Studies on Plover Cove Reservoir, Hong Kong

The four periphytic communities established in Plover Cove Reservoir (the epiphyton, epihthon, epipelon and epipsammon) were investigated between November, 1970 and December, 1971. A rich flora of diatoms was found to dominate all four peri-phytic communities, and, for this reason, assessment of diatom numbers was used to monitor each community during this survey. The standing crop of each community, measured by cell counts and by chlorophyll a determinations, showed distinct seasonal patterns. Except for the epipsammon, each community displayed a maximum growth in winter, a moderate spring and autumn growth period and a low summer growth. The episammic flora stood apart from the other attached floras in that it exhibited a prolonged maximum growth period in summer. Relatively small numbers of species were found to form the main bulk of all four communities (the so-called ‘constant forms’) and these belonged predominantly to the pennate genera Achnanthes, Fragilaria, Nitzschia and Synedra.     

Ecology of the Major Periphytic Diatom Communities from the Mesta River,Bulgaria

Epilithon, epiphyton, epipelon, epipsammon and plocon diatom samples and water chemistry samples were collected bimonthly from 11 stations along the Mesta River, Bulgaria between December 1989 and April 1991. Principal component analysis (PCA), correlation, and dominance analysis were employed for describing the seasonal dynamics of diatom assemblages and estimating the correlation between diatom distribution and the physico-chemical parameters. All periphytic communities were compared by PCA, MANOVA and Fisher's LSD multiple comparison test. Ionic strength and eutrophication were the major abiotic factors affecting diatom distribution in the epilithon, epiphyton, epipelon and epipsammon. Current velocity had an important influence on the diatom assemblages from the epilithon and epiphyton. Epilithon showed the lowest correlation with most of the environmental factors and had significantly lower species diversity than epiphyton, epipelon and epipsammon. Multivariate analysis of the diatom data suggested that in all benthic habitats of the Mesta River seasonal replacement of diatom assemblages was controlled by the water chemistry rather than substratum, current velocity or discharge. The oligotrophic, mesotrophic and eutrophic diatom communities in the Mesta River comprised early-, mid- and late-successional colonizers respectively. Multiple comparisons of all periphytic communities showed that habitat specificity was positively correlated with current velocity.     

Developing biomonitoring protocols for shallow Arctic lakes using diatoms and artificial substrate samplers

Growing concerns over effects of climate warming and other stressors on shallow Arctic lakes and ponds stimulate the need to develop and implement effective protocols to track changes in ecological integrity. This study assesses seasonal and spatial variability of periphytic diatom communities in a shallow Arctic lake in northern Yukon Territory to establish biomonitoring protocols. Artificial substrate samplers, which mimic macrophytes, allow direct measurement of biotic responses to shifting environmental conditions and control for possible confounding factors (e.g., accrual time and microhabitat type). Artificial substrate samplers were deployed at three locations and retrieved at three times (early, mid, and late) during the ice-free season. Analyses identified that diatom abundance increased exponentially and community composition changed significantly over the ice-free season, despite little variability in water chemistry, but did not differ among the three sampling locations within the lake. Patterns of seasonal succession in diatom community composition were characterized by first arrival of well-dispersed taxa, which included several planktonic taxa, followed by a transitional phase composed of planktonic and periphytic taxa, and culminated with dominance by periphytic species, mainly Achnanthes minutissima (Kützing). Results highlight the role of seasonal succession on artificial substrate colonization and the need to deploy artificial substrate samplers for the duration of the ice-free season to capture peak periphytic algal abundance. Low spatial variability of shallow Arctic lakes allows for samplers to be deployed at one single location to characterize diatom community composition.     

空间层次及人工基质对着生藻类建群特性的影响

为全面了解着生藻类在建群中群落变化的生态学特性,揭示着生藻类的建群规律,在以丝状藻类为优势藻的生态塘中,采用花岗岩和瓷砖为附着材料,设置水体底部和中部为附着位点,进行频次为10d的采样分析。结果表明,生态塘中共检出8门73属117种着生藻类,其中以硅藻、蓝藻、绿藻为优势类群。同时不同人工基质和不同空间层次条件下着生藻类的建群特征较一致,早期以单细胞硅藻如舟形藻(Navicula sp.)、脆杆藻(Fragilaria sp.)、曲壳藻(Achnanthes sp.)等为优势,后期以丝状藻类如鞘丝藻(Lyngbya sp.)、颤藻(Oscillatoria sp.)、伪鱼腥藻(Pseudanabaena sp.)等为优势;研究结果发现不同人工基质(花岗岩和瓷砖)对着生藻类的种类组成、细胞密度、生物量和藻类多样性无显著影响,花岗岩和瓷砖上附着的着生藻类具有较高的相似性;但不同的空间层次对着生藻类建群特征影响明显,水体底部具有更多的硅藻种类数,中部具有更多的绿藻,随着建群时间的发展,蓝藻比例不断增加;就生物量而言,底部的着生藻类叶绿素a显著高于水体中部,但两者的细胞密度无显著性差异;随着建群过程的发展,水体底部的着生藻类生物量达峰值所需的时间比中部更长。通过相关性分析,生态塘中着生藻类的生长主要受总磷的影响。     

Seasonal succession of lotic epiphyton: effects of macrophyte cover and grazing by chironomid larvae

The epiphyton is a community of periphyton on the aquatic plants. The seasonal dynamics of biomass, production and community structure of epiphytic algae on Potamogeton perfoliatus was studied at the Moscow River reach with low flow velocity from May to October 2000. The relative importance of physical-chemical environmental variables and herbivorous pressure in structuring the epiphyton community was accessed using multivariate redundancy analysis. Algal composition was mainly determined by the macrophyte cover, suggestion the overriding importance of the underwater light availability in seasonal development of epiphyton. There was a significant positive relationship between biomass of attached diatom Cocconeis placentula and abundance of chironomid larvae (r = 0.57; p < 0.01). This indicates that increase in herbivorous pressure caused the shift in epiphyton community structure. However, the intensity of herbivorous impact on epiphyton was ultimately determined by light availability in macrophyte stands. At low irradiance level and consequent slow growth of algae the upper layer of epiphyton was seriously destroyed by chironomids that resulted in dominance of C. placentula. As irradiance level and epiphyton productivity increased chironomids were unable to prevent biomass accumulation of the upper layer thus inhibiting the growth of C. placentula. The high concentrations of nutrients and relatively stable discharge determined the crucial role of light regime in the regulation of trophic interactions between epiphyton and chironomid larvae.     

The ecology of periphytic rotifers

The ecology of rotifer assemblages in the periphyton has received little attention relative to that of pelagic rotifers. This paper reviews the ecology of periphytic rotifers, with particular emphasis on the role of macrophytes in the structuring of rotifer assemblages spatially and temporally, and compares these aspects with the dynamics of better known pelagic rotifer communities. Littoral rotifer periphyton communities are typically diverse in lakes, and have composition dissimilar to that of the open water. In rivers, diversity and composition in the pelagic and littoral appear to be similar. Rotifers show preference for macrophyte species they associate with, probably through differences in physical structure or complexity, food concentration or composition, chemical factors, macrophyte age, and differences in the degree of protection from predation provided by macrophytes. These mechanisms are in general not well investigated in rotifers. Factors affecting the seasonal dynamics of periphytic communities appear to be similar to pelagic communities, with seasonal dynamics of substrates and disturbance by flooding or drying also being important.     

Littoral diatoms as indicators for the eutrophication of shallow lakes

The littoral zone of shallow water bodies in the Czech Republic has been studied quite consistently at several fishponds. The use of algae, especially diatoms, for the monitoring of the state of lotic freshwater also has a long tradition. The main objective of the presented paper is to validate the feasibility of the use of littoral periphyton comunities for the biomonitoring of standing waters. At the investigated sites, littoral periphytic diatoms were studied together with selected enviromental variables (pH, conductivity, nutrients – especially total phosphorus) on three types of natural substrates (epilithon, epiphyton, epipelon). The evaluation of the diatom community was performed on the basis of the checklists of algal indicator species published by authors from the Czech Republic, Austria and the Netherlands. The data were subjected to statistical software NCCS 2000 (GLM Anova and ``Ward's minimum'' variance cluster analysis). Littoral periphytic diatoms appear to be good indicators of the fishpond water quality. The selected substrates show non-significant differences therefore the average values from all substrates were used. The best indicatory system for evaluation of Czech fishponds was van Dam's index.

     

Seasonality and distribution of epilithic diatoms,macroalgae and macrophytes in a spring-fed stream system in Ontario,Canada

A study of the epilithic diatom, macroalgal and macrophyte communities from a spring-fed stream in Ontario, Canada was undertaken from September 1996 to July 1997. The relative abundance of the epilithic diatom flora, percent cover of macroalgal and macrophyte taxa, and several physical and chemical stream conditions were monitored along a 20-m stretch at each of four sites, approximately every 2 months. Several stream conditions were relatively constant over the sampling period (pH, maximum width and maximum depth), while others exhibited a distinct seasonal pattern (water temperature, specific conductance and daylength) and some fluctuated strongly with no discernable seasonal pattern (turbidity, current velocity). A total of 124 taxa were identified from the four sites, including 79 epilithic diatoms, three macroalgal diatom species (large gelatinous masses), one cyanobacterium, two red algae, eight green algae, one chrysophyte alga, one tribophyte alga, three mosses, three horsetails and 23 angiosperm taxa. Species richness was positively correlated to stream channel maximum width and depth, indicating that the total number of species tends to increase in a downstream direction. Distribution of several diatom and macroalgal species was significantly correlated to stream conditions (e.g. Gomphonema parvulum and Phormidium subfuscum with current velocity); however, the vast majority of species did not display seasonal variation in abundance that could be explained by changes in stream conditions. Many of the taxa identified from Blue Springs Creek are common elsewhere in North America.     

Studies on the ichthyo-fauna in Plover Cove Reservoir, Hong Kong: I. Sequence of fish population changes

Gill-net surveys were made weekly from May 1971 to April 1974 in Plover Cove Reservoir, Hong Kong and the results analysed to determine the fish species composition in the reservoir, the seasonal fluctuation of catches and the length frequency distribution of some major species.
Over 20 species were represented in the fish fauna including almost all the naturally occurring species as well as the stocked species. Of the twenty species, some were collected regularly in gill-net samples while others occurred rarely. Sarotherodon (Tilapia) mossam-bicus (Peters) was the dominant species and contributed the main bulk of the catch. This species also showed distinct age groups in the reservoir and modal changes occurred seasonally. Thus, among the fish species studied only S. mossambicus showed a steady and progressive increase in abundance in the reservoir and the full development of this fish population with its wide range of feeding habits should be beneficial.     

Experimental Analysis of Grazing by the Mayfly Meridialaris chiloeensis on Different Successional Stages of Stream Periphyton

In this study we determined grazing effects of the South Andean endemic mayfly Meridialaris chiloeensis on periphyton at different stages of successional development. Grazing effects were studied through a two‐factor experimental design (colonization stages X grazer density) in a stream‐side channel in spring and winter. Our results showed an absence of proportionality between grazer density and periphyton decline in response to grazers at low and intermediate levels of periphytic biomass; however, when periphyton biomass was high a direct inverse relationship was observed between post‐grazing biomass and grazer density. The relationship between periphytic algae (chlorophyll a concentration) and periphyton (total periphytic ash‐free dry mass) (C/OM index) was used as an estimation of the autotrophic fraction in the total periphyton matrix. Grazing did not alter the C/OM index indicating that both autotrophic and heterotrophic fractions of the periphyton components were reduced in the same proportion. Ordination of samples using the relative abundance of diatom species showed that herbivore effect was less evident at intermediate and late stage of colonization than at early one. These results support the statement that the outcome of the herbivore‐periphyton interaction may depend on the successional stage of the periphyton community. In spring Fragilaria pinnata relative abundance, on the basis of cell counts, was reduced by grazing and Nitzschia palea was enhanced. In the winter experiment, grazing decreased Achnanthes minutissima relative abundance. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Laboratory experiments on the impact of biofilms on the plankton of a large river

1. Benthic organisms can have a strong effect on the plankton in rivers, although normally only members of the macrofauna are considered as important consumers. In the present study we conducted experiments on four different dates (in December, March, June and September) to assess the potential role of periphytic heterotrophic flagellates (HF), ciliates and rotifers in the control of potamoplankton (bacteria, algae, HF and ciliates). 2. Natural periphyton was established on the walls of circular flow channels by exposing them to river water (River Rhine, Germany). The experimental channels (with periphyton) and control channels (without periphyton) were filled with riverine water and the increase rates of planktonic bacteria, algae, HF and oligotrich ciliates were determined for the two treatments. 3. The abundance of periphytic ciliates and rotifers at the beginning of the four experiments showed large differences with low values in December and March, and high values in June and September. Dominant potential consumers of plankton were the heterotrich ciliate Stentor sp. and bdelloid rotifers. 4. The rates of increase of planktonic algae, HF and ciliates were significantly smaller in the presence of periphyton compared with those in their absence. Significant interactions between the treatment (with and without periphyton) and the time of experiment were found for the planktonic HF and algae, indicating that the impact of the periphyton varied temporarily. The planktonic groups responded differently to the periphyton with the planktonic HF showing the highest loss rate. Significant differences were also found among the loss rates of different HF groups and different diatom size classes. 5. These laboratory experiments demonstrate that periphytic ciliates and rotifers are potentially important consumers of different planktonic groups. The quantitative impact of periphyton on plankton with respect to the selective feeding needs further attention.     

西湖湖西浮游与着生藻类季节变化及相互关系

2014年11月至2015年8月调查了西湖湖西沿岸带浮游藻类和不同基质(植物、石块和底泥)上着生藻类的群落结构及季节变化, 分析了着生丝状藻与浮游丝状藻的相互关系以及它们与环境因子的相关性, 探讨湖西生态修复过程中季节性暴发的丝状藻水华的原因。结果表明浮游藻类和植物、底泥、石头上着生藻类中均以硅藻门种类数(分别占52.5%、60.4%、86.7%和72.7%)最多, 蓝藻门(分别占10.1%、8.9%、6.7%和15.2%)和绿藻门(分别占26.3%、19.8%、5.6%和10.6%)次之, 其他门类相对较少, 浮游藻类与着生藻类优势种季节差异较大。附植丝状藻密度显著高于附泥和附石丝状藻, 且狐尾藻上着生丝状藻密度与浮游丝状藻密度呈显著正相关, 表明狐尾藻着生丝状藻可能是浮游丝状藻较重要的来源之一, 该结果可为西湖丝状藻水华的控制提供一些参考。相关性分析表明, 着生藻类和丝状藻与各理化因子(水深、透明度、溶解氧、水温、pH、TN、SRP、TP等)均无显著相关性。     

Periphyton growth and diatom community structure in a cooling water pond

Periphyton (Aufwuchs) accumulation was measured on artificial substrates in a pond in central Finland which receives warm cooling-water effluent from a power plant. The growth of periphyton was generally more rapid on the substrates during the first two weeks of colonization near the inflow of the warm water effluent than in the middle of the pond. The maximum accumulation of periphyton was in spring and autumn (dry weight maximum at warm effluent was in spring 3.5 mg DW cm⁻²,2.65 mg AFDW cm⁻²; chlorophyll a maximum 3.96 μg cm⁻² was found in autumn at pond-middle station). During mid-winter months the growth was strongly limited by solar radiation, but the growth was also slow at both stations in the summer months, when the power plant was out of operation. The periphyton accumulation rate was fastest near the water surface and decreased rapidly with increasing depth. A total of 167 diatom species were found in periphyton samples. However, most species were rare; many of the dominants were common to both plankton and periphyton. Species similarity analyses (Jaccard's similarity) between 10 different diatom communities (including periphyton from 9 different types of substrates and phytoplankton) indicated low similarity index values although differences between communities were not significant.     

The use of simultaneous sampling bottle and vertical net collections to describe the dynamics of a zooplankton population

Simultaneous collections of zooplankton were made at four stations in the Plover Clove Reservoir using Friedinger sampling bottles and vertical Nakai plankton net hauls. Comparison of the results obtained revealed certain obvious numerical and spatial anomalies, and it is suggested that these result from inherent characteristics of the two types of apparatus together with behavioural responses and physical attributes of the individual zooplankton species. Statistical correlation between these two methods was generally good in terms of the seasonal patterns of distribution of the population, but in terms of depth distribution and the relative abundance of the individual species of the population few significant correlations resulted. It is therefore suggested that unless merely seasonal trends are required, it is advisable to use more than one sampling apparatus to obtain valid data concerning the overall dynamics of such a zooplankton population.Department of Botany, University of Hong Kong     

Comparative study of periphyton community structure in long and short-hydroperiod Everglades marshes

The Florida Everglades is a mosaic of short and long-hydroperiod marshes that differ in the depth, duration, and timing of inundation. Algae are important primary producers in widespread Everglades’ periphyton mats, but relationships of algal production and community structure to hydrologic variability are poorly understood. We quantified differences in algal biomass and community structure between periphyton mats in 5 short and 6 long-hydroperiod marshes in Everglades National Park (ENP) in October 2000. We related differences to water depth and total phosphorus (TP) concentration in the water, periphyton and soils. Long and short-hydroperiod marshes differed in water depth (73 cm vs. 13 cm), periphyton TP concentrations (172μg g⁻¹ vs. 107 μg g⁻¹, respectively) and soil TP (284 μg g⁻¹ vs. 145 μg g⁻¹). Periphyton was abundant in both marshes, with short-hydroperiod sites having greater biomass than long-hydroperiod sites (2936 vs. 575 grams ash-free dry mass m⁻²). A total of 156 algal taxa were identified and separated into diatom (68 species from 21 genera) and “soft algae” (88 non-diatom species from 47 genera) categories for further analyses. Although diatom total abundance was greater in long-hydroperiod mats, diatom species richness was significantly greater in short- hydroperiod periphyton mats (62 vs. 47 diatom taxa). Soft algal species richness was greater in long-hydroperiod sites (81 vs. 67 soft algae taxa). Relative abundances of individual taxa were significantly different among the two site types, with soft algal distributions being driven by water depth, and diatom distributions by water depth and TP concentration in the water and periphyton. Periphyton communities differ between short and long-hydroperiod marshes, but because they share many taxa, alterations in hydroperiod could rapidly promote the alternate community. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Seasonal variations of metal concentrations in periphyton and taxonomic composition of the algal community at a Yenisei River littoral site

The concentrations of metals K, Na, Ca, Mg, Fe, Mn, Zn, Cu, Ni, Pb, Co and Cr, in the water and periphyton (epilithic algal communities) were studied at a site in the middle stream of the Yenisei River (Siberia, Russia) during three years using monthly sampling frequencies. Despite considerable seasonal variations in aquatic concentrations of some metals, there was no correlation between metal contents in the water and in periphyton. Seasonal concentration variations of some metals in periphyton were related to the species (taxonomic) composition of periphytic microalgae and cyanobacteria. Enhanced levels of Ni and Co in periphyton in late autumn, winter, and early spring were likely caused by the predominance of cyanobacteria in the periphytic community, and annual maximum levels of K in periphyton in late spring and early summer were attributed to the domination of Chlorophyta, primarily Ulothrix zonata.     

Cadmium and lead toxicity on tropical freshwater periphyton communities under laboratory-based mesocosm experiments

Periphyton constitutes an important community that is useful for assessment of ecological conditions in lotic systems. The objective of this study was to assess the effects of different mixtures of Cd and Pb on periphyton growth as well as Cd and Pb mixtures toxicity to diatom assemblages in laboratory mesocosm experiments. A natural periphyton community sampled from the Monjolinho River (South of Brazil) was inoculated into five experimental systems containing clean glass substrates for periphyton colonization. The communities were exposed to mixtures of dissolved Cd and Pb concentrations of 0.01 and 0.1 mg l⁻¹ Cd and 0.033 and 0.1 mg l⁻¹ Pb. Periphyton ash-free dry weight, growth rate, diatom cell density and diatom community composition were analyzed on samples collected after 1, 2 and 3 weeks of colonization. High Cd concentration (0.1 mg l⁻¹) has negative effects on periphyton growth while high concentration of Pb (0.1 mg l⁻¹) decreased the toxic effects of Cd on periphyton growth. Shifts in species composition (development of more resistant species like Achnanthidium minutissimum and reduction of sensitive ones like Cymbopleura naviculiformis, Fragilaria capucina, Navicula cryptocephala, Encyonema silesiacum, Eunotia bilunaris, and Gomphonema parvulum), decreases in species diversity of diatom communities with increasing Cd and Pb concentrations and exposure duration have been demonstrated in this study making diatom communities appropriate monitors of metal mixtures in aquatic systems.     

Seasonality of macroalgae and epilithic diatoms in spring-fed streams in Texas, USA

A seasonal study of two spring-fed stream systems in south-central Texas was undertaken over a 15-month period from June 1996 to September 1997. Relative abundance of the epilithic diatom flora, percent cover of macroalgae, and several physical and chemical conditions were monitored in one 20-m stretch in each of the streams at approximately two-month intervals. Six additional spring-fed stream segments were sampled in May 1996 for macroalgae and measured for the same conditions, in order to determine how representative the macroalgal floras of the study sites were of south-central and western Texas. Conditions in the two stream segments were relatively constant over the 15 months, except for maximum depth; this finding is similar those reported for other spring-fed systems worldwide. Sixty-eight diatom taxa and nine macroalgae taxa were identified from the San Marcos River, which compares to 46 diatom taxa and six macroalgae taxa from the Comal River. Several diatom and macroalgae species were significantly correlated to stream conditions (e.g. Dichotomosiphon tuberosus and Hildenbrandia angolensis with daylength, and Amphora pediculus with maximum depth). Twenty-one macroalgal taxa were identified from the six additional spring-fed steam segments. Conditions in these streams were very similar to those measured in the San Marcos River and Comal River, except that they had a higher average pH _x= 8.1 versus _x= 7.6). The epilithic diatom flora of the San Marcos River and the Comal River contains many of the diatom and some macroalgal taxa commonly reported from springs globally. This revised version was published online in July 2006 with corrections to the Cover Date.     

Studies on the ichthyo-fauna in Plover Cove Reservoir, Hong Kong: feeding and food relations

The feeding biology of the fish species in Plover Cove Reservoir, Hong Kong has been investigated with special reference to Sarotherodon mossambicus (Peters). The food spectra of various fish species were analysed and compared and the results indicated that S. mossambicus played an important role in the ecology of this reservoir since all major food sources were exploited.