Are algal communities driven toward maximum biomass?

In this continental-scale study, we show that in major benthic and planktonic stream habitats, algal biovolume--a proxy measure of biomass--is a unimodal function of species richness (SR). The biovolume peak is observed at intermediate to high SR in the benthos but at low richness in the phytoplankton. The unimodal nature of the biomass-diversity relationship implies that a decline in algal biomass with potential harmful effects on all higher trophic levels, from invertebrates to fish, can result from either excessive species gain or species loss, both being common consequences of human-induced habitat alterations. SR frequency distributions indicate that the most frequent richness is habitat-specific and significantly higher in the benthos than in the plankton. In all studied stream environments, the most frequent SR is lower than the SR that yields the highest biovolume, probably as a result of anthropogenic influences, but always within one standard deviation from it, i.e. they are statistically indistinguishable. This suggests that algal communities may be driven toward maximum biomass.     

Trans-generational specificity within a cnidarian–algal symbiosis

Ocean warming and other anthropogenic stresses threaten the symbiosis between tropical reef cnidarians and their dinoflagellate endosymbionts (Symbiodinium). Offspring of many cnidarians acquire their algal symbionts from the environment, and such flexibility could allow corals to respond to environmental changes between generations. To investigate the effect of both habitat and host genotype on symbiont acquisition, we transplanted aposymbiotic offspring of the common Caribbean octocoral Briareum asbestinum to (1) an environmentally different habitat that lacked B. asbestinum and (2) an environmentally similar habitat where local adults harbored Symbiodinium phylotypes that differed from parental colonies. Symbiont acquisition and establishment of symbioses over time was followed using a within-clade DNA marker (23S chloroplast rDNA) and a within-phylotype marker (unique alleles at a single microsatellite locus). Early in the symbiosis, B. asbestinum juveniles harbored multiple symbiont phylotypes, regardless of source (parent or site). However, with time (~4 yr), offspring established symbioses with the symbiont phylotype dominant in the parental colonies, regardless of transplant location. Within-phylotype analyses of the symbionts revealed a similar pattern, with offspring acquiring the allelic variant common in symbionts in the parental population regardless of the environment in which the offspring was reared. These data suggest that in this host species, host–symbiont specificity is a genetically determined trait. If this level of specificity is widespread among other symbiotic cnidarians, many cnidarian–algal symbioses may not be able to respond to rapid, climate change-associated environmental changes by means of between-generation switching of symbionts.     

The benthic algal vegetation of the Mjóifjörđur,Eastern Iceland

The benthic algal vegetation of Mjóifjör?ur, situated in the central area of the East Icelandic coast, is described regarding the species distribution from the head to the mouth of the fjord, the main algal associations and zonation patterns. The vegetation gradient along the fjord coast is related to the hydrographic conditionsviz. the influence of freshwater discharge in the inner area and that of the cold water masses of the East Icelandic Current in the outer area. Comparisons are made with the vegetation of other Icelandic fjords investigated during surveys of the Icelandic algal vegetation as a whole.     

Isolation and characterization of brown algal polyphenols as inhibitors of α-amylase,lipase and trypsin

Extracts ofAscophyllum nodosum, Fucus serratus, F. vesiculosus andPelvetia canaliculata contain inhibitors of α-amylase, lipase and trypsin. The inhibitors were isolated and identified by¹H NMR spectroscopy as polyphenols which have apparent molecular weights in the range from 30 000 to 100 000 daltons, as determined by ultra-filtration with Amicon membranes. These polyphenols account for the whole of the inhibitory activity in crude algal extracts. The compounds inhibit α-amylase and trypsin in an apparently non-competitive manner, when preincubated with the enzymes, and the inhibition is directly proportional to the concentration of the inhibitor. Starch protects α-amylase when added to the enzyme together with the inhibitors. Under this condition the effectiveness of the inhibitors is reduced ten-fold.     

Why do cladocerans fail to control algal blooms?

Field studies show that even at high nutrient loads phytoplankton may be kept at low levels by filter-feeding zooplankton for a period of weeks (spring clear water phase in lakes) or months (low-stocked fish-ponds). In the absence of planktivorous fish, large-bodied cladocerans effectively control the abundance of algae of a broad size spectrum. Laboratory experiments show that, although difficult to handle and of poor nutritional value, filamentous algae can also be utilized by large-bodiedDaphnia and prevented from population increase, exactly as the principles of the biomanipulation approach would predict. This is not always the case, however. Even when released from predation, large cladocerans often cannot grow and reproduce fast enough to prevent bloom formation. Sometimes, they disappear when the bloom becomes dense, and the biomanipulation approach is not applicable any more. Recent experimental data on four differently-sizedDaphnia species are used in an attempt to (1) explain why cladocerans fail to control filamentous cyanobacteria when filament density is high, and (2) determine the critical filament density at whichDaphnia becomes ineffective. At this critical concentration,Daphnia growth and reproduction is halted, and no positive numerical response to growing phytoplankton standing crop should be expected fromDaphnia population. Bloom formation thus becomes irreversible. The question of what can be done to overcome this bottleneck of the biomanipulation approach may become one of the most challenging questions in plankton ecology in the nearest future.     

Complexity in the eutrophication–harmful algal bloom relationship,with comment on the importance of grazing

This article seeks to guide the conceptual development and field application of the eutrophication–HAB hypothesis. After considering the evidence for this hypothesis, the importance of exogenous nutrients as a chemical habitat conditioner and the “family” of nutrient regulated effects that occur are discussed. The various definitions of eutrophication are applied; the conceptual ambiguity over how to perceive eutrophication, and the need to view eutrophication as a process and not as an ecological state are considered. The habitat irradiance-nutrient-flushing gradient regulates the bloom potential in response to exogenous nutrients. There is an apparent species-specific paradox within the eutrophication–HAB hypothesis related to the phycotoxin synthesis–nutrient relationship. Two nutrient–toxin relationships occur: toxin biosynthesis during nutrient sufficiency, and biosynthesis that requires a nutrient limitation. HAB events can be just as much nutrient depletion events as nutrient stimulated events, and whether the former develops depends upon the specific cellular toxicity–nutrient relationship of the bloom species. The importance of grazing in bloom regulation is highlighted. HABs and red tides generally should be viewed as blooms that are regulated by coupled nutrient-grazer processes – nutrient stimulation alone is inadequate, even when exogenous nutrients are not a factor. In assessing the eutrophication–HAB relationship, the collective grazing behavior of the micro-zooplankton, herbivorous copepods, filter feeding benthos, benthic larvae and, when present, omnivorous nekton must be considered. The importance of grazing in the bloom behavior of HAB species is illustrated using field and experimental data during a 5-month brown tide in Narragansett Bay. A cascade in grazing pressure regulated this bloom, with the initial collapse and then restoration of grazing pressure progressing through 7 stages of collective grazing pressure by micro-zooplankton, herbivorous copepods, benthic larvae, benthic filter feeders, and lytic virus infection.     

Raman microspectroscopy of algal lipid bodies: β-carotene quantification

Advanced optical instruments can serve for analysis and manipulation of individual living cells and their internal structures. We have used Raman microspectroscopic analysis for assessment of β-carotene concentration in algal lipid bodies (LBs) in vivo. Some algae contain β-carotene in high amounts in their LBs, including strains which are considered useful in biotechnology for lipid and pigment production. We have devised a simple method to measure the concentration of β-carotene in a mixture of algal storage lipids from the ratio of their Raman vibrations. This finding may allow fast acquisition of β-carotene concentration valuable, e.g., for Raman microspectroscopy assisted cell sorting for selection of the overproducing strains. Furthermore, we demonstrate that β-carotene concentration can be proportional to LB volume and light intensity during the cultivation. We combine optical manipulation and analysis on a microfluidic platform in order to achieve fast, effective, and non-invasive sorting based on the spectroscopic features of the individual living cells. The resultant apparatus could find its use in demanding biotechnological applications such as selection of rare natural mutants or artificially modified cells resulting from genetic manipulations.     

A carboxysomal carbon-concentrating mechanism in the cyanelles of the 'coelacanth' of the algal world, Cyanophora paradoxa?

Cyanelles are the peculiar plastids of glaucocystophyte algae that retained a peptidoglycan wall from the ancestral cyanobacterial endosymbiont. All cyanobacteria and most algae possess an inorganic carbon-concentrating mechanism (CCM) that involves a microcompartment--carboxysomes in prokaryotes and pyrenoids in eukaryotes--harboring the bulk of cellular (plastidic) Rubisco. In the case of the living fossil, Cyanophora paradoxa, the existence of a CCM was a matter of debate. Microarray data revealing 142 CO(2)-responsive genes (induced or repressed through a shift from high to low CO(2) conditions), gas exchange measurements and measurements of photosynthetic affinity provided strong support for a CCM. We favor a recent hypothesis that glaucocystophyte cyanelles as the closest cousins to cyanobacteria among plastids contain 'eukaryotic carboxysomes': bicarbonate enrichment within cyanelles should be considerably higher than in chloroplasts with their pyrenoid-based CCM. Thus, the stress-bearing function of the peptidoglycan layer, the other unique heritage, would be indispensable. An isolation method for cyanelle 'carboxysomes' was developed and the protein components other than Rubisco analyzed by MS. Rubisco activase was identified and corroborated by western blotting. The well-established cyanelle in vitro import system allows to use them as 'honorary cyanobacteria': assembly processes of supramolecular structures as phycobilisomes and carboxysomes thus can be studied after import of nucleus-encoded precursor proteins and subsequent fractionation. Even minor components can easily be tracked and a surprisingly dynamic view is obtained. Labeled pre-activase was imported into isolated cyanelles and 30% of the mature protein was found to be incorporated into the carboxysome fraction. A final decision between carboxysome or pyrenoid must await the identification of cyanelle carbonic anhydrase and, especially, the demonstration of shell proteins.     

How protective are refuges? Quantifying algal protection in rock crevices

1. Refuges can be functionally important if they harbour sufficient organisms during disturbance to augment population recovery. I quantified the protection of stream algae in crevice refuges using the applied, severe disturbance of scrubbing. Scrubbing effectively removed visible surface algae, and algae remaining on stones were considered protected. 2. In a field experiment, substrata with different quantities of crevice (glass bottles; greywacke; schist; pumice) were incubated in a channelised stream. The possible influence of growth conditions was investigated concurrently; half of the substrata were suspended in the water column, the rest were placed on the bottom (providing differential access to grazers and exposing them to different flow conditions). 3. Rougher substrata had greater total algal biomass than smoother substrata; this pattern resulted from more algal biomass in crevices of the rougher substrata. Protection from scrubbing ranged from about 5% of total algal biomass on glass and greywacke to 80% on pumice. In contrast, algal biomass removed by scrubbing was similar among the experimental substrata. Suspended substrata had more chironomid grazers than those on the bottom, and also greater algal biomass, possibly because of high algal concentrations in the chironomid retreats. 4. A survey of stones from three rivers supported the experimental results; namely, rough pumice protected more algae from scrubbing than did smoother greywacke. 5. In a separate experimental assay, there was no difference in algal growth on agar plates with and without added powdered rock substrata, suggesting that crevice characteristics and not substratum chemistry produced the differences in algal assemblages between rough and smooth surfaces. 6. Results indicate that rough stream stones may protect sufficient algae to augment their recovery in streams following disturbance.     

Participation of algal–bacterial community in the formation of modern stromatolites in Cock Soda Lake,Altai Region

Modern dolomite stromatolites are found in Cock Soda Lake (Kulunda Steppe) at a salinity of 100–200 g/L and pH of 10. The mineralogical analysis has revealed the presence in the stromatolites of Ca?Mg-carbonates of various compositions. The organisms–edificators of the phototrophic community developing in the lake are determined. They are identified as a part of the mineralized biota (cyanobacteria, bacteria, and eukaryotic alga Ctenocladus circinnatus). Morphological and ultrastructural features of exopolysaccharides secreted by cyanobacteria and bacteria dominant in the phototrophic community are characterized. It is shown that polysaccharides secreted primarily by cyanobacteria have the utmost importance for the formation of stromatolites in Petukhovskoe Soda Lake.     

Temporal effects of ocean warming and acidification on coral–algal competition

Coral Reefs - While there is an ever-expanding list of impacts on coral reefs as a result of ocean warming and acidification, there is little information on how these global changes influence...     

Comparative ecotoxicity of suspended sediment in the lower Rhone River using algal fractionation,Microtox® and Daphnia magna bioassays

The toxicity associated with suspended sediments from the Rhone River (Switzerland-France) was determined with three acute bioassays. Large volume water samples were centrifuged for recovery of suspended solids in November 1989; one sample was taken as a control upstream from Lake Geneva and the 9 remainder downstream from Geneva to the Mediterranean Sea, with a single sample of the major tributary the Saône at Lyon. Heavy metals (Hg, Cd, Cr, Cu, Ni, Pb, Zn) and organic contaminants (OCs, PCBs, PAHs) bound to sediment were analysed and extracted by elutriation with filtered lake water and by organic solvent (dichloromethane). Sediment water elutriates were tested with algal fractionation bioassays (AFB) using Lake Geneva ambient phytoplankton, with Daphnia magna and Microtox® acute toxicity tests, whereas organic extracts were utilized in the latter two bioassays to evaluate the potential sediment toxicity.The bulk analyses of the sediment together with elutriate metal concentrations indicated the highest contamination of sediment downstream of Lyon. Medium contamination appeared for the stations downstream of Geneva, in the Saône River and at the Rhone River mouth. The station upstream of Lyon had low concentrations, comparable to the values in the Upper Rhone. Organic contaminants are mainly observed downstream of Lyon and their concentrations decline onwards to the sea. The bioassays Microtox® on organic extracts and AFB on the elutriates show a similar toxicity trend, but differ in that Microtox was more sensitive to organics whereas the algal test responded predominantly to metals. This difference is believed to be due to the different extraction procedures used, rather than to the tests themselves. Daphnia magna was the least sensitive and appeared to give a broader band response to the observed contaminants in the sediment. The bioassay results when integrated confirm that the biotoxicity trends relate well to the composition of the sediment, a factor which emphasizes the need for battery testing in ecotoxicological assessment.     

Does ambient substrate composition influence consumer diversity effects on algal removal?

Benthic substrates constitute an important habitat template for aquatic communities and may affect the contributions of benthic organisms to ecological processes. To test the effects of ambient substrate composition on the process of algae accrual and removal, we conducted an experiment to examine how substrate type influenced consumer richness effects. We hypothesized that algal removal from focal substrates (ceramic tiles) would be influenced by the surrounding ambient substrate through its effect on nutrient cycling and subsequent algal growth. We manipulated consumer richness in mesocosms at one or three species while holding consumer biomass constant. Aquatic consumers were an amphipod, a snail, and a water boatman, and ambient substrates were either sand or gravel. After 21 days, ambient substrate influenced epilithic algal accrual on tiles, affected physio-chemical parameters within mesocosms, and modified consumer behavior. Chlorophyll a was approximately 2× greater on control tiles surrounded by sand, and FPOM and turbidity were greater on sand than gravel when consumers were present. Substrate modified consumer behavior such that consumers congregated around focal substrates in sand, but dispersed around them in gravel. Consumers also had substrate-specific influences on epilithic chlorophyll, causing a decrease in sand and an increase in gravel. Algal assemblages on focal tiles were dominated by diatoms, and their composition responded to consumer richness and identity, but not substrate. Our data suggest that direct effects (e.g., consumptive removal of epilithon from focal tiles) were more pronounced in sand, whereas indirect effects (e.g., bioturbation and enhanced mixing) promoted algal accrual in gravel. These results show that algae production on exposed surfaces may change as underlying substrate composition changes, and that substrate type can alter consumer diversity effects on algal removal.     

Effects of the discharge of thermal effluent from a power station on Lake Wabamun,Alberta, Canada — The epipelic and epipsamic algal communities

1. The epipelic algal standing crops were increased by the discharge of thermal effluent into Lake Wabamun, particularly in the discharge canal at station (03–04) and 05.
2. The increase in the standing crop size of the epipelon was due to Oscillatoria amoena and O. borneti in the heated area, while the discharge canal provided the inoculum of the algae for the heated area of the lake.
3. At station (03–04) the increased standing crop size was also a function of increased light penetration to the sediment due to the heated effluent keeping an area of the lake free of ice during the winter.
4. The species composition of the diatoms was similar at all stations except in the discharge canal where there was a reduction in the number of diatom species.
5. Navicula cuspidate developed best in the discharge canal in the summer where water temperatures of 31°C were recorded.
6. Amphora ovalis var. pediculus was the dominant diatom species during the winter under ice-cover.
7. The heated effluent had no effect upon the standing crop or species composition of the epipsammon.
8. Results obtained from the sediment core study showed that the shallow littoral zone of the lake is very disturbed due to wind-induced wave action.