The genus Pseudo-nitzschia includes several species capable of producing domoic acid, the causative agent of Amnesic Shellfish Poisoning. Some of these species have been recorded frequently in the Gulf of Naples. For one of the species, P. multistriata, which has been recurrently found in our sampling area since 1995, this is the first report for European waters. Here we provide further details on the fine structure of this species. Pseudo-nitzschia multistriata was the only one found to produce domoic acid among all the Pseudo-nitzschia species from the Gulf of Naples, and this finding raises the number of potentially toxic species in this genus to nine. Phylogenetic relationships among several Pseudo-nitzschia species were assessed using the hypervariable domains (D1–D3) of the large subunit (LSU) rDNA. The match between the phylogeny obtained and important taxonomic characters used in this genus are discussed. Results show that P. multistriata clusters with wider species lacking a central larger interspace in the raphe. Close genetic relationships were determined between P. fraudulenta and P. subfraudulenta, and between P. pungens and P. multiseries. Genetic differences among these pairs of species are comparable to those among isolates of P. pseudodelicatissima from the Gulf of Naples, indicating high intraspecific genetic diversity of Pseudo-nitzschia species in the relatively conserved LSU region. This could explain the problematic results obtained when testing a match between species-specific Pseudo-nitzschia LSU probes and our sequences.

The global carbonate cycle has been controlled and maintained by life processes for at least 3.5 billion years. Within the exogenic carbonate cycle and in very different environments cyanobacteria appear in ‘key positions’ in that they actively and passively influence carbonate cycling. In the carbonate cycle, cyanobacteria play an important and sometimes decisive role. Cycling of carbon and carbonate is linked to biological processes. Some build up specific carbonate structures, some destroy carbonate substrates and others do both simultaneously. All these processes take place from the high mountains down to the sea in various terrestrial and freshwater as well as marine environments. The photosynthetic activity of cyanobacteria, their extracellular polymeric substances and possibly also their adherent heterotrophic bacteria are responsible for the construction of various carbonate structures and the ability to penetrate carbonate material. Boring activity of euendoliths results in biological corrosion and disintegration of carbonate surfaces. Grazing organisms on carbonate surfaces colonized by epi- and endolithic cyanobacteria produce specific biokarst forms and specific grains which can contribute to nearshore sedimentation. Biological corrosion and abrasion together constitute bioerosion. The results of all these processes are calcareous crusts, typical traces and biokarst forms which in many cases have a high fossilization potential, and therefore can be powerful ecological, palaeoecological and facies indicators in recent as well as in fossil environments.

Free-floating Ulva L. biomass in the eutrophic brackish ‘Veerse Meer’ lagoon (southwest Netherlands) consists of four morphologically identified species: U. curvata (Kützing) De Toni, U. lactuca L., U. rigida C. Agardh and U. scandinavica Bliding. U. curvata could be recognized easily because of the characteristic central cavity in the holdfast of the attached plants, the arrangement of cells in rows and the single pyrenoid in each cell. U. rigida was distinguished by the thick thallus and the large number of pyrenoids. The Veerse Meer isolate, however, was slightly different from the isolate from the Oosterschelde estuary (the Netherlands). U. lactuca and U. scandinavica showed a high degree of overlap in thallus thickness and cell size, but U. scandinavica usually possessed more pyrenoids. However, doubts have frequently been expressed about the use of some morphological characters in Ulva taxonomy. To determine the validity of such characters in the identification of Ulva species, the morphological variation within and between morphological species was recorded and a molecular data set generated. To detect possible ecophysiological differences between species, optimum temperatures and salinities for growth were determined experimentally. The sequences of the nuclear ribosomal DNA internal transcribed spacer 2 (ITS2) and flanking regions of U. lactuca, U. rigida and U. scandinavica from the Veerse Meer were all identical, but differed from that of U. rigida from the Oosterschelde estuary. Ulva species from the Veerse Meer were most closely related to U. armoricana and U. rigida from Brittany (2·9% and 3·5% divergence respectively); the difference between U. rigida from the Veerse Meer and from the Oosterschelde estuary was 7·5%. Rooted trees, based on a comparison of these sequences with sequences of other Ulva and Enteromorpha species obtained from the literature, using Monostroma arcticum as outgroup, suggested that Ulva is paraphyletic with respect to Enteromorpha. The optimum temperature for growth of U. curvata was 25 °C; for all other species it was 10 °C. The optimum salinity for growth was 30 °C for all isolates. It is concluded that U. lactuca, U rigida and U. scandinavica from the Veerse Meer are all members of one highly polymorphic species.

In this work, we attempt to quantify pulse amplitude modulated (PAM) chlorophyll fluorescence measurements in marine macroalgae in terms of photosynthetic rates. For this, the effective electron transfer quantum yield of photosystem II measured for two Ulva species, at various irradiances and inorganic carbon (Ci) concentrations, was multiplied by the estimated flux of photons absorbed by the photosynthetic pigments associated with this photosystem. The rates of electron transport (ETR) calculated in this way were then compared with rates of photosynthetic O2 evolution as measured in association with the fluorescence measurements. It was found that the calculated ETRs correlated linearly with rates of ‘gross’ O2 evolution (net O2 exchange corrected for dark respiration as measured immediately after turning off each irradiance level) within the range of irradiances applied (up to 608 μmol photons m−2 s−1). The average molar O2/ETR ratio was 0·238 for Ulva lactuca and 0·261 for Ulva fasciata, which is close to the theoretical maximal value of 0·25. Rates of O2 evolution at various concentrations of Ci also showed linear correlations with ETR, and the average molar O2/ETR ratio was 0·249. These results show that PAM fluorometry can be used as a practical tool for quantifying photosynthetic rates at least under moderate irradiances in thin-bladed macroalgae such as Ulva possessing a CO2-concentrating system. A comparison between the PAM-101 (which was used in Sweden for the light- and Ci-response measurements of Ulva lactuca) and the newly developed portable Diving-PAM (used for Ulva fasciata in Israel) showed that such fluorescence-based photosynthetic rate measurements can also be carried out in situ.

The utility of absorbance and fluorescence-emission spectra for discriminating among microalgal phylogenetic groups, selected species, and phycobilin- and non-phycobilin-containing algae was examined using laboratory cultures. A similarity index algorithm, in conjunction with fourth-derivative transformation of absorbance spectra, provided discrimination among the chlorophyll [Chl] a/phycobilin (cyanobacteria), Chl a/Chl c/phycobilin (cryptophytes), Chl a/Chl b (chlorophytes, euglenophytes, prasinophytes), Chl a/Chl c/fucoxanthin (diatoms, chrysophytes, raphidophytes) and Chl a/Chl c/peridinin (dinoflagellates) spectral classes, and often between/among closely related phylogenetic groups within a class. Spectra for phylogenetic groups within the Chl a/Chl c/fucoxanthin, Chl a/Chl c/peridinin, Chl a/phycobilins and Chl a/Chl c/phycobilin classes were most distinguishable from spectra for groups within the Chl a/Chl b spectral class. Chrysophytes/diatoms/raphidophytes and dinoflagellates (groups within the comparable spectral classes, Chl a/Chl c/fucoxanthin and Chl a/Chl c/peridinin, respectively) displayed the greatest similarity between/among groups. Spectra for phylogenetic groups within the Chl a/Chl c classes displayed limited similarity with spectra for groups within the Chl/phycobilin classes. Among the cyanobacteria and chlorophytes surveyed, absorbance spectra of species possessing dissimilar cell morphologies were discriminated, with the greatest range of differentiation occurring among cyanobacteria. Among the cyanobacteria, spectra for selected problematic species were easily discriminated from spectra from each other and from other cyanobacteria. Fluorescence-emission spectra were distinct among spectral classes and the similarity comparisons involving fourth-derivative transformation of spectra discriminated the increasing contribution of distinct cyanobacterial species and between phycobilin- and non-phycobilin-containing species within a hypothetical mixed assemblage. These results were used to elucidate the application for in situ moored instrumentation incorporating such approaches in water quality monitoring programmes, particularly those targeting problematic cyanobacterial blooms.

This article considers molecular biological to global environment work on inorganic carbon acquisition processes in the algae sensu lato (i.e. including the cyanobacteria).

At least 95% of the organic C in photolithotrophic algae has been fixed by RUBISCO, while the remaining 5% or so has involved a range of anaplerotic carboxylases. The catalytic characteristics of RUBISCO show substantial phylogenetic variation; for some algal RUBISCOs (those from cyanobacteria and, possibly, Dinophyta) the kinetics of the carboxylase and oxygenase activity are such that net photosynthetic CO2 fixation could not occur with diffusive CO2 entry from air-equilibrium solution. In many other algae the kinetics of inorganic C assimilation are at variance with in vitro RUBISCO kinetics, and, as in cyanobacteria and Dinophyta, a CO2-concentrating mechanism is hypothesized. In many cases, the operation of such a mechanism can be demonstrated as a higher internal than external CO2 level during photosynthesis. In cases where such a CO2 concentration difference cannot be demonstrated, mechanisms may produce CO2 from HCO3− in an extracellular or intracellular compartment maintained at a lower pH than the cytosol and stroma but, with the exception of the acid zones on the surface of certain characeans, such mechanisms have not been experimentally verified. Reactions downstream of RUBISCO include the polyphyletic metabolic processes which deal with the products of RUBISCO oxygenase activity subsequent to phosphoglycolate phosphatase; even when a CO2-concentrating mechanism is present there is a minor C flux through phosphoglycolate. There are important consequences for bioenergetics, for the allocation among solutes of the low intracellular osmolarity of some freshwater algae, and of the occurrence of CO2-concentrating mechanisms or of diffusive CO2 entry. Some algae today are inorganic C-limited for photosynthesis in their natural environment under otherwise optimal conditions; even in these organisms it is not clear that they are C-limited in nature. The chances of C limitation in the past would have been greater with the low CO2 concentrations of the last glacial maximum 18,000 years ago, but would have been less likely to be C limited in the pre-pleistocene past, and in the anthropogenically CO2-enriched future, than at present. The evaluation of inorganic C acquisition mechanisms must be viewed against the general decrease in CO2, and increase in O2, over the almost 4 billion years since RUBISCO-based CO2 fixation evolved. It is not yet clear whether (polypheletic) CO2 concentrating mechanisms or (polyphyletic) mechanisms of glycolate metabolism evolved first.

The past decade has seen substantial breakthroughs in understanding the biochemistry, molecular biology and regulation of nitrate reductases (NR) in higher plants and green algae. In contrast, although there has been considerable interest in using various measurements of NR to provide ecophysiological information, comparable knowledge of NR is largely lacking in algal groups other than chlorophytes. Applying information about NR from chlorophytes and higher plants to other algae may be difficult. There is evidence that non-chlorophyte forms of NR are diverse and distinct in terms of biochemical characteristics and regulatory features. Key areas to be pursued in non-chlorophyte algae include the identification and adoption of model organisms for NR research in different algal groups; the creation of selected and engineered mutants; the purification, biochemical characterization and production of antibodies to different algal forms of NR; the identification of NR genes; and the undertaking of coordinated research on nitrate uptake proteins and other enzymes in pathways of nitrate assimilation.

The brown macroalga Laminaria saccharina exhibits a type of HCO3− utilization that could be almost completely inhibited either by proton buffers or by acetazolamide, an inhibitor of extracellularly operating carbonic anhydrase. This means of HCO3− utilization featured properties similar to direct HCO3− uptake in that photosynthetic rates were proportional to the HCO3− concentration of the seawater over a wide pH range (pH 7·0–9·5). Despite this, it must be characterized as carbonic anhydrase-catalysed external HCO3− dehydration and not as direct HCO3− uptake. A mechanism is suggested involving a CO2-concentrating capability located at the cell membrane. This mechanism, which might be common in brown algae, is suggested to have an adaptational advantage in colder regions of the sea (as compared with the direct HCO3− uptake of green macroalgae). This means of HCO3− utilization is inhibited even by fairly low concentrations of buffer, with consequences for the interpretation of earlier experimental studies on L. saccharina (and possibly other brown algae). These consequences relate both to ecology (e.g. determination of inorganic C affinity) and physiology (e.g. assessing mechanisms for inorganic C uptake).

The diversity and abundance of terrestrial, lithophytic cyanobacteria in tropical biomes and the variety of rock habitats which they occupy are discussed. The following results are presented in detail. Exposed rock surfaces on different continents and under different climatic conditions are occupied by a cosmopolitan, well-adapted, low-diversity microbial community dominated by cyanobacteria and cyanobacterial lichens. For inselbergs (isolated rock outcrops) in dry savanna, the ratio of rock covered by lichens to that covered by free cyanobacteria is approximately 5:3. In humid savannas this ratio is approximately 1:26, and in rainforests there are hardly any lichens on rocks. The primary production of epilithic communities, expressed as CO2 fixed calculated from chlorophyll a, can reach an annual 27 g m−2. When calculated for a hypothetical inselberg, production values for very dry thorn bush savanna, dry savanna and humid savanna are 1:3·2:4·2 on the basis of the entire inselberg, and 1:3·2:1·4 when calculated on a square metre basis (due to a larger area covered but lower productivity in the humid savanna). Biofilm communities are important in biogenic weathering and they enrich the soils surrounding the rocks with nitrogen.

The marine diatom Skeletonema costatum was grown at different pH values in a semicontinuous cultivation system which kept the pH at a pre-set value. Growth rate was nearly constant at pH 6·5–8·5 (average 2·4 divisions day−1) and declined at pH > 9. Organic carbon (C) production decreased from an average of 5·3 mg l−1 at pH 6·5–8·5 to 2 and 1 mg l−1 at pH 9·0 and 9·4, respectively. Storage β-1,3-linked glucan decreased from a high of 7·1 mg l−1 at pH 6·5 to 0·2 mg l−1 at pH 9·4, and, concomitantly, the percentage of total organic C as glucan C decreased from 60% to 10%. Cellular concentration of amino acids varied from about 62 to 8 mM over the pH range 8·0–9·4. At pH 9·4 the concentration of glutamine was below the detection limit. The extracellular production of carbohydrates in the pH range 6·5–8·5 was only 3·7% (average) of total C production and increased at pH 9·0 and 9·4. The decrease in growth rate at pH > 9·0 might be caused by a decrease in the rate of some important biochemical reactions, as well as by a change in cell membrane properties in this pH range.

The effects on photosynthesis of CO2 and desiccation in Porphyra haitanensis were investigated to establish the effects of increased atmospheric CO2 on this alga during emersion at low tides. With enhanced desiccation, net photosynthesis, dark respiration, photosynthetic efficiency, apparent carboxylating efficiency and light saturation point decreased, while the light compensation point and CO2 compensation point increased. Emersed net photosynthesis was not saturated by the present atmospheric CO2 level (about 350 ml m−3), and doubling the CO2 concentration (700 ml m−3) increased photosynthesis by between 31% and 89% at moderate levels of desiccation. The relative enhancement of emersed net photosynthesis at 700 ml m−3 CO2 was greater at higher temperatures and higher levels of desiccation. The photosynthetic production of Porphyra haitanensis may benefit from increasing atmospheric CO2 concentration during emersion.

We examined three species of diminutive Porphyra,Porphyra suborbiculata Kjellman from the North Pacific, Porphyra lilliputiana W. A. Nelson, G. A. Knight et M. W. Hawkes from the South Pacific, and Porphyra carolinensis Coll et J. Cox from the western North Atlantic. These taxa were compared in terms of morphology, habitat data and sequence haplotypes of nuclear small subunit rDNA (SSU) and internal transcribed spacers of the nuclear rDNA cistron (ITS). These three species have similar morphologies and growth habits, and share very similar type descriptions and habitat records. Haplotype variation was found within the 11 samples of P. lilliputiana we examined and within P. suborbiculata samples from two locations, but the single P. carolinensis haplotype (from collections from two separate locations) was identical to one found in several widespread P. lilliputiana samples. Unrooted phylogenetic trees based on sequence data do not support any of the three species as being a monophyletic group. We conclude that these three taxa represent a single species with the oldest name P. suborbiculata having nomenclatural priority. It is likely that P. suborbiculata has recently been introduced to the western Atlantic from the Pacific region.

The algal vegetation of five diving profiles situated at exposed sites of the outer Öregrund archipelago, southern Bothnian Sea, Sweden, was investigated by SCUBA diving in 1996. The vegetation of the same profiles had been described earlier in 1943–4 and 1984. In the present study, special attention was paid to the occurrence of the structurally important belt-forming brown algae Fucus vesiculosus and Sphacelaria arctica in comparison with the situation 52–53 and 12 years earlier. Prominent differences between the 1940s and 1996 were found. The weighted average depth of the F. vesiculosus belt in 1996 was about 1·7 m shallower than in the 1940s, and the lower distribution limit of this species was about 2·5 m shallower. At its lower end the Fucus belt was replaced by epilithic red algae, mainly Furcellaria lumbricalis, Rhodomela confervoides and Polysiphonia fucoides. These results were similar to those of the 1984 study and show neither an improvement nor a deterioration of the belt during the past 12 years. In four of the five diving profiles, a conspicuous belt of S. arctica occurred in the lower sublittoral, similar to that observed in the 1940s, but in one of the five profiles the S. arctica belt was heavily impoverished. These results contrast with the 1984 study which reported that S. arctica had practically disappeared from all profiles. The epiphytic cover of annual filamentous algae, dominated by Pilayella littoralis and Ceramium gobii, was higher in 1996 than in 1943–4. The results of this comparative study are discussed in relation to the general eutrophication of the Baltic Sea.

Several macroalgae from the Swedish West Coast (11 green, 5 red and 11 brown algal species) and two Ulva spp. from the Mediterranean were tested for mechanisms of HCO3− utilization. In all except one (Palmaria palmata), photosynthesis supported by inorganic carbon (Ci) at pH 8.7 was rapidly and substantially (>50%) inhibited by acetazolamide (AZ), an inhibitor of extracellular carbonic anhydrase activity. This suggests that extracellular dehydration followed by uptake of the CO2 formed is an important component of the HCO3− utilization mechanism(s) of these algae. In representatives of most of the green algal genera, e.g. Enteromorpha, Ulva, Chaetomorpha and Monostroma, a specific inhibitor response could be induced. This response, a sensitivity to the anion exchange inhibitor 4,4′-diisothiocyanatostilbene-2,2′-disulphonate (DIDS) in the presence of AZ, is characteristic of an additional mechanism of HCO3− utilization, a direct import of HCO3− across the plasma membrane, which has been previously described only for some Ulva spp. and Enteromorpha intestinalis. The DIDS sensitivity could be induced in several ways, all involving a potential shortage of the supply of CO2 for photosynthesis: through photosynthesis at high pH, through growth in strong light and nutrient-rich seawater, or through photosynthesis in the presence of AZ. Induction of photosynthesis at high pH (which is a specific feature of green macroalgae) was not always accompanied by a development of this specific DIDS sensitivity; it occurred in Chaetomorpha melagonium but not in C. linum. For Ulva lactuca cultivated in natural seawater (in continuous moderate irradiance), induction of DIDS sensitivity by high pH treatment was successful all year round, except during a period in late August. The results thus suggest that green macroalgae capable of developing photosynthesis at high pH are also capable of developing a DIDS-sensitive mechanism for HCO3− uptake, but that some additional conditions (other than low CO2 availability) must be fulfilled. The ability to dehydrate extracellular HCO3− still remained after induction of the direct HCO3− uptake, and the two mechanisms for HCO3− utilization may operate independently of one another. In fact the response to DIDS was more pronounced after the addition of AZ. The possibility that the results are related to a plasticity of the HCO3−-utilizing mechanisms of green macroalgae is discussed. Neither red nor brown macroalgae showed any sensitivity to DIDS in the presence of AZ.

Effects of nitrogen (N) and phosphorus (P) limitation on calcification and coccolith production in Emiliania huxleyi were investigated in batch and chemostat cultures by means of chemical analyses of calcium (Ca) and organic carbon (C), counts of coccoliths and cells, and scanning electron microscopy. In a normally calcifying (C-cell) clone growing in the absence of nutrient limitation in batch or semi-continuous cultures, c. 36 attached plus detached coccoliths were present per cell. In batch cultures as well as in chemostats, the number rose to 70–120 when either N or P became strongly limiting. The molar Ca/C ratio, measured in chemostats, showed a corresponding increase from 1·07 to c. 1·38. The two types of limitation had opposing effects on the calcification of individual coccoliths: the mean Ca content of a coccolith decreased from a normal value of 0·60 pg to 0·46–0·49 pg under N limitation, and increased to 0·67–0·73 pg under P limitation. These effects were accompanied by corresponding modifications of coccolith morphology. In batch cultures of one naked (N-cell) clone grown to the stationary phase, P limitation but not N limitation induced the formation of c. 40 coccoliths per cell; these coccoliths were of aberrant shape. In another N-cell clone, P limitation had no such effect. The results suggest on one hand that coccolith formation is generally less dependent on N and P nutrients than is cell replication, and on the other hand that stages exist in the growth and calcification of a coccolith that are specifically influenced by either N- or P-containing cell constituents.

Turbidostat cultures of Dunaliella salina (Chlorophyceae) and Thalassiosira weissflogii (Bacillariophyceae) were grown at fluctuating concentrations of nitrate, phosphate and silicate. In-line measurements of PAM fluorescence were used to monitor the effects of fluctuating nutrient supply on the photochemical efficiency of photosystem II reaction centres of light-adapted cells (ΔF/F'm). Besides the maximal photochemical efficiency of photosystem II reaction centres of dark-adapted cells (Fv/Fm), chlorophyll a, particulate organic carbon, nitrogen and phosphorus, and the cell number were measured frequently during the experiments. Following nutrient-replete growth, the cells were supplied with medium from which either nitrate, phosphate or silicate was omitted. When significant effects of nutrient starvation were indicated by the fluorescence parameters, a pulse of the deficient nutrient was added to the cultures. Our experimental set-up for in-line fluorescence measurements provided sensitive and reproducible detection of the various fluorescence signals, revealing strong influences of nutrient supply on the photochemical efficiency of photosystem II. In general the fluorescence values changed substantially within 1–30 min after re-addition of the deficient nutrient. Addition of phosphate and silicate induced an immediate characteristic decrease in fluorescence, whereas nitrate addition was characterized by a strong, delayed increase in fluorescence. Complete recovery to pre-starvation fluorescence values took about 48 h in all experiments. The physiological background of nutrient uptake is used to explain the observed tight couplings between fluorescence responses and nutrient re-addition. Our study clearly demonstrates that in-line fluorescence measurements provide a new tool for the investigation of phytoplankton reactions to fluctuating nutrients and offer the possibility to detect nutrient starvation in the field.

The excretion of extracellular polymeric substances (EPS) by an axenic culture of the benthic diatom Cylindrotheca closterium was investigated. Two sequential extraction steps proved to be sufficient to remove the bulk of the EPS present. Soluble EPS was recovered by a simple centrifugation step and represented a fraction that was not or was only loosely associated with diatom cells. For the extraction of bound EPS, different procedures were compared. The best results were obtained using distilled water as extraction solvent (1 h, 30 °C). The sugars that were recovered using this procedure were typically associated with aggregates of diatoms. In addition to the distinct differences in localization of the different types of EPS, their temporal dynamics differed in relation to the light–dark cycle. Soluble EPS were continuously released into the medium at a rate of 1·6 pg cell−1 day−1. In contrast, the production of bound EPS was highly light-dependent. In the dark, this bound EPS rapidly disappeared, probably as the result of its utilization by the diatoms.

For activity and survival in extreme terrestrial Antarctic habitats, lithobiontic cyanobacteria depend on key biomolecules for protection against environmental stress and for optimization of growth conditions. Their ability to synthesize such molecules is central to their pioneering characteristics and major role as primary producers in Antarctic desert habitats. Pigmentation is especially important in protecting them against enhanced UVB damage during stratospheric ozone depletion (the Ozone Hole) during the Antarctic spring and subsequent photoinhibition in the intense insolation of the summer. To be effective, especially for the screening of highly shade-adapted photosystems of cyanobacteria, protective pigments need to be located strategically. Antarctic lithic cyanobacterial communities are therefore stratified, as in soil biofilms of Alexander Island, the benthic stromatolitic mats of ice-covered hypersaline lakes in the McMurdo Dry Valleys, and the endolithic communities within translucent Beacon sandstone outcrops of Victoria Land. The protective pigments include scytonemin, carotenoids, anthroquinones and mycosporine-like amino acids. To detect and locate photoprotective pigments in situ in free-living cyanobacteria and cyanolichens from hot and cold desert habitats, we have used Fourier-transform Raman micro-spectroscopy. With appropriate power inputs for labile molecules, this high-precision, non-intrusive laser-based technique can not only identify biomolecules in their natural state but also locate them spatially within the habitat relative to the components of the community, which require protection. In conjunction with direct and epifluorescence microscopy it provides a spatial and functional description of the protective strategy of a community. We present the unique Raman spectrum of scytonemin and use its primary and corroborative peaks to identify it within the plethora of other biochemical constituents of several natural cyanobacterial communities, including an Antarctic endolith. The remote-sensing aspect of this technique makes it suitable not only for spatial biochemical analysis of present and palaeontological Antarctic communities but also for analogous putative habitats on Mars.

The crude phlorotannins from the brown alga Eisenia bicyclis showed inhibitory activity against 10 of 13 kinds of glycosidases present in the viscera of the turban shell Turbo cornutus. Phloroglucinol and its oligomers – eckol (a trimer), phlorofucofuroeckol A (a pentamer), dieckol and 8,8′-bieckol (hexamers), and an unidentified tetramer – were isolated from the crude phlorotannins by column and thin-layer chromatography. Phlorofucofuroeckol A, dieckol and 8,8′-bieckol inhibited α-fucosidase, β-galactosidase and β-mannosidase partially purified from T. cornutus, while phloroglucinol, eckol and the unidentified tetramer were weakly active. Dieckol was a competitive inhibitor of α-fucosidase with an inhibition constant (Ki) of 0.12 mM. The amounts of phlorotannins released after the immersion of freshly collected E. bicyclis in seawater or deionized water were estimated by high-performance liquid chromatography. Nearly all the phlorotannins were exuded into the medium following the death of the algae, whereas no phlorotannins were detected in the medium of living algae. These findings indicate that the phlorotannins deter the feeding of marine herbivorous gastropods by inhibiting the glycosidases.

The habitat of the acido- and thermophilic red algae Galdieria sulphuraria and Cyanidium caldarium was examined in acidic hot sulphur springs in the vicinity of Naples (Italy). These species grew on soil and rocks, but a large part of the populations was cryptoendolithic. The endolithic algal layer (1–3 mm in thickness) was covered by amorphous silica (1–2 mm in thickness) containing traces of hydrotroilite (FeS.nH2O) and elemental sulphur. Organotrophic bacteria and fungi were not found in the algal layer. Light penetration measurements showed that 0·1–1% of the sunlight reached the upper part of the algal layer. Thus, low-light-adapted algae should be able to perform some photosynthesis in this endolithic habitat. Under conditions where light is even more limited, e.g. in winter or after darkening of the covering layer, many of the cells might not survive. Aqueous extracts of these algae are excellent growth substrates for Galdieria sulphuraria. Therefore, we propose that compounds released from dead cells in the endolithic layer are used by the surrounding Galdieria cells for heterotrophic metabolism. This would increase their chance of surviving prolonged periods under detrimental conditions.