to rapidly restore hard corals on these patch reefs, which have slowly transitioned to algal dominance since first described in 1970.

Water Quality and Bacterial Population Driving Mechanism of Algae Vertical Succession in Stratified Reservoir

Phytoplankton and bacteria are important components of the aquatic food web, and play a critical role in substance circulation and energy exchange in freshwater ecosystems. The succession of algae is closely related to the metabolism and structural succession of bacterial populations in the water column. Thus, in this study, the vertical succession characteristics of phytoplankton and bacteria community structure and their coupling with water quality were investigated during an algal bloom in the Lijiahe Reservoir using high-throughput DNA sequencing and Biolog technologies. The results showed that the Lijiahe Reservoir was in the thermal stratification stage in August, and the pH, dissolved oxygen, and NH4+-N of the water column gradually decreased with depth (P<0.001). Algal cell concentration and chlorophyll a exhibited a simultaneous trend (P<0.001), and the maximum values in the surface layer were 3363.33×104 cells·L-1 and 7.03 μg·L-1, respectively. The algal community structure was dominated by Microcystis at water depths of 0 m and 3 m, and at 6 m water depth, Cyclotella replaced Microcystis as the most dominant algae, with a relative abundance of 57.28%. Biolog analysis indicated that the outbreak of Microcystis had a significant impact on bacterial metabolic activity and its relative abundance, but the diversity of bacterial population metabolic activity varied less. A total of 1420 operational taxonomic units were found by high-throughput sequencing, belonging to 10 bacterial phyla. Of these, Actinobacteria and Proteobacteria dominated in all water layers, and their relative abundances were more than 50%. The relative abundance of Chlorobi and Planctomycetes varied significantly with water depth, reaching their maxima at a depth of 6 m with values of 10.29% and 6.78%, respectively, which were both negatively correlated with algal density (P<0.05). Firmicutes and Gemmatimonadetes were positively correlated with algal density (P<0.05). A heat map fingerprint showed that the vertical distribution of the bacterial community structure of the Lijiahe Reservoir varied significantly, and with the increase in water depth, the bacterial community was more uniformly distributed and tended to diversify. Redundancy analysis (RDA) showed that the vertical distribution of the bacterial and algal community structure was regulated by different water qualities, and the difference was significant. This study investigated the coupling mechanism of algal and bacterial communities during the algal bloom in the Lijiahe Reservoir, and the results provided a scientific basis for the investigation of the molecular microecological driving mechanism of water-source algal blooms.

Biomarker evidence of algal-microbial community changes linked to redox and salinity variation, Upper Devonian Chattanooga Shale (Tennessee, USA)

AbstractLate Devonian marine systems were characterized by major environmental perturbations and associated biotic community changes linked to climate change and widespread oceanic anoxia. Here, we provide high-resolution lipid biomarker chemostratigraphic records from the Upper Devonian Chattanooga Shale (Tennessee, USA) to investigate algal-microbial community changes in the southern Illinois Basin that were related to contemporaneous shifts in marine redox (as proxied by trace metals, Fe-species, and Corg/P) and salinity conditions (as proxied by B/Ga, Sr/Ba, and S/total organic carbon). The Frasnian was characterized by dominantly bacterial lipids (high hopane/sterane), near-marine salinity, and a shift from oxic to increasingly reducing conditions in response to increasing organic carbon sinking fluxes. Aryl isoprenoids and aryl isoprenoid ratios reveal that the O2-H2S chemocline was unstable and intermittently shallow (i.e., within the photic zone). The Frasnian-Famennian boundary was marked by a shift in microalgal community composition toward green algal (e.g., prasinophyte) dominance (lower C27 and higher C28 and C29 steranes), a sharp reduction in watermass salinity, and a stable O2-H2S chemocline below the photic zone, conditions that persisted until nearly the end of the Famennian. We infer that changing watermass conditions, especially a sharp reduction in salinity to possibly low-brackish conditions (&amp;lt;10 psu), were the primary cause of concurrent changes in the microalgal community, reflecting tolerance of low-salinity conditions by green algae. Transient spikes in moretane/hopane (M/H) ratios may record enhanced terrestrial weathering at the Frasnian-Famennian and Devonian–Carboniferous boundaries, triggered by coeval glacio-eustatic falls and increased inputs of soil organic matter. High M/H and pristane/phytane, in combination with low chemical index of alteration and K/Al, record a decrease in chemical weathering intensity during the Famennian that may have been due to contemporaneous climatic cooling, and a concurrent reduction in silt content may reflect stabilization of land surfaces by vascular plants and resulting reduced sediment yields. This study demonstrates the effectiveness of combining organic and inorganic geochemical proxies (including novel paleosalinity indices) for determination of environmental controls on the composition and productivity of plankton communities in paleomarine systems.

New insights into spatiotemporal source apportionment of n-alkanes under mixed scenario: A pilot study on Lake Chaohu, China

N–alkanes are ideal molecular markers for the source apportionment of organic matter. However, the estimation of both biogenic and anthropogenic sources under mixed scenario using n–alkanes and their related proxies still remains an issue. In this study, we investigated spatiotemporal variations of n–alkanes in suspended particulate matter of Lake Chaohu for their source apportionment. Overall, Σ29 n–alkanes ranged from 324.1 to 113685 ng·L−1. C17H36 was the most abundant homologue and was followed by C18, C27 and C29 homologues. Carbon preference indexes (CPIs) in most samples (at least 85%) were < 3, indicating mixed sources of n–alkanes in Lake Chaohu. Therefore, biogenic and anthropogenic n–alkanes were separated by subtraction to avoid potential bias. Our results showed Σ biogenic and Σ anthropogenic n–alkanes ranged from 14.8 to 3531.6 ng·L−1 and 257.6 to 4938.5 ng·L−1, respectively. For biogenic n–alkanes, their carbon–chain distributions posed a preponderant peak at C17, indicating algae were the main contributors to biogenic n–alkanes in Lake Chaohu. Biogenic average chain length (ACLbio) was developed to quantify the contributions of different biogenic sources. We recommended ACLbio < 21 for algae dominance and ACLbio > 26 for terrestrial plant dominance. For anthropogenic n–alkanes, their carbon–chain distribution presented obviously spatiotemporal variations. The sources of anthropogenic n–alkanes in summer and winter were typical dominances of light petroleum and incomplete fossil fuel burning/heavy oil emission, respectively. New developed proxies, anthropogenic average chain length (ACLanthro) and the ratio of unit short– to long–carbon anthropogenic n–alkanes (L/H), are effective for quantifying the relative contributions of different anthropogenic sources. We recommend log10L/H > 0.5 and ACLanthro < 20.5 for light petroleum input dominance, log10L/H < −0.5 and ACLanthro > 26.5 for incomplete fossil fuel burning at high temperature/heavy oil emission dominance.

Bioremediation of Landoltia punctata to Microcystis aeruginosa Contaminated Waters

Microcystis aeruginosa is one of the dominant algae in the “phytoplankton bloom” phenomenon. A high density of microcystins (MCs) are produced when algae have explosive growth, which can damage the water environment and pose a great threat to aquatic animals, plants, and human health. Duckweed (Landoltia punctata) is a morphologically highly degraded flowering plant with a short growth cycle and wide environmental adaptability. Importantly, duckweed can grow in eutrophic water and has great potential in water remediation. The present study aims to analyze the physiological and biochemical changes of L. punctata when co-culturing with M. aeruginosa in the laboratory. Our results showed that all the biomass, chlorophyll content, antioxidant enzyme activities, and amylase activity of L. punctata increased in 2 × 108 cells/L and 4 × 108 cells/L for M. aeruginosa, and also significantly reduced in 1.6 × 109 cells/L for M. aeruginosa, while cytotoxic substance (malondialdehyde (MDA)) content showed a completely opposite trend. After co-culturing, it was found that the MC content in L. punctata reduced to 138.87 g/g, and the MC removal rate was 29.48%. These results indicate that L. punctata can grow normally in high-density M. aeruginosa, which paves the way for L. punctata’s bioremediation of water polluted by M. aeruginosa.

Modeling for multi-temporal cyanobacterial bloom dominance and distributions using landsat imagery

Cyanobacterial blooms pose great risks to aquatic systems due to its increase in frequency and severity worldwide. This study developed multi-temporal satellite remote sensing models that accurately portray spatial distribution of freshwater cyanobacterial blooms, which traditional monitoring methods cannot accomplish. The models were developed using multiple linear regression involving in-situ measurements and Landsat imagery in Lake Champlain for cyanobacterial blooms and other water quality variables i.e. chlorophyll-a, total phytoplankton, chlorophyte, chrysophyta, pyrrophyta, secchi disk and temperature. The developed models with Landsat imagery successfully captured the distribution of cyanobacterial blooms and other variables (adjusted R2 = 0.6–0.98). Multi-temporal analysis of remote sensing highlighted the high bloom years with quantified cyanobacterial levels over the entire water body, associated with temperature, indicating the impact of precipitation on cyanobacterial bloom growth. The modeling approach in this study can provide information to improve our understanding of algal dominance and dynamics. This approach can be applied to other freshwater systems, providing a pathway for rapid response systems.

Succession Characteristics of Algae Functional Groups and Water Quality Assessment in a Drinking Water Reservoir

To understand the temporal and spatial succession characteristics of algae functional communities and water quality changes in a drinking water reservoir, the Lijiahe Reservoir was selected to monitor variations in water quality and algae from September 2018 to June 2019. The algae community was classified into functional groups following the method proposed by Reynolds and Padisák. The relationship between algal functional community and water quality was discussed, and the water quality was assessed using the water quality index (WQI) method. The results showed that 56 species of algae were obtained, belonging to 4 families and 28 genera, which were divided into 15 functional groups. The dominant algae functional communities were B, D, G, J, L0, Mp, P, W1, and X1. The algae structure of Lijiahe Reservoir showed obvious seasonal characteristics. The algal density in the mixed period was significantly lower than that in the stratification period. The main functional algae in the mixed period were Chlorella and Cyclotella, but Navicula and Synedra were the dominant functional algae in the stratification period. Redundancy analysis showed that the water temperature, mixing depth, and relative water column stability index were the main factors driving algae succession. WQI analysis indicated that the water quality of Lijiahe Reservoir was "good", and the water quality during the mixed period was slightly better than that in the stratification period. This study demonstrates that water-lifting aerators can change the succession characteristics of algae functional groups, and effectively contribute to improvement in water quality in a drinking water reservoir.

Decline of zooplankton food resources of Limnothrissa miodon fishery in Lake Kariba: Global warming‐induced ecosystem disruption by Cylindrospermopsis raciborskii

AbstractThe present study was conducted on the Lake Kariba portion of the Middle Zambezi Biosphere Reserve. Magadza (2011) previously reported the pelagic Lake Tanganyika sardine (Limnothrissa miodon) fishery introduced into Lake Kariba was declining. This phenomenon was attributed to observed climate‐change‐related warming of the lake, facilitating establishment of the invasive Cylindrospermopsis raciborskii, currently the dominant alga in the lake. Chlorophyceae contribute to less than 10% of the phytoplankton biomass. Accordingly, it was postulated that its dominance in the lake resulted in a food chain disruption because this cyanobacterium was not preferred by zooplankton grazers. Accordingly, the present study examined the feeding behaviour of L miodon with reference to available food items in the Sanyati Basin of Lake Kariba. The results highlighted a virtual absence of entomostraca zooplankton in the Sanyati Basin of Lake Kariba, in contrast to previous findings of previous studies, the avoidance of C. raciborskii in the diet of L. miodon, as measured by the Ivlev electivity index, a low stomach fullness index, the movement of L. miodon to macroinvertebrates associated with the littoral zone as a food source, and unfavourable dietary indicators of L. miodon. These results collectively suggest a food deficit for L. miodon in Lake Kariba, leading to the previously observed decline in the lake fishery.