Distribution Of Benthic Diatoms Research Articles

Composition and Distribution of Benthic Diatoms in Different Habitats of Burdur River Basin

Diatoms constitute an essential component for biomonitoring studies to determine the ecological quality of waterbodies. In this study, benthic diatoms of Burdur River Basin were investigated as a consequence of a project on river basin management plan. This is the first detailed taxonomical study of diatoms taken from 13 streams, 4 lakes and 6 reservoirs of Burdur River Basin and a total of 223 taxa have been observed. Among genera, Navicula Bory (27) and Nitzschia Hassal (27) were represented with the highest numbers of taxa and followed by Gomphonema Agardh with a total of 22 species. Navicula antonii Lange-Bertalot and Nitzschia palea var. debilis (Kützing) Grunow had the highest relative abundance with 17.1% and 15.5% respectively. As a closed basin, salinity varied greatly from fresh to saline water between the sampling stations and diatom composition contained species with a different tolerance level. Navicula antonii and Nitzschia frustulum (Kützing) Grunow observed in all habitats indicating their euryhaline characters; however Navicula digitoconvergens was only detected in saline Acıgöl lake with a high relative abundance (38%) in autumn. Other two dominant species were Halamphora coffeiformis (Kützing) Levkov and Navicula cincta (Ehrenberg) Ralfs in Acıgöl lake showing their tolerance to high salt content as a brackish species. According to first results, 11 species were new records for Turkish diatom flora. The high biodiversity of diatoms revealed the presence of different habitat characteristics within the basin. These results are an important contribution of Turkish diatom flora and could be useful for monitoring specific areas like Burdur River Basin.

Diversity, ecology and distribution of benthic diatoms in thermo-mineral springs in Auvergne (France) and Sardinia (Italy).

This study investigated and compared the diatom flora from thermo-mineral springs in Auvergne (France) and Sardinia (Italy). Samples were collected from rock/cobbles and fine sediments in 16 springs between January 2015 and March 2017. A total of 207 taxa (59 genera) were found. Multivariate analyses revealed significant differences in species composition and abundance among diatom assemblages both within each geographic region and between Auvergne and Sardinia (global R = 0.516; p = 0.002), suggesting the importance of local and climatic factors in species distribution. Based on abundance and common occurrence in multiple sites, some taxa can be considered more representative of springs in each region: Crenotia thermalis for Auvergne and Lemnicola exigua, Nitzschia amphibia, N. inconspicua and Rhopalodia operculata for Sardinia. pH, conductivity and HCO3− were the most significant environmental variables for diatom assemblages. Our results highlight the high heterogeneity of these spring systems. Future taxonomic insights can be useful to define the identity of some abundant and dominant taxa not identified at the species level in this study. Their identification is a crucial step for a more precise ecological characterization and comparison of these peculiar spring systems.

Ecosystem health indicators in the Ganga Basin (Uttarakhand, India): Biodiversity, spatial patterns in structure and distribution of benthic diatoms, macro-invertebrates and ichthyofauna

This is the pioneering attempt to study the spatial patterns in structure of lotic ecosystems that form the Ganga River system in the Himalaya. The diversity of source (glacier-fed [GF], snow-fed [SN] and spring-fed [SF]) and stream-size (both interrelated) across the altitudinal panorama, create numerous habitats that contribute to structural diversity. The spatial patterns in richness, density and taxonomic composition and distribution of benthic diatoms are less affected by source compared with macro-invertebrates but shows strong influence on the distribution of fish fauna that are poikiliotherms, because a glacier-fed river carries ice-cold water (usually <20°C) in contrast to normal waters in spring-fed system (22°C near snowline, 32°C in foothills). The abundance patterns of biota of lower organisation grade (diatoms, macro-invertebrates) do not differ sharply even across distant river basins as they are more influenced by proximate factors; thus the sub-basins of the Alaknanda resemble more by virtue of one basin and there is notable resemblance between distant SF Bemunda (lower Ganga basin) and SF Gomti (East Rāmgangā basin) and even the farthest Yamuna and Rāmgangā. Fish are more sensitive to temperature and current velocities that are related to altitude and hence longitudinal rather than the spatial gradients in the mountains. The lotic ecosystem of Doon Valley harbour rich and diverse diatom flora, macroinvertebrate fauna and ichthyofauna. The examination of trophic, saprobic and ecological status shows that organic pollution, degradation and anthropogenic eutrophication are non-existent in the Lesser Himalayan rivers and streams, but the fragile Doon Valley is under severe anthropogenic stress. This and habitats fragmented by hydropower projects in the major rivers has threatened the iconic game fish Himalayan mahseer in the Ganga.

长江口及东海春季底栖硅藻、原生动物和小型底栖生物的生态特点

PDF HTML阅读 XML下载 导出引用 引用提醒 长江口及东海春季底栖硅藻、原生动物和小型底栖生物的生态特点 DOI: 10.5846/stxb201207090964 作者: 作者单位: 中国科学院海洋研究所,中国科学院海洋研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划（973）项目（2011CB403604）；中国科学院知识创新工程重要方向项目（KZCX2-EW-Z-5）；中国科学院海洋研究所"一三五"专项资助项目（2012IO060104） Ecological characteristics of benthic diatoms, protozoa and meiobenthos in the sediments of the Changjiang Estuary and East China Sea in spring Author: Affiliation: Institute of Oceanology,Chinese Academy of Sciences,Institute of Oceanology,Chinese Academy of Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:利用Ludox-QPS方法并结合沉积环境因子的综合分析，研究了2011年4月采自长江口及东海10个站位以底栖硅藻、纤毛虫和异养小鞭毛虫为代表的微型底栖生物及小型底栖生物的组成、丰度和生物量、分布及生态特点。结果表明，底栖硅藻的丰度（5.92×104 个/10 cm2）和生物量（83.29 μg C/10 cm2）远高于纤毛虫（丰度为1036 个/10 cm2，生物量为3.33 μg C/10 cm2）、异养小鞭毛虫（丰度为4451 个/10 cm2，生物量为2.51 μg C/10 cm2）和小型底栖生物（丰度为（1947±849）个/10 cm2，生物量为（49.01±22.05）μg C/10 cm2）。在鉴定出的11个小型底栖生物类群中，线虫占小型底栖生物总丰度的90%和总生物量的37%。底栖硅藻生物量在长江口及东海海域呈由近岸向外海逐渐降低的分布特点，而底栖纤毛虫、异养小鞭毛虫及小型底栖生物的分布则正相反。在垂直分布上，76%的硅藻和80%的线虫分布在0-2 cm沉积物表层，仅1%的硅藻和6%的线虫分布在5-8 cm分层。统计分析表明，底栖硅藻的现存量与沉积物中叶绿素a含量呈极显著的正相关，与底层水温度呈弱的正相关;该海域底栖原生动物和小型底栖生物的分布受多个因子而非单一环境因子的共同作用。对比分析表明，长江口及东海单位体积沉积物中的硅藻丰度较水体中的硅藻丰度高2个数量级，沉积物中相当部分的叶绿素a含量可能系底栖硅藻所贡献；表层8 cm沉积物中纤毛虫的丰度约是上层30 m水柱中纤毛虫丰度的30倍，生物量约是后者的40倍。尽管纤毛虫在生物量上远小于小型底栖生物，但其估算的生产力约是后者的3倍；而异养小鞭毛虫由于个体更小，其周转率可能较纤毛虫更高。长江口及东海陆架区原生动物和小型底栖生物的高现存量及生产力预示着其在该海域生态系统中的重要作用。 Abstract:Using the newly developed Ludox-QPS method, we investigated the community composition, abundance and biomass, and distribution of benthic diatoms, ciliates and heterotrophic microflagellates (HMF) and meiobenthos in combination with the analysis of benthic environmental variables at ten stations in the Changjiang (Yangtze) Estuary and East China Sea in April 2011. The benthic diatoms were dominant both in the abundance (5.92×104 ind/10 cm2) and biomass (83.29 μg C/10 cm2), followed by benthic ciliates (abundance: 1036 ind/10 cm2, biomass: 3.33 μg C/10 cm2) and HMF (4451 ind/10 cm2, 2.51 μg C/10 cm2). The abundance of meiobenthos in the upper 8 cm of sediments was (1947±849) ind/10 cm2 and the biomass was (49.01±22.05) μg C/10 cm2. Among the 11 meiobenthos groups identified, nematodes accounted for 90% of the total abundance and 37% of the total biomass. The biomass of benthic diatoms was distinctly higher in the coastal region than that in the offshore area, while the distribution pattern of benthic ciliates, HMF and meiobenthos was exactly opposite. On average 76% of diatoms and 80% of nematodes were distributed in the 0-2 cm sediment layers, while the respective proportions were only 1% and 6% in the 5-8 cm layers. Statistical analyses showed that the standing crops of benthic diatoms had significantly positive correlation with sediment chlorophyll-a contents and weak positive correlation with bottom water temperature, and benthic protozoa and meiobenthos might be structured by the interaction of multiple rather than single environmental variables. Our data indicate that the density of benthic diatoms in the sediments was very high, about two orders magnitude higher per unit volume than that in the water column of the Changjiang Estuary and East China Sea, where a great proportion of sediment chlorophyll a was contributed by benthic diatoms. The benthic ciliate abundance in the upper 8 cm of sediments were 30 times higher and the biomass was 40 times higher than those in the water column of upper 30 m of the Changjiang Estuary and East China Sea. Although the biomass of ciliates was lower than that of meiobenthos, their production was up to 3 times higher than that of meiobenthos. The relative turnover rate of heterotrophic microflagellates might even be much higher due to their small size. The high standing crops and production of benthic protozoa and meiobenthos indicate their important role in the ecosystem structure and function of the Changjiang Estuary and East China Sea. 参考文献 相似文献 引证文献

東京湾の3干潟における底生珪藻の分布

東京湾の3干潟における底生珪藻の分布

Distribution of benthic diatoms in Korean rivers and streams in relation to environmental variables

The diatoms are an ecologically important group of algae that have been extensively studied by ecologists and taxonomists. However, the large-scale patterns of diatom distribution and the factors under- lying this distribution are largely unknown. The aims of this study were to identify the large-scale spatial patterns of benthic diatom assemblages in Korean streams and rivers, and to assess the importance of numer- ous environmental factors on diatom distribution. We classified 720 study sites based on diatom flora. Benthic diatoms, water chemistry, altitude, and riparian land cover and use were characterized by multivariate analyses, Monte Carlo permutation tests, and indicator species analysis. In total, we identified 531 diatom taxa. Diatom assemblages were mostly dominated by species of the genera Achnanthes, Navicula, Nitzschia, Cocconeis, Fragilaria (Synedra included), Cymbella, Gomphonema, and Melosira. Cluster analysis partitioned all 720 sites into eight groups based on diatom species composition. Canonical correspondence analysis in- dicated that altitude, land cover and use, current velocity, electrical conductivity, and nutrient levels explained a significant amount of the variation in the composition of assemblages of benthic diatoms. At the national scale, a downstream ecological gradient was apparent, from fast-flowing, mostly oligotrophic highland streams to slow-flowing, mostly eutrophic lowland rivers. Our data suggest that spatial factors explain some of the variation in diatom distribution. The present investigation of the spatial patterns of benthic diatoms, the ecological determinants of diatom occurrence, and the identification of diatom indicator species contributes to development of a program for assessing the biological integrity of lotic ecosystems in Korea.

Using Diatoms as Ecological and Paleoecological Indicators in Riverine Environments

Fossil diatom assemblages are useful for reconstructing past environmental changes in riverine systems. However, few studies have attempted to utilize paleolimnological techniques in these settings. Analysis of sediments from riverine environments can provide key information predating the impact of human development, which cannot be acquired by other means. Paleolimnological techniques can be used to determine the natural variability in these systems and to estimate the magnitude and rates of change that the environment may have undergone as a result of anthropogenic or climatic factors, and to provide realistic goals for management of negatively-impacted systems.Reconstructing past riverine settings requires an understanding of the factors that control the spatial distribution of diatoms in riverine settings; this paper discusses the impact of resources, stressors, and disturbance events, which are the primary controls on the distribution of benthic diatoms in modern riverine environments. A selection of case studies that utilize paleolimnological techniques to infer past stream hydrology are also discussed; these examples encompass the use of fossil diatom assemblages from sediments recovered from lowland floodplain and meandering river systems, estuarine environments, fluvial lakes, arctic deltaic environments, and terminal lakes.

NEW FINDINGS ON THE ECOLOGY AND ULTRASTRUCTURE OF CYMBELLA ANCYLI CLEVE

Cymbella ancyli is a diatom species inhabiting oligotrophic lakes with a carbonate substratum. C. ancyli has a relatively wide geographic distribution and is considered to be rare in present day assemblages, while it is more common in subfossil material (particularly in the Ancylus Clay). During a comprehensive investigation on the ecology and depth distribution of benthic diatoms of Lake Tovel, C. ancyli was found to colonise stone and rock surfaces in the intermediate depth zone of the lake. The intermediate depth zone is stable, because it is not influenced by water level fluctuations, temperatures are low and nearly constant, and light is attenuated but sufficient. This niche may constitute a relict refugium for Cymbella ancyli. Analysis of the ultrastructure of C. ancyli revealed that apical pores were present, not only at the footpole, but also the headpole. This finding gives further support to the opinion that this taxon is closer taxonomically to Cymbella sensu lato than to Gomphocymbella.

Distribution of benthic diatoms in U.S. rivers in relation to conductivity and ionic composition

Summary We quantified the relationships between diatom relative abundance and water conductivity and ionic composition, using a dataset of 3239 benthic diatom samples collected from 1109 river sites throughout the U.S.A. [U.S. Geological Survey National Water‐Quality Assessment (NAWQA) Program dataset]. This dataset provided a unique opportunity to explore the autecology of freshwater diatoms over a broad range of environmental conditions. Conductivity ranged from 10 to 14 500 μS cm−1, but most of the rivers had moderate conductivity (interquartile range 180–618 μS cm−1). Calcium and bicarbonate were the dominant ions. Ionic composition, however, varied greatly because of the influence of natural and anthropogenic factors. Canonical correspondence analysis (CCA) and Monte Carlo permutation tests showed that conductivity and abundances of major ions (HCO + CO, Cl−, SO, Ca2+, Mg2+, Na+, K+) all explained a statistically significant amount of the variation in assemblage composition of benthic diatoms. Concentrations of HCO + CO and Ca2+ were the most significant sources of environmental variance. The CCA showed that the gradient of ionic composition explaining most variation in diatom assemblage structure ranged from waters dominated by Ca2+ and HCO + CO to waters with higher proportions of Na+, K+, and Cl−. The CCA also revealed that the distributions of some diatoms correlated strongly with proportions of individual cations and anions, and with the ratio of monovalent to divalent cations. We present species indicator values (optima) for conductivity, major ions and proportions of those ions. We also identify diatom taxa characteristic of specific major‐ion chemistries. These species optima may be useful in future interpretations of diatom ecology and as indicator values in water‐quality assessment.

Distribution of benthic diatoms in relation to environmental variables in lowland streams

The composition (% relative abundance) of diatom assemblages from soft bottom sediments was studied at 75 sites situated in 46 rivers, brooks, and ditches in the islands of Hiiumaa and Saaremaa and in the lowland of West Estonia. Although the total number of recorded taxa was 205, the studied diatom assemblages consisted of 54, 55, 48, and 50 constant species in the drainage basin of Moonsund, the Gulf of Riga, Hiiumaa, and Saaremaa, respectively. The habitats of the dominating taxa were heterogenous and the most widespread species were Achnanthidium minutissimum, Martyana martyi, Meridion circulare, Cocconeis placentula, Planothidium lanceolatum, and Amphora pediculus. The Shannon–Weaver diversity (H′) index varied from 2.09 to 4.63. Multivariate analyses were used to identify the environmental variables governing the composition and structure of the benthic diatom assemblage. Principal Component Analysis (PCA) and Redundancy Analysis (RDA), based on 56 most abundant taxa, indicated differences in the composition and structure of diatom assemblages between different drainage basins as well as between the upper and lower stream courses. In the headwaters there prevailed small epipsammic diatoms (Martyana, Planothidium, Staurosira, Staurosirella). Different motile epipelic species from the genera Amphora, Navicula, Nitzschia, etc. were distributed abundantly in the lower courses of the streams. There was a positive correlation between order of the stream site and trophic level of water (R=0.35; p<0.05). Along a river system, the increasing order of the stream was accompanied by higher trophic level of water.

Short-term dynamics in microphytobenthos distribution and associated extracellular carbohydrates in surface sediments of an intertidal mudflat

Two field studies were conducted to study the in situ net production of extracellular carbohydrates and the distribution of benthic diatoms over a period of 24 h per study. A comparison was made between a situation where a clear surface biofilm of diatoms had developed and a situation where this was not the case, Vertical profiles were made by sampling the top 2 mm of the sediment at depth intervals of 0.2 mm using the 'cryolander' technique. In the presence of a biofilm, diatom distribution showed a consistent pattern when the sediment was emersed. In the light, most of the diatoms were present in the top 0.2 mm while in the dark, diatoms were homogeneously distributed in the upper 2 mm of the sediment. When a biofilm was absent, no clear patterns were observed. Extracellular carbohydrates were extracted from the sediment and separated in 2 operationally defined fractions (colloidal and EDTA- extractable). The 2 carbohydrate fractions showed a different dynamic behaviour. The colloidal carbohydrate fraction was highly variable while the EDTA-extractable fraction behaved more conservatively. Only in the light and in the presence of a diatom biofilm, was production of extracellular carbohydrates observed, The maximum rate of chlorophyll-normalized production of extracellular carbohydrates, expressed in glucose equivalents (g g(-1)), amounted to 20 h(-1) in the upper 0.2 mm. The molecular size distribution of both carbohydrate fractions was similar. The monosaccharide composition was also similar, except that the EDTA-extractable fraction contained a higher percentage of uronic acids, Carbohydrates produced during tidal emersion were rich in glucose and were rapidly turned over. [KEYWORDS: extracellular polymeric substances (EPS); polysaccharides; microphytobenthos; mud flat; monosaccharide composition; cryolander Polysaccharide hydrolysis rates; benthic microalgae; marine-sediments; epipelic diatoms; cohesive sediments; organic-carbon; chlorophyll-a; environments; assemblages; irradiance]

Distribution of benthic diatoms in the littoral zone of the Gulf of Riga, the Baltic Sea

The composition (% relative abundance) of the benthic diatom community was studied in the littoral zone (0–5 m) of the NW and E coasts of the brackish, non-tidal Gulf of Riga, in the Baltic Sea. The samples were collected concomitantly with measurements of sediment primary productivity and chlorophyll a during three cruises, representing three seasons (autumn, spring, summer). At all depths, the living diatom community was dominated by epipsammic species, the most abundant taxa being Martyana atomus, a species of Fragilariaceae and Achnanthes delicatula. The community was characterized by a stable composition and a high species diversity throughout the study period (Shannon–Weaver, mean H′ = 4.4). Principal Component Analyses (PCA), together with Redundancy Analysis (RDA) based on 129 taxa, revealed both spatial (site and depth) and seasonal differences in the diatom communities. However, these differences were mainly caused by the varying proportions of taxa common in both sampling areas in all three seasons, rather than by actual major taxonomic changes in the species present in communities. The distribution of the typical epipsammic species along the depth gradient was not uni-directional. The dominance of attached life forms, and the absence of a well-developed epipelic community, reflects the physically dynamic substratum, particularly in the eastern part of the Gulf. As a result, primary productivity is kept rather low, decreasing rapidly with depth due to frequent turbidity of the water column.

Distribution of benthic diatoms in the littoral zone of the Gulf of Riga, the Baltic Sea

The composition (% relative abundance) of the benthic diatom community was studied in the littoral zone (0–5 m) of the NW and E coasts of the brackish, non-tidal Gulf of Riga, in the Baltic Sea. The samples were collected concomitantly with measurements of sediment primary productivity and chlorophyll a during three cruises, representing three seasons (autumn, spring, summer). At all depths, the living diatom community was dominated by epipsammic species, the most abundant taxa being Martyana atomus, a species of Fragilariaceae and Achnanthes delicatula. The community was characterized by a stable composition and a high species diversity throughout the study period (Shannon–Weaver, mean H′ = 4.4). Principal Component Analyses (PCA), together with Redundancy Analysis (RDA) based on 129 taxa, revealed both spatial (site and depth) and seasonal differences in the diatom communities. However, these differences were mainly caused by the varying proportions of taxa common in both sampling areas in all three seasons, rather than by actual major taxonomic changes in the species present in communities. The distribution of the typical epipsammic species along the depth gradient was not uni-directional. The dominance of attached life forms, and the absence of a well-developed epipelic community, reflects the physically dynamic substratum, particularly in the eastern part of the Gulf. As a result, primary productivity is kept rather low, decreasing rapidly with depth due to frequent turbidity of the water column.

Distribution of diatoms in the surficial sediments of the Mangyung-Dongjin tidal flat, west coast of Korea (Eastern Yellow Sea)

The relationship between the distribution of benthic diatoms and sediment characteristics of the Mangyung-Dongjin tidal flat on the west coast of Korea was investigated during June and July 1988. Diatoms were collected from the upper 5 mm of sediments at 60 sites along eight transect lines running perpendicular to the shore line. Of the 371 taxa encountered in the study area, 88% were pennate diatoms. Genera represented by the greatest number of species were Navicula, Nitzschia, Amphora, Cocconeis, Fragilaria and Achnanthes. The most abundant species were Paralia sulcata, Navicula sp. #1, N. arenaria and Cymatosira belgica; all were broadly distributed across the tidal flats. The 60 sites could be assigned to eight clusters with respect to similarity in species composition. Discriminant analysis showed that separation cluster was primarily related to the mean grain size of the sediment. The species could not be separated into groups based on similarities in occurrence; a high degree of spatial overlap was observed. The preferences of the more abundant species for grain size were, therefore, analysed by plotting numerical abundance against mean grain size. There were at least four patterns: species groups could be associated with finegrained sediments, those of intermediate size and coarser sediments and the last group showed no discernible pattern.

Taxonomy and Distribution of Benthic Diatoms from Mono Lake, California, U.S.A.

The benthic diatom flora of Mono Lake is described from samples taken from three localities at depths of approximately 1, 5, and 10 meters on rock and sediment substrates. Relative abundances of 30 taxa were recorded from duplicate counts of 500 valves from each of 18 samples. Dominant taxa included Navicula crucialis, Nitzschia frustulum, N. latens, N. reimerii sp. nov., N. monoensis, sp. nov. and Anomoeoneis sphaerophora var. minor var. nov.; taxonomy, morphology, and distribution of these taxa are considered. Navicula crucialis, previously recorded from saline lakes in North Africa and highly variable in outline, was most abundant in sediment samples. Anomoeoneis sphaerophora var. minor, Nitzschia reimeri, and N. monoensis were most abundant in deeper waters whereas both N. latens and N. frustulum occurred most frequently in collections from shallow waters. Smaller individuals of N. latens were broader than larger specimens, and some N. frustulum cells resembled N. austriaca. Nitzschia monoensis has numerous girdle bands and prominent external distal raphe ends. Navicula crucialis, A. sphaerophora var. minor, and Nitzschia monoensis were observed with internal valves. Mono Lake, located at the western edge of the Great Basin (Fig. 1), is a hypersaline (95 g/L in 1990) and alkaline (pH 10.0) (Herbst, unpublished data) remnant of Pleistocene Lake Russell. At a current surface elevation of 1,943 m, the lake has fluctuated considerably in the late Holocene (Stine, 1990). During the past 50 years, the lake has undergone a net decline of 14 m and a doubling of salinity, both attributable to diversion of tributary streams by the city of Los Angeles (National Academy of Sciences, 1987). The major ion content is dominated by sodium, with high anion concentrations of bicarbonate in addition to carbonate, chloride, and sulfate (Herbst, 1988). The benthic environment is composed of sand and organic-rich mud sediments over much of the basin. Hard substrates occur as localized calcareous tufa formations, pumice and alluvial granite cobble, and gravel along the west, north, and south shores (Herbst, 1990). The high salinity of Mono Lake restricts macrofaunal diversity to eight known benthic insects, all dipteran larvae (Herbst, 1988) and a single zooplankton species, Artemia monica Verrill. The dominant benthic insect is the alkali fly Ephydra hians Say (Ephydridae), a herbivore that grazes epilithic algae and epipelic microbial mats. Benthic algae from Mono Lake with which diatoms are known to occur include Ctenocladus circinnatus Borzi (Chlorophyceae) ' Portions of this study and support for D. B. H. were provided by a grant from the University of California Water Resources Center. We thank T. J. Bradley for informative discussions and C. W. Reimer for use of the Diatom Herbarium, Academy of Natural Sciences of Philadelphia. Publication costs, in part, are being met by a grant from the Darbaker Fund of the American Microscopical Society. TRANS. AM. MICROSC. Soc., 111(4): 338-355. 1992. ? Copyright, 1992, by the American Microscopical Society, Inc. This content downloaded from 207.46.13.64 on Sat, 03 Sep 2016 04:09:50 UTC All use subject to http://about.jstor.org/terms VOL. 111, NO. 4, OCTOBER 1992

Limiting Factors on the Distribution of Benthic Diatoms in Coastal Regions

Limiting Factors on the Distribution of Benthic Diatoms in Coastal Regions

Influence of the St. Marys River Plume on Northern Lake Huron Phytoplankton Assemblages

Analysis of phytoplankton samples from the Straits of Mackinac region yielded high species diversity and species richness values at the outfall of the St. Marys River due to entrained benthic diatoms. Epilithic, psammonic, epipelic, and epiphytic diatoms originating in the St. Marys River and Detour Passage area were removed from their primary habitats and transported into northern Lake Huron. Southward movement of the St. Marys River plume, as determined from suspended benthic diatom distribution and abundance, was strongly indicated for 3 km. Moderate influence of the plume was noted at 6 km and weaker association with the plume was detected for as far as 32 km. Apparently, loss of suspended riverine species from the upper water column in this area was primarily due to sinking. Sinking, calculated from residence times based on river discharge data, was estimated to range between 0.76 and 5.99 m/day. Total phytoplankton abundance and chlorophyll a values were lower near the rivermouth. Conversely, 14C uptake was significantly greater near the river. Benthic populations comprised as much as 40% of the assemblage and an additional amount of dead and fragmentary diatoms was also observed. Viable benthic diatoms may contribute as much as 25% of the algal assemblage on a cell volume basis. Upon death and decomposition, they may constitute an important source of carbon and nutrients in the immediate vicinity.

Benthic diatom distribution and grazing by Sarotherodon mossambicus in Lake Sibaya, South Africa

SUMMARY. Distributions of benthic diatoms and benthic floc in Lake Sibaya were examined to determine if preferential grazing by juvenile Sarotherodon mossambicus on benthic detrital aggregate in shallow water maximized diatom concentrations in the diet of the fish. Between 0.1 and 12.0 m depth, the range of diatom densities was 1–60 × 104 cells cm−2 with high but extremely variable densities above 3 m and consistently low densities at greater depths. Light intensity and burial by wave action appear to be primary factors affecting diatom abundance, but the effect of unidentified factors causing local patchiness is also evident. Substrate stabilization by diatoms was observed between 0.3 and 1.8 m depth. Weight of benthic detrital aggregate generally increased with depth such that diatom concentrations were variable above 3 m but were extremely low in benthic detrital aggregate at greater depths. Comparison of diatom concentrations in fish stomachs and benthic detrital aggregate shows that within the shallow waters, fish do not selectively graze those areas richest in diatoms.