Epiphytic Diatoms Research Articles

An 1800-year water-quality and vegetation record from Junction Park Billabong, Murray River, Australia: an assessment of European impacts and sensitivity to climate

The Murray River is Australia’s economically most important river system. As a result of its economic importance, land use change and river regulation have resulted in ecological degradation of the river and associated river wetlands (known throughout Australia as “billabongs”). Palaeolimnology can provide otherwise unobtainable information about the relative impacts of stressors and identify “refuges” from such impacts. We examine an approximately 1800 year history of water quality and vegetation at Junction Park Billabong, on the Murray River approximately 25 km upstream of the Murrumbidgee River confluence. Throughout this period the billabong has maintained a strong connection to the Murray River. Planktonic Aulacoseira granulata has been the dominant diatom in the Murray River, while surrounding vegetation has been dominated by open eucalpyt woodland. Around 500 years before present (BP), there was an increase in effective rainfall as indicated by a decline in Chenopodioideae (Amaranthaceae: saltbush) and an increase in Callitris (native pine) pollen. At the same time, there was an expansion in wetland submerged aquatic macrophytes, as evidenced through increases in the relative abundance of the epiphytic diatom, Cocconeis placentula and sediment organic matter. European settlement resulted in declines in aquatic macrophytes and nutrient enrichment but minimal increases in diatom-inferred salinity. There was relatively little post-settlement change in both the diatom stratigraphy and inferred water quality from Junction Park Billabong which contrasts somewhat with that observed in floodplain water bodies both upstream and downstream of Junction Park. The record from Junction Park Billabong highlights the sensitivity of floodplain wetlands to climate change and suggests that examination of these records can provide insights into late Holocene climate from a region where few high-resolution records from other sources exist.

First finding of a genus Haslea Simonsen in Serbia and new diatom taxa for the country's flora in extreme and unique habitats in the Vojvodina Province

Salt habitats are extreme and unique environments found from Austria through Hungary to the Vojvodina Province in Serbia. In our study, we investigated eight saline habitats (channeled salt marshes, moist salt meadows and saline ponds), from which we collected plankton, epipelic and epiphytic diatoms. Seventeen diatom taxa new for the Serbian diatom flora were recorded. In addition, the genus Haslea, with one species (H. spicula), was recorded for the first time in Serbia. The identified taxa were sporadic or rare in the samples.

Heterogeneity of epiphytic diatoms in shallow lakes: Implications for lake monitoring

Abstract Current diatom assessments of shallow lakes typically use littoral epiphytic diatoms as bioindicators for eutrophication pressure. However, challenges in establishing robust ecological assessments still exist because of the natural pressures that shallow lakes are subjected to which are difficult to quantify (e.g., water-level fluctuations or wave action). Information on the spatial and temporal variability of epiphytic communities within a shallow lake is limited although important for the development of robust bioassessment protocols. We compared epiphytic diatom taxa and functional group compositions between the littoral and pelagic zone of three least-disturbed shallow lakes in the northeastern part of South Africa along a temporal gradient. In comparison to the pelagic zone, the littoral zone was characterized by almost double in species richness. Temporal variability was significantly higher for littoral diatom communities and littoral water physico-chemistry than those of the pelagic. Overall, water depth was a good predictor of the epiphytic diatom taxa and functional group composition. We also found that pelagic diatom taxa and functional groups correlated better with pelagic physico-chemistry than littoral diatoms to littoral physico-chemistry. This could be attributed to un-modeled factors related to natural physical pressures that will have more of an impact on littoral habitats than less exposed pelagic habitats. Given these findings, using pelagic epiphytic diatoms as a bioindicator in shallow lake monitoring programs could be more efficient than littoral diatoms at providing robust ecological assessments due to their relatively low variability.

A comparison between the morphological and molecular approach to identify the benthic diatom community in the St Lucia Estuary, South Africa

The use of diatoms as bioindicators to detect human-induced change is a globally accepted monitoring tool. DNA metabarcoding is an effective complementary tool to standard microscopic methods for species identification, providing reliable and timeous diatom assessments in a range of aquatic ecosystems. This study evaluated the suitability of the DNA metabarcoding approach for diatom monitoring in the St Lucia Estuary, South Africa. Results obtained from the standard microscopic (morphological) and molecular methods were compared and indicated a low similarity in the vegetated (11%), unvegetated (12%) and epiphytic (12%) habitats at species level for the epipelic and epiphytic diatom communities. The difference between the methods was expected given the challenges pertaining to the incomplete molecular reference database, intragenomic variability, physiological differences (number of chloroplasts) and highly variable microphytobenthos biomass. While the molecular method was unable to identify the presence of all the dominant diatom species (routinely used as ecological indicators), the available molecular operational taxonomic units (MOTUs) provided an effective complementary tool to determine the relevant community diversity estimates required for the application of the South African estuarine health index (EHI).

Large-scale geographical and environmental drivers of shallow lake diatom metacommunities across Europe

Disentangling the relative role of species sorting and dispersal limitation in biological communities has become one of the main issues for community ecologists and biogeographers. In this study, we analysed a data set of epiphytic diatoms comprising 34 lakes from six European countries. This data set covers a relatively large latitudinal gradient to elucidate which processes are affecting the distribution of diatom communities on a broad spatial extent. Our results show strong environmental effects on the composition of the diatom communities, while the spatial factor effects were weak, emphasising that compositional variation was mainly due to species turnover. Our data support information from the literature that local abiotic factors are the main predictors controlling the compositional variation of diatom assemblages in European shallow lakes. More specifically, changes in species composition were driven mainly by nutrient content in Northern Europe, whereas lakes located in Southern Europe were more affected by conductivity and lake depth. Our results solve pending questions in the spatial ecology of diatoms by proving that species turnover is stronger than nestedness at any spatial scale, and give support to the use of epiphytic diatoms as biological indicators for shallow lakes.

Diatom flora of Hasina pond, Morang, Nepal

Epiphytic diatoms of Hasina pond were studied during winter, summer, and monson seasons in 2014-2015. Samples were collected by squeezing submerged roots and leaves of hydrophytes and frustules were cleaned using nitric acid. A total 59 diatoms under 27 genera and 19 families were reported among which 33 diatoms were new to the country. Epithemia adnata, Rhopalodia gibba, Gomphonema truncatum, Nitzschia palea, Ulnaria acus, U. ulna and Pinnularia amabilis were dominant in the pond. Diatom species were found maximum in summer (40%) and minimum in monsoon (28%) seasons.

Trait-based community assembly of epiphytic diatoms in saline astatic ponds: a test of the stress-dominance hypothesis

The stress dominance hypothesis (SDH) postulates that strong environmental gradients drive trait convergence in communities over limiting similarity. Previous studies, conducted mostly with terrestrial plant communities, found controversial evidence for this prediction. We provide here the first test for SDH for epiphytic diatoms. We studied community assembly in diatom communities of astatic ponds. These water bodies serve as a good model system for testing SDH because they exhibit stress gradients of various environmental factors. Functional diversity of diatom communities was assessed based on four traits: (1) combined trait reflecting the trade-off between stress tolerance and competitive dominance, (2) cell size, (3) oxygen requirement and (4) N-uptake strategy. According to our results, salinity, pH and the width of the macrophyte belt appeared as significant predictors of the trait convergence/divergence patterns presumably acting through influencing the availability of carbon dioxide and turbidity. Lower trait diversity was found in turbid, more saline and more alkaline ponds and functional diversity was higher in transparent, less saline and less alkaline ponds. Overall, our results supported the stress dominance hypothesis. In habitats representing increased environmental stress, environmental filtering was the most important community assembly rule, while limiting similarity became dominant under more favourable conditions.

Sea urchin recruitment: Effect of diatom based biofilms on Paracentrotus lividus competent larvae

Eight different experimental substrates were tested on Paracentrotus lividus competent larvae in order to evaluate their potential for inducing metamorphosis and enhance survival after recruitment. Two benthic diatoms species, Nitzschia laevis (NL) and Halamphora coffeaeformis (HC), were selected according to their capacity to adhere and to form strong biofilms. They were tested in monocultures and in a mixed biofilm (MIX) that was also tried in combination with Gamma-Aminobutyric Acid, involved in triggering some invertebrate metamorphosis (MIX + GABA). Histamine (HIS) was also used as a treatment according to the high metamorphosis rates that have been recorded for this compound on other sea urchin species. Finally, a natural microphytobenthic biofilm (NATURAL) and oyster shells particles colonized by epiphytic diatoms (SHELL) were sampled from the mud of a refining oyster pond. Batches of 21 days-old larvae were placed on each experimental substrate and their effect was compared to a negative control of filtered sea water (without any treatment; FSW). Metamorphosis rate was daily recorded in each treatment. The sea urchin larvae on substrates NL, NATURAL, GABA + MIX and SHELL showed significantly higher metamorphosis rates than larvae on the other treatments (P < 0.001), reaching more than 90% in 72 h. Survival rate was assessed at 10 days post-metamorphosis in these four treatments. No difference was observed between them in terms of metamorphosis rate or survival rate (more than 60% for the four experimental substrates). Results demonstrate that the transition from planktonic larvae to benthic juvenile could be promoted through diatom-based biofilms. These substrates represent efficient metamorphosis inducers for P. lividus larviculture but we suggest to use preferably N. laevis biofilms in order to promote practical and safe solutions for farmers.

Interactive effects of warming and eutrophication on population dynamics and stalk production of epiphytic diatoms in transitional waters

The interactive effects of temperature and nitrogen:phosphorus stoichiometry were assessed by an experiment that involves cultures of the stalked epiphytic diatom Licmophora colosalis at different N:P ratios (5, 10, 16, 21 and 42) and temperatures (26, 31 and 36 °C) to simulate predictions of global warming effects on a Mediterranean coastal lagoon. At 26 °C, which seemed optimal for L. colosalis, it grew well at the N:P ratios within the 16–21 range, but a different stoichiometry reduced cell growth. The 5 °C increase had deleterious effects on diatom fitness as growth reduced, mortality increased and carbohydrates accumulation amplified under N or P deficiency. In contrast, this temperature stress was better overcome at N:P = 16. The 36 °C temperature proved lethal. Stalk production was specifically stimulated when growth was P-limited at both 26 °C and 31 °C, which suggests that a high proportion of stalks, which would form macroscopic colonies, may serve as an indicator of warming and high N:P ratios in transitional waters.

Epiphytic diatom assemblages on invasive Caulerpa taxifolia and autochthonous Halimeda tuna and Padina sp. seaweeds in the Adriatic Sea – summer/autumn aspect

Abstract This study focuses on the taxonomy of epiphytic diatoms in the area of invasive macroalgae from the genus Caulerpa. Caulerpa species are characterized by the presence of secondary metabolites, such as caulerpenyne (CYN), the main function of which is a chemical defense mechanism against herbivores and epiphytes. Epiphytic diatoms were studied on fronds of Caulerpa taxifolia (“killer seaweed”) and, for comparison, on autochthonous macroalgae Padina sp. and Halimeda tuna at the eastern Adriatic Sea coast (Island of Hvar) in the summer and autumn of 2010. The qualitative analysis was performed with the use of light and scanning electron microscopy. The Shannon–Wiener Diversity Index determined for Caulerpa taxifolia showed a wide range of values (3.11–4.88), with a maximum in August and a minimum in October. While the number of taxa on Caulerpa taxifolia fronds increased from June (41) to August (88), it declined in autumn due to the high relative abundance of Cocconeis caulerpacola, which is a diatom typical for Caulerpa. On the other hand, the largest number of taxa on Padina sp. was observed in September (82). The detailed composition of epiphytic diatoms and seasonal dynamics in the area affected by the invasive macroalga Caulerpa taxifolia have been determined for the first time.

ECOLOGICAL STUDY OF EPIPHYTIC DIATOMS ON TWO SUBMERGED AQUATIC MACROPHYTES IN TIGRIS RIVER, IRAQ

This study was aimed to provide the baseline information of epiphytic diatom communities in the Tigris river within Wasit Province to fill the information gap on the algal distribution. This investigation was conducted on epiphytic diatoms from two macrophytes (Ceratophyllum demersum and Myriophyllum alterniflorum) and related physicochemical parameters of the river from June 2015 to May 2016. Three sites were selected along the river (Al-Aziziyah, Zubaidiyah, and Numaniyah). Qualitative and quantitative study of epiphytic diatoms was investigated. A total of 277 species of epiphytic diatoms were identified on both macrophytes, these diatoms belonged to 27 genera for C. demersum and 28 genra for M. alterniflorum. A total number of diatom species were ranged from 801.8× 104 cell.g-1 at site 3 to 1159.72 ×104 cell.g-1 at 1for C. demersum, while on M. alterniflorum were ranged (87.24 × 104 -545.68×104 cell.g-1) at site1. The study revealed that diatoms were abundant, reflecting the quality of water and determine the extent of pollution and polluted type.

Inducers of settlement and metamorphosis of the shrimp Hippolyte inermis Leach in Posidonia oceanica

Larvae of the caridean shrimp Hippolyte inermis persist in the plankton of the Mediterranean up to about one month. Since they need to reach appropriate coastal areas for their recruitment in seagrass meadows, we hypothesized that leaves of Posidonia oceanica or, alternatively, algae present in their epiphytic biofilms, might be physically recognised as target substrates and trigger larval metamorphosis and settlement. Chemical cues could improve the finding of suitable habitats for settlement. Thus, the effects of leaves of P. oceanica and biofilms of the diatom Cocconeis scutellum parva, seasonally abundant in the leaf epiphytic stratum, were investigated along with the effect of volatile organic compounds (VOCs) extracted from the epiphytic diatom. The physical induction with P. oceanica accelerated larval settlement, stimulating an earlier and faster metamorphosis of larvae. C. scutellum parva produced a weaker effect on settlement; however, diatom’s VOCs had evident influence and accelerated metamorphosis and settlement. We concluded that such chemical cues as the VOCs produced by epiphytic diatoms, reinforce the effect of physical cues for the identification of suitable settlement locations for this shrimp.

Response of benthic algae to environmental conditions in an urban lake recovered from eutrophication, China

Benthic algae communities dominate the primary production in littoral zone of shallow lake. To understand the long-term effect of alteration in the composition of benthic algae community assemblage in such as a lake in China, we analyzed the benthic algae developments and indicators in the Donghu Lake in Wuhan, central China in 2004 and 2014. We compared the benthic algae biomass, compositions, and species richness of aquatic macrophytes and the changes of primary physicochemical parameters. The results show that in the 10-year period, chl a and conductivity declined significantly but nutrient level of the whole lake remained largely stable. The benthic algae biomass doubled and the relative proportion of green algae increased, whereas the benthic diatom ratio decreased. The benthic diatom assemblages and taxa differed in a number of ways, showing more epiphytic diatom species, and the relative abundance and species richness changed markedly. The number of aquatic macrophyte species increased from 3 in 2004 to 15 in 2014, presenting a remarkable recovery from previous eutrophication conditions. The changes of water level, chl a, and conductivity played a crucial role in governing aquatic macrophytes re-colonization in the littoral zones in the period. The ecological characteristics of littoral benthic diatoms reflect habitat coupling as indicated by redundancy analysis. Therefore, the close link between benthic algae and macrophyte recovery demonstrates that the benthic algae metrics are much more useful than nutrient levels to quantify the process of restoration in the lake.

Ocean acidification influences plant-animal interactions: The effect of Cocconeis scutellum parva on the sex reversal of Hippolyte inermis.

Ocean acidification (O.A.) influences the ecology of oceans and it may impact plant-animal interactions at various levels. Seagrass meadows located at acidified vents in the Bay of Naples (Italy) are considered an open window to forecast the effects of global-changes on aquatic communities. Epiphytic diatoms of the genus Cocconeis are abundant in seagrass meadows, including acidified environments, where they play key ecological roles. A still-unknown apoptogenic compound produced by Cocconeis triggers the suicide of the androgenic gland of Hippolyte inermis Leach 1816, a protandric hermaphroditic shrimp distributed in P. oceanica meadows located both at normal pH and in acidified vents. Feeding on Cocconeis sp. was proven important for the stability of the shrimp’s natural populations. Since O.A. affects the physiology of diatoms, we investigated if, in future scenarios of O.A., Cocconeis scutellum parva will still produce an effect on shrimp’s physiology. Cell densities of Cocconeis scutellum parva cultivated in custom-designed photobioreactors at two pH conditions (pH 7.7 and 8.2) were compared. In addition, we determined the effects of the ingestion of diatoms on the process of sex reversal of H. inermis and we calculated the % female on the total of mature individuals-1 (F/mat). We observed significant differences in cell densities of C. scutellum parva at the two pH conditions. In fact, the highest cell densities (148,808 ±13,935 cells. mm-2) was obtained at day 13 (pH 7.7) and it is higher than the highest cell densities (38,066 (±4,166) cells. mm-2, day 13) produced at pH 8.2. Diatoms cultured at acidified conditions changed their metabolism. In fact, diatoms grown in acidified conditions produced in H. inermis a proportion of females (F/mat 36.3 ±5.9%) significantly lower than diatoms produced at normal pH (68.5 ±2.8), and it was not significantly different from that elicited by negative controls (31.7 ±5.6%).

Epiphytic diatoms as bioindicators of trophic status of Lake Modrac(Bosnia and Herzegovina)

Biodiversity of diatoms and applicability of diatom indices in biomonitoring based on littoral epiphytic samples of Lake Modrac were investigated. Diatoms were taken mostly from Phragmites australis stems in 2017, during which physical and chemical parameters of the water were measured. A total of 85 diatom taxa were identified. Gomphonema (13 spp.), Navicula (11 spp.), and Nitzschia (8 spp.) were the most abundant genera. Obtained values of trophic indices (TID, TvD, and TDIL) pointed to meso- to eutrophic status for most localities, while values of the IBD, EPI, ?D, and IPS indices indicated good ecological status, except for localities at the mouth of 2 main tributaries which had moderate or poor ecological status. Based on the hierarchical group average clustering and nonmetric multidimensional scaling, 4 groups were identified, mainly related to the sampling period, with higher spatial variation in species composition during summer. Since environmental legislation in Bosnia and Herzegovina still does not provide detailed instructions on using diatoms in biological assessment, results of this study can be useful for the development of biomonitoring tools for lakes in Bosnia and Herzegovina.

Relationship between regional climate change and primary ecosystem characteristics in a lagoon undergoing anthropogenic eutrophication, Lake Mokoto, Japan

Annual-scale environmental and ecosystem changes since the mid-19th century were reconstructed in a seasonally frozen lagoon, Lake Mokoto, located along the Okhotsk Sea coast of Hokkaido, northern Japan. X-ray fluorescence (XRF) and diatom analyses of laminated sediment were conducted to determine the impact of short-term climate oscillations and anthropogenic eutrophication on the lagoon ecosystem. In this lagoon, eutrophication has progressed since the early 20th century due to deforestation and human activity in the catchment area, such as development of the cattle industry and field agriculture. In particular, the sedimentation rate of Lake Mokoto and potassium and phosphorus contents of lake sediment have increased rapidly since 1970, in association with an increase in the number of cattle. In addition, the Lake Mokoto ecosystem shows interannual and decadal cyclic fluctuations that are separate from the anthropogenic effects. Prior to anthropogenic eutrophication, the nutrient condition of Lake Mokoto showed a close relationship with the Pacific decadal oscillation (PDO). The growth of seagrass, inferred from epiphytic diatom abundance, showed a clear decadal cycle following variation in solar irradiance.

A STUDY OF PROPERTIES OF GENERALIZED MODEL FOR INTERANNUAL DYNAMICS OF EPIPHYTIC DIATOM COMMUNITIES

Modeling the dynamics of the relative number of diatoms in epiphytic diatom communities of the macrophyte Ulva lactuca Linnaeus from three different coastal areas of Peter the Great Bay, Sea of Japan (Amur Bay, Ussuri Bay, and the Stark Strait), based on a tool of recurrent equations, makes it possible to identify the communities’ own natural dynamics in the water areas studied [Parensky, Levchenko, 2018]. It has been found that the reproductive capacity of the epiphytic diatom communities decreases in the following sequence: Amur Bay — Ussuri Bay — Stark Strait. As reported in literature, the nitrogen and phosphorus enrichment of the above-mentioned water areas decreases in the same sequence [Zvalinsky et al., 2013]. A relationship existing between the relative number of epiphytic diatoms and the level of trophicity of their habitat is assumed. Possible variants of relationships of the model coefficients with the trophicity level, including the necessary point (X = 0, Z = 0), are considered. Trophicity has proven to regulate all parameters of the multistep recurrent models describing the relative number of epiphytic diatoms. A generalized recurrent model for regulation of the relative number of epiphytic diatoms has been built; in this model, a regulating (trophic) factor is added to two limiting factors (photosynthetically active radiation and oxygen). A study of the model has shown that the trophicity level influences the interannual dynamics of the relative diatoms’ number and the duration of communities’ existence.

Diatoms associated with two South African kelp species: Ecklonia maxima and Laminaria pallida

Kelp forests are believed to host a large biomass of epiphytic fauna and flora, including diatoms, which constitute the base of aquatic food webs and play an important role in the transfer of energy to higher trophic levels. Epiphytic diatom assemblages associated with two common species of South African kelps, Ecklonia maxima and Laminaria pallida, were investigated in this study. Primary blades of adult and juvenile thalli of both kelp species were sampled at False Bay in July 2017 and analysed using scanning electron microscopy. Our findings showed that both kelp species hosted relatively low densities of diatoms (ranging from 7 [SD 5] cells mm−2 on adult specimens of L. pallida to 43 [SD 66] cells mm−2 on blades of juvenile E. maxima), with Amphora and Gomphoseptatum reaching the highest absolute abundances. Although non-metric multidimensional scaling showed overlapping and largely scattered sample sets, a significant relationship between the diatom communities and the species and age of the host macroalga was detected by two-way PERMANOVA. In general, more abundant and diverse diatom communities were observed on juvenile thalli than on adult thalli, with species belonging to Navicula and Rhoicosphenia contributing significantly to the observed dissimilarity. Due to a significant interaction between species and age effects, however, the overall ability of kelp species, their age, and their interaction to explain the variation in diatom community structure was limited. We suggest that the low densities of epiphytic diatoms were directly related to the sloughing of epithelial cells observed in both kelp species. We further speculate that on such unstable substrata some diatom taxa might adapt to an endophytic life to avoid the antifouling mechanisms developed by their hosts.

Local habitat heterogeneity determines the differences in benthic diatom metacommunities between different urban river types

Benthic diatoms are useful indicators of the ecological state of river systems. To understand the factors determining benthic diatom metacommunity composition in urban rivers, we studied in situ surface sediment diatom communities from 23 rivers in Shanghai City. Based on our study results on the metacommunity structure of benthic diatoms and hierarchical cluster analysis (HCA), we found substantial differences between restored (G1) and unrestored rivers (G2–G4) in taxa richness, relative abundances, and dominant and indicator taxa of benthic diatoms. The epiphytic diatoms Cocconeis placentula and Amphora libyca var. baltica were representative of the restored rivers (G1), where aquatic macrophytes were more abundant and the water was clearer. The motile epipelic diatoms Navicula recens and Navicula germainii dominated the moderately polluted rivers (G2). The eutrophic taxa Cyclotella meneghiniana, Aulacoseira granulata, and Cyclostephanos tholiformis dominated in G3, which comprised relatively heavily polluted rivers with low organic matter sediment and high disturbance. The polysaprobic taxon Nitzschia palea and the halophilous taxon Fallacia pygmaea represented relatively heavily polluted rivers with a comparatively higher sedimentary salinity (SSal) (G4). Redundancy analysis (RDA) revealed that total phosphorus (TP), dissolved organic carbon (DOC), silicon dioxide (SiO2), dissolved oxygen (DO), Secchi depth (SD), SSal, and the ratio of carbon to nitrogen (C/N) in the sediment were important environmental factors explaining variation among benthic diatom metacommunity composition. Partial RDA (pRDA) implied that the relative importance of environmental factors in structuring benthic diatom metacommunity was much higher than spatial factors. Classification and regression trees (CART) further indicated that DOC, the sediment C/N ratio, and SSal were the key local environmental factors affecting grouping patterns of benthic diatom metacommunities. Our study proposes that benthic diatom metacommunities respond to the complex characteristics of local environment in urban rivers and provides useful knowledge for consideration in the ecological monitoring of urban river systems.

Periphytic diatom colonization and litter decomposition in an intermittent stream of South India.

We examined the dynamic of periphytic diatom colonization and litter decompositional pattern in an intermittent stream of South India. Litter bags containing 5 g of fresh fallen leaves (belongs to five different species of angiosperms) were fixed in the five stream pools and they were collected after 7, 14, 21, and 28 days of incubation. This experiment showed the diversity, richness, and abundance of diatoms developed on leaf litter. In total, 131 µl-1 cells of diatoms under four species in three families were collected from decomposing leaves in benthic area of stream pools. During experiment, 142 µl-1 cells representing 11 taxa in 10 families were observed in litter bags. The colonization of epiphytic diatom was rapid in early stage of litter decomposition. The higher number of colonization made by Asterionella and Stenopterobia found in litter bags of all experimental weeks. These findings suggest that the rapid microbial colonization (ephiphytic algae) was occurred in the early stage of litter decomposition in an intermittent tropical stream and a comprehensive ecological investigation in perennial natural streams in India is needed.