A nonautonomous model for the effects of refuge and additional food on the dynamics of phytoplankton-zooplankton system

In this paper, a mathematical model for the interacting dynamics of phytoplankton-zooplankton is proposed. The phytoplankton have the ability to take refuge and release toxins to avoid over predation by zooplankton. The zooplankton are provided some additional food to persist in the system. The phytoplankton are assumed to be affected directly by external toxic substances whereas zooplankton are affected indirectly by feeding on the affected phytoplankton. We incorporate seasonal variations in the model, assuming the level of nutrients, refuge and the rate of toxins released by phytoplankton as functions of time. Our results show that when high toxicity and refuge cause extinction of zooplankton, providing additional food supports the survival of zooplankton population and controls the phytoplankton population. Prey refuge and additional food have stabilizing effects on the system; higher values of the former results in extinction of zooplankton whereas phytoplankton disappear for larger values of the latter. Seasonality in nutrients level and toxins released by phytoplankton generate higher periodic solutions while time-dependent refuge of phytoplankton causes the occurrence of a period-three solution. The possibility of finding additional food for zooplankton may push back the ecosystem to a simple stable state from a complex dynamics.     

Dynamics of nutrient-phytoplankton interaction in the presence of viral infection

The present paper deals with the problem of a nutrient-phytoplankton (N-P) populations where phytoplankton population is divided into two groups, namely susceptible phytoplankton and infected phytoplankton. Conditions for coexistence or extinction of populations are derived taking into account general nutrient uptake functions and Holling type-II functional response as an example. It is observed that the three component systems persist when the infected phytoplankton population is not able to consume nutrient.     

台湾海峡小型浮游植物的物种多样性和分布特征

在整合两岸学者有关台湾海峡的浮游植物物种多样性研究的基础上, 作者提出了一份台湾海峡小型浮游植物物种名录, 共包含620种, 并按照其生态类群和赤潮种类进行了区分。同时以1984年5月至1985年2月在福建海岸带和台湾海峡共86个观测站四个季度月浮游植物的344份调查资料为基础, 来阐明物种分布的基本格局和丰度变化的时空趋势。结果表明: 此次调查所鉴定的299种浮游植物中硅藻门为199种, 其丰度占浮游植物丰度的99.25%, 对本海区浮游植物的分布起支配作用。浮游植物的种类数和丰度年高峰均在夏季。就平面分布而言, 海峡区的种类数多于近岸区, 与海水的温度和盐度成正相关关系; 而近岸区的丰度高于海峡区, Shannon-Wiener指数和均匀度则是海峡区高于近岸区。     

筼筜湖浮游植物细胞裂解率的时空变化

酶测定法作为现场测定浮游植物裂解速率的方法已被广泛应用于各种水体环境中。本论文对厦门市筼筜湖的浮游植物裂解速率的时空变化展开调查,探讨了浮游植物裂解速率的时空变化及其影响因素。调查期间,测定了内湖与外湖的溶解性酯酶活性,颗粒态酯酶活性及浮游植物裂解速率,同时测定了水体的叶绿素浓度及其他环境参数。综合分析各种指标,结果显示:浮游植物细胞裂解速率在空间上变化不大,时间上变化较大。在七月份由于水体中的病毒含量较高,浮游植物裂解速率较高。裂解速率在八月份与九月份降低,并且其数值变化不大。     

Novel interactions between phytoplankton and microzooplankton: their influence on the coupling between growth and grazing rates in the sea

Understanding the processes that regulate phytoplankton biomass and growth rate remains one of the central issues for biological oceanography. While the role of resources in phytoplankton regulation (`bottom up' control) has been explored extensively, the role of grazing (`top down' control) is less well understood. This paper seeks to apply the approach pioneered by Frost and others, i.e. exploring consequences of individual grazer behavior for whole ecosystems, to questions about microzooplankton–phytoplankton interactions. Given the diversity and paucity of phytoplankton prey in much of the sea, there should be strong pressure for microzooplankton, the primary grazers of most phytoplankton, to evolve strategies that maximize prey encounter and utilization while allowing for survival in times of scarcity. These strategies include higher grazing rates on faster-growing phytoplankton cells, the direct use of light for enhancement of protist digestion rates, nutritional plasticity, rapid population growth combined with formation of resting stages, and defenses against predatory zooplankton. Most of these phenomena should increase community-level coupling (i.e. the degree of instantaneous and time-dependent similarity) between rates of phytoplankton growth and microzooplankton grazing, tending to stabilize planktonic ecosystems. Conversely, phytoplankton, whose mortality in the sea is overwhelmingly due to microzooplankton grazing, should experience strong pressure to evolve grazing resistence. Strategies may include chemical, morphological, and `nutrient deficit' defenses. Successful deployment of these defenses should lead to uncoupling between rates of phytoplankton growth and microzooplankton grazing, promoting instability in ecosystem structure. Understanding the comparative ecosystem dynamics of various ocean regions will require an appreciation of how protist grazer behavior and physiology influence the coupling between rates of phytoplankton growth and microzooplankton grazing.     

The influence of the accuracy of sampling and processing methods on the parameters of the phytoplankton community of Rybinsk reservoir

The influence of the sampling and processing-method accuracy on the bioindication parameters of the taxonomic and size structure of the phytoplankton community, fluorescence, and saprobic index has been studied in Rybinsk Reservoir. The studied parameters have been ranked in accordance to their sensitivity to the method accuracy. The comparative analysis of the relative errors of the studied parameters has been performed for Rybinsk Reservoir and the White Sea phytoplankton communities. Recommendations about the most useful parameters to assess the status of the phytoplankton community are given.     

Phytoplankton of the Amga River and chemical composition of the water: Contemporary state

This is the first study of phytoplankton of the full length of the Amga, a large river crossing Central and Southern Yakutia. The study has revealed characteristics of phytoplankton assemblages and formation of the hydrochemical regime of the river. We conducted a complex assessment of the water quality based on physicochemical indices, saprobic algae, and phytoplankton biomass. The results can serve as reference data for monitoring the river status during the operation of the East Siberia-Pacific Ocean oil pipeline.     

Compensatory dynamics and the stability of phytoplankton biomass during four decades of eutrophication and oligotrophication

The link between compensatory dynamics and regime shifts is not well understood. We analyse a regime shift in phytoplankton in a large lake with respect to: (1) environmental forcing and (2) the type of dynamics (compensatory or synchronous) between phytoplankton groups. The regime shift in phytoplankton was related to gradual changes in nutrient levels, but unrelated to an almost concurrent shift in climatic conditions. The relationship between total phytoplankton biomass and phosphorus concentrations was sigmoid. Trajectories of phytoplankton biomass and community dynamics suggest that eutrophication effects can successfully be reversed when management efforts decrease nutrient loading to a level sufficiently low to overcome community resilience. The regime shift was associated with a loss of biomass compensation and compensatory dynamics among the phytoplankton groups. This suggests that the type of interactions is important for a better understanding of the existence and shape of nonlinear responses of phytoplankton biomass to environmental change.     

Hypertrophic phytoplankton and the Intermediate Disturbance Hypothesis

The provisions of Connell's Intermediate Disturbance Hypothesis (IDH) were investigated in relation to the behaviour of freshwater phytoplankton in a hypertrophic lagoon, paying special attention to the link between species-diversity and environmental disturbances. Phytoplankton diversity yielded different indices depending on the basic unit of calculations (cells, particles, phytoplankton units, biomass). Although their ranges were approximately equal, they did not covary so could not be considered mutually substitutable. For the purpose of IDH testing, biomass diversity was chosen.Equilibrium states were considered to obtain in those periods with a very high fraction of total phytoplankton biomass, shared by no more than three phytoplankton species. Disturbances were considered as counterparts of equilibrium states. Disturbance factors were mostly abiotic, environmental features of the lake operating on the phytoplankton community at different time scales (co-occurring and with 1- and 2-weeks' lags). These scales may relate to the time required to establish phytoplankton community structure.IDH could be suspected not to hold for the phytoplankton of this hypertrophic lake, which experienced seven near-equilibrium phases and six disturbance periods throughout the study. As a rule, equilibrium states lasted longer than disturbance periods. The expected relationships between both disturbance intensity or frequency were not shown. Furthermore, no relationship was demonstrated between diversity (and hence IDH) and the phytoplankton community change rate. Wind stress probably played a minor role in triggering disturbance events. Disturbances were shown partly to promote small-sized phytoplankton communities.Finally, a plea for studying hypertrophic phytoplankton in greater detail is stressed if its responses to disturbances are to be fully understood.     

一座南亚热带小型贫营养水库浮游植物群落结构及季节变化

库容大小是影响水体水动力学过程的一个重要变量,它能在很大程度决定生态系统的结构,特别是浮游植物的群落结构.为了解小型贫营养水库浮游植物的群落特点,于2006年4、8、12月对位珠海市的贫营养小型水库-吉大水库的浮游植物群落结构进行采样和计数分析.3次采样共检出浮游植物32种,浮游植物细胞丰度的变化范围在69～342 cells·mL^-1,生物量的变化范围在1.34～3.69 mg·L^-1,夏季浮游植物的丰度和生物量明显高于冬季.甲藻是最主要的优势种类,且相对优势度较为稳定.夏季,隐藻门的隐藻(Cryptomonas sp.)和绿藻门的鼓藻(Cosmarium spp.)大量出现,甲藻的相对优势度有所降低.冬季,隐藻数量急剧下降,但硅藻门的颗粒直链藻(Aulacoseira granulata)大量出现,与甲藻共同成为水体中的优势种.由降雨引起的营养盐浓度增加是浮游植物变化的主要影响因子,而透明度全年维持较高的水平为浮游植物的生长形成了有利条件,此外,较为稳定的水体和甲藻利用营养盐的能力使得甲藻成为浮游植物中的最主要的优势种.     

Use of marker pigments and functional groups for assessing the status of phytoplankton assemblages in lakes

Phytoplankton is a key biological quality element for the establishment of the Water Framework Directive (WFD) ecological status in reservoirs and lakes. In freshwaters, inverted microscope examination is the traditional standard method for estimating phytoplankton and assessing taxonomic composition. Based on the enumeration of algal units and measurements for biovolume calculation, this technique is cumbersome and time-consuming. In large monitoring programmes, such as the application of the WFD in lakes and reservoirs, chemotaxonomy (HPLC pigment analysis and CHEMTAX treatment) is ideally suited as an alternative method because it allows the rapid processing of large numbers of samples from numerous locations and depths, thereby providing ideal temporal and spatial resolution. The low taxonomical detail obtained by HPLC and CHEMTAX (phytoplankton classes or phyla) can easily be overcome by a rapid inverted microscope screening with identification of the dominant species. Combining HPLC and microscopy provides a useful method for monitoring phytoplankton assemblages, which can be used to implement the WFD with respect to phytoplankton. Here, we present the application of a method combining marker pigments and microscopy to phytoplankton samples from 12 Belgian reservoirs. This method substantially reduced the workload and enabled us to assess the status of the phytoplankton assemblage in these lakes. The method complies with the WFD, as it takes into account taxonomic composition, assesses abundance and biomass of the phytoplankton taxa, and easily detects blooms. Additionally, a set of templates of probability of occurrence of phytoplankton functional groups at the maximal ecological potential for reservoirs from the Central/Baltic region is presented, based on reference conditions defined for natural lakes from other regions.     

Microzooplankton grazing and the control of phytoplankton biomass in the Suwannee River estuary,USA

Microzooplankton grazing can have significant impacts on the distribution and abundance of phytoplankton, thereby influencing the frequency and duration of algae blooms. Observations of high ciliate abundances in the Suwannee River estuary, Florida, suggest a significant potential for top-down pressure on the phytoplankton community by microzooplankton. We examined the composition of the microzooplankton and determined grazing mortality losses for phytoplankton within the Suwannee River estuary from 2001 to 2002. Our results indicated grazing mortality rates of 1.4 d⁻¹, equivalent to a loss of up to 76% of phytoplankton standing crop and up to 83% of total daily primary production. The microzooplankton community was primarily composed of ciliates, dinoflagellates, and copepod nauplii. The densities of ciliates in the estuary were comparable to densities reported in highly eutrophic ecosystems (9,400–72,800 ciliates l⁻¹). Grazing pressure on small phytoplankton may be further enhanced because ciliates and small dinoflagellates have growth rates similar to those of phytoplankton, and therefore can keep up with surges in abundance. Handling editor: Judit Padisak     

Phytoplankton biodiversity in the two perennial lakes of Coimbatore,Tamil Nadu,India

The present study was focused to evaluate the phytoplankton biodiversity in two freshwater perennial lakes of Sulur and Ukkadam of Coimbatore District, Tamil Nadu, India. The study period was two years from March 2012 to February 2014. Results revealed that totally 50 species of phytoplankton include 14 Cyanophyceae, 19 Chlorophyceae, 14 Bacillariophyceae, and 3 Euglenophyceae were recorded from the Sulur lake and 36 species of phytoplankton comprising 9 species of Cyanophyceae, 15 species of Chlorophyceae, 10 species of Bacillariophyceae and 2 species of Euglenophyceae were noticed in Ukkadam lake during the study period. The recorded phytoplankton density was ranged between 22,380 and 80,590 cells/l in Sulur lake and 29,350 and 1,16,255 cells/l in Ukkadam lake. Thus, the present study overall dominance of phytoplankton group was Chlorophyceae followed by Cyanophyceae, Bacillariophyceae, and Euglenophyceae. The phytoplankton population was recorded maximum in Ukkadam lake when compared to Sulur lake. Hence, the study revealed that both Ukkadam and Sulur lakes possess an appreciable quantum of phytoplankton and it can be used for fish culture.     

Herbivores and the Spatial Distributions of the Phytoplankton. I. The Plankton Market

Planktonic herbivores forage on phytoplankton cells which were produced at some earlier time and at a distant place. A steady state, one dimension model of the birth, death and eddy diffusion of phytoplankton illustrates phytoplankton smooth both temporal and spatial variations as they are transported. When the eddy diffusivity is k and the phytoplankton doubling time is b, the average distance traveled by a phytoplankton cell is (kb)^1/2 and the average time spent doing so is b. Only those spatial variations with wavelengths greater than 2π(kb)^1/2 and temporal variations with periods greater than 2πb will be observed in the phytoplankton distributions at more than half their original amplitude. Both k and b control the length scale of phytoplankton distributions in a cartesian coordinate system. Planktonic herbivores view the phytoplankton from a diffusing coordinate system in which the spatial scales of the phytoplankton distribution are transformed into time scales.     

An Examination of Cell Volume in Dominant Phytoplankton Species of the Central and Southern Adriatic Sea

The phytoplankton biomass expressed as total cell volume is often of doubtful value due to cell size and volume variations in the organisms present. Cell volume calculations for 95 phytoplankton species and volume-frequency diagrams for 25 dominant species were analyzed for the Adriatic Sea. Recommendations for more precise work dealing with phytoplankton cell volume and biomass are given. Temporal variations in the average microplankton cell volume are presented and discussed.     

长江口北支浮游植物群落结构周年变化特征

2010年10月至2011年9月对长江口北支水域的浮游植物进行周年调查,共采集到183种（包括变种和变型）,隶属于7门60属,其中硅藻门种类最多,有35属137种,占浮游植物总种类数的75%。周年优势种为具槽直链藻、中肋骨条藻、条纹小环藻、两栖颤藻、小伪菱形藻双楔变种、颗粒直链藻和小环藻未定种。本次调查中,季节间浮游植物的丰度差异不显著（P〉0.05）,但各月间浮游植物丰度差异显著（P〈0.05）,全年丰度在2.83×10^3～6.18×10^4cells/L之间,其中6月的丰度最高,1月的丰度最低,全年的平均丰度为1.73×10^4cells/L。Pearson相关性分析显示,浮游植物丰度与硝酸盐浓度显著正相关（P〈0.05）,与氨氮浓度极显著正相关（P〈0.01）,含氮营养盐对浮游植物的影响明显。     

巢湖双桥河底泥疏浚过程中浮游植物功能群分类研究

浮游植物功能群分类分析可以精确地反映水体环境变化对水生生物群落的影响。为探究巢湖双桥河底泥疏浚工程对浮游植物群落及水生生态系统的影响,对2017年6月—2018年3月双桥河底泥疏浚期间的水体理化因子、浮游植物群落结构和功能群划分开展了研究。研究发现,底泥疏浚工程能够大量削减双桥河水体中的氮、磷营养盐,但疏浚后的双桥河仍处于中-富营养状态;双桥河浮游植物群落依据其生态功能可划分为M、H1、H2、MP、S1、L_O、X2、X1、J、F、N、G、X3、C、D、Y、W1、L_M、E、T、S_N、K、P等23个功能群,绝对优势功能群为以微囊藻为主的M功能群和以硅藻为主的MP、P功能群。底泥疏浚工程对双桥河浮游植物种类的影响不大,但藻类密度和生物量在疏浚后有显著地下降,浮游植物多样性指数也有提升。将浮游植物功能群生物量与环境因子进行冗余分析(RDA)和Pearson分析发现,水环境因子变化对双桥河浮游植物功能群产生了较大影响,双桥河浮游藻类优势功能群由底泥疏浚前的M、MP、P、W1、Y类转变为底泥疏浚后的C、F、J、M、MP、P、Y类。其中,底泥疏浚工程造成的氮营养盐削减可以对双桥河浮游植物功能群产生较大影响。研究认为双桥河底泥疏浚工程在改善河流浮游植物生态功能,减轻水体污染程度上有积极的作用。     

Structural Compositions of Pelagic Communities in the River Warnow and their Changes

The phytoplankton and heterotrophic microbial communities from the Oberwarnow and Unterwarnow were analyzed from November 1987 to May 1988. The production potential of the microorganisms was quantified in laboratory experiments. On the average, phytoplankton accounted for 73 % of the total biomass in the Oberwarnow and 59 % in the Unterwarnow. The corresponding figures for bacterial biomass were 24 % and 33 %, respectively. If the nutrient supply is unlimited and phytoplankton biomass predominates, the development of primary producers in eutrophic to polytrophic waters is not regulated by metazooplankton. Top-down regulation is possible only if prevailing conditions limit the growth of the dominant phytoplankton species.     

The structure and dynamics of phytoplankton assemblages from the inner part of the Thermaikos Gulf,Greece. I. Phytoplankton composition and biomass from May 1988 to April 1989

Qualitative and quantitative analyses of phytoplankton from the inner part of Thermaikos Gulf were carried out in the period May 1988–April 1989. A total of 154 taxa were identified in the phytoplankton. the monthly values of the phytoplankton biomass ranged between 614 and 6700 mg/m³ (wet weight). The seasonal development of the phytoplankton biomass exhibited three peaks. Diatoms, dinoflagellates and cryptophytes were the most important constituents of the gulf phytoplankton. Throughout the year, five different phytoplankton assemblages were distinguished.     

Warming alters the size spectrum and shifts the distribution of biomass in freshwater ecosystems

Organism size is one of the key determinants of community structure, and its relationship with abundance can describe how biomass is partitioned among the biota within an ecosystem. An outdoor freshwater mesocosm experiment was used to determine how warming of～4 °C would affect the size, biomass and taxonomic structure of planktonic communities. Warming increased the steepness of the community size spectrum by increasing the prevalence of small organisms, primarily within the phytoplankton assemblage and it also reduced the mean and maximum size of phytoplankton by approximately one order of magnitude. The observed shifts in phytoplankton size structure were reflected in changes in phytoplankton community composition, though zooplankton taxonomic composition was unaffected by warming. Furthermore, warming reduced community biomass and total phytoplankton biomass, although zooplankton biomass was unaffected. This resulted in an increase in the zooplankton to phytoplankton biomass ratio in the warmed mesocosms, which could be explained by faster turnover within the phytoplankton assemblages. Overall, warming shifted the distribution of phytoplankton size towards smaller individuals with rapid turnover and low standing biomass, resulting in a reorganization of the biomass structure of the food webs. These results indicate future environmental warming may have profound effects on the structure and functioning of aquatic communities and ecosystems.