Algal Species Composition Research Articles

Spatial variation in groundwater-related resource supply influences freshwater benthic algal assemblage composition

The landscape position of a lake relative to local and regional groundwater flow patterns has important ecosystem consequences. The local hydraulic gradient sets up seepage regimes, influences hydrologic and nutrient budgets, and alters site stoichiometry (molar N:P). However, little is known about the biotic (ecological) consequences of groundwater–lake coupling. We investigated the relationship between groundwater flux (resource supply rates), resource supply ratios, and species patterns of benthic algae in Sparkling Lake, Wisconsin, USA, a north-temperate flow-through seepage lake. Nutrient fluxes of seepage waters influenced both local benthic algal biomass and species composition. Sites of high groundwater discharge (HGD) were characterized by low N:P flux, high algal biovolume, and low species richness and diversity. In contrast, low groundwater discharge (LGD) and low groundwater recharge (LGR) sites had high N:P, low algal biovolume, and high richness and diversity. HGD sites were dominated by diatoms and cyanobacteria characteristic of high P, whereas LGD and LGR sites were characterized by taxa associated with low P. Many species were unique to the local flow regimes, increasing overall benthic algal species richness in Sparkling Lake.

Effects of desiccation duration on the community structure and nutrient retention of short and long-hydroperiod Everglades periphyton mats

Responses of periphyton communities to different relevant durations of dry down were assessed. Long-hydroperiod sites within Everglades National Park remain wet for greater than 8 months of the year while short-hydroperiod mats are wet for fewer than 4 months of the year. Dry down duration of long and short-hydroperiod Everglades periphyton was manipulated from 0 to 1, 3, or 8 months after which periphyton was rewetted 1 month and examined for algal species composition. The effects of desiccation and rewetting on periphyton nutrient retention were also assessed. Relative abundance of diatoms declined from an average of 47% in the long-hydroperiod community at the start of the experiment to 24% after 1 month of desiccation and only 12% after 8 months of desiccation. Short-hydroperiod periphyton contained a lower proportion of diatoms at the outset (3%), which declined to less than 1% after the 8-month desiccation treatment. A significant increase in the filamentous cyanobacteria Schizothrix calcicola occurred in long-hydroperiod periphyton mats during this same period, but not in short-hydroperiod mats. Long-hydroperiod periphyton communities had a greater response to desiccation overall, but short-hydroperiod community structure responded to desiccation more rapidly. Because short-hydroperiod communities dry frequently, they appear to cope better to desiccating conditions than long-hydroperiod periphyton communities. This is indicated by the dominance of desiccation resistant algal taxa such as the cyanobacterial filaments S. calcicola and Scytonema hofmanni. Long-hydroperiod periphyton mat communities converge compositionally to short-hydroperiod periphyton communities after prolonged desiccation. Desiccation and rewetting caused long-hydroperiod periphyton to flux greater concentrations of nutrients than short-hydroperiod periphyton. Significant increases in efflux occurred from 1 to 8 months for total phosphorus (TP) and from 1 to 3 and 8 months for total nitrogen (TN) and total organic carbon (TOC). Thus, changes in periphyton mat community structure and function with altered hydroperiod may have long-term ecosystem effects.

Chlorophyll extraction methods for the quantification of green microalgae colonizing building facades

Abstract The occurrence of microalgae on man-made surfaces such as roof tiles, concrete, building facades and other artificial surfaces in urban areas, where it causes aesthetically unacceptable discolouration of the surfaces, represents a conspicuous problem because of its contribution to biodeterioration and accelerated weathering. So far, microbial colonization has been recorded mainly macroscopically, and hence semi-quantitatively evaluated by the degree of discolouration, and the visual data assigned to a colour scale for algal infestation intensity. However, these assessments lack inter-calibration and suffer from colour modifications because of co-occurring fungi or background properties. By using chlorophyll a as a specific biomarker of aeroterrestrial microalgae, an extraction method was therefore developed to quantify biomass. Two green microalgae, Stichococcus sp. and Chlorella sp., were isolated from facades of buildings, established as monocultures and used in the present study. Algal samples are best preserved by freezing in liquid nitrogen followed by lyophilisation and subsequent storage at −18 °C. Dimethyl formamide (DMF) proved to be the best extraction solvent. Mechanical homogenisation improved extraction by up to 20%. However, chlorophyll a extraction efficiency was strongly species-specific and further influenced by the growth conditions, i.e. whether cells were in logarithmic or stationary growth phase. To achieve maximum values for chlorophyll a from samples of unknown algal species composition and physiological state it was found necessary to make at least two 24-h extractions in DMF. If the second extraction step contributed > 20 % to the total chlorophyll a concentration, a third DMF extraction was applied. Using this biomarker assay, up to 313 mg chlorophyll a m−2 was obtained from building facades, equivalent to c. 100 g algal fresh weight, which represents a high organic load.

Effects of solar ultraviolet radiation on the periphyton community in lotic systems: comparison of attached algae and bacteria during their development

The effects of solar ultraviolet radiation (UVR) on the development of a periphyton community were studied in an outdoor artificial stream apparatus. Algal biomass, species composition, and bacterial cell density were measured under full sunlight and non-UVR (photosynthetically active radiation [PAR]-only) conditions. Attachment of algae was detected on days 6–9. Although the chlorophyll-a concentration under non-UVR conditions was 2–4 times that under full sunlight (PAR + UVR) throughout the experiment, neither net algal growth rate nor species composition differed significantly between the two light conditions. The relative carotenoid pigment contents of attached algae in the PAR + UVR condition were 1.1–1.3 times those in the non-UVR condition. Rates of increase of bacterial cell densities under the PAR + UVR condition were depressed by solar UVR for the first few days, although there were no apparent differences in the rates of increase between the light conditions later in the experiment. The small effect of UVR on the development of this periphyton community may be attributable to low UV flux at this study site and to the experimental conditions under which the algae were kept: a high physiological state with high nutrient conditions. Attached bacteria and algae that colonize substrata first are likely to be sensitive to solar UVR, and the negative effects of UVR are mitigated by the development of a periphyton community.

Changes in benthic algal attributes during salt marsh restoration

To assess attributes of algal assemblages as indicators of salt marsh restoration, we chose eight pairs of salt marshes in North Carolina, USA, each pair with one restored marsh (from 1 to 28 years old) and a nearby existing salt marsh. Algae on both Spartina alterniflora and sediments (sediment algae) were collected in each marsh during spring and summer 1998 for assaying algal biomass (dry mass (DM), ash free dry mass (AFDM), chl a content, algal biovolume), algal species composition and diversity, and gross primary production. An attribute restoration ratio was calculated by dividing attribute values from each restored marsh by values from a paired reference marsh. Controlling for regional variation in reference marshes substantially increased precision in relations between attributes and the increase in age of restored marshes. The organic matter restoration ratio of sediments increased with age of restored marshes in both spring and summer. The algal biomass restoration ratios of epiphytes, calculated with algal biovolume and chl a, increased with restored marsh age in summer but not during spring. Biomass of sediment algae was not related to marsh age. The species diversity of sediment algae in summer showed an asymptotic relationship with sediment nutrient concentration. The similarity of diatom species composition between paired restored and reference sites increased with age of restored marshes during spring and summer. Primary production by epiphytic and sediment algae in summer showed site-specific changes and did not change consistently with marsh age. Algal biomass, algal diversity, and diatom species composition during summer were positively correlated with sediment nitrogen and phosphorus concentration. We concluded that other structural and functional development of restored wetlands, especially nutrient storage in sediments, regulates algal species composition and algal biomass accumulation, which can be used to evaluate salt marsh restoration.

Cycling of colloidal organic carbon and nitrogen during an estuarine phytoplankton bloom

To establish the influence of phytoplankton blooms on the cycling of dissolved and particulate species of organic carbon and nitrogen, we conducted a field study during a series of blooms in a coastal embayment on Shelter Island, NY. Using cross‐flow filtration, we collected high‐ and low‐molecular‐weight (HMW and LMW) dissolved organic matter (DOM), along with particulate organic matter (POM). There was a significant and near equivalent enhancement in levels of particulate organic carbon (POC) and dissolved organic carbon (DOC) during phytoplankton blooms. HMW organic carbon was responsible for most (80%) of the DOC increase. In contrast, substantial amounts of organic nitrogen were produced in all size fractions (particulate organic nitrogen [PON], HMW, and LMW) during blooms. POC:PON and HMW C:N ratios exceeded Redfield stoichiometry and were well correlated with chlorophyll concentrations, which suggests that phytoplankton were the primary source of C‐enriched particles and colloids in this system. DOM C:N ratios were higher during periods of elevated nitrate than during low nitrate conditions, which were dominated by phytoplankton with heterotrophic capabilities. This suggests that, in some coastal systems, the accumulation of C‐enriched organic matter may be more dependent on algal species composition than ambient inorganic nitrogen levels. After the collapse of algal blooms, bacterial densities rose markedly, and all organic pools rapidly decreased to near prebloom levels. Despite substantial production and turnover rates of HMW organic carbon during blooms, longer residence times of other, more refractory, organic carbon pools such as the LMW fraction indicated that considerable portions of organic matter produced during estuarine phytoplankton blooms may be exported to continental shelves.

Vertical mixing as a determinant of trophic status in deep lakes: a case study from two lakes south of the Alps (Lake Garda and Lake Iseo)

The identification of the factors and mechanisms determining a particular lake’s typology is crucial for the correct interpretation of trophic evolution. Nutrient concentrations are not the only properties which determine the trophic characteristics of lakes; others, such as morphometry, hydrology and climatic conditions, also have a major influence on the development of algal biomass and species composition. Large, deep lakes belong to a well defined typology. Their trophic status depends not only on algal nutrient loads, but also on the extent of the spring vertical mixing and renewal time. These factors are closely interrelated, for the actual renewal time approaches the theoretical renewal time only during the complete overturn. This paper compares the influence of different circulation patterns on the trophic status of two deep subalpine lakes with contrasting mixing characteristics. Lake Garda is the largest lake in Italy (S=368 km2, V=49 km3, Zmax=350 m). It is characterised by irregular circulation events (oligomixis); during the 1990s, complete homogenisation of the water column occurred in 1991 and 1999-2000. The years between these episodes showed an increase of hypolimnetic temperatures and a progressive vertical stratification of nutrients. Full overturn episodes were characterised by a sudden decrease of temperature and complete homogenisation of the chemical and physical variables along the water column, with a corresponding increase of nutrients and algal biomasses at the surface. In contrast, the last mixing involving the deepest waters in Lake Iseo (S= 60,9 km2, V=7,6 km3, Zmax=251 m) occurred at the beginning of the 1980s, after which the reduced water renewal and the high trophic level resulted in a marked decrease in oxygen concentrations and in the establishment of conditions of anoxia during the 1990s. At present the lake is meromictic. In 1999 and 2000, when a complete overturn was observed in lakes Maggiore and Como as well as in Lake Garda, Lake Iseo experienced a spring mixing which was still limited, but able to determine an increase in the algal biomass.

Effects of zebra mussels on phytoplankton and ciliates: a field mesocosm experiment

Many observational studies in North American lakes have documented decreases in phytoplankton abundance after the invasion of the zebra mussel (Dreissena polymorpha). However, few field experiments have examined in detail the effect of zebra mussels on phytoplankton abundance and species composition over an extended period. Replicated in situ mesocosms were used to evaluate the impact of natural densities of zebra mussels on phytoplankton and ciliate biovolume, anal algal species composition over a 5-week period in a habitat that lacked extant mussel populations. Mussel biomass used in the experiment was determined using a regression model based on a data analysis that predicts zebra mussel biomass from total phosphorus concentration. Within 1 week, zebra mussels decreased phytoplankton biovolume by 53% and ciliate biovolume bi 71%. The effect of zebra mussels on dilate biovolume was sustained throughout the study. However, the effect of zebra mussels on phytoplankton abundance gradually waned over the remaining 4 weeks of the experiment, such that the declining effect of zebra mussels could not be explained by a shift towards less edible and/or faster growing algal species. The mussels' declining condition could help to explain the effect observed over the course of the experiment.

Abundance and Vertical Distribution of the Phytobenthic Community within a Pool and Riffle Sequence of an Alpine Gravel Stream

AbstractIn the 2nd order mountain brook “Oberer Seebach” (Austria), diatoms and cyanoprokaryotes dominate the microphytobenthos, with the diatoms forming the richest species group.Comparative investigations of different habitats clearly show seasonal variations in algal species composition and biomass throughout the year. Pool habitats hold a higher number of taxa than riffle sites. In addition, phytobiomass is two‐ to nearly fourfold higher in pools. Based on investigations of the chlorophyll‐a vertical profiles within the coarse gravel sediments, the light discontinuity layer was determined to be situated at 7–10 cm sediment depth. Vertical distribution showed a maximum of taxa a few centimeters below the sediment surface. The same diatom taxa were found throughout all sampling dates, sediment depths and sampling sites.The results of exposed perforated metal tubes clearly indicate that the occurrence of phytobenthos in aphotic zones is primarily controlled by saltatory movements of the upper sediment layers driven by discharge.

STRUCTURE AND FUNCTION OF BENTHIC ALGAL COMMUNITIES IN AN EXTREMELY ACID RIVER1

The composition of algal species and pigments and the structural and functional characteristics of the algal community were investigated in an acid stream of southwestern Spain, the Río Tinto. The algal community had low diversity and showed few seasonal differences. It was mainly made up of Klebsormidium flaccidum Kütz. (Silva, Mattox & Blackwell) that produced long greenish or purplish filaments, Pinnularia acoricola Hust. (producing brown patches) and Euglena mutabilis Schmitz. The algal filaments made up a consistent biofilm that also included fungal hyphae, iron bacterial sheaths, diatoms, and mineral particles. HPLC analyses on Río Tinto samples showed that undegraded chl accounted for 67% of the total chl in the filamentous patches but were a minority in the brown patch (2.6%). The brown patch had a concentration of carotenoids eight times lower than that observed in the green patch. When chl concentrations were weighted for the proportion of the different patches on the streambed, undegraded chl a accounted for 89.2 mg chl a·m−2 of stream surface area (5.4 g C·m−2). This high algal biomass was supported by relatively high nutrient concentrations and by a high phosphatase activity (Vmax = 137.7 nmol methylumbelliferyl substrate·cm−2·h−1, Km = 0.0045 μM). The remarkable algal biomass in Río Tinto potentially contributed to the bacterial–fungal community and to the macroinvertebrate community and emphasizes the role that the algae may have in the organic matter cycling and energy flow in extreme systems dominated by heterotrophic microorganisms.

Eutrophication of freshwater and coastal marine ecosystems: a global problem.

Humans now strongly influence almost every major aquatic ecosystem, and their activities have dramatically altered the fluxes of growth-limiting nutrients from the landscape to receiving waters. Unfortunately, these nutrient inputs have had profound negative effects upon the quality of surface waters worldwide. This review examines how eutrophication influences the biomass and species composition of algae in both freshwater and costal marine systems. An overview of recent advances in algae-related eutrophication research is presented. In freshwater systems, a summary is presented for lakes and reservoirs; streams and rivers; and wetlands. A brief summary is also presented for estuarine and coastal marine ecosystems. Eutrophication causes predictable increases in the biomass of algae in lakes and reservoirs; streams and rivers; wetlands; and coastal marine ecosystems. As in lakes, the response of suspended algae in large rivers to changes in nutrient loading may be hysteretic in some cases. The inhibitory effects of high concentrations of inorganic suspended solids on algal growth, which can be very evident in many reservoirs receiving high inputs of suspended soils, also potentially may occur in turbid rivers. Consistent and predictable eutrophication-caused increases in cyanobacterial dominance of phytoplankton have been reported worldwide for natural lakes, and similar trends are reported here both for phytoplankton in turbid reservoirs, and for suspended algae in a large river A remarkable unity is evident in the global response of algal biomass to nitrogen and phosphorus availability in lakes and reservoirs; wetlands; streams and rivers; and coastal marine waters. The species composition of algal communities inhabiting the water column appears to respond similarly to nutrient loading, whether in lakes, reservoirs, or rivers. As is true of freshwater ecosystems, the recent literature suggests that coastal marine ecosystems will respond positively to nutrient loading control efforts. Our understanding of freshwater eutrophication and its effects on algal-related water quality is strong and is advancing rapidly. However, our understanding of the effects of eutrophication on estuarine and coastal marine ecosystems is much more limited, and this gap represents an important future research need. Although coastal systems can be hydrologically complex, the biomass of marine phytoplankton nonetheless appears to respond sensitively and predictably to changes in the external supplies of nitrogen and phosphorus. These responses suggest that efforts to manage nutrient inputs to the seas will result in significant improvements in coastal zone water quality. Additional new efforts should be made to develop models that quantitatively link ecosystem-level responses to nutrient loading in both freshwater and marine systems.

Individual, Population, Community, and Ecosystem Consequences of a Fish Invader in New Zealand Streams

Abstract: Knowledge of the population biology of invading species will often be necessary to develop effective management procedures and policies. But because invaders can have unexpected indirect effects in food webs, invasion ecologists need to integrate processes at the population level and other ecological levels. I describe a series of coordinated studies in New Zealand streams that address the effect of an exotic fish on individual behavior, population, community, and ecosystem patterns. Such case studies are important as an aid to the formulation of policy about invasions that are especially likely to become problematic. At the individual level, grazing invertebrates showed changes in behavior as a result of the introduction of brown trout ( Salmo trutta), a predator that exerts a very different selection pressure than do native fish. At the population level, trout have replaced nonmigratory galaxiid fish in some streams but not others, and have affected the distributions of crayfish and other large invertebrates. At the community level, trout have suppressed grazing pressure from invertebrates and are thus responsible for enhancing algal biomass and changing algal species composition. Finally, at the ecosystem level, essentially all annual production of invertebrates is consumed by trout ( but not by galaxiids), and algal primary productivity is six times higher in a trout stream. This leads, in turn, to an increased flux of nutrients from the water to the benthic community. The trout invasion has led to strong top‐down control of community structure and ecosystem functioning via its effects on individual behavior and population distribution and abundance. Particular physiological, behavioral, and demographic traits of invaders can lead to profound ecosystem consequences that managers need to take into account.

Dynamics of Ecological–Biochemical Characteristics of Sea Ice in Coastal Waters of the White Sea

The distribution of salinity, silicon and phosphorus contents, and hydrolytic enzyme activities along a sea–coast transect was studied in melted ice cores and water samples taken from under the ice cover in the periods of active ice formation and melting in the Kandalaksha Bay, White Sea. The species list of identified algae was compiled, which included 170 species and varieties (90% of them belonged to diatoms). Strong correlations were revealed between the salinity of water samples and the content of silicon, protease activity, and the species composition of algae. Preliminary estimations of the rate of photosynthetic processes in individual cells of algae belonging to the mass species of the ice flora are discussed.

Laboratory sources of error for algal community attributes during sample preparation and counting

Applied algal studies typically require enumeration of preserved cells. As applications of algal assessments proliferate, understanding sources of variability inherent in the methods by which abundance and species composition data are obtained becomes even more important for precision of measurements. We performed replicate counts of diatoms on permanently fixed coverglasses and all algae in Palmer–Maloney chambers to assess precision and accuracy of measurements derived from common counting methods. We counted diatoms and all algae with transects and random fields. Variability estimates (precision) of diatom density, species diversity, and species composition on permanent coverglasses were low between replicate subsamples and between replicate transects. However, average density estimates of diatoms settled on coverglasses determined with transect methods were 42–52% greater than density estimates made with random fields. This bias was due to a predictable, nonrandom distribution of diatoms on the coverglass with few diatoms near edges. Despite bias in density when counting diatoms along coverglass transects, no bias was observed in estimates of species composition. Estimates of density and taxa richness of all-algae in Palmer–Maloney chambers also had low variability among multiple transects and high similarity in species composition between transects. In addition, counting method in Palmer–Maloney chambers did not affect estimates of algal cell density, taxa richness, and species composition, which suggested that counting units were distributed randomly in the chambers. Thus, most sources of variability in sample preparation and analysis are small; however, transect counts should not be used to estimate cell density, and sufficient numbers of random fields must be counted to account for edge effects on cell distribution with material settled on permanently fixed coverglasses.

Species composition of algae of the Paramushir Island (The Northern Kurils)

A list of macrophytobenthos of the Paramushir Island is presented; the list contains 167 species of algae (Chlorophyta - 33, Phaeophyta - 41, Rhodophyta - 93). Data on phytogeography, frequency quotients and shelf area where these species occur are included. Thirty-one species (Chlorophyta — 5, Phaeophyta - 5, Rhodophyta - 21) belonging to 25 genera are new records for the flora of Paramushir.

Examination of Alive Algal Cells in the Sediments in Meiliang Bay of Taihu Lake during Winter Period

Three layers of a sediment core collected from Meiliang bay of Taihu Lake in December of 2002, were examined under microscope to identify algae species composition and cultured axenically in MA medium to find the living cells and its vertical distribution in sediment. Many species of algae were found in the surface of the core sample(0-3cm) and three of them (Microcystis aeruginosa Kutz, Cyclotella bodanica Eul, Scenedesmus obliquus(Turp) Kutz) were able to develop in culture 8 them. Less algae species could be found in the layer (10-13cm) of the core sample and only two of them(Microcystis aeruginosa Kutz, Cyclotella bodanica Eul) were developed in culure. Two algae species could be identified in the layer(20-23cm) of the core sample and no algae cell could be developed in culture. It showed that Microcystis aeruginosa Kutz, and Cyclotella bodanica Eul, the dominant phytoplankton populations in summer bloom, could be survive the environment of the sediment in Taihu Lake during the winter period.

Periphyton algal communities from the flooded quarry Škalí - species composition, vertical distribution and seasonal changes

The benthic algal community was studied in a flooded quarry situated in Southern Bohemia (Czech Republic), using artificial substrates. The quarry represents a deep, mesotrophic and strongly stratified water body. The variations in species composition and algal biomass observed during one vegetation season are related to depth, temperature, water transparency, and oxygen concentration. Algae typical for the different seasons were distinguished. Bacillariophyceae, Chlorophyceae, Conjugatophyceae and Cyanophyta were dominant almost all the time. Chrysophyceae dominated during a short period in the spring only. Tychonema bornetii, a bluegreen alga known from alpine and Scandinavian regions, was found to be common. This ist the first published record of this species in the Czech Republic. Algal biomass and species composition showed a clear vertical stratification. On the basis of these phenomena, 4 depth zones could be distinguished. During the spring and summer, some species associations from shallower depths moved into deeper zones. In autumn, they moved back into the shallower depth zones.

Algal growth and species composition under experimental control of herbivory, phosphorus and coral abundance in Glovers Reef, Belize

The proliferation of algae on disturbed coral reefs has often been attributed to (1) a loss of large-bodied herbivorous fishes, (2) increases in sea water nutrient concentrations, particularly phosphorus, and (3) a loss of hard coral cover or a combination of these and other factors. We performed replicated small-scale caging experiments in the offshore lagoon of Glovers Reef atoll, Belize where three treatments had closed-top (no large-bodied herbivores) and one treatment had open-top cages (grazing by large-bodied herbivores). Closed-top treatments simulated a reduced-herbivory situation, excluding large fishes but including small herbivorous fishes such as damselfishes and small parrotfishes. Treatments in the closed-top cages included the addition of high phosphorus fertilizer, live branches of Acropora cervicornis and a third unmanipulated control treatment. Colonization, algal biomass and species composition on dead A. palmata “plates” were studied weekly for 50 days in each of the four treatments. Fertilization doubled the concentration of phosphorus from 0.35 to 0.77 μM. Closed-top cages, particularly the fertilizer and A. cervicornis additions, attracted more small-bodied parrotfish and damselfish than the open-top cages such that there was moderate levels of herbivory in closed-top cages. The open-top cages did, however, have a higher abundance of the chemically and morphologically defended erect algal species including Caulerpa cupressoides, Laurencia obtusa, Dictyota menstrualis and Lobophora variegata. The most herbivore-resistant calcareous green algae (i.e. Halimeda) were, however, uncommon in all treatments. Algal biomass increased and fluctuated simultaneously in all treatments over time, but algal biomass, as measured by wet, dry and decalcified weight, did not differ greatly between the treatments with only marginally higher biomass ( p<0.06) in the fertilized compared to open-top cages. Algal species composition was influenced by all treatments with a maximum between-treatment Bray–Curtis similarity of only 29%. The fertilized cages showed rapid colonization by a mixed turf community largely composed of the filamentous brown ( Hincksia mitchelliae) and green ( Enteromorpha prolifera) species. Algal cover in the fertilized cages leveled at 80% after 20 days compared to less than 50% in the other treatments. There was no evidence that A. cervicornis suppressed algal colonization compared to the unmanipulated controls. Instead, the herbivore susceptible Padina sanctae-crucis was the most abundant algae followed by Jania capillacea in this treatment in contrast to the more chemically defended Dictyota menstrualis that dominated the unmanipulated controls. We conclude that A. cervicornis was not suppressing algae as a group and its loss cannot account for the observed changes in algal abundance in most reefs except for creating space. In contrast, A. cervicornis appears to attract aggressive damselfish that may reduce herbivory by larger herbivores. Phosphorus enrichment can lead to rapid colonization of space by filamentous turf communities but not high biomass and dominance of erect frondose algae within 50 days. Moderate levels of herbivory by large-bodied herbivores promoted moderately herbivore-resistant erect brown and green algae that are commonly reported on disturbed reefs. Consequently, all the studied factors influenced algal communities but seldom as commonly predicted.

Trace metal/phytoplankton interactions in the Skagerrak

Algal community species composition, as estimated by high performance liquid chromatography (HPLC) pigments and microscopy analysis, and trace metal speciation (Cu and Co) and distributions (Fe, Zn, Co and Cu) were measured along a summer transect across the Skagerrak. In waters of Baltic origin, with elevated trace metals levels, but very low macronutrients, a mix of dinoflagellates and haptophytes dominated the low biomass. In the Jutland current, which had high dissolved iron concentrations, a mixed bloom (4–6 μg/l chl a) of diatoms (major species— Leptocylindricus danica) and dinoflagellates ( Ceratium sp.) was present. In the waters of the central Skagerrak derived from the North Sea, below the low salinity Baltic water, a large diatom (major species— L. danica) bloom (7.7 μg/l) was present at 35 m. This bloom formed below the pycnocline, and was located at the nutricline for silicate. The lowest concentrations of trace metals were found in the water of North Sea origin. Synechococcus-like cyanobacteria were observed in the upper waters across the survey area, as were strong binding ligands for Cu, but no clear numerical relationship existed between them, as had been observed by Moffett [Deep-Sea Res. 42 (1995) 1273]in the Sargasso Sea. The [Co]/[Zn] hypothesis of Sunda and Huntsman [Limnol. Oceanogr. 40 (1995) 1404] for coccolithophorids and diatoms was examined using the field data collected.

Use of microbenthic algal communities in ecotoxicological tests for the assessment of water quality: the Ter river case study

The tolerance of microbenthic algal communities to two model toxicants, atrazine and copper, was studied in the Ter river during spring and summer. Artificial substrata were colonised at 9 sites and used to perform short-term (1–4 h) toxicity tests in the laboratory and to obtain photon yield as the ecotoxicological endpoint. The tolerance was lower in spring than in summer for both toxic substances and varied according to the site studied. Copper toxicity was associated with physico-chemical conditions (total suspended solids and water pH) and, especially, with several biomass-related parameters, whereas atrazine toxicity was related to algal abundance and species composition. Temporal and spatial changes in nutrient concentration may alter the biomass and species composition of the communities and thus affect their tolerance to toxic substances. It has to be therefore considered that the environmental characteristics of the river system may determine relevant direct and indirect effects on the algal communities, then affecting their specific ecotoxicological responses. Once this is assumed, the empirical expressions obtained on calculating EC50 and EC10 can be used to predict the community-level transient effects of toxic exposures.