Daniel Spitale

Diatoms in springs of the Alps: spring types, environmental determinants, and substratum

Abstract.  Spring habitats are highly diverse and have a mosaic microhabitat structure. They are endangered by diffuse exploitation as drinking-water resources, an impact likely to increase with climate change. Diatoms were sampled from stones and bryophytes in 110 nonthermal, near-natural springs in the southeastern Alps (Trentino) and 16 carbonate springs in the Dolomiti Bellunesi National Park. Fuzzy clustering identified 6 assemblages in the main types of springs. Carbonate rheocrenes hosted Achnanthidium spp., Gomphonema elegantissimum, and Nitzschia fonticola. Several of these species are rheophilic. This group was divided into 4 subassemblages defined by decreasing A. lineare and increasing A. pyrenaicum with increasing flow. Carbonate rheocrenes with shading or moderate NO3− enrichment contained a majority of sciaphilic and NO3-tolerant taxa: Cocconeis taxa, Amphora spp., Caloneis fontinalis, Reimeria spp., and Eunotia arcubus. Well-buffered siliceous rheocrenes supported Diatoma spp., Eunotia minor, Encyonema minutum, Navicula exilis, and Planothidium lanceolatum. Many of these species are heliophilic and rheophilic. Carbonate rheocrenes with lower conductivities or seasonal desiccation contained typical taxa of unstable environments: Diadesmis spp., Planothidium frequentissimum, Meridion circulare, and Achnanthidium dolomiticum. Carbonate rock-face seepages and some tufa springs supported xerotolerant diatom species with a preference for higher conductivities: Encyonopsis spp., Delicata spp., Gomphonema lateripunctatum, Denticula spp., and Cymbopleura spp. Siliceous seepages and pool springs, some very-low alkalinity rheocrenes, and 1 iron spring were characterized by acidophilous mire taxa, such as Eunotia spp., Frustulia crassinervia, and Tabellaria flocculosa, and very-low-alkalinity indicators, such as Psammothidium acidoclinatum. The other iron springs harbored species-poor assemblages with low numbers of cells. Many diatom species showed a significant preference for stones or bryophytes. Epibryon had higher richness and diversity than epilithon, and mean diversity did not differ among the most frequent bryophyte species. Bryophytes are quick and easy to sample and are proposed as the target substratum for diatom-based assessments of springs.

Are benthic algae related to spring types

Abstract.  Benthic algae were used to identify reference conditions of springs for bioassessment purposes. Benthic algae and environmental factors were quantified in 70 springs (nonthermal and mostly near-natural) in the southeastern Alps. Spring types were identified by fuzzy clustering of nondiatom, benthic algal assemblages. Canonical Correspondence Analysis (CCA) and indicator species analysis (IndVal) were used to identify the most relevant environmental determinants of taxonomic composition in springs and to characterize the ecological traits of key taxa. A total of 120 macro- and microscopic benthic pro- and eukaryotic algae (excluding diatoms) were identified. Cyanobacteria (especially Chroococcales and Oscillatoriales) were strongly prevalent. Seven spring types were identified by fuzzy clustering of nondiatom, benthic algal assemblages. IndVal identified 22 taxa that were significant indicators of spring type, and fuzzy clustering based on environmental preferences identified 18 other important taxa associated with spring type. Spring types differed in environmental features, species richness, and diversity. Mid-to-high altitude, oligotrophic, carbonate flowing springs (rheocrenes) with medium conductivity were the most common spring type and were characterized by shade-tolerant (Chroococcales) or rheophilic (Tapinothrix varians) cyanobacteria. Low-altitude, shaded, and slightly NO3-N-enriched carbonate rheocrenes with medium-to-high conductivity supported rheophilic or eutraphentic cyanobacteria and red algae. Siliceous rheocrenes had benthic algal assemblages dominated by soft-water, rheophilic cyanobacteria and by the rheobiontic chrysophyte, Hydrurus foetidus. Mostly siliceous seepages and pool springs supported predominantly chlorophytes, especially filamentous Zygnematales. Xerotolerant cyanobacteria were common on carbonate rock-face seepages. Tufa springs were characterized by cyanobacteria and by the desmid, Oocardium stratum. In iron springs, benthic algae (mainly filamentous green algae and xanthophytes) were poorly developed, whereas iron bacteria were common. The most influential factors were pH and conductivity, shading, NO3-N, temperature, current velocity, and substratum particle size. The spring types identified may prove useful as references for assessments of ecological integrity naturalness value, at least for the Alps ecoregion.

Diversity and distribution of benthic and hyporheic fauna in different stream types on an alpine glacial floodplain

Although processes involved in the relationship between hyporheic and benthic zone have been elucidated in recent years, the spatial and temporal dynamics of the invertebrate assemblages is unclear in alpine streams. A field study was carried out in a glacier-fed stream and in its main spring-fed tributary, in the Italian Alps. Benthic hyporheic connectivity was investigated by means of a pond net, a pump, and artificial substrates. The main determinant in structuring the community was the habitat (=benthic, hyporheic), accounting for 22% of the total faunal variation. A strong similarity was detected between the two streams in structure, function, and species seasonal variations of the hyporheos, that was, in both, more species rich than the benthos. In contrast, benthos was generally very different between the two streams, with a more pronounced turnover in the glacier-fed than in the spring-fed stream. Overall, the highly disturbed glacial system hosted a simplified benthos and hyporheos compared to the stable spring system, in agreement with the intermediate disturbance hypothesis. Our findings provided also evidences about the trophic-sink effect between benthos and hyporheos. Spatial connectivity that we highlighted might have a key role in the dispersal of invertebrates facing changes in habitats features due to climate change.

Relative importance of space and time in determining the biotic structure in the upper part of spring-fed streams

Abstract.  An increasing number of recent investigations of a wide range of species have considerably changed perspectives in spring ecology. However, relatively little is known about the differences between the eucrenon and assemblages in downstream habitats. We studied changes in environmental conditions and in 4 taxonomic groups along a downstream continuum. Assemblages of diatoms, other benthic macroalgae including cyanobacteria, macroinvertebrates, and bryophytes were compared among eucrenal, hypocrenal, and epirhithral stations in 2 spring-fed streams of the southeastern Italian Alps. Environmental factors were less variable at the eucrenal station than at downstream stations, but this pattern was not reflected by an equivalent response of biotic assemblages. The eucrenon clearly differed from assemblages at downstream stations in ways that varied between taxonomic groups and time. Diatom and macroinvertebrate assemblage compositions were more variable at the eucrenal station than at downstream stations. Space was a more important factor than time for diatoms and benthic macroalgae, whereas space and time were almost equally important for macroinvertebrates. Downstream changes were inconsistent between taxonomic groups, and a larger number of spring-fed streams must be studied to detect more generally valid patterns in downstream variation of different taxonomic groups.

Depth distribution of epilithic cyanobacteria and pigments in a mountain lake characterized by marked water-level fluctuations

Abstract: Lake benthic cyanobacteria and algae are distributed along a depth gradient. At the extremes of the gradient, irradiance is a selecting factor because of excess (UV exposure in shallow waters) or extreme reduction (light limitation at the bottom of the euphotic zone). We tested whether, how, and to what extent epilithic cyanobacteria assemblages change with depth in a carbonate meromictic lake (Lake Tovel, southeastern Alps) that undergoes marked water-level fluctuations. Fixed stations were placed along a transect at 2- to 3-m depth intervals from 0 to 24 m and were sampled by SCUBA divers. Three depth-distribution zones were identified based on the composition of cyanobacterial assemblages and primary benthic algal pigments: shallow, middepth, and deep. The autecological traits of the cyanobacteria indicators identified by indicator value (IndVal) analysis suggested that the shallow, mid-depth, and deep zones were disturbed by water-level fluctuations, highly stable with favorable growth conditions, and severely light-limited, respectively. The shallow zone was colonized mainly by pseudaerial cyanobacteria and by UV-resisting phenoecodemes with yellow—brown sheaths (scytonemin). Shannon—Wiener diversity was highest in the shallow zone, probably because taxa characteristic of periodically inundated habitats mixed with lacustrine taxa. The most unique morphospecies were in the lower part of the mid-depth and in the deep zone. These species frequently had colorless sheaths or pink—red—violet cell contents. We found clear patterns in the depth distribution of benthic cyanobacteria and algal pigments that indicated adaptation to the principal evolutionary pressures at the extremes of the depth gradient: water-level fluctuation and light attenuation. These features have implications for quality assessments, biodiversity inventories, and identification of areas affected by water-level fluctuations.

Long-term ecological research in springs of the Italian Alps: six years of standardised sampling

At the beginning ofthe 1990s a comprehensive study of 30 springs within the Adamello-Brenta Natural Park (ltalian Alps) was carried out. This study considered ecomorphology, hydrochemistry, algae, mosses, higher plants and zoobenthos (CANTONATI 1998a). In 1998 five ofthese springs were chosen for a long-term ecological research programme (CANTONATI & MAIORANA 200 l). Springs are characterised by seasonal fluctuations ofthe main environmental parameters (e.g. temperature and alkalinity), which are low compared to other freshwater habitats, and they integrate direct and indirect impacts on the drainage basin in space and time (CANTONATI et al. 2005). For these reasons we considered springs to be ideal monitoring sites, in particular of global impacts such as warming, acidification, increased atmospheric N input. A further integration step in time is undertaken ifbiological parameters are considered. We focussed mainly on water mites, which include a high number of species exclusive to the springs ( crenobionts; DI SABATINO et al. 2003) and several ofwhich are excellent indicators of environmental stability, and diatoms, which are present with a high number o f taxa and several o f which are sensitive indicators o f mineral content, alkalinity, nitrate and other water quality components (CANTONATI & ÜRTLER 1998). Data on ecomorphology and macroscopic phytobenthos were collected as well, although considered non-core parts o f the programme. The aim of this study was to highlight potentialities and problems of this long-term spring monitoring project by considering a selection of results gained during the first six years o f standardized monitoring. This first organization and analysis o f the biological material s sampled and o f the morphological, physical and chemical data is expected to conclude a first phase leading to the final structure o f this spring monitoring programme through the optimization of sampling sites and procedures.

Comparison between natural and impacted Alpine lakes six years after hydropower exploitation has ceased

Abstract Many lakes in mountain regions have been used for hydropower generation since the 1950s. It has been estimated that as many as 79% of the rivers in the Alps have been affected by the presence of hydropower plants. In this context, the shutting down of hydropower plants on a group of Alpine lakes represented a good opportunity to study the ecological impact on them. We selected nine lakes that had been affected and nine that had not, and analysed the differences in environment, littoral diatoms and zoobenthos, phytoplankton, zooplankton, and fish. Results showed that benthic biota -diatoms and zoobenthos- were the most affected by water-level drawdown during winter months. Even six years after the end of hydroelectric operations, diatom species richness and diversity were lower in impacted lakes. Assemblage structure was different for both diatoms and zoobenthos. Phytoplankton and zooplankton were similar in impacted and unaffected lakes in terms of both species richness (and diversity) and assemblage structure. The degree of impact on fish was unclear because illegal stocking of lakes with allochthonous fish species had taken place. This study showed that compared to limnetic biota, littoral communities were the most affected by the decrease in water volume every winter. Six years after the end of hydroelectric operations, diatoms, and to lesser extent zoobenthos, were still different compared to those in natural (unaffected) lakes. Planktic communities seem to be either more resistant to the disturbances, or else able to recover more quickly to their former condition.

The benthic chlorophyte genus Jaoa (Ulvales), a putative China endemic, in Lake Garda, Italy: ecology, taxonomy, and molecular analyses

Abstract: An unknown green alga (order Ulvales) was a dominant macroalga in the rocky littoral zone of Lake Garda (southeastern Alps). Morphological and phylogenetic analyses indicated the alga was in the genus Jaoa, considered endemic to China. The alga in Lake Garda had numerous rhizoids, a subspherical hollow thallus with irregularly lobate—saccate morphology, and 3 layers (an outer layer of small cells with distinct chloroplasts, 2 pseudoparenchymatous, large, round, and mainly hyaline cell layers). Most characteristics were in agreement with the description of Jaoa bullata, 1 of 2 species belonging to the genus Jaoa. Phylogenetic analysis based on 3 loci (rbcL, nrDNA 18S, and ITS) placed the alga in a clade with a sample identified as Jaoa prasina from a Chinese population, but with a considerable sequence distance, a result suggesting it might be a separate species. The Lake Garda alga is a siphonaxanthin-type species that possesses only nonP lipids as structural components of chloroplast (monogalactosyl diacylglycerols, digalactosyl diacylglycerols, and sulfoquinovosyl diacylglycerols) and other cell membranes (diacylglyceryl-N,N,N-trimethylhomoserine lipids). The alga is easily detected with the naked eye, occupies a characteristic belt in the eulittoral zone, and can be found wherever hard substrata are available. Neither this species nor similar taxa are mentioned in historical (end of the 19th century) papers on benthic algae of Lake Garda, so the alga probably was introduced to the lake in relatively recent times. This alga belongs to a little-known genus, but is easily observed and was discovered in Italys largest lake, a tourist resource of outstanding importance. It is a striking example of the degree to which lake benthic algae are understudied in many areas.

Fine‐Scale Spatial Patterns of Mature and Immature Filaments and Bioorganic Compounds of the Rhodophyte Bangia atropurpurea in the Supra‐ and Eulittoral Zones of a Large Lake1

Bangia atropurpurea (Mertens ex Roth) C. Agardh is a freshwater red alga species that is distributed worldwide. B. atropurpurea is highly adaptable due to its stress‐tolerance, which ensures survival under desiccation periods and under radiation extremes typical of the supra‐ and upper eulittoral zones. Whereas a number of previous investigations addressed some of the physiological and biochemical traits involved in stress‐tolerance, we studied the spatial arrangement of the mature (multiseriate) and immature (uniseriate) filaments and of selected bioorganic compounds along a gradient defined by distance from the waterline. Substantial physiological and biochemical differences were previously observed among phenological stages in the marine environment. In this study, we showed a nonrandom spatial structure of both phenological stages and photosynthetic pigments and photoprotective compounds, R‐phycocyanin and R‐phycoerythrin along the supralittoral‐eulittoral gradient. This observed pattern strongly suggests a complex interplay between physio‐morphological regulation and spatial arrangement of mature and immature filaments in conferring the typical stress tolerance of B. atropurpurea.

Vertical migration of a dinoflagellate in a column-shaped enclosure in Lake Tovel (Adamello-Brenta Natural Park, Italian Alps)

Efficient flagellar motion coupled with phototactic capacity provides dinoflagellates with a great ability to migrate vertically throughout the water column for great depths (e.g. LIEBERMAN et al. !994, GRAHAM & WILCOX 2000). The diel vertical migration (DVM) enables the exploitation ofboth high light in the nearsurface water and nutrient resources from within or below the thermocline (WHIITINGTON et al. 2000). DVM gives many advantages: reduced losses due to sinking, hydraulic wash-out and grazing, avoidance of nutrient limitation by obtaining access to deeper reserves, avoidance of surface high light intensities (WHITTINGTON et al. 2000) and the possibility to become dominant in the phytoplankton community during stratified conditions (LIEBERMANN et al. 1994). Many authors suggest that motility depends upon an endogenous circadian rhythm, not dependent upon the light-dark cycles, which, however, serve to confer phase to the system (e.g. LEVANDOWSKI & KANETA 1987, TAYLOR 1990, PARK et al. 200 l). For others, on the contrary, DVM is primarily induced by environmental conditions. According to TILZER (1973), migration is primarily light induced. For LEVANDOWSKI & KANETA (1987) the rhythm would be an alternation between negative and positive geotaxis. Experimental studies using laboratory cultures (e.g. HEANEY & EPPLEY 1981) have variously indicated the importance of gradients oflight and temperature, the availability of nitrogen, and population age in modifying pattems ofmigration. For KAMYKOWSKI & YAMAZAKI (1997) taxis-directed orientation is based on positive phototaxis during daylight and positive geotaxis at night, simulating a circadian rhythm set by the daylight cycle. Most dinoflagellates exhibit DVM characterized by daytime ascent and dark descent ( e.g. EPPLEY et al. !968, KAMYKOWSKI 1995, PARK et al. 2001). In high mountain lakes (T!LZER 1973, Rorr 1988) the dominant flagellates usually ascend in the evening and migrate downwards with increasing Iight intensities, thus avoiding high-Iight-induced, slow-recovering, non-photochemical quenching of photosystem li (WHITTINGTON et al. 2000). Some dinoflagellates, however, do no t show DVM ( e.g. KAMYKOWSKI et al. 1998).