Toxin-allelopathy among phytoplankton species prevents competitive exclusion

Toxic or allelopathic compounds liberated by toxin-producing phytoplankton (TPP) acts as a strong mediator in plankton dynamics. On an analysis of a set of phytoplankton biomass-data that have been collected by our group in the North-West part of the Bay of Bengal, and by analysis of a three-component mathematical model under a constant as well as a stochastic environment, we explore the role of toxin-allelopathy in determining the dynamic behaviour of the competing-phytoplankton species. The overall results, based on analytical and numerical wings, demonstrate that toxin-allelopathy due to the toxin-producing phytoplankton (TPP) promotes a stable coexistence of those competitive phytoplankton that would otherwise exhibit competitive exclusion of the weak species. Our study suggests that TPP might be a potential candidate for maintaining the coexistence and diversity of competing phytoplankton species.Comment: 29 pages, 6 figures, Journal Pape

Dynamical Complexity in Some Ecological Models: Effects of Toxin Production by Phytoplankton

We investigate dynamical complexities in two types of chaotic tri-trophic aquatic food-chain model systems representing a real situation in the marine environment. Phytoplankton produce chemical substances known as toxins to reduce grazing pressure by zooplankton [1]. The role of toxin producing phytoplankton (TPP) on the chaotic behavior in these food chain systems is investigated. Holling type I, II, and III functional response forms are considered to study the interference between phytoplankton and zooplankton populations in the presence of toxic chemical. Our study shows that chaotic dynamics is robust to changes in the rates of toxin release as well as the toxin release functions. The present study also reveals that the rate of toxin production by toxin producing phytoplankton plays an important role in controlling oscillations in the plankton system. The different mortality functions of zooplankton due to toxin producing phytoplankton have significant influence in controlling oscillations, coexistence, survival or extinction of the zooplankton population. Further studies are needed to ascertain if this defence mechanism suppresses chaotic dynamics in model aquatic systems

Chaos to Order: Role of Toxin Producing Phytoplankton in Aquatic Systems

Toxin producing phytoplankton (TPP) plays an important role in aquatic systems. To observe the role of TPP, we consider a three species food chain model consisting of TPP-zooplankton-fish population. The similar type of model considered by Upadhyay et al. [1] for terrestrial ecosystem and obtained chaotic dynamics in some region of parametric space. We modify their models by taking into account the toxin liberation process of TPP population and represented as aquatic systems. We consider Holling type I, type II and type III functional forms for this process. We observe that increasing the strength of toxic substance change the state from chaos to order. Our conclusion is that TPP has a stabilizing contribution in aquatic systems and may be used as a bio-control mechanism

Chaos to order: role of toxin producing phytoplankton in aquatic system

Toxin producing phytoplankton (TPP) plays an important role in aquatic systems. To observe the role of TPP, we consider a three species food chain model consisting of TPP-zooplankton-fish population. The similar type of model considered by Upadhyay et al. [1] for terrestrial ecosystem and obtained chaotic dynamics in some region of parametric space. We modify their models by taking into account the toxin liberation process of TPP population and represented as aquatic systems. We consider Holling type I, type II and type III functional forms for this process. We observe that increasing the strength of toxic substance change the state from chaos to order. Our conclusion is that TPP has a stabilizing contribution in aquatic systems and may be used as a bio-control mechanism

Mathematical analysis of plankton population dynamics

Harmful algal blooms (HABs) event that causes enormous economic loss and health effect raises concerns among environmentalists. In this paper, a mathematical model of interaction between nutrient, toxin-producing phytoplankton (TPP), non-toxic phytoplankton (NTP), zooplankton, and toxic chemicals is proposed to study on how the process of these HABs occurred. The model of interaction is represented by Ordinary Differential Equations (ODEs) and stability analysis of the model is conducted. Several conditions for the system to be stable around trivial and interior equilibrium point are obtained. From the analysis, it is observed that under nutrient limitation, the amounts of toxic chemicals secreted out by the TPP are increased. As a result, NTP population and zooplankton population are affected by the situation. If this situation is prolonged, this will result in the extinction of both populations. Overall, this study shows that TPP release more toxic chemicals when the nutrient is limited and gives a better understanding on the occurrence of HABs event

Comparison of the Effects of Toxic Cyanobacteria on the Reproductive Success of Eurytemora affinis Populations in the Baltic Sea and Green Bay, Wisconsin

The Northern Baltic Sea, off the southern coast of Finland, and Green Bay, off Lake Michigan in Wisconsin, both experience large toxic cyanobacteria blooms, especially during the summer and early fall months. Nodularia spumigena is the toxic algae in the Baltic Sea and produces the toxin Nodularin. Nodularin is a toxin that has branched from the toxin Microcystin, which is produced by Microcystis, the toxic algae forming blooms in Green Bay. While the toxin often acts as a defense mechanism to deter zooplankton from grazing, the calenoid copepod Eurytemora affinis, with populations in both the Baltic and Green Bay, does feed and consume these toxic algal cells and is able to survive. The consequences in terms of reproductive success from the consumption of this toxin are relatively unexplored. This study focuses on whether or not the two populations have similar responses to feeding on each of these toxic algae in laboratory studies. In both locations, the copepods were collected from the field and put through grazing experiments to examine their grazing and filtration rates in addition to their egg production in various food treatments. Both populations were able to feed and survive but had decreased egg production in a treatment consisting of a mixture of toxic algae and algae considered a good food source (Rhodomonas in Baltic experiments; Scenedesmus in Green Bay experiments). When exposed to the mixture of the good food source with the filtrate of the toxic algae, the Baltic population had a 43% decrease in survivorship, but egg production was comparable to that of the Rhodomonas control. The filtrate treatment had a 91% survivorship in Green Bay and nearly a double increase in egg production compared to the Scenedesmus control. This leads to the need for further investigation of the effects of the intracellular and intercellular toxins on both copepod populations

A delay differential equation model on harmful algal blooms in the presence of toxic substances

The periodic nature of blooms is the main characteristic in marine plankton ecology. Release of toxic substances by phytoplankton species or toxic phytoplankton reduce the growth of zooplankton by decreasing grazing pressure and have an important role in planktonic blooms. A simple mathematical model of phytoplankton-zooplankton systems with such characteristics is proposed and analysed. As the process of liberation of toxic substances by phytoplankton species is still not clear, we try to describe a suitable mechanism to explain the cyclic nature of bloom dynamics by using different forms of toxin liberation process. To substantiate our analytical findings numerical simulations are performed and these adequately resemble the results obtained in our field study

Mikroskoopiast geenideni – kuidas tuvastada toksilisi sinivetikaid madalas eutroofses järves

A Thesis for applying for the degree of Doctor of Philosophy in Applied Biology.Väitekiri filosoofiadoktori kraadi taotlemiseks rakendusbioloogia erialal.Global warming paired with eutrophication processes is shifting phytoplankton communities towards the dominance of bloom-forming and potentially toxic cyanobacteria. Cyanobacterial blooms are considered an increasing threat in freshwater. Traditional monitoring predominantly relies on cyanobacterial biomass as an indicator of potential toxin presence, disregarding that toxin concentrations can rapidly increase even when cyanobacterial biomass is low. The concentration of toxins in the water is related to the abundance of toxin-producing species and the amount of toxin per cell – toxin quota. My research provides valuable information about the cyanobacterial community composition, the abundance of toxic genotypes, microcystin concentrations, microcystin quota and the environmental factors that promote toxic cyanobacterial blooms in the large and shallow freshwater lake Peipsi. This is the first study to utilise molecular methods as complementary to routine monitoring to determine cyanobacterial toxicity potential in lake Peipsi. In situ studies on zooplankton taxon-specific ingestion of potentially toxic cyanobacteria are still limited. My study focused on the importance of cyanobacteria as a food source for the dominant crustacean grazers. Among the first studies using qPCR targeting cyanobacterial genus-specific mcyE synthase genes in zooplankton gut content analysis, we show that potentially toxic strains of Microcystis can be ingested directly or indirectly by different zooplankton grazers. Information gathered from this study expanded our knowledge on the ecology of toxic cyanobacteria, provided an indication of how molecular methods can improve traditional risk assessment concerning the abundance of cyanobacteria and their cyanotoxins and broadened our knowledge of how target specific molecular tools could be further used in aquatic food-web studies. In the current thesis, I present a synthesis of spatial and temporal variability of potentially toxic cyanobacteria and the importance of cyanobacteria as a food source for crustacean zooplankton in large and shallow lake. The thesis is based on three published papers each dedicated to a different aspect of the whole. This thesis improves our knowledge of potentially toxic cyanobacteria and cyanotoxins in large and shallow eutrophic lakes and also provides the first insight into the in-situ consumption of toxic Microcystis by cladoceran and copepod grazers dominating in the lake. The knowledge gained from this study will guide us to further important questions that should be addressed in future research regarding the functioning of the food web of lake Peipsi. Phytoplankton community through high throughput sequencing would allow analysing the relation of cyanobacterial community composition along with concentration and diversity of cyanotoxins. This would include small-sized cyanobacteria in analysis, which are now excluded from the research. To elucidate the processes underlying cyanotoxin dynamics in more detail, further exploration focusing on the expression of toxin genes along with toxin concentration would be beneficial. Toxin gene expression could better indicate potential risks, especially in water bodies comprising mixed assemblages of toxic and non-toxic cyanobacteria.Sinivetikad ehk tsüanobakterid on üks edukaimaid elustikurühmi Maal. Ajalooliselt on nad täitnud ülitähtsat rolli rikastades Maa atmosfääri hapnikuga. Kahjuks on aga sinivetikate hulgas ka selliseid liike, kes oma elutegevuse käigus toodavad inimesele ja paljudele teistele organismidele ohtlikke mürke. Need bioaktiivsed ained on looduslikest ühenditest ühed toksilisemad. Sinivetikaõitsengud on kujunenud väga teravaks keskkonnaprobleemiks. Õitsengud mõjutavad oluliselt nii veekogu enda ökosüsteemi kui ka ökosüsteemiteenuseid ning on ohuks inimeste ja loomade tervisele. Soojem kliima ja veekogude toiteainetega rikastumine toob kaasa õitsengute intensiivistumise. Seega on järjest olulisem õitsengute varajane avastamine ja sellest tulenevate riskide hindamine. Traditsiooniliselt kasutatakse sinivetikate tuvastamiseks mikroskoopiat, aga väliste tunnuste alusel pole võimalik toksilisi ja mittetoksilisi sinivetikaid teineteisest eristada. Selliselt saadud hinnangud õitsengute toksilisusele on kaudsed, pole ennetavad ja ei täida oma eesmärki. Mürgiste ainete kogus vees on otseselt seotud toksiini tootvate sinivetikate arvukuse ja toksiini kogusega raku kohta. Siiski pelgalt sinvetikate hulgale tuginedes võime toksiinidest tulenevat riski ebatäpselt hinnata. Doktoritöös uurisin, millised seosed on tsüanobakterite liigilise koosseisu, mürgiste sinivetikate arvukuse ja toksiini kontsentratsiooni vahel nii vees kui ka rakkudes. Selgitasin välja mürgiste sinivetikate rolli erinevate zooplankterite toiduobjektina Peipsi järves. Tulemuste põhjal hindasin, millised keskkonnategurid mõjutavad toksiliste sinivetikate vohamist suures ja madalas järves. Sinivetikate toksilisuse hindamiseks kasutasin molekulaarseid meetodeid, mis on väga tundlikud ja võimaldavad hinnata riski toksilise õitsengu tekkeks juba enne õitsengu algust. Uurimistöö tulemused näitasid, et õitsengut põhjustavate sinivetikate kooslus on Peipsi järve osades erinev ning kõige enam soosib selle kujunemist nitraatide kättesaadavus ja vee temperatuur. Leidsin, et sinivetikate poolt toodetud maksamürgid – mikrotsüstiinid, on järves väga levinud ja peamiselt toodavad neid mürke sinivetikad perekonnast Microcystis. Koloonialised sinivetikad, peamiselt perekonnast Microcystis, moodustavad üllatavalt suure osa Peipsi järves domineerivate filtreerivate vesikirbuliste toidust ja seetõttu võivad just vesikirbulised olla olulised toksiinide edasikandmisel toiduahela kõrgematele tasemetele. Töö on üks esimestest maailmas, mis annab ülevaate mikrotsüstiine tootvate sinivetikate tarbimisest veekogu toiduahelas ja nende rollist vesikirbuliste toiduobjektidena. Samuti annab töö hädavajalikke eelteadmisi sinivetikamürkide võimaliku edasikandumise kohta mööda toiduahela lülisid kõrgematele troofilistele tasemetele. Käesolev uuring näitas, et töös kasutatud molekulaarsed meetodid on tänuväärne täiendus praegu kasutatavatele seiremeetoditele võimaldades hinnata mürke tootvate sinivetikate arvukust. Edasised toksiinigeenide ekspressiooniuuringud tõstavad veelgi meetodi tundlikkust ja spetsiifilisust.Publication of this thesis is supported by the Estonian University of Life Sciences

Chaotic Dynamic Analysis of Aquatic Phytoplankton System

This study analyzed the effect of nonlinear dynamic parameter of phytoplankton toxin emission on the system. Many previous studies have indicated that the zooplankton, mollusks, and habitat factors generate nonlinear chaotic dynamic behavior, which is hardly controlled random behavior. Therefore, in order to understand in what parameter conditions the system has this nonlinear behavior, the linear and nonlinear behaviors resulting from different conditions are discussed. This study used numerical analysis of differential transformation method to analyze the phase of system and applied bifurcation diagrams, trajectory diagrams, Poincaré maps, and spectrograms to discuss and validate whether the system has chaos phenomenon