Epiphytic Diatom Communities Research Articles

Assessing long-term diatom changes in sub-Arctic ponds receiving high fluxes of seabird nutrients.

Algal bioindicators, such as diatoms, often show subdued responses to eutrophication in Arctic lakes because climate-related changes (e.g., ice cover) tend to be the overriding factors influencing assemblage composition. Here, we examined how sub-Arctic ponds historically receiving high nutrient inputs from nesting seabirds have responded to recent climate change. We present diatom data obtained from 12 sediment cores in seaduck-affected ponds located on islands through Hudson Strait, Canada. All study cores show consistently elevated values of sedimentary ẟ15N, an established proxy for tracking marine-derived nutrients, indicating seabirds have been present on these islands for at least the duration of the sediment records (~100 to 400 years). We document diverse epiphytic diatom assemblages to the base of all sediment cores, which is in marked contrast to seabird-free Arctic ponds-these oligotrophic sites typically record epilithic diatom flora prior to recent warming. Diatoms are likely responding indirectly to seabird nutrients via habitat as nutrients promote the growth of mosses supporting epiphytic diatom communities. This masks the typical diatom response to increased warming in the Arctic, which also results in habitat changes and the growth of mosses around the pond edges. Changes in sedimentary chlorophyll a were not consistently synchronous with large changes in ẟ15N values, suggesting that primary production in ponds is not responding linearly to changes in seabird-derived nitrogen. Across all ponds, we recorded shifts in diatom epiphytic assemblages (e.g., increases in % relative abundance of many Nitzschia species) that often align with increases in chlorophyll a. The changes in diatoms and chlorophyll a, although variable, are most likely driven by climate change as they are generally consistent with longer ice-free conditions and growing seasons. Together, our results show that to effectively use diatoms in animal population reconstructions across the sub-Arctic and Arctic, a strong understanding of eutrophication and climate change, based on supplementary proxies, is also required.

Environmental drivers of genetic variability in common diatom genera: Implications for shallow lake biomonitoring

Diatoms are microalgae, known to present several characteristics that make them excellent bioindicators. In this study, we analyzed the epiphytic diatom communities of ponds, with the aim of exploring the genetic variability explained by physical, chemical or geographical variables. We selected 77 lakes within the Spanish part of the Duero River Basin characterized by wide chemical variability. In each lake, physical parameters were measured in situ and water samples were taken to determine nutrient levels in the laboratory. Diatom communities were collected and identified by DNA-metabarcoding, amplifying a genetic barcode of rbcL gene. We analyzed the phylogenetic signal for several environmental parameters at the genus level for the three most representative genera of these lakes. Our results indicate significant phylogenetic signals that differ from a genus to another. Processes related to spatial scales appear to be the main predictors controlling the genetic diversity of diatom communities in these ponds, with genetic variants differing among geographical areas for a given species. These molecular studies confirm the enormous diversity present in the diatom communities that inhabit these ecosystems, but further research is needed to apply diatom-based techniques in ponds monitoring or conservation programs. Our results reinforce the view that considering not only morphological but also molecular and ecological characters are necessary to describe new living diatom species, whenever possible, especially given the high number of species described each year.

Diversity and Variation of Epiphytic Diatoms on Ruppia maritima L., Related to Anthropogenic Impact in an Estuary in Southern Brazil

Knowledge about the diversity and spatiotemporal variability of epiphytic diatom communities in estuarine meadows has great relevance for coastal ecology and, thus, contributes to understanding the impact of natural and anthropogenic changes on seagrass meadows. The community of epiphytic diatoms in Ruppia maritima L. meadows was investigated in two environments with different levels of anthropogenic impact and nutrient loads. Both impacted and non-impacted meadows had similar conditions in terms of water depth, temperature and transparency but distinct nutrient loads and salinity ranges. A total of 159 diatom taxa were found on Ruppia maritima leaves during the monitoring period, including freshwater (30.8%), marine (25.1%), brackish (9.4%) and cosmopolitan (8.8%) taxa. The most abundant species were C. placentula, T. tabulata, M. pumila and T. fasciculata, in addition to A. tenuissimus, C. adhaerens and M. moniliformis. Although present in both sites, C. placentula and T. tabulata were the dominant species in the impacted site. We found that 32% of the taxa were exclusive to the non-impacted site, 23% to the impacted site and 45% were common to both sites. The study sites showed marked differences in community attributes; i.e., higher richness, diversity and equitability and lower dominance were found in the non-impacted site, which is distant from anthropogenic sources of domestic and industrial sewage and has low concentrations of dissolved N and P in water and low values of sediment organic matter. Nutrient concentration and salinity were the main factors behind the spatial and temporal variability in the structure of the epiphytic community when all other environmental variables were similar (water depth, temperature, transparency and host plant). The influence of temperature and salinity on community structure was site-dependent. This study revealed the high richness and diversity of epiphytic diatoms in the meadows of the Patos Lagoon estuary (PLE) and the high spatial and temporal heterogeneity of the communities, and it shows the potential of epiphytic community studies for the assessment of environmental quality in seagrass meadow habitats.

Diatom community composition on submerged macrophyte species from an Ontario (Canada) lake.

The introduction of invasive macrophyte species can affect submerged macrophyte community composition and abundance, which in turn can alter the functions of lake ecosystems. Knowing when and how invasive macrophytes arrive and spread can help disentangle the effects of invasive species from other stressors on lake ecosystems. This requires a long-term (decades) perspective of macrophyte community composition, which is rarely available. An alternative is paleolimnological inferences of macrophyte community composition from fossil diatom assemblages, which requires knowledge of epiphytic diatom communities. Here, we investigated the epiphytic diatom community composition of three common submerged macrophyte species (Chara sp., Potamogeton robbinsii, and the invasive Myriophyllum spicatum) in a typical temperate, mixed forest lake, Chandos Lake, Ontario, Canada, to provide a basis for future paleolimnological research. Non-parametric, multivariate analysis of variance indicated a statistically significant difference in the epiphytic diatom communities of different macrophyte species, despite principal components analysis showing some overlap among the diatom communities. Diatom community composition of all macrophytes had abundant Achnanthidium minutissimum and Cocconeis placentula. Generalized linear models and univariate analysis of variance identified six diatoms (Encyonopsis microcephala, Epithemia turgida, Gomphonema parvulius, Navicula gerloffi, Rhopalodia gibba, and Rossithidium anastasiae) that were significantly different among macrophyte species. Although it remains uncertain whether these differences are sufficient to infer historical macrophyte community composition from epiphytic diatom fossil assemblages, our results indicate the potential of such an approach and offer suggestions for future research.

Comparisons of diatoms and fishes as toxic metal bioindicator: a case study of an A-class wetland in northwest Turkey under effect of an intensive paddy cultivation stress.

In this research, diatoms as the first step and fishes as the last step of the food chain were compared as toxic metal accumulation bioindicator in an A-class wetland in Turkey. Bioaccumulations of potentially toxic elements (PTEs) were determined in liver, gill and muscle tissues of two commercially consumed fish species Carassius gibelio and Cyprinus carpio and in frustules of epiphytic diatom communities living on submerged macrophytes. Samples were collected seasonally from the Gala Lake, which is among the best stopover habitats of birds migrating between Europe and Africa, considering the paddy harvest period that is a major stress factor for the ecosystem. Also, potential human health risks associated with the consumption of fishes and consumption - dermal contact of diatoms were evaluated both for summer - before paddy harvest (BPH) and autumn - after paddy harvest (APH) periods. As a result of this research, the investigated toxic metal concentrations were increased significantly in diatoms in the APH period, while less significant exchanges were recorded in fishes. The bioaccumulations of PTEs were ranked as follows: Zn > Mn > Se > Cu > B > Cr > Ni > As > Pb > Cd for C. gibelio; Zn > Mn > Se > Cu > B > Cr > As > Ni > Pb > Cd for C. carpio; and Mn > Zn > Se > Pb > B > Ni > Cr > Cu > As > Cd for diatom frustules. Although the HI values in diatoms detected in the APH period were statistically significantly higher (about 1000 times; p < 0.05) than detected in the BPH period, they were less than the limit of 1 in both seasons. However, the HI coefficients of fishes were quite higher than the limit (an average of 23.59 for C. gibelio and 19.18 for C. carpio), which means quite high probable non-carcinogenic health risks for humans. Furthermore, the CR coefficients of Cr, Ni and As in muscle tissues of fishes were considerably higher than the limit of 10-4, which reflects a significant carcinogenic health risk for consumers. The data showed that although the fishes at the top of the food chain bioaccumulate the PTEs in their tissues much higher than the diatoms at the bottom of the food chain, the diatoms are much more sensitive to changes in the environmental conditions than the fishes and they are more effective biological tools as toxic metal accumulation bioindicators.

Epiphytic diatoms on herbarium material from the Central Forest phytogeographic region of the Democratic Republic of the Congo

Background and aims – Epiphytic diatoms are excellent bio-indicators of the present and past ecological condition of aquatic ecosystems. In order to reconstruct the diatom history and to evaluate its diversity in the Democratic Republic of the Congo, epiphytic diatoms were sampled from herbarium specimens of aquatic plants deposited at the National Herbarium of the Congo at Yangambi (YBI) and at the herbarium of Meise Botanic Garden (BR).Material and methods – In YBI, nine specimens belonging to the Nymphaeaceae, three to the Ceratophyllaceae, and 12 to the Lentibulariaceae collected in the Central Forest phytogeographic region were sampled for diatom investigation. In addition, nine Nymphaea lotus specimens were sampled in BR. Semi-quantitative analyses were performed by light microscopy on permanent diatom slides.Key results – Analyses of the epiphytic diatom communities on YBI and BR materials showed a large diversity of 132 species belonging to 44 genera. Taxa belonging to the genus Eunotia were relatively the most abundant in all studied samples followed by Frustulia saxonica and a Desmogonium sp. The diatom communities on Nymphaea were as varied as on Ceratophyllum, while on Utricularia, a significant lower diversity was observed. The Trophic Diatom Index (TDI) and Generic Diatom Index (GDI) showed that the water quality in the Central Forest phytogeographic region was overall good during the 20th century. They point to oligotrophic conditions for the running waters with a slight increase towards more mesotrophic conditions from the 1950s onwards. The only sample in the present study indicating mesotrophic condition was from a swamp.Conclusions – The results on the epiphytic diatoms present on herbarium material can serve as a basis for sustainable management of aquatic ecosystems in D.R. Congo. In absence of an in-depth knowledge of the species and their ecological preferences, a genus-based TDI and IDG have proven to be valuable tools for water quality monitoring in tropical Africa.

Epiphytic diatom community structure and richness is determined by macroalgal host and location in the South Shetland Islands (Antarctica).

The marine waters around the South Shetland Islands are paramount in the primary production of this Antarctic ecosystem. With the increasing effects of climate change and the annual retreat of the ice shelf, the importance of macroalgae and their diatom epiphytes in primary production also increases. The relationships and interactions between these organisms have scarcely been studied in Antarctica, and even less in the volcanic ecosystem of Deception Island, which can be seen as a natural proxy of climate change in Antarctica because of its vulcanism, and the open marine system of Livingston Island. In this study we investigated the composition of the diatom communities in the context of their macroalgal hosts and different environmental factors. We used a non-acidic method for diatom digestion, followed by slidescanning and diatom identification by manual annotation through a web-browser-based image annotation platform. Epiphytic diatom species richness was higher on Deception Island as a whole, whereas individual macroalgal specimens harboured richer diatom assemblages on Livingston Island. We hypothesize this a possible result of a higher diversity of ecological niches in the unique volcanic environment of Deception Island. Overall, our study revealed higher species richness and diversity than previous studies of macroalgae-inhabiting diatoms in Antarctica, which could however be the result of the different preparation methodologies used in the different studies, rather than an indication of a higher species richness on Deception Island and Livingston Island than other Antarctic localities.

An Assessment of the Influence of Host Species, Age, and Thallus Part on Kelp-Associated Diatoms

Diatom community composition and abundances on different thallus parts of adult and juvenile specimens of Eckloniamaxima and Laminariapallida were examined in False Bay, South Africa, using light and scanning electron microscopy. Altogether, 288 thallus portions were analysed. Diatom abundances ranged from 0 to 404 cells mm−2 and were generally higher on E. maxima and juvenile thalli than L. pallida and adult specimens. Moreover, diatom abundances differed between the various thallus parts, being highest on the upper blade and lowest on the primary blade. A total of 48 diatom taxa belonging to 28 genera were found. Gomphoseptatum Medlin, Nagumoea Witkowski and Kociolek, Cocconeis Ehrenberg, and Navicula Bory were the most frequently occurring genera, being present in 84%, 65%, 62.5%, and 45% of the analysed samples, respectively. Among these, Cocconeis and Gomphoseptatum were the most abundant, contributing 50% and 27% of total diatom cells counted collectively across all samples. Permutational multivariate analysis of variance (PERMANOVA) revealed that all investigated main factors (kelp species and age and thallus part), as well as their two- and three-way interactions, except for the interaction between the host species and age, were significant. The high residual variance (72%) indicated that the sum of other unexamined factors contributed the largest component of the variation observed in the kelp-associated diatom communities, and grazing and possible defence strategies utilised by kelps are proposed as processes playing an important role in the structuring of epiphytic diatom communities. Possible endophytism of tissue-boring diatoms colonizing both kelp species is briefly discussed.

Using Diatom Indices to Evaluate Water quality In Abu-Zirig Marsh Thi-Qar Province /south of Iraq

The study attempts to assess water quality in Abu-Zirig Marsh which used epiphytic Diatom community for assessing water quality. Many of Diatom indices {Trophic diatom index (TDI), Diatom index (DI), Generic diatom index (GDI) have been used to give qualitative information about the status of the freshwater ecosystem(good, moderate, high pollution). In this study, the epiphytic diatoms on both host aquatic plants Phragmites australis and Typha domengensis were collected from Abu-Zirig Marsh within Thi-Qar Province at three sites in Autumn, 2018 and winter, 2019. Epiphytic diatoms were Identified by the preparation of permanent slides method, some species of epiphytic diatom showed dominance such as Cyclotella meneghiniana, Gomphonema angustatum, Cocconies placentula, Cymbella affinis, Navicula cryptoephala, Nitzschia linearis, N. dissipata, Surirella ovalis. Abundant diatoms indicated trophic conditions of the Marsh. The results of diatom indices revealed that IPS (10-12.5) is a moderate pollution condition of marsh, DI (2.9-3.4) range from high to moderate pollution condition, TDI (47.2-60.8) indicates trophic condition ranging from (oligo-mesotrophic to eutrophic) condition of marsh while GDI a range between (11.6-13.7) moderate pollution condition, the aim of the study that is about evaluating water quality of Abu-Zirig Marsh by using Diatom indices (IPS,DI,TDI and GDI), as well as due to scarce local previous studies of epiphytic diatoms and used as bio-indicator of water quality in Abu-Zirig Marsh, therefor suggested this study .

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).

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.

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.

A Study of the Properties of the Multi-Step Recurrent Models for the Interannual Dynamics of Epiphytic Diatom Communities

Communities of epiphytic diatoms develop seasonally. On macroalgae, they reach the highest density in the middle of summer and decline to a minimum value in winter. This discrete pattern makes it possible to use the tool of difference (recurrent) equations for testing the concept of density regulation on the interannual dynamics of the number of epiphytic diatoms. The properties of the obtained multi-step recurrent models for the interannual dynamics of the number of diatoms in the epiphyton of the macroalga Ulva lactuca Linnaeus collected from three areas of coastal waters in Peter the Great Bay, Sea of Japan (Amur Bay, Ussuri Bay, and Stark Strait), are considered. The proposed multi-step recurrent models do not contradict the primary data of observations. Each of the obtained descriptions for different water areas is characterized by its specific pattern of dynamics. The reproductive capacity of epiphytic diatom community is the lowest in the Stark Strait; the highest reproductive capacity is observed in Amur Bay. According to the models, the epiphytic diatom communities in different parts of Peter the Great Bay exhibit generally complex, pseudochaotic, dynamics of their number.

Unexpected consequences of bombing. Community level response of epiphytic diatoms to environmental stress in a saline bomb crater pond area.

The spatial response of epiphytic diatom communities to environmental stress was studied in a moderately saline wetland area located in the plain of Danube-Tisza Interfluve, Hungary. The area is characterised by World War II bomb crater ponds and can be regarded as an excellent ecological model system where the dispersion of species is slightly limited by distance. To study the effect of environmental variables on the communities, canonical correspondence analysis was applied. Salinity, pH, total suspended solids, total phosphorous and depth proved to be significant environmental drivers in this analysis. The ecological status of the ponds was assessed with Ziemann’s halobity index, as the trophity-depending metric cannot be applied to these habitats (due to the naturally high phosphorus content). Ponds in “good” ecological status significantly differed from those appertaining to water quality category of “not-good” ecological status considering characteristic of natural astatic soda pans (e.g. salinity, pH, ammonium, total phosphorous concentration, nitrogen:phosphorous ratio and turbidity). The differences between epiphytic diatom communities inhabiting the ponds were detected using non-parametric multidimensional scaling. The samples formed three groups according to the types of ponds (“transparent”, “transitional” and “turbid”) based on the width of the macrophyte belt around them. Indicator species related to the ecological status of the ponds and diatom communities contributing to the separation of groups of ponds were identified. One of the indicator species differed from species already described. Light and scanning electron microscopy features and phylogenetic analyses based on three genes (18S and 28S rRNA genes, rbcL) proved that it was a new species of Nitzschia genus, closely related to Nitzschia frustulum and Nitzschia inconspicua. Therefore, description of a new species, Nitzschia reskoi Ács, Duleba, C.E.Wetzel & Ector is proposed. We concluded that the increasing abundance of Nitzschia reskoi was a signal of the degradation of the intermittent saline wetlands.

A STUDY OF PROPERTIES OF THE RECURRENT MULTI-STEP MODELS FOR INTERANNUAL DYNAMICS OF DIATOM ALGAE COMMUNITIES IN EPIPHYTON

Epiphytic diatoms develop seasonally. On macrophytes they reach the highest density in the middle of summer and have the minimum density in winter. This pattern gives an opportunity to apply a tool of difference (recurrent) equations for testing the concept of density regulation in interannual dynamics of their number. Detailed scheme of the model is developed; the model is applied for the diatoms dynamics in macroalgae epiphyton of Ulva lactuca Linnaeus in three areas of Peter the Great Bay, Japan Sea (Amur Bay, Ussuri Bay, and Stark Strait). The model parameters are evaluated by means of SYSTAT 5 and STATISTICA 8 software. The model results do not contradict the data of observations. Its determination (R2 ) exceeds 0.62 in all cases. Selected coefficients of the model have rather small relative errors (&lt; 11 %) which never change the sign of the coefficients. Generally, the modelled dynamics of relative number of epiphytic diatom communities is complicated, pseudochaotic. It differs between the areas. Reproductive capacity of the epiphytic diatom community is the lowest in the Stark Strait and the highest in the Amur Bay. In both these areas, alternation patterns are modelled as periods of chaotic dynamics and the periods with a limit cyclicity. Resistance of the epiphytic diatom communities to variations of the main limiting factors of the environments decreases in the order: Amur Bay — Stark Strait — Ussuri Bay.

Multivariate analyses document host specificity, differences in the diatom metaphyton vs. epiphyton, and seasonality that structure the epiphytic diatom community

Epiphytic diatom community structure associated with selected macroalgae collected from jetties at Galveston, Port Aransas, and Port Isabel, Texas was investigated using multivariate and community statistics. Redundancy analyses revealed community variation attributable to treatment (4% in Galveston, up to 8–12% at Port Isabel and Port Aransas), to host plant (6–9%) and to season (ca 14%). Shared effects between pairs of factors were between 1 and 2% or less, indicating factors tested acted independently and significantly to vary the diatom community structure over a two year period. A coastal salinity gradient explained 16% of the variation. Host specificity was documented and correlated with season. Treatment included a wash, tip and base preparation processed to analyze metaphyton and epiphyton separately and determine zonation on hosts and within the narrow intertidal (11–25 cm). Wash assemblages were statistically different and more diverse than attached assemblages during the fall/spring but were more alike in winter when hosts were senescent. It is recommended that future studies of epiphytic communities take advantage of rinsing or washing the host plant to capture this important and significant part of the diatom community associated with macroalgae. Variation between hosts was greater than variation among host replicates, in abundance rather than identity.

Diatom-based models for inferring water chemistry and hydrology in temporary depressional wetlands

Information on the response of temporary depressional wetland diatoms to human-induced disturbances is a limited and important component for the development of temporary wetland biological assessments in human-modified landscapes. Establishing a reference condition of variation due to natural disturbances in depressional wetlands using diatoms is necessary for further investigations of anthropogenic impacts. We examined the temporal and spatial responses of epiphytic diatom communities to natural environmental disturbances within three least disturbed wetlands in the Mpumalanga Province, South Africa. Alkalinity, Na+ and Cl−, water depth and total relative evapotranspiration (ETo) accounted for the highest proportion of temporal variation in composition of epiphytic diatoms, as revealed by canonical correspondence analysis (CCA). Alkalinity, Na+, and Cl− explained a much higher proportion of species variation, using partial CCA. A simple WA with inverse deshrinking produced reasonably robust models for Na+ (r boot 2 = 0.71), depth (r boot 2 = 0.64) and alkalinity (r boot 2 = 0.46), not for Cl− and ETo. We determined species optima and tolerances for Na+, depth and alkalinity which can facilitate identification of anthropogenic impacts based on changes of indicator taxa assemblages. Our study provides a basis for newly developed quantitative tools to be used in biomonitoring studies and evaluations of reference conditions for temporary wetland management.

Biological traits of diatoms in the characterization of a reservoir and a stream in a subtropical region

The structure of epiphytic diatom communities in a reservoir and a stream were studied with regard to different taxonomic levels (species, genera, and families) and biological traits (strategies of attachment to the substrate). We expected that strongly attached diatoms would abound in the stream, and those employing a loosely attached strategy should predominate in the reservoir due to the lentic flow condition. The congruence of high taxonomic levels and biological traits of the species was assessed and tested against an equal pattern of distribution. Our hypothesis was that taxonomic levels and biological traits have high congruence with species community. As periphytic diatoms have specialized structures to colonize substrates, we believed biological trait groups would show greater congruence with the species than groups formed by taxonomic levels. In fact, we observed the prevalence of strongly attached strategies in the lotic environment and stalked, prostrate, motile, and planktonic strategies predominated in the reservoir. The congruence between species and biological traits was stronger in both environments than that with different taxonomic levels. These results suggest that the strategies of attachment represent a key factor to the occurrence and distribution of species. The attached strategy showed greater competitive advantages under unstable environmental conditions than the loosely attached strategy, which predominated under stable conditions. Our results demonstrated a strong association of the diatom community with environmental conditions and suggest that biological traits may be an additional alternative for characterizing environments.

A comparison of epiphytic diatom communities on Plocamium cartilagineum (Plocamiales, Florideophyceae) from two Antarctic areas

Our understanding of diatoms, one of the most important Antarctic primary producers, is based mostly on investigations of plankton, sea-ice, and sediment samples. Herein, we contribute to the limited research devoted to benthic Antarctic diatoms by presenting a study on epiphytic diatom communities sampled in two remote Antarctic regions: Admiralty Bay (maritime Antarctica, Antarctic Peninsula) and Terra Nova Bay (Ross Sea). Recent studies have demonstrated that the most critical factor for the local epiphytic diatom communities was the nature of the substrate. In order to eliminate this factor so we could evaluate other potential controls, we sampled epiphytic diatoms from only one substrate that is common to both regions: the macroalgae Plocamium cartilagineum (L.) Dixon. Thalli of P. cartilagineum and their associated microalgal community was collected in January 2011 (Admiralty Bay) and 2012 (Terra Nova Bay) from a water depth of 5–25 m. Dehydrated macroalgal pieces were placed on stubs and sputter-coated, which allowed observation of diatoms attached to the substrate in their original position using scanning electron microscopy. A total of 72 taxa were observed, of which 31 taxa were common to both regions. Cell abundance and diatom growth form dominance were significantly different in Admiralty Bay and Terra Nova Bay samples. Total diatom abundance was higher in Admiralty Bay samples, dominated by adnate diatoms (Cocconeis spp.), but the number of taxa found as well as the values of ecological indices were higher for samples from the Ross Sea, where motile forms were dominant (Navicula spp.). Our results suggest that Antarctic shallow-water benthic habitats may present a high degree of microniche heterogeneity and highlight the need of fine-scale analyses in microbial studies. We also suggest grazers as a factor that contributes greatly to the observed differences.

Zooplankton and diatoms of temporary and permanent freshwater pans in the Mpumalanga Highveld region, South Africa

This paper provides a description of the zooplankton and epiphytic diatom communities of permanent and temporary freshwater pans in the Mpumalanga Highveld region of South Africa. Few studies have investigated the biota of pans in this area, which is seriously threatened by mining and agricultural development. Nineteen pan sites within a 20 kmradius covering a wide range of water chemistries were sampled once for zooplankton, epiphytic diatoms and water physico-chemical data in 2009. Collected zooplankton and diatom samples were identified to species or genus level. Many of the zooplankton taxa reported in this study were not recorded in similar pan studies in South Africa and southern Africa. The study revealed a difference among the compositions of zooplankton and diatom communities between temporary pans and permanent pans. Zooplankton found exclusively in freshwater temporary pans included cladocerans (Megafenestra aurita and Scapholeberis kingi), calanoids (Mesocyclops major and Thermodiaptomus mixtus), a cyclopoid (Acanthocyclops vernalis) and a rotifer (Platyias quadricornis). Permanent pans were characterized by taxa such as cladocerans (Ceriodaphnia rigaudi and Dunhevedia crassa), a calanoid (Metadiaptomus transvaalensis), cyclopoids (Paracyclops fimbriatus and Eucyclops gibsoni) and rotifers (Brachionus dimidiatus and Brachionus plicatilis). The most commonly occurring diatom taxa in temporary pans included taxa indicative of slightly acidic to circumneutral, dystrophic and nutrient-poor waters such as Nitzschia acidoclinata, Gomphonema gracile and Eunotia bilunaris. Permanent pan assemblages were characterized by taxa typical of saline waters, including Nitzschia frustulum, Amphora veneta and Planothidium engelbrechtii. Species of the genera Pinnularia and Eunotia were almost totally absent from permanent pans.