COMMUNITY DYNAMICS AND METABOLISM OF BENTHIC ALGAE COLONIZING WOOD AND ROCK SUBSTRATA IN A FOREST STREAM

Colonization dynamics and metabolism of algal communities on wood (small pieces of Douglas fir) and artificial rock (tiles) substrata were investigated in an open reach in Mack Creek, Cascade Mountain Range, Oregon, for 42 days. Chlorophyll a concentration was not significantly different between the two algal communities (ANOVA, P = 0.119). Even though differences in cell densities were not significantly different between the two algal communities (ANOVA, P = 0.063), biovolume and diversity were greater in epixylic than in epilithic communities (ANOVA, P = 0.011 and 0.002, respectively). The same algal taxa occurred on both substrata, but some of them (e.g. Ceratoneis arcus Grun., Cymbella minuta Hilse ex Rabh., Zygnema sp.) were more numerous on wood, whereas a few others preferred tiles (e.g. Achnanthes lanceolata (Bréb.) Grun.). Scanning electron microscopy revealed a much higher surface roughness on wood, which likely led to a patchy distribution of the algae and the development of stalked diatom species. However, adnate species adapted much better to the mainly flat surfaces of tiles. Net community primary productivity (NCPP) measured in 42-day-old substrata was moderate on tiles but negative on wood. Community respiration (CR) was significantly higher on wood than on tiles. Epixylic algal communities exhibited greater nitrogen demand than epilithic communities after ammonium addition. NCPP shifted to positive values on wood but did not increase on tiles. Despite metabolic differences, the variations between the two communities are more closely related to the physical characteristics of the substrata and the attachment abilities of the algal taxa.     

The reproductive cycle in the population of Saccostrea cuccullatta (Born) from the coast of Karachi,Pakistan

Periphytic diatom communities on clay tile and sterilized rock substrates were compared with those on natural substrates. Clay tiles yielded diatom communities with the least variability between replicate samples, and the greatest similarity to the natural substrate assemblage. The advantages of utilizing introduced substrate communities and problems encountered with their simulation of the natural substrate community are discussed.     

Comparison of attached algal communities on natural and artificial substrata along a thermal gradient

Colonization rate and community structure of periphyton assemblages was examined on aluminium and glass substrata and compared to populations on four submerged macrophyte species in three temperature zones in Cholla Lake, Arizona, U.S.A. Higher densities were achieved over shorter incubation intervals in the warmer zones (26–35° C). Representatives from the planktonic diatom community were first to colonize artificial substrata during the initial two hour incubation period in all temperature zones. Two periphyton diatom representatives, Amphora coffeiformis and Cocconeis placentula var. lineata were the numerical dominants after one week. Cocconeis placentula var. lineata was most competitive on natural substrata at temperatures <26°C, while Amphora coffeiformis dominated temperature zones >26°C with no significant preferences for artificial or natural substrata. The significance of temperature, specific conductance and availability of living hosts is discussed with respect to regulating populations of these two common periphytic diatom species in alkaline waters in southwestern U.S.A. Similarity indices (SIMI) were used to compare algal assemblages on various natural and artificial substrata pairs. Periphyton assemblages were very similar on all natural substrata within similar temperature zones, with little or no preference for macrophyte species displaying similar leaf morphology. Diatom assemblages were quite similar on aluminium and glass substrata throughout the incubation period in all temperature zones, while blue-green algal populations were significantly different, particularly in the higher temperature zones (>28°C). Natural periphyton communities were best represented after four weeks incubation with aluminium substrata in warmer temperature zones (>28°C) or where filamentous blue-green algae dominated. The selection of adequate incubation time when employing artificial substrata to evaluate natural assemblages for different environmental conditions and algal populations is discussed.     

Optimal colonization and growth of marine benthic diatoms on artificial substrata: protocol for a routine use in bioindication

Benthic diatoms growing on hard substrata are used for their bioindication ability in freshwater quality monitoring. Artificial substrata are needed in cases where any natural substrate is present or to achieve similar sampling conditions between sites. Prior to use marine benthic diatoms for monitoring, a standardized protocol for sampling on artificial substrata must be set up. Two major types of information are required: (1) the time needed for a diatom community to be well developed and mature (climax stage); (2) the optimal growth conditions, given that the substrataum nature and texture are important parameters for the initial phase of biofilm development and can influence the future diatom assemblage. Three substrataum types were tested: frosted Plexiglass®, frosted glass, and rough enameled tiles. They were submerged for 8 weeks and sampled weekly. The experiment was conducted at five sites of distinct morphology and water chemistry, along the coastal area of Martinique Island, French West Indies. Development of diatom community was studied through biofilm dry weight, valve density, species richness, and species relative abundances. Globally, substratum type had no significant effect on any parameter. Frosted Plexiglass® was found to be the most interesting substratum because of higher valve densities and practical use. The asymptotic phase of biofilm development was encountered between 5 and 8 weeks depending on site and parameter. A compromise between community development and vandalism or loss through time was fixed to 5 weeks. This period is longer than for stream environments and is valid for tropical oligotrophic marine environments.     

Dynamics of grazing protozoa follow that of microalgae in natural biofilm communities

This study investigates the dynamics of protozoan community in biofilms formed on inert artificial surfaces suspended in various freshwater environments. The results also test the hypothesis that the dynamics of protozoan and microalgal communities in biofilms are interdependent because the latter form one of the major food items of benthic protozoa. Cleaned glass slides were suspended in surface waters at four sampling locations to collect biofilm communities. The glass slides after retrieval were observed under a microscope for diatom and protozoan density and their generic composition. Members of protozoa belonging to phylum Sarcomastigophora dominated the protozoan community followed by phylum Ciliophora in all sampling locations. The variation of protozoan feeding groups showed an initial abundance of autotrophs/holophytes which gave way to heterotrophs, predators, and bacterivores towards the end of the study. The density and generic composition of protozoa varied significantly with the age of biofilm and sampling location. The density variation of protozoa followed that of diatoms in all four sampling locations and this has resulted in a significant positive correlation between diatom and protozoan densities. This suggests the dependency and/or food web connectedness of these two communities in natural biofilms.     

Emigration and immigration can be important determinants of benthic diatom assemblages in streams

SUMMARY.

• 1 Interspecific differences in diatom abundances in stream drift (plankton), immigration, and natural benthic assemblages were compared to assess the importance of emigration and immigration in benthic diatom community dynamics. Water samples were collected throughout a 24-h period to measure diel changes in diatom drift abundances and to estimate benthic diatom emigration rates. Immigration was assessed with 24-h colonization of bare tiles.
• 2 Dissimilarity in species composition of drift, immigration, and natural substrate assemblages indicated differential emigration and immigration among diatom species.
• 3 A mathematical model indicated that reproduction by diatoms in the plankton could not account for diel drift peaks and that diel variation in drift was an informative measure of benthic diatom emigration.
• 4 Emigration and immigration of some species constituted substantial proportions of diatom abundances on natural substrata. We conclude that emigration into the drift and immigration onto substrata can be important processes that regulate benthic diatom species composition and standing crop in streams.

     

Mechanisms of benthic algal recovery following spates: comparison of simulated and natural events

We conducted a manipulative field experiment to examine individual and interactive effects of scour and short-term nutrient enrichment (4 h exposure) on postspate recovery of benthic algae in a desert stream. We then compared recovery from these simulated-spate conditions to algal recovery patterns following a natural spate that increased water-column nutrient levels for 2 weeks. That event differentially scoured communities on artificial substrata in place for a long-term experiment, significantly reducing biomass in 49-day-old communities but causing no significant reduction of biomass in older, 133-day-old communities. Thus, we were able to examine recovery of scoured and non-scoured benthic algal communities under natural post-spate conditions. Both natural and simulated spates reduced actual and relative abundances of diatoms within communities. In the manipulative experiment, scoured communities accrued biomass more rapidly than those not subjected to scour, but short-term enrichment had not effect. Accrual of diatoms and green algae was stimulated by the scour manipulations, while cyanobacteria maintained equal rates of growth in all treatments. Following the natural spate, diatom and green-algal densities increased in scoured communities, but recovery of algal biomass was slow on both scoured and non-scoured substrata, primarily because cyanobacteria, the dominant algal group on all tiles, did not increase under exposure to highly nitrate-enriched waters. Rates of algal cell accrual were inversely correlated with the amount of algal biomass present at the start of a recovery sequence. Algal immigration rates measured immediately after the natural spate and during an interflood period in the same season did not differ, indicating that the algal drift pool was not augmented by disturbance. Benthic algal recovery following spates is strongly influenced by the degree of scour generated by the event, but recovery patterns are also affected by the length of post-spate enrichment and the taxonomic composition of the affected community.     

EFFECTS OF LIGHT AND WAVE DISTURBANCE ON VERTICAL ZONATION OF ATTACHED MICROALGAGE IN A LARGE RESERVOIR1

Experimental field manipulations of artificial substrata were used to examine the mechanisms controlling attached algal zonation down the face of the dam in Lake McConaughy, a large reservoir in western Nabraska. Sets of clay tiles were incubated in the upper (2.5 m depth) and lower (8 m depth) growth zones for two weeks. Five sets tiles were then switched from the upper to the lower growth zone and vice versa. Five additional sets of tiles were switched to the lower zone and artificially disturbed. Diatom cell densities increased rapidly in both the zones; however, wind-induced turbulence caused dramatic declines (up to 61%) in densities in the upper zone. Consequently, cell densities in the upper and lower growth zones were not significantly different after four weeks, despite the 17–30% higher light levels in the upper zone. Based on cell densities and relative abundances on clay tiles and naturally occurring rocks, 26 of the 32 most common diatom taxa had a significant upper (10) or lower (16) zone preference. Of these, 15 taxa exhibited a consistent response to one or both switching manipulations, confirming a growth zone preference, and two showed a clear preference for disturbed substrata. Diatom growth form appeared to play a major role in determining the vertical zonation of attached communities, since actively motile taxa exhibited a lower zone preference and stalked forms occurred primarily in the upper zone. The present study indicates that light attenuation and wave disturbance are primary mechanisms that control the vertical zonation of freshwater epilithic algae.     

Protozoan communities in chalk streams

This study assessed the individual effects of three mayflies (Paraleptophlebia sp., Ephemerella subvaria McDunnough and Epeorus sp.) and one caddisfly (Psilotreta sp.) on periphyton communities associated with clay tiles and leaves. Algal densities were estimated for leaf discs and tiles from experimental chambers (with individual grazers) and control chambers (i.e., no grazers). Scanning electron micrographs (SEM) of leaf discs and tiles also were taken for all mayfly grazing experiments. Densities of algae on leaf discs were two to five times lower than on tiles. Mouthpart morphology influenced how different insects grazed the periphyton community. Paraleptophlebia had typical collector-gatherer mouthparts and had no effect on diatom densities associated with leaves whereas diatom densities on grazed tiles were higher than densities on tiles from control chambers. Epeorus had brusher mouthparts and had little impact on diatom densities regardless of substratum type. The other two grazers had the blade-like mandibles of a scraper. Psilotreta did not reduce the numerical abundance of diatoms on either substratum, but did alter community structure by significantly reducing densities of stalked Gomphonema olivaceum and large species of Navicula and Nitzschia; densities of smaller diatoms (Achnanthes spp) increased. However, E. subvaria reduced densities of most algal species regardless of size on both substrata and also significantly altered community structure. SEMs of substrata grazed by mayflies showed reductions in fungal hyphae on all grazed leaf discs, decreases in filamentous algal forms on grazed tiles, and greatly shortened stalks of G. olivaceum (Paraleptophlebia only). Thus, periphyton communities are different on leaves versus tiles and grazers with different mouthpart morphologies have varying effects on both algal and heterotrophic microbial community structure.     

Comparative algological and bacteriological examinations on biofilms developed on different substrata in a shallow soda lake

According to the European Water Framework Directives, benthic diatoms of lakes are a tool for ecological status assessment. In this study, we followed an integrative sample analysis approach, in order to find an appropriate substratum for the water qualification-oriented biomonitoring of a shallow soda lake, Lake Velencei. Six types of substrata (five artificial and one natural), i.e., andesite, granite, polycarbonate, old reed stems, Plexiglass discs and green reed, were sampled in May and in November. We analysed total alga and diatom composition, chlorophyll a content of the periphyton, surface tension and roughness of the substrata and carbon source utilisation of microbial communities. Water quality index was calculated based on diatom composition. Moreover, using a novel statistical tool, a self-organising map, we related algal composition to substratum types. Biofilms on plastic substrates deviated to a great extent from the stone and reed substrata, with regard to the parameters measured, whereas the biofilms developing on reed and stone substrata were quite similar. We conclude that for water quality monitoring purposes, sampling from green reed during springtime is not recommended, since this is the colonization time of periphyton on the newly growing reed, but it may be appropriate from the second half of the vegetation period. Stone and artificially placed old reed substrata may be appropriate for biomonitoring of shallow soda lakes in both spring and autumn since they showed in both seasons similar results regarding all measured features.