Ecological studies of phytoplankton in Tai Tam Bay,Hong Kong

Of the 141 phytoplankton species found during the sampling period, the Bacillariophyceae was the most important group and included 70% of the total number of species; the Dinophyceae comprised a smaller percentage (28%) of the taxa; and only 3 chrysophyte species occurred throughout the study period. In terms of numbers of individuals, the Bacillariophyceae remained as the dominant group and contained 97% of the total numbers whereas the Dinophyceae represented only 3% of the total phytoplankton population.The most dominant diatom species was Thalassiosira allenii Takano which constituted 35% of the Bacillariophyceae group whereas the most abundant dinoflagellate was Prorocentrum gracile Schutt which represented 40% of the total Dinophyceae numbers.Chlorophyll a levels varied from 0.40 to 32.31 mg m^–3 at the surface and from 0.33 to 33.91 mg m^–3 at the bottom.Seasonal trends of phytoplankton abundance and chlorophyll a concentration were observed in the survey area with generally high peaks in summer and low values during winter months. Such variations can be attributed to the interactions between, and changes of, various environmental parameters, such as temperature, salinity and nutrient availability (particularly silicate).     

Impact of invasive apple snails in Hong Kong on wetland macrophytes,nutrients, phytoplankton and filamentous algae

1. Grazing by invasive species can affect many aspects of an aquatic system, but most studies have focused on the direct effects on plants. We conducted mesocosm and laboratory experiments to examine the impact of the invasive apple snail Pomacea canaliculata on macrophytes, filamentous algae, nutrients and phytoplankton. 2. In a freshwater pond, we confined 500 g of Myriophyllum aquaticum or Eichhornia crassipes with 0, 2, 4 or 8 apple snails in 1 m × 1 m × 1 m enclosures for approximately 1 month. Apple snails grazed heavily on both species of macrophytes, with higher overall weight losses at higher snail densities. The damage patterns differed between the two macrophytes. In M. aquaticum, both leaves and stems suffered from substantial herbivory, whereas in E. crassipes, only the roots suffered significant weight reduction. 3. In addition to grazing on macrophytes, apple snails appeared to have controlled the growth of filamentous algae, as these did not develop in the snail treatments. The ability of P. canaliculata to control filamentous algae was supported by a laboratory experiment where the consumption was as high as 0.25 g g⁻¹ snail DW d⁻¹. Because of a lack of native herbivorous snails in the pond, the growth of filamentous algae (mainly Spirogyra sp.) reached 80.3 g m⁻², forming a spongy pond scum in the no‐apple snail control. Together with previous reports that apple snails could eat the juveniles and eggs of other freshwater snails, our results indicated that P. canaliculata could have out‐competed native herbivorous snails from the pond by predation on their juveniles or eggs. Alternatively, P. canaliculata might have out‐competed them by monopolisation of food resources. 4. Nitrogen and phosphorous concentrations remained low throughout both experiments and were not correlated with apple snail density. The treatment effects on chlorophyll a (Chl a) and phytoplankton composition varied in the two experiments. In the M. aquaticum experiment, with increasing snail density, Chl a increased, and the phytoplankton community became dominated by Cryptophyceae. In the E. crassipes experiment, Chl a level was independent of snail density, but with increasing snail density, the phytoplankton community became co‐dominated by Cryptophyceae, Chlorophyceae and Bacillariophyceae. 5. Given the multiple effects of P. canaliculata on wetland biodiversity and function, management strategies should be developed to prevent its further spread. In invaded wetlands, strategies should be developed to eradicate the apple snail and re‐introduce native snails which can control the development of filamentous algae.     

Combined effects of nutrients and grazers on bacterioplankton and phytoplankton abundance in an Antarctic lake with even food-chain links

The goal of this study was to address the top-down and bottom-up controls on different microbial web components (bacterioplankton, picophytoplankton, and >3 μm phytoplankton) in an Antarctic lake. Two experiments using a size fractionation approach and nutrient addition were conducted at microcosm scale (2.5 l). The variation in net growth rates (k′) of bacterioplankton and phytoplankton size fractions was analyzed after 5 days. The results determined significant differences; whereas bacterioplankton and large phytoplankton showed an increase in their k′ when their predators were removed, the picophytoplankton showed a decrease. All the studied plankton components presented the highest k′ when nutrients were added. It is suggested that, in this lake, both the top-down and bottom-up regulations account for the regulation of bacterioplankton and large phytoplankton. As for picophytoplankton, the bottom-up control was evident and grazing did not pose a negative impact and rather, had a positive effect probably due to liberation of nutrients.     

Interactive effects of light and nutrients on phytoplankton stoichiometry

The stoichiometric composition of autotrophs can vary greatly in response to variation in light and nutrient availability, and can mediate ecological processes such as C sequestration, growth of herbivores, and nutrient cycling. We investigated light and nutrient effects on phytoplankton stoichiometry, employing five experiments on intact phytoplankton assemblages from three lakes varying in productivity and species composition. Each experiment employed two nutrient and eight irradiance levels in a fully factorial design. Light and nutrients interactively affected phytoplankton stoichiometry. Thus, phytoplankton C:N, C:P, and N:P ratios increased with irradiance, and slopes of the stoichiometric ratio versus irradiance relationships were steeper with ambient nutrients than with nutrients added. Our results support the light–nutrient hypothesis, which predicts that phytoplankton C:nutrient ratios are functions of the ratio of available light and nutrients; however, we observed considerable variation among lakes in the expression of this relationship. Phytoplankton species diversity was positively correlated with the slopes of the C:N and C:P versus irradiance relationships, suggesting that diverse assemblages may exhibit greater flexibility in the response of phytoplankton nutrient stoichiometry to light and nutrients. The interactive nature of light and nutrient effects may render it difficult to generate predictive models of stoichiometric responses to these two factors. Our results point to the need for future studies that examine stoichiometric responses across a wide range of phytoplankton communities.     

Nutrient pulsing as a regulator of phytoplankton abundance and community composition in Galveston Bay, Texas

Galveston Bay, Texas, is a large shallow estuary with a watershed that includes 60% of the major industrial facilities of Texas. However, the system exhibits low to moderate (2-20 μg l⁻¹) microalgal biomass with sporadic phytoplankton blooms. Both nitrogen (N) and phosphate (P) limitation of phytoplankton growth have been proposed for the estuary. However, shifts between N and P limitation of algae growth may occur due to annual fluctuations in nutrient concentrations. The primary goal of this work was to determine the primary limiting nutrient for phytoplankton in Galveston Bay. Nutrient addition bioassays were used to assess short-term (1-2 days) phytoplankton responses (both biomass and community composition) to potentially limiting nutrients. The experimental bioassays were conducted over an annual cycle using natural water collected from the center to lower part of the estuary. Total phytoplankton biomass increased in the nitrate (10 μM) additions in 11 of the 13 bioassays, but no significant increases were detected in the phosphate (3 μM)-only additions. Bioassay results suggest that the phytoplankton community was usually not phosphate limited. All major groups increased in biomass following nitrate additions but diatoms increased in biomass at a faster rate than other groups, shifting the community composition toward higher relative abundance of diatoms. The results of this study suggest that pulsed N input events preferentially favor increases in diatom biomass in this estuary. The broader implications of this study are that N pulsing events, primarily due to river discharge, play an important role in structuring the phytoplankton community in the Galveston Bay estuary.     

Study of phytoplankton characteristics in Tolo Harbour,Hong Kong,by HPLC analysis of chemotaxonomic pigments

Spatial and seasonal characteristics of phytoplankton in Tolo Harbour, Hong Kong, were studied by microscopic observation of phytoplankton samples and HPLC analysis of chemotaxonomic pigments. Diatoms dominated the phytoplankton. Common diatoms included Skeletonema costatum and species of Cerataulina, Leptocylindrus, Pseudo-nitzschia and Thalassiosira. Dinoflagellates occurred sporadically and mainly in the inner part of the harbour. The dinoflagellate Scrippsiella trochoidea was the causative organism for the red tide occurrences in March, April and September 2001. Significant positive correlations between fucoxanthin and diatoms and between peridinin and dinoflagellates suggested that fucoxanthin and peridinin were valuable chemotaxonomic markers for diatoms and dinoflagellates, respectively. Analysis of pigment ratios revealed that red tide events caused by dinoflagellates were marked by increase in the value of PERI:chl a and decrease in the value of FUCO:chl a. Increase in the value of FUCO:chl a also revealed the presence of a dense population of Pseudo-nitzschia that was not indicated by increase in chlorophyll a and fucoxanthin concentrations. Pigment analysis also revealed the presence of cyanobacteria, silicoflagellates, cryptophytes and green algae in the surface waters of Tolo Harbour.     

Temperature modulated effects of nutrients on phytoplankton changes in a mountain lake

Piburger See, a dimictic mountain lake in Austria, experienced moderate cultural eutrophication in the 1950s. Lake restoration led to a re-oligotrophication in the 1990s with a decrease in seasonal phytoplankton biovolume until the late 1990s, but a reversed trend from the early 2000s onwards. We hypothesize that recent changes in phytoplankton biomass and functional structure are triggered by changes in lake nitrogen and silica concentrations, and we expect climate-related factors to modulate the trophic status of Piburger See. Phytoplankton data were analyzed by non-metric multidimensional scaling (NMDS) applied on biovolume of morpho-functional groups, combined with correlation analyses of environmental variables. Since the 2000s, short-term changes in phytoplankton of Piburger See were explained by varying concentrations and ratios of nitrogen and silica, while the inter-annual variability in phytoplankton species composition was rather attributed to superimposed rising water temperature and lake thermal stability. Our results underline the co-dominant role of phosphorus and nitrogen as phytoplankton drivers in lakes that experience periods of nitrogen limitation. The combined impact of nutrients and climate on phytoplankton development can thus mimic short-term increases in the trophic level of less productive lakes.     

Effects of limiting nutrients and N:P ratios on the phytoplankton growth in a shallow hypertrophic reservoir

The purpose of this study was to evaluate the effects of limiting nutrients and the N:P ratios on the growth of phytoplankton (mainly cyanobacteria) in a shallow hypertrophic reservoir between November 2002 and December 2003. Nutrient enrichment bioassays (NEBs) were conducted, along with analyses of seasonal ambient nutrients and phytoplankton taxa, in the reservoir. The average DIN:TDP and TN:TP mass ratios in the ambient water were 90 (range: 17–187) and 34 (13–60), respectively, during the study period. The dissolved inorganic phosphorus showed seasonal variation, but less than that of inorganic nitrogen. The TN:TP ratios ranged from 13 to 46 (mean: 27 ± 6) during June–December when the cyanobacteria, Microcystis, dominated the phytoplankton composition. The NEBs showed that phytoplankton growth was mainly stimulated by the phosphorus (all of total 17 cases), rather than the nitrogen concentration (8 of 17 cases). The rapid growth rate of cyanobacteria was evident with TN:TP ratios less than 30. According to the results of the NEBs with different N concentrations (0.07, 0.7 and 3.5 mg l⁻¹), but the same N:P ratios and when the nitrogen concentration was highest, the cyanobacterial growth reached a maximum at N:P ratios <1. Overall, the response of cyanobacterial growth was a direct function of added phosphorus in the NEBs, and was greater with increased N concentrations. Thus, cyanobacterial blooms favored relatively low N:P ratios in this hypertrophic reservoir system. An erratum to this article is available at .     

The composition and abundance of phytoplankton in Lake Bukoni,western Uganda

Lake Bukoni is one of the crater lakes in western Uganda. Investigations into this lake is limited compared to other African lakes. Data on phytoplankton ecology in the lake are lacking. Phytoplankton consists of a community of photosynthetic, microscopic plants adapted to suspension in water. They constitute ‘hidden flora’ which make an important contribution to the primary productivity of a water mass. Some phytoplankton taxa, among them species belonging to Cyanophyta, are known to influence ecological transformations and to cause health hazards in water bodies that are used by humans. From July 2004 to December 2005, phytoplankton was collected from two sites (inshore and offshore) in Lake Bukoni. An inverted microscope, Sedgwick counting chamber and multiple tally denominator were used to quantify the phytoplankton. Phytoplankton was dominated by nonheterocystous cyanoprokaryotes especially Lyllgbya limnetica followed by the diatoms Synedra ulna and Fragillaria mutabilis. The inshore site had more phytoplankton species. Differences in phytoplankton diversity and density were mainly attributed to mixing and presence of macrophytes. The occurrence of large numbers of cyanoprokaryotes poses a potential health hazard to the local people who utilize the water from Lake Bukoni. The dominance of cyanoprokaryotes might result in ecological transformations like loss of biodiversity.     

大亚湾澳头水域浮游植物群落结构及周年数量动态

对1997年至1998年广东省大亚湾澳头水域的浮游植物群落进行调查和分析。结果发现浮游植物65属198种;硅藻在种类组成和数量上都比甲藻占有优势,存在春季和秋季高峰,主要优势类群依次是角毛藻、骨条藻、拟菱形藻等;甲藻只存在春季高峰,代表种类有裸甲藻、原甲藻等。主要优势种类的生长与调查水域的盐度没有明显关系,但全年水温的季节性变化对优势种类的消长影响显著。Simpson多样性指数、Shannon-Weaver多样性指数、均匀度的年平均值分别是0.611、2.107、0.557,多样性指数没有明显的季节变化规律和水平分布规律。       

The ecology of six Rhododendron species (Ericaceae) with contrasting local abundance and distribution patterns in Hong Kong,China

Six native Rhododendron species grow in thedegraded, fire-prone landscape of Hong Kong: R. simsii andR. farrerae are common and widespread, R.moulmainense is relatively restricted, and R.championiae, R. hongkongense, and R.simiarum are rare. For all species except the rare R.simiarum, there was direct or indirect evidence of regrowth afterfire, but only the two smallest and commonest species grow in sites which arefrequently burned. Both flowered within 18 months of a fire. Most populationsofall species, except R. simiarum, had a deficiency ofindividuals in the smaller basal circumference classes. Seedlings were foundonly in three out of four plots of R. simiarum, and one ofR. farrerae. A few seedlings of the other rare specieswereseen in open, litter-free microsites outside the study plots, but no seedlingsof the most common species, R. simsii, were seen anywhere.In logistic regression models, one or more measures of plant size weresignificant positive predictors of flowering at least once in the three yearstudy period for all species, while percentage cover by surrounding vegetationhad a significant negative impact on all except R. simsiiand R. farrerae, for which no populations arestrongly-shaded. Although the absence of current recruitment is not necessarilya cause for concern in long-lived species that can resprout after fire, werecommend that active vegetation management should be tried to enhance thesurvival and reproduction of R. moulmainense, R.championiae and R. hongkongense, and that newpopulations of these species and R. simiarum should becreated.     

Temporal patterns and variations in phytoplankton community organization and abundance in Narragansett Bay during 1959-1980

Incident irradiance, surface water temperature and phytoplanktonspecies abundances were measured at weekly intervals in NarragansettBay from 1959 through 1980. Stepwise discriminant analyses (SDA)of this 22-year data set indicate that fundamental ecosystemchanges occurred between the 1960s and 1970s, with 1969 beingthe key transitional year in these decadal shifts in phyto planktontaxonomic structure and seasonal abundance. This decadal shiftwas accompanied by the increased summer abundance of small Thalassiosiraspp., which first appeared in 1966 and by 1969 became the sixthmost important phytoplankton component in this bay. Decadaltrends in phyto plankton community organization and abundancewere also accompanied by distinct long-term climatological gradientsof temperature and light. The 1960s were generally colder andbrighter than the 1970s. Prior to 1969, the annual phytoplanktonmaximum occurred most commonly during winter; in the 1970s,the annual maximum generally shifted to a summer event. Three5-year phytoplankton cycles occurred between 1959 and 1974.During each pentade, the phytoplankton community returned toa similar taxonomic organization and abundance cycle after divergingin the intervening years. Pentade cycles did not occur after1974; the phytoplankton community thereafter diverged significantlyfrom each preceding year. Five species [Skeletonema costatum,Detonula confervacea, Asterionellopsis glacialis, Hererosigmaakashiwo (= Olisthodiscus lureus) and Thalassiosira nordenskioeldii]dominated the phytoplankton over the 22-year period. SDA revealeda high degree of similarity and constancy in the annual occurrencepatterns of these taxa. The decadal shifts revealed by SDA weremore directly related to the considerable interannual variabilitythat characterized the abundance and seasonality of the lessabundant species.     

The indigenization of neurasthenia in Hong Kong

Despite its origin in Western psychiatry, neurasthenia has become a popular concept in Chinese folk medicine, referring to a variety of somatic and psychological symptoms. Review of Chinese medicinal materials and patent medicines shows that neurasthenia is associated more often with somatic symptoms in tonic type medicine and with psychological and psychosomatic symptoms in sedative and tranquilizer type medicine. Popular Chinese books on neurasthenia suggest that causes might be attributed to lifestyle, psychological factors, and health problems. Recommendations on treatment emphasize self-help approaches through changing lifestyle, examining attitudes, tonic care, and relaxation. As a broad term used loosely by professionals and the lay public in Hong Kong, neurasthenia serves the important function of destigmatizing psychiatric disorders. Psychosexual problems may also be conveyed discreetly through somatic presentation. The indigenization of neurasthenia exemplifies how an originally Western concept acquires cultural meaning. Implications of illness conceptualization and the medical paradigm are discussed.     

The effects of nitrate and phosphate enrichments on the phytoplankton from Marsaxlokk Bay,Malta (Central Mediterranean)

The technique of artificial enrichment of seawater has been employed in an attempt to define nutrients critically limiting the growth of phytoplankton in Marsaxlokk Bay, Malta. While both nitrates and phosphates are scarce, phosphate is the primary factor limiting phytoplankton growth. There appear to be no seasonal changes in the respective roles of phosphates and nitrates as factors limiting primary productivity. The higher incubating temperatures of theJune cultures resulted both in a quicker attainment of the peak values of chlorophyll a and in a higher peak concentration of this pigment as compared with the November and February experiments. There appeared to be no major changes in the relative composition of the phytoplankton populations in all enrichment experiments. Diatoms, mainly Skeletonema costatum and Chaetoceros spp., dominated all culture vessels. These results are discussed in the light of the values obtained for the ratio of pigment absorption at 430 nm to that at 665 nm.     

The intelligence of six-year-olds in Hong Kong

Evidence has accumulated to suggest that the mean IQs of Orientals in the United States and in the countries of the Pacific Basin are higher than those of Whites (Caucasoids) in the United States and Britain. This paper presents evidence from IQ tests on 4858 6-year-old Chinese children in Hong Kong. On the Coloured Progressive Matrices these children obtained a mean IQ of 116. Samples from Australia, Czechoslovakia, Germany, Romania, the UK and the US obtain IQs in the range 95-102. It is suggested that these results pose difficulties for the environmentalist explanations commonly advanced to explain the low mean IQs obtained by some ethnic minorities in the United States.     

香港瓮缸群岛野生植物资源调查研究

香港瓮缸群岛共有维管植物166种,隶属于69个科138个属,其中蕨类植物7科8属10种,裸子植物2科2属2种,被子植物60科128属154种。瓮缸群岛为香港著名离岛,植被生境无人为干扰,野生植物资源利用度较低,本文通过对瓮缸群岛的植被类型和野生植物资源进行统计分析,结果表明,该群岛可供利用的植物资源共10类,分别为：药用植物103种、观赏植物107种、食用植物21种、牧草及饲用植物23种、材用植物17种、油脂植物22种、芳香精油植物25种、纤维植物13种、鞣料植物11种、有毒植物26种等,都有很高的开发利用潜力,在此基础上提出相应的保育及开发利用建议,旨在更好地保护和合理利用该群岛的野生植物资源。     

An experimental study of the influence of periphytic algae on invertebrate abundance in a Hong Kong stream

1. Small cages (294cm²) containing unglazed clay quarry tiles were used to investigate the influence of periphytic algae on macroinvertebrate abundance in a Hong Kong stream. Algal biomass was manipulated by shading cages with plastic sheets. Individual cages were assigned to one of three treatment groups: unshaded, shaded and deeply shaded. Invertebrate densities and algal biomass within cages were monitored after 23, 37 and 65 days. 2. Multiple-regression analysis revealed that algal biomass, invertebrate morphospecies richness and total abundance declined with greater shading intensity. The responses of individual invertebrate taxa varied: some (especially Trichoptera) were unaffected by shading, whereas grazers (Baetidae, Psephenidae and Elmidae) declined as shading increased. 3. Significant regressions of the densities of individual taxa upon algal and detrital standing stocks in cages had positive slopes, but algal biomass increased during the study while detrital standing stocks declined. Abundance of invertebrates declined or remained rather stable over time. Density increases resulting from a positive association with algae were apparently offset by declines in abundance correlated with reductions in detritus. 4. Declines in algal biomass were associated with greater shading to which animals may respond directly. To uncouple the link between scarcity of algae and reduction of light intensity, the plastic covers on two groups of cages (deeply shaded and unshaded) which had been placed in the stream for 28 days were reversed so that cages which had been shaded became unshaded and vice versa. The cages were recovered on day 33, Only Coleoptera demonstrated a positive association with atgae inside cages; no relationship between population densities and algal biomass or light intensity was apparent for other taxa. However, the design may have been confounded by deposition of sediment in the cages (due to declining stream discharge) which reduced population densities of colonizers. 5. This study documents changes in invertebrate abundance and morphospecies richness in response periphyton and detritus standing stocks within patches. Summation of such responses may account for observed variations in benthic communities among Hong Kong streams which differ in the extent of shading by riparian vegetation.