Benthic Algal Communities Research Articles

Seasonal changes in benthic algal communities of the upper subtidal zone in Sanya Bay (Hainan Island, China)

A floristic study of the marine plants and algae at Luhuitou reef, Sanya Bay, Hainan Island, China, was conducted during the rainy (October 2008 and November 2010) and dry seasons (April 2009 and February 2012). Specimens were collected in the upper subtidal zone (from 0.5 to 3 m depth at low tide). A total of 156 taxa were collected, including 143 macrophyte species (90%), 12 blue–green algal species (10%), and the seagrass, Thalassia hemprichii. The most diverse group was the Rhodophyta (79 taxa or 55%), followed by the Chlorophyta (38 taxa or 25%) and then the Phaeophyceae (26 taxa or 20%). In the upper subtidal zone, macroalgae formed two types of communities: polydominant communities of turf-forming algae and monodominant and bidominant communities of foliose or fleshy algae. Seasonal changes occurred in the dominant species, which appear to be caused by periodic annual events of thalli detachment and subsequent community succession. In spite of heavy pollution from dissolved inorganic nitrogen and phosphorus in Sanya Bay, the subtidal flora has not undergone any dramatic changes in species numbers or composition and is similar to that of unpolluted regions in the Indo-Pacific.

Nitrogen-fixing cyanobacteria (free-living and diatom endosymbionts): their use in southern California stream bioassessment

A weight-of-evidence approach was used to examine how nutrient availability influences stream benthic algal community structure and to validate nutrient-response thresholds in assessing nutrient limitation. Data from 104 southern California streams spanning broad nutrient gradients revealed that relative abundance of N2-fixing heterocystous cyanobacteria (Nostoc, Calothrix), and diatoms (Epithemia, Rhopalodia)-containing cyanobacterial endosymbionts, decreased with increasing ambient inorganic N concentrations within the low end of the N gradient. Response thresholds for these N2 fixers were 0.075 mg l−1 NO3-N, 0.04 mg l−1 NH4-N, and an N:P ratio (by weight) of 15:1. The NO3-N threshold was independently validated by observing nitrogenase gene expression using real-time reverse transcriptase PCR. Morphometric analysis of cyanobacterial endosymbionts in Epithemia and Rhopalodia indicated that endosymbiont biovolume per diatom cell decreased with increasing NO3-N. Our findings indicate that abundance of heterocyst-containing cyanobacteria and endosymbiont-containing diatom cells are good indicators for rapid nutrient biomonitoring. Because heterocystous cyanobacteria and Epithemia/Rhopalodia were not always recorded together at N-limited sites, examining both assemblages jointly may provide a more comprehensive assessment of stream nutrient limitation than using either assemblage alone.

Herbivores strongly influence algal recruitment in both coral- and algal-dominated coral reef habitats

Coral reefs can exist as coral- and macroalgae-dominated habitats often separated by only a few hundred metres. While herbivorous fish are known to depress the abundance of algae and help maintain the function of coral-dominated habitats, less is known about their influence in algae-dominated habitats. Here, we quantified herbivorous fish and benthic algal communities over a 6 mo period in coral-dominated (back-reef) and algal-dominated (lagoon) habitats in a relatively undisturbed fringing coral reef (Ningaloo, Western Australia). Simulta - neously, we tested the effects of herbivorous fish on algal recruitment in both habitats using recruitment tiles and fish exclusion cages. The composition of established algal communities differed consistently between habitats, with the back-reef hosting a more diverse community than the Sargassum-dominated lagoon. However, total algal biomass and cover only differed between habitats in autumn, coinciding with maximum Sargassum biomass. The back-reef hosted high coral cover and a diverse herbivorous fish community, with herbivore biomass an order of magni- tude greater than the lagoon. Despite these differences in herbivore composition, exclusion of large herbivores had a similar positive effect to foliose macroalgae recruitment on experimental tiles in both back-reef and lagoon habitats. Additionally, territorial damselfish found in the back- reef increased turf algae cover and decreased crustose coralline algae cover on recruitment tiles. Collectively, our results show that disparate herbivorous fish communities in coral- and algae- dominated habitats are similarly able to limit the recruitment of foliose macroalgae, but suggest that when herbivorous fish biomass and diversity are relatively low, macroalgal communities are able to escape herbivore control through increased growth.

Didymosphenia geminata invasion in South America: Ecosystem impacts and potential biogeochemical state change in Patagonian rivers

The diatom Didymosphenia geminata has emerged as a major global concern, as both an aggressive invader of rivers and streams in the southern hemisphere, and for its ability to form nuisance blooms in oligotrophic systems in its native range. South American D. geminata blooms were first documented in Chilean Patagonia in May 2010, and have spread to over five regions and three provinces, in Chile and Argentina respectively. The Patagonian invasion represents a distinct challenge compared to other regions; not only are affected systems poorly characterized, but also a general synthesis of the nature and magnitude of ecosystem impacts is still lacking. The latter is essential in evaluating impacts to ecosystem services, forms the basis for a management response that is proportional to the potentially valid threats, or aids in the determination of whether action is warranted or feasible. Based on a revision of the recent literature, some of the most significant impacts may be mediated through physical changes: substantially increased algal biomass, trapping of fine sediment, altered hydrodynamics, and consequent effects on biogeochemical states and processes such as redox condition, pH and nutrient cycling in the benthic zone. Surveys conducted during the early invasion in Chile show a strong correlation between benthic biomass and associated fine sediments, both of which were one–two orders of magnitude higher within D. geminata blooms. Experimental phosphorous amendments showed significant abiotic uptake, while interstitial water in D. geminata mats had nearly 10–20 fold higher soluble reactive phosphorous and a pronounced pH cycle compared to the water column. A dominant and aggressive stalk-forming diatom with this combination of characteristics is in sharp contrast to the colonial cyanobacteria and bare gravel substrate that characterize many Patagonian streams. The potential displacement of native benthic algal communities with contrasting functional groups, increased primary producer biomass, and fine benthic sediment accumulation, all may have a significant effect on stream nutrient cycling and ecosystem function, in Patagonia and elsewhere where nuisance blooms have been reported.

The effect of ocean acidification on early algal colonization stages at natural CO2 vents

Marine algae exhibit different responses to ocean acidification, suggesting that a decrease in pH does not always favour marine photosynthetic organisms. In order to understand the effect of acidification on algal community development, early colonization stages were investigated using carbon dioxide vents around the Castello Aragonese (Ischia, Italy) as a natural laboratory. Settlement tiles were placed in zones with different pH (normal, medium and low), and species composition and coverage measured after 2, 3 and 4 months of deployment. The number of species decreased by 4 and 18 % at medium and low pH zones, respectively (P < 0.05). The structure of the algal assemblage differed between pH zones during the 4 months of the experiment, due to the addition and/or replacement of new species. This leads to a change in the succession of morphological forms as soft crustose algae replaced calcareous species, and turf species were dominant in cover; more complex thalli started to occur only at medium pH. These results support previous findings that ocean acidification will induce changes in benthic algal communities.

A physical and biological context for Karenia brevis seed populations on the northwest Florida shelf during July 2009

The current effort focuses on characterizing physical and biological conditions across the northwest Florida shelf during summer as they influence Karenia brevis distributions and phytoplankton/microphytobenthos community associations. Phytoplankton and benthic algal communities were examined in the context of cross-shelf hydrography and sediment conditions during July 2009 between the 20 and 65m isobaths off Panama City, FL. A towed undulating profiler (SeaSciences Acrobat) mapped water column characteristics between near-surface and ∼1m above the sediment. A CTD/rosette provided hydrographic profiles and collected water samples at 17 cross-shelf locations at selected depths for nutrient concentration, phytoplankton biomass determination, and chemotaxonomic and taxonomic phytoplankton identification. In addition, a CTD/rosette time series sample set was collected following a holey sock drogue set at ∼34m along the ∼50m isobath, and cores were collected at eight stations approximately along the 30, 40 and 55m isobaths. Cross-shelf, a pycnocline existed at ∼10m depth, the 1% light level penetrated to ∼45m depth, and nitrate–nitrite (NO3−+NO2−) concentrations increased in the lower 10m of the water column to the 50m isobath and then below 40-m depth to the 65m isobath. A chlorophyll a peak occurred near-bottom between the 25 and 35m isobaths. Gyroxanthin dinoflagellates (GD) representing K. brevis occurred across the shelf in near-surface and near-bottom waters. Near-surface GD co-occurred with cyanophytes at low density in the upper 20m of the water column where NO3−+NO2− concentrations were low. Above sediments in the euphotic zone, near-bottom GD were most abundant between the 25 and 35m isobaths where the NO3−+NO2− concentrations were 1–4µM and where microphytobenthos competed for nutrient sources. Below the euphotic zone, GD were present near-bottom to the 60m isobath where NO3−+NO2− concentrations approached 6µM. A pattern consistent with dinoflagellate diel vertical migration was inferred at the 50-m isobath time-series station. The results provide insight into offshore K. brevis seed populations and their associations with other phytoplankton and microphytobenthos. Under summer light and nutrient conditions along the northwest Florida shelf, K. brevis coastal blooms may be seeded by diffuse near-surface populations during occasional downwelling conditions and by more concentrated near-bottom populations during more prevalent upwelling conditions.

Evaluating the use of algal pigments to assess the biological condition of streams

Assessments of stream condition using benthic algal communities have traditionally relied on taxonomy-based approaches to compare community structure at sites exposed to a stressor versus reference sites. Taxonomy-based methods are often effective, but they require high levels of training and are relatively time consuming and expensive. We examined the utility of assessing stream biological condition using algal pigments. We used gradient and control-impact study designs in 2008 and 2009 to compare the extent that algal pigments versus taxonomic descriptors of algal community structure varied along a 10.5-km stretch of the Flat River (South Nahanni River watershed, NWT, Canada) encompassing a gradient of nutrients and metals at sites upstream, adjacent to and downstream of a northern metals mine. We also calculated costs to quantify algal pigments relative to taxonomy-based methods. Multivariate analyses (ANOSIM tests, redundancy analysis) identified that pigment concentrations from benthic algal samples differed significantly (p < 0.05) between non-exposed and exposed river sites and were related to variations in water physico-chemical conditions. By contrast, community composition determined from taxonomy-based enumeration to the Order and Family levels did not differ significantly between non-exposed and exposed sites, and relations with water physico-chemical conditions were weaker and inconsistent between the study years. In-house costs to quantify algal pigments were lower than commercial rates to describe community structure using taxonomy. Thus, our data suggests that analysis of benthic algal pigments represents a viable and cost-effective bio-monitoring method for assessing anthropogenic effects on stream condition that merits further evaluation.

三亚岩相潮间带底栖海藻群落结构及其季节变化

In order to investigate the current situation of benthic algal community in the intertidal zone of Sanya,field sampling was carried out including six rocky intertidal sections from Jan.2008 to Nov.2008.The changes of community structure and diversity of benthic algae in the intertidal zone were analyzed by species diversity indices and cluster analysis.A total of 130 species in four seasons were identified,among them,67 species of 41 genera belong to Rhodophyta,31 species of 16 genera belong to Phaeophyta,29 species of 15 genera belong to Chlorophyta and 3 species of 3 genera belong to Cyanophyta.Species number altered slightly in four seasons,and its vertical distribution indicated a decreasing trend along with increased vertical gradient.Moreover,mutual species were found at mid-tide and low-tide zone,especially during the summer.Although the average biomass of benthic algae in summer and winter seemed slightly higher than that in spring and autumn,there was no significant difference between them.Dominant species of benthic algae varied with different seasons,indicating their functions in the community changed with seasons.Dominant species were Padina boryana,Ceramium japonicum,Sargassum hemiphyllum,Polyopes polyideoides in spring;Chondrophycus undulates,Sargassum cristaefolium,Amphiroa dilatata,Gelidium amansii in summer;S.cristaefolium,C.undulates,Ishige foliacea in autumn;and,Sargassum vachellianum,Symphyocladia marchantioides,Corallina officinalis,P.boryana,C.japonicum in winter.The diversity index and Margalef′s species richness peaked in the winter,while the diversity index and the Pielou′s evenness bottomed in the summer.The benthic algae in the intertidal zone of Sanyaare mainly composed of tropical-subtropical species,followed by warm temperate species,which generally in accordance with the taxonomic features of the Southern South China Sea.These results suggest that the community structure and diversity of benthic algae in Sanya varies with seasons despite of no significant seasonal differences in species number and biomass.

Opisthobranch Assemblages from a Coral Reef System: The Role of Habitat Type and Food Availability

The present study examines how the habitat type and food availability influence the small scale distribution and assemblages of opisthobranch species in the National Park Arrecife Alacranes, the largest coral reef system in the southern Gulf of Mexico. Samples were collected during December 2009, and April and September 2010 over different habitats (green, red, and brown algae, seagrass meadows, drifting Sargassum spp., rocks, corals, and sand). In total, 32 species were identified and a multidimensional scaling (MDS) analysis based on the Bray-Curtis similarity index was used to determine the main opisthobranch assemblages. The degree of association between the habitat type and the species composition was tested by a chi-square test and the significance of its value was determined by Monte Carlo randomizations. MDS results defined four faunal associations (algal, Thalassia, Sargassum, and rocky assemblages), which showed a significant relationship between the composition of opisthobranch species and the habitat type. These results suggest that food supplies and feeding strategies play a dominant role in the coexistence of species and their small-scale spatial distribution within the reef. The algal assemblage, the group with the highest species richness, was mainly composed of herbivores inhabiting several types of benthic algal communities, whereas the Sargassum assemblage, was a less diversified group comprised of carnivores feeding on epibiont hydroids and was well adapted to the pelagic environment. The distribution of the opisthobranchs over the different habitats largely reflected the variety and availability of their food items.

Epilithic Community Metabolism as an Indicator of Impact and Recovery in Streams Affected by Acid Mine Drainage

We measured biomass and metabolism of epilithic communities on five dates in different seasons at four sites in a watershed that has received extensive restoration for acid mine drainage (AMD) through the construction of passive treatment systems. Chlorophyll a biomass and productivity directly corresponded to AMD stress from coal mining. The site downstream of extensive passive treatment had significantly greater biomass and gross primary productivity rates than the site receiving only untreated AMD, but values were below those for two reference sites, indicating incomplete recovery. The degree of difference in these metrics among sites varied seasonally, primarily related to differences in canopy cover changes, but the ranking of sites in terms of stress generally was consistent. Reference sites had a significantly greater chlorophyll a/pheophytin ratio than untreated and treated sites, also indicating AMD stressed the communities. Community respiration was less affected by AMD stress than productivity or chlorophyll a. Productivity measures are not widely used to assess AMD impacts, and have been shown to both increase and decrease with AMD stress. The elimination of herbivores in AMD-impacted streams can increase productivity in the benthic algal community. Our study found productivity decreased with increasing AMD stress. Although sites with AMD stress had reduced herbivore populations, light, nutrients and metal precipitates appear to have limited growth of AMD-tolerant algal taxa. Therefore, it appears changes in food web structure due to AMD stress had less of an effect on epilithic productivity than environmental conditions within the stream.

Assessment of AHS (Airborne Hyperspectral Scanner) sensor to map macroalgal communities on the Ría de vigo and Ría de Aldán coast (NW Spain)

Ria de Vigo and Ria de Aldan have high biological richness that is reflected in the number of environmental protection areas like the Atlantic Islands National Park and five places of community interest. Benthic algal communities play an important role in these ecosystems due to their ecological functions and support a great part of this biological richness. We tested by means of bio-optical modelling and Airborne Hyperspectral Scanner (AHS) images to what extent remote sensing could be used to map these communities in Ria de Vigo and Ria de Aldan (NW Spain). Reflectance spectra of dominating macroalgae groups were modelled for different water depths in order to estimate the separability of different bottom types based on their spectral signatures and the spectral characteristics of the AHS. Our results indicate that separation between three macroalgae groups (green, brown and red) as well as sand is possible when the bottoms are emerged during low tide. The spectra differences decrease rapidly with increasing water depth. Two types of classifications were carried out with the three AHS images: maximum likelihood and spectral angle mapper (SAM). Maximum likelihood showed positive results reaching overall accuracy percentages higher than 95 % and kappa coefficients higher than 0.90 for the bottom classes: shallow sand, deep sand, emerged rock, emerged macroalgae and submerged macroalgae. Sand and algae substrates were then separately analysed with SAM. These classifications showed positive results for differentiation between green and brown macroalgae until 5 m depth and high differences between all macroalgae and sandy substrate. However, differences between red and brown macroalgae are only detectable when the algae are emerged.

Changing approaches to monitoring during the period of the ‘Use of Algae for Monitoring Rivers’ symposia

The literature on monitoring rivers using benthic algal communities is reviewed, especially that for Europe during the past 20 years. In particular, papers in a series of symposia at approximately 3-year intervals are considered to assess the extent to which aims and methods have shifted. A variety of methods were being tested in the early 1990s, and some put to practical use. However, the requirements of the EU Urban Waste Water Directive in 1991 have gradually narrowed procedures in most countries outside Scandinavia to the use of indices based on benthic diatoms to monitoring nutrients, especially phosphate. Most countries in Europe now adopt one of a few indices. The same indices are being used to deal with the requirements of the EU Water Framework Directive introduced in 2000 to achieve good ecological status by 2015. It is argued, however, that features of upland river sites require the development of revised indices for this purpose. Features of many sites include highly variable nutrient concentrations and ratios, and the greater importance of organic phosphate. Two possible approaches are suggested to developing a revised index. One is a diatom index which incorporates information about the environmental features important here. The other is to use an index which incorporates data on genera from all algal phyla, with emphasis on those which are long-lived.

A mine of information: Benthic algal communities as biomonitors of metal contamination from abandoned tailings

Various biomonitoring approaches were tested in the field to assess the response of natural periphythic algal communities to chronic metal contamination downstream from an abandoned mine tailings site. The accumulation of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn) as well as the production of phytochelatins, the presence of diatom taxa known to tolerate high metal concentrations, diatom diversity and the presence of teratologies were determined. We observed highly significant relationships between intracellular metal and calculated free metal ion concentrations. Such relationships are often observed in laboratory studies but have been rarely validated in field studies. These results suggest that the concentration of metal inside the field-collected periphyton, regardless of its species composition, is a good indicator of exposure and is an interesting proxy for bioavailable metal concentrations in natural waters. The presence of teratologies and metal-tolerant taxa at our contaminated sites provided a clear indication that diatom communities were responding to this metal stress. A multi-metric approach integrating various bioassessment methods could be used for the field monitoring of metal contamination and the quantification of its effects.

Do macrophytes, diatoms and non-diatom benthic algae give redundant information? Results from a case study in Poland

We analyzed species composition and abundance of macrophytes, diatoms and non-diatom benthic algae, water chemistry and habitat structure of 24 river sites in Poland, in order to better understand which parameters structure macrophyte and benthic algae communities. Community patterns for macrophytes and diatoms are most closely related, while macrophytes and non-diatom benthic algae have the weakest relationship. Environmental parameters best explaining community patterns are channel substrate parameters for non-diatom benthic algae, and a combination of channel substrate and river bank characteristics for submerged macrophytes, emergent macrophytes and diatoms. Among the organism groups investigated, the diatom community pattern is best correlated to the environmental data similarity matrix. We hypothesize that the results can be explained by the shorter generation time of diatoms compared to macrophytes, and by a higher dispersal rate of diatoms compared to macrophytes and non-diatom benthic algae. This has several practical consequences for bioindication: (1) Diatoms are usually the organism group most closely following environmental parameters, for both increasing and decreasing impact. (2) Since the biotic indices developed for the Water Framework Directive are meant to primarily indicate ecological changes, not water chemistry, the nature of diatoms to closely reflect water chemistry is not necessarily advantageous. (3) The applicability of macrophyte and probably also non-diatom benthic algae indices is more locally restricted, while diatom indices are applicable to greater areas. (4) In ecosystems which are subject to changing environmental conditions, differences in biotic indices between macrophytes, diatoms and non-diatom benthic algae are to be expected. These differences could provide information relating to ecosystem stability. (5) In stable ecosystems, analyzing one of the three organism groups “diatoms”, “non-diatom benthic algae” and “macrophytes” will be sufficient to characterize the quality element “macrophytes and phytobenthos”, as required by the Water Framework Directive. However, in ecosystems subject to increasing pressure, macrophytes likely will have a tendency to indicate “too good”, while in ecosystems subject to decreasing pressure, diatoms will have a tendency to indicate “too good”.

Macroalgal Community Structure on the Rocky Shores of Ongdo, Jusamdo, and Woejodo Islands of the Yellow Sea, Korea

The benthic algal community structures of the seaweed biomass, vertical distribution of dominant seaweeds, and species composition were examined on the rocky shores of Ongdo, Jusamdo, and Woejodo Islands, Korea, in August 2006. A total of 68 seaweeds were identified, comprising 5 green, 11 brown, and 52 red algae from the three study sites. The number of species at Ongdo (32 species) was less than that at Jusamdo (45 species) and Woejodo (44 species). Jusamdo exhibited the maximum seaweed biomass (73.99 g dry <TEX>$wt/m^2$</TEX>), while the minimum value was found at Woejodo (36.90 g dry <TEX>$wt/m^2$</TEX>). On the three islands, coarsely branched forms were the most dominant functional group in terms of species number and biomass among benthic algal species. The dominant species were Gelidium amansii, Chondrus ocellatus, and Chrysymenia wrightii at Ongdo, Sargasum thunbergii, Ulva pertusa, and Sargassum fusiformis at Jusamdo, and U. pertusa, Undaria pinnatifida, and Corallina pilulifera at Woejodo. Perennial seaweeds were abundant at Ongdo (G. amansii and C. ocellatus) and Jusamdo (S. thunbergii and S. fusiformis), whereas the sheet form of U. pertusa was relatively abundant at Woejodo Island.

Algal bioassessment metrics for wadeable streams and rivers of Maine, USA

AbstractMany state water-quality agencies use biological assessment methods based on lotic fish and macroinvertebrate communities, but relatively few states have incorporated algal multimetric indices into monitoring programs. Algae are good indicators for monitoring water quality because they are sensitive to many environmental stressors. We evaluated benthic algal community attributes along a landuse gradient affecting wadeable streams and rivers in Maine, USA, to identify potential bioassessment metrics. We collected epilithic algal samples from 193 locations across the state. We computed weighted-average optima for common taxa for total P, total N, specific conductance, % impervious cover, and % developed watershed, which included all land use that is no longer forest or wetland. We assigned Maine stream tolerance values and categories (sensitive, intermediate, tolerant) to taxa based on their optima and responses to watershed disturbance. We evaluated performance of algal community metrics used in mu...

Diatom-based paleolimnological reconstruction of regional climate and local land-use change from a protected sinkhole lake in southern Florida, USA

Despite their sensitivity to climate variability, few of the abundant sinkhole lakes of Florida have been the subject of paleolimnological studies to discern patterns of change in aquatic communities and link them to climate drivers. However, deep sinkhole lakes can contain highly resolved paleolimnological records that can be used to track long-term climate variability and its interaction with effects of land-use change. In order to understand how limnological changes were regulated by regional climate variability and further modified by local land-use change in south Florida, we explored diatom assemblage variability over centennial and semi-decadal time scales in an ~11,000-yr and a ~150-yr sediment core extracted from a 21-m deep sinkhole lake, Lake Annie, on the protected property of Archbold Biological Station. We linked variance in diatom assemblage structure to changes in water total phosphorus, color, and pH using diatom-based transfer functions. Reconstructions suggest the sinkhole depression contained a small, acidic, oligotrophic pond ~11000–7000 cal yr BP that gradually deepened to form a humic lake by ~4000 cal yr BP, coinciding with the onset of modern precipitation regimes and the stabilization of sea-level indicated by corresponding palynological records. The lake then contained stable, acidophilous planktonic and benthic algal communities for several thousand years. In the early AD 1900s, that community shifted to one diagnostic of an even lower pH (~5.6), likely resulting from acid precipitation. Further transitions over the past 25 yr reflect recovery from acidification and intensified sensitivity to climate variability caused by enhanced watershed runoff from small drainage ditches dug during the mid-twentieth Century on the surrounding property.

Influence of groundwater spring discharge on small‐scale spatial variation of an alpine stream ecosystem

AbstractThe influence of groundwater discharge on aquatic ecosystems of alpine streams at the patch to reach‐scale (1–100 m) has received little attention to date. In this study, small‐scale variation was evaluated for an alpine stream in the Canadian Rockies receiving groundwater on one side from a large spring. The evaluation was based on measures of (1) spatial changes in the physico‐chemical properties that are commonly used to classify stream types for ecological purposes and (2) variation in periphyton (predominantly diatom and macroalgal) communities. Stream water and algae were sampled along longitudinal and lateral transects of the stream. The results showed that groundwater discharge increased stream flow, electrical conductivity, pH, nitrate concentrations, and turbidity, and lowered temperature. This caused variation in stream physico‐chemical properties along the stream reach and laterally across the mixing area. The influence of the groundwater discharge was reflected in a change in the stream's ecological classification from nivo‐krenal (i.e. snowmelt–groundwater mix) to krenal (i.e. groundwater dominated). The discharge of groundwater to the stream was also associated with changes in the algal community both downstream (reach‐scale) and across the mixing area (sub‐reach‐scale), as indicated by differences in relative abundance of dominant diatom taxa and macroalgae, including a proliferation of the chrysophycean alga Hydrurus. Groundwater‐affected areas also showed reduced species richness, but increased biomass. These findings have implications for the sampling of benthic algal communities in alpine settings and their use as indicators of climate and land‐use changes. Copyright © 2010 John Wiley &amp; Sons, Ltd.

The role of cyanobacteria in Southern California salt marsh food webs

AbstractUnderstanding wetland food webs is critical for effective habitat management, restoration and conservation. Microalgae are recognized as key food sources for marsh invertebrates but the importance of different groups under various conditions is rarely examined. We tested the hypothesis that faunal utilization of microalgae, and cyanobacteria in particular, is significant in Southern California created and natural salt marshes but varies with habitat type (creek bank versus marsh interior) and season (spring versus autumn). We used stable isotope analysis and mixing models (IsoSource) to compare food webs in adjacent young (created) and mature (natural) salt marshes. Isotopic values of some primary producers, macrofauna, epifauna, and fish demonstrated significant differences between the adjacent salt marshes. δ13C and δ34S values of the benthic microalgal community varied with taxonomic composition (diatoms versus cyanobacteria) and to a lesser extent with season. Depleted δ15N values of benthic diatoms and macroalgae indicated that N2 fixed within algal mats was recycled within the benthic algal community. Marsh fauna, including most major macrofauna taxal, Cerithidea, and Fundulus, also exhibited seasonal differences in isotopic composition, and Cerithidea and selected macrofauna (oligochaetes, polychaetes) from the marsh interior were more enriched in 13C and depleted in 15N than those from the creek bank. In the young marsh, the cyanobacteria contributed a minimum of 17–100% of the primary production in food webs supporting macrofauna, and cyanobacteria contributed at least 40% of the primary production included in Cerithidea and Fundulus food webs. A wider range of primary producers contributed to food webs in the mature marsh. Cyanobacteria were a greater source of trophic support for macrofauna from the marsh interior than the creek bank, whereas Spartina was a more important food source for creek bank macrofauna in both marshes. Insect larvae largely consumed cyanobacteria, whereas polychaetes exhibited greater utilization of Spartina. Phytoplankton was the primary food resource for mussels in both marshes. Although the spatial and temporal complexity of food webs has traditionally been collapsed into the study of relatively simplified food webs, isotope signatures reveal fine‐scale patterns in food web structure that may be used to make more accurate assessments of ecosystem state. Accurate interpretation of marsh trophic structure using natural abundance stable isotopes requires fine‐scale resolution in space and time, a large number of samples, and a high level of taxonomic resolution.

Bentoso dumblių bendrijos skirtingos vandens kokybės Lietuvos upėse

Straipsnyje pateikti 2004–2006 m. duomenys apie bentoso dumblių bendrijas skirtingos vandens kokybės Lietuvos upėse. Skirtingos vandens kokybės upėse daugiausia dominuoja Cladophora glomerata–Vaucheria sessilis–Fontinalis antipyretica dumblių samanų bendrija. Skirtingos vandens kokybės upių būklę geriau rodo bendrijose vietomis gausiai besivystančios dumblių rūšys. Švarių vandens telkinių – Hildenbrandia rivularis, Audouinella chalybea ir A. hermanii; mažai užterštų – Vaucheria sessilis ir Fontinalis antipyretica; vidutiniškai užterštų Stigeoclonium nanum, S. tenue, Aulacoseira islandica ir Melosira varians. Skirtingos vandens kokybės ir atskirų upių išilginiame pjūvyje bentoso dumblių bendrijų struktūra kito. Tai galėjo lemti substrato heterogeniškumas, vandens tekėjimo greičio, upės gylio, šviesos intensyvumo bei pagrindinių biogenų koncentracijos pokyčiai.