Heavy metal tolerance of marine phytoplankton. I. The tolerance of three algal species to zinc in coastal sea water

Tolerance levels to zinc ions of three diatoms (Skeletonema costatum (Grev.) Cleve, Thalassiosira pseudonana (Hust.) Hasle and Phaeodactylum tricornutum (Bohlin) grown in dialysis culture in the local fjord water were studied. Declining relative growth rates were observed by addition of 50, 250 and 25,000μg/l of zinc ions, respectively, for the three algae. Reduced final cell concentrations were found at lower zinc levels. At least for one species a significant increase in zinc uptake by the cells took place at zinc levels which did not seem to influence the growth and development of the alga. Two clones of Skeletonema costatum studied showed significant intraspecific differences regarding the tolerance to zinc pollution. Dialysis bioassay was found suitable for monitoring heavy metal pollution of aquatic recipients.     

The amino acid and gross composition of marine diatoms potentially useful for mariculture

The amino acid and gross compositions of three benthic diatoms (Cylindrotheca fusiformis Reimann and Lewin, Navicula jeffreyi Hallegraeff et Burford and Nitzschia closterium (Ehr. W. Smith) and three chain-forming diatoms (Lauderia annulata Cleve, Skeletonema costatum (Greville) Cleve and a tropical Skeletonema sp. (CS-252)), were determined during late-logarithmic growth phase.Four of the six species were rich in protein, ranging from 31% (S. costatum) to 38% (N. closterium) of the dry weight, and contained 4.9 to 6.5% carbohydrate and 9.4 to 18% ash. The other two species, C. fusiformis and L. annulata contained only 16% protein but had nearly twice the total carbohydrate (11 to 12%) and two to three times the ash (29 to 35%) of the other species. All species contained a similar percentage of lipid (18 to 20%), and a high protein quality based on their total amino acid composition.The usefulness of these diatoms for mariculture will be determined by growth rates, gross composition and acceptability to the animal. N. closterium had the fastest growth rates of the benthic mat-forming diatoms, it was rich in protein, and it may be a good candidate for abalone culture. The two Skeletonema spp. had the fastest growth rates of the chain-forming diatoms, and are already widely used for prawn larval culture in Australia. Feeding trials are now necessary to confirm the high nutritional value of these diatom species for specific animals.     

Growth of the plankton diatom Thalassiosira nordenskioeldii Cleve at low silicate concentrations

The combined effect of low silicate concentration and temperature on the growth of the marine plankton diatom Thalassiosira nordenskioeldii Cleve was investigated by means of batch and semi-continuous cultures. Growth rates were measured in thin cell suspensions (less than 500 cells/ml) to prevent the silicate concentration in the medium from decreasing by more than 25 % during the period of measurement.Half-saturation constants of silicate-limited growth were calculated according to the Michaelis-Menten equation. At 3 °C, the constant was 0.09 μg-at. Si/I and at 10 °C, 0.02μg-at. Si/I. In semicontinuous cultures grown for one month at silicate concentrations of 0.3-0.4μg-at. Si/I, the mean cell division rates were 80–100% of the maximum rates recorded at the respective temperatures.It seems unlikely that decreasing silicate concentrations could influence the course of the spring succession of plankton diatom species in arctic or temperate coastal waters.     

PELAGIC AND BENTHIC ENVIRONMENTAL CONTROLS ON THE SPATIAL DISTRIBUTION OF A VIABLE DIATOM PROPAGULE BANK ON THE SWEDISH WEST COAST1

The distribution of viable diatom resting stages in sediments on the Swedish west coast was assessed by the most probable number (MPN) culture technique. Multivariate analyses correlated benthic and pelagic environmental factors to the observed spatial variations in the size and taxonomic composition of the propagule bank. Viable diatom resting stages were plentiful (0.2–4.8 million cells·g ^{? 1} 1 Received 11 September 2001. Accepted 12 June 2002.
dry weight) and were dominated by the genera Skeletonema, Detonula, Chaetoceros, and Thalassiosira. Size of the propagule bank was primarily related to planktonic biomass (measured as chl a) and was highest in the Orust‐Tjörn fjord system. Species composition in this fjord system was dominated by D. confervacea (Cleve) Gran and T. nordenskioeldii Cleve in contrast to stations on the outer coast, which contained more cells of T. minima Gaarder, Asterionellopsis glacialis (Castracane) Round, and Leptocylindrus danicus Cleve. These taxonomic variations were principally influenced by deep water oxygen concentrations and water column stability. Benthic resting cells of S. costatum (Greville) Cleve were abundant all along the coast but showed reduced viability in low oxygen environments. Calculations based on MPN values estimated that resuspension of sediment could provide a sizable inoculum to the plankton, although the development of planktonic blooms will also depend on forces of hydrography and weather. Although benthic resting stages may not be absolutely necessary for survival of all diatoms, these cells may be important in determining species cycles, succession, and the spatial distribution of diatoms.     

Diatoms in the plankton and sediments of two lakes of different trophic type

Species composition, quantity and distribution of diatoms in both the plankton and the surface sediments (0–30 cm) of mesotrophic Lake Krasnoye and eutrophic Lake Vishnevskoye (Karelian Isthmus) were studied. In the mesotrophic lake the composition of dominant diatoms (mainly Melosira) corresponded to those in the plankton. The Araphidineae/Centrales (A/C) ratio was 0.2–0.3%, increasing in the upper layers to 7%. Alkaliphilous and alkalibiontic forms constituted 60% of the total. In the eutrophic lake diatoms with thin valves (mainly Synedra) predominated in the plankton but their quantity in the sediments was insignificant in comparison with other plankton. Nevertheless, the A/C ratio was much higher, 17–35%. Alkaliphilous and alkalibiontic forms accounted for 78–90% of the total number of valves. In both lakes the highest number of diatom valves was registered in the upper layer of the sediments. From the ratio of the total number of diatoms in the upper 5 cm layer to their annual flux to the sediment from the plankton the approximate sediment accumulation rate was calculated to be 1.9 mm a^?1 for the mesotrophic lake and 2.5 mm a^?1 for the eutrophic one.     

The use of outdoor phytoplankton continuous cultures to analyse factors influencing species selection

Natural phytoplankton populations have been grown in outdoor continuous cultures at three dilution rates (D = 0.5, 0.25, and 0.1 · day^?1) under nitrogen (N) or silicon (Si) limitation and two light intensities. At a high specific nutrient flux (high dilution rate) under N limitation an assemblage of primarily small, fast growing centric diatoms such as Skeletonema costatum (Grev.) Cleve and Chaetoceros spp. dominated with a low percentage of flagellates. At a low specific nutrient flux, a mixture of larger, slower growing centric diatoms, small flagellates, and pennate diatoms was obtained. Similar trends were observed under silicate limitation. Decreasing the light intensity at the lowest dilution rate selected for an assemblage similar to that observed at the high dilution rate and high light intensity.The results of these competition experiments suggest that specific nutrient flux (dilution rate) is an important factor in determining between group dominance (e.g., centric and pennate diatoms and small flagellates). Successful competitors representing broad phytoplankton groups can be arranged along a resource gradient of specific nutrient flux (dilution rate), with groups such as centric and pennate diatoms, represented as high and medium flux species, respectively.     

Heavy metal tolerance of marine phytoplankton. II. Copper tolerance of three species in dialysis and batch cultures

The tolerance to copper ions of three diatoms, namely, Skeletonema costatum, (Grev.) Cleve, Thalassiosira pseudonana (Hust.) Hasle and Phaeodactylum tricornutum Bohlin grown in dialysis and batch cultures in the local fjord water has been established. Reduction of growth rates was observed by the addition of 10, 25 and 400 μg/1 of copper ions, respectively for the three species investigated. At the higher levels of copper addition (400 and 700 MS/1) cells of P. tricornutum in dialysis culture increased their copper content to more than 200 times over those of the controls, the ratio of copper to chlorophyll in the cells increasing 150 times.All three species showed marked increases in copper content when a copper salt was added to batch cultures of the algae. The two clones of Skeletonema costatum tested showed nearly identical sensitivity to copper ions, but they differed markedly in their zinc tolerance.     

A comparison of epiphytic diatom communities on <Emphasis Type="Italic">Plocamium cartilagineum</Emphasis> (Plocamiales,Florideophyceae) from two Antarctic areas

Our understanding of diatoms, one of the most important Antarctic primary producers, is based mostly on investigations of plankton, sea-ice, and sediment samples. Herein, we contribute to the limited research devoted to benthic Antarctic diatoms by presenting a study on epiphytic diatom communities sampled in two remote Antarctic regions: Admiralty Bay (maritime Antarctica, Antarctic Peninsula) and Terra Nova Bay (Ross Sea). Recent studies have demonstrated that the most critical factor for the local epiphytic diatom communities was the nature of the substrate. In order to eliminate this factor so we could evaluate other potential controls, we sampled epiphytic diatoms from only one substrate that is common to both regions: the macroalgae Plocamium cartilagineum (L.) Dixon. Thalli of P. cartilagineum and their associated microalgal community was collected in January 2011 (Admiralty Bay) and 2012 (Terra Nova Bay) from a water depth of 5–25 m. Dehydrated macroalgal pieces were placed on stubs and sputter-coated, which allowed observation of diatoms attached to the substrate in their original position using scanning electron microscopy. A total of 72 taxa were observed, of which 31 taxa were common to both regions. Cell abundance and diatom growth form dominance were significantly different in Admiralty Bay and Terra Nova Bay samples. Total diatom abundance was higher in Admiralty Bay samples, dominated by adnate diatoms (Cocconeis spp.), but the number of taxa found as well as the values of ecological indices were higher for samples from the Ross Sea, where motile forms were dominant (Navicula spp.). Our results suggest that Antarctic shallow-water benthic habitats may present a high degree of microniche heterogeneity and highlight the need of fine-scale analyses in microbial studies. We also suggest grazers as a factor that contributes greatly to the observed differences.     

Mysis in the Okanagan Lake food web: a time-series analysis of interaction strengths in an invaded plankton community

Mysis introductions to the lakes of western North America have shown they are important predators on zooplankton, especially daphnids, and intercept energy flows that would otherwise be available to pelagic fishes. However, understanding of the ecological roles of Mysis within invaded communities following their establishment remains weak. We analyzed zooplankton and phytoplankton data collected from Okanagan Lake, British Columbia, within a time-series framework to evaluate the strength of ecological interactions between Mysis and the other dominant plankton. Top-down effects of Mysis in the plankton community were only detected on cyclopoid copepods and cyanophytes. Mysis dynamics were mostly driven by bottom-up effects from diatoms and from small cladocerans whose dynamics were driven primarily by the abundance of edible phytoplankton. This result supports the growing appreciation of the importance of omnivory in mysids and was consistent between the two main basins of the lake. We also analyzed published stable C and N isotope data from the plankton of Okanagan Lake with an isotope mixing model to estimate the relative importance of various potential energy sources to Mysis. This analysis supported the time-series results suggesting the importance of diatoms and small zooplankton to Mysis. However, the isotopes also suggested important resource flows from Daphnia to Mysis, an interaction not detected in the time-series analysis. Taken together, these results suggest that Mysis is a strong interactor in the Okanagan Lake food web, relying in part on energy flow through Daphnia. However, subsidies from diatoms likely decouple seasonal Mysis population dynamics from the seasonal population dynamics of Daphnia.     

Studies on N-limited growth of diatoms in dialysis culture

N-limited growth of Skeletonema costatum (Grev.) Cleve in dialysis culture has been studied. The division rate of exponentially growing cells was independent of the nitrate concentration in the growth medium in the range from 886 down to 0.25 μM N-salt, while no growth beyond one division took place in cultures to which no nitrogen salt was added. The half saturation constant, K₃, for growth must, therefore, be in the range 0–0.13 μM, provided the growth-nutrient relationship is hyperbolic for S. costatum.Contrary to growth rate, cellular chlorophyll and protein were markedly reduced in media poor in nitrogen salts. A dialysis culture chamber was used to demonstrate that the measurement of half saturation constants for S. costatum was influenced by stirring, the stirred culture growing almost twice as fast as the unstirred control under identical conditions. The ability of diatoms to grow rapidly at low nitrogen levels was used to remove nutrients from sewage enriched media. Removal efficiencies corresponding to 80 and 90 % were obtained for nitrate and ammonia, respectively, using the diatom Phaeodactylum tricornutum Bohlin. It was found that both this diatom and S. costatum as well as Thalassiosira pseudonana Hust (Hasle) tolerated ammonia up to at least 450 μM with no deleterious effects on growth rate.     

The colonization of two Phaeocystis species (Prymnesiophyceae) by pennate diatoms and other protists: a significant contribution to colony biomass

The association of Phaeocystis spp. with small pennate diatoms during three Phaeocystis-dominated spring blooms were investigated in the Eastern English Channel (2003 and 2004) and in coastal waters of Western Norway during a mesocosm experiment (2005). In each of these studies, colonization of the surface of large Phaeocystis spp. colonies by small needle-shaped diatoms (Pseudo-nitzschia spp.) were observed. In the English Channel the diatom Pseudo-nitzschia delicatissima colonized the surface of large (>100 μm) Phaeocystis globosa colonies. The abundance of Pseudo-nitzschia delicatissima reached 130 cells per colony and formed up to 70% of the total carbon associated with Phaeocystis cells during late bloom stages. In Norwegian waters, the surface of large (>250 μm) Phaeocystis pouchetii colonies were colonized by Pseudo-nitzschia cf. granii var. curvata and to a lesser degree by other phytoplankton and protist species, although the abundance of these diatoms was never greater than 40 cells per colony. Based on these observations we suggest that diatoms utilize Phaeocystis colonies not only as habitat, but that they are able to utilize the colonial matrix as a growth substrate. Furthermore, these observations indicate that a considerable fraction of biomass (chlorophyll) associated with Phaeocystis colonies, especially large colonies concerned with intense and prolonged blooms, are due to co-occurring plankton species and not exclusively Phaeocystis cells.     

Seasonal variation in light- and temperature-dependent growth of marine planktonic diatoms in in situ dialysis cultures in the Trondheimsfjord,norway (63°N)

Three species of diatoms, Skeletonema costatum (Grev.) Cleve, Thalassiosira gravida Cleve, and T. pseudonana (Hustedt) Hasle et Heimdal, were grown in in situ dialysis culture in the Trondheimsfjord at depths of 0.5 and 4 m. The rates of growth and the chemical composition of exponentially growing cells were monitored and related to seasonal changes in illumination and temperature. Functions correlating growth rate with temperature were deduced. Growth took place from February to November. During this period temperature ranged from ?1 to 16°C, the average photon flux density (ifI) (per 24 h) from 9 to 570 μE · m^?2 · s^?1 (0.5 m depth), and the length of the days (I > 1 μE · m^?2 · s^?1) from 6 to 24 h. Light-limited growth was evident when the product of the average daily light and the chlorophyll/N ratio was < 10; this occurred mostly in early spring and late autumn. Peak densities (> 800 for the Thalassiosira spp. and > 1300–1400 μE · m^?2 · s^?1 for Skeletonema) seem to inhibit growth. The highest rates recorded were ≈1.6 doubl. · day^?1 (July, 15–16°C).The three species exhibit different ecological behaviour. Skeletonema is eurythermal (Q₁₀ = 1.8), whereas Thalassiosira pseudonana favours high temperatures, and T. gravida temperatures < 10°C. Moreover, Skeletonema has generally less chlorophyll and more phosphorus and ATP (≈ 1.4 ×) than the other two species. In Skeletonema, the ATP level seems related to the light-governed growth rate, and independent of temperature. In Thalassiosira no such correlation was found.     

Modification de la fonction antibiotique de deux diatomées marines, Asterionella japonica (Cleve) et Chaetoceros lauderi (Ralfs), par le dinoflagelléProrocentrum micans (Ehrenberg)

Two diatoms, Asterionella japonica (Cleve) and Chaetoceros lauderi (Ralfs), produced a similar lipidic antibiotic, whose activity increased after irradiation by visible light.In mixed cultures with the dinoflagellate Prorocentrum micans Ehrenberg, their cells contained higher amounts of the photoactivated antibiotic and a lower quantity of carotenoid pigments.These observations suggest the action of a chemical mediator released into the medium by P. micans, which inhibits the synthesis of pigments, thus leading to an increase of the photoactivation of the lipidic antibiotics in vivo. A similar inverse relationship between the concentration of carotenoids and the antibiotic activity was observed in several clones of Asterionella japonica isolated from different sea-water samples, and in cultures of the same diatom in the presence of diphenylamine. The importance of such phenomenon in a natural environment is discussed.     

THE IMPACT OF NONPHOTOCHEMICAL QUENCHING OF FLUORESCENCE ON THE PHOTON BALANCE IN DIATOMS UNDER DYNAMIC LIGHT CONDITIONS1

The nonphotochemical quenching (NPQ) of fluorescence is an important photoprotective mechanism in particular under dynamic light conditions. Its photoprotective potential was suggested to be a functional trait of algal diversity. In the present study, the influence of the photoprotective capacity on the growth balance was investigated in two diatoms, which possess different NPQ characteristics. It was hypothesized that under fluctuating light conditions Cyclotella meneghiniana Kütz. would benefit from its large and flexible NPQ potential, whereas the comparably small NPQ capacity in Skeletonema costatum (Grev.) Cleve should exert an unfavorable impact on growth. The results of the study clearly falsify this hypothesis. Although C. meneghiniana possesses a fast NPQ component, this diatom was not able to recover its full NPQ capacity under fluctuating light. On the other hand, the induction of NPQ at relatively low irradiance in S. costatum resulted in rather small differences in the fraction of energy dissipation by the NPQ mechanism in the comparison of both diatoms. Larger differences were found in the metabolic characteristics. Both diatoms differed in their biomass composition, with a higher content of lipids in C. meneghiniana but higher amounts of carbohydrates in S. costatum. Finally, the lower degree of reduction in the biomass compensated for the higher respiration rates in S. costatum and resulted in a higher quantum efficiency of biomass production. An indirect correlation between the photoprotective and the metabolic capacity is discussed.     

Effects of nitrogen,phosphorus, iron and silicon on growth of five species of marine benthic diatoms

The effects of nitrogen, phosphorus, iron and silicon on growth of five species of marine benthic diatoms, namely Navicula patrickae, Nitzschia panduriformis, Navicula thienemannii, Nitzschia longissima and Navicula atomus were studied by single factor experiments and the optimal concentration ratios of the four nutrient elements beneficial for diatoms growth were screened out separately using the L₉ (3⁴) orthogonal design. The results highlighted that nitrogen, phosphorus, iron and silicon all had highly significant effects on growth of five diatoms while the diatoms growth rates reached the highest averagely in the 2nd to the 6th culture day. In addition, the optimal concentrations (mg/L) of four nutrients suitable for diatoms growth were found higher than that in f/2 medium except that Nitzschia longissima had the same concentration of nitrogen as that in f/2 medium which is optimal for growth. Moreover, the optimal growth concentrations of four elements for five diatoms varied in the range of 12.36–74.16 mg/L for nitrogen, 1.70–3.98 mg/L for phosphorus, 2.00–4.00 mg/L for iron, 23.01–69.03 mg/L for silicon, respectively. By means of the orthogonal test of four nutrients for five benthic diatoms, the optimal concentration ratios N:P:Fe:Si (mg/L) were obtained as follows: 74.16:2.27:3.33:23.01 for N. patrickae; 37.08:3.98:4.00:11.50 for N. panduriformis; 49.44:3.98:3.33:34.51 for N. thienemannii; 12.36:1.70:4.00:11.50 for N. longissima; 74.16:2.27:4.00:69.03 for N. atomus.     

Effect of growth conditions on accumulation of internal nitrate,ammonium, amino acids,and protein in three marine diatoms

The capacity of marine phytoplankton to change their cellular content of nitrate, ammonium, amino acids, and protein in response to different growth conditions was systematically investigated. Cellular concentrations of these compounds were measured in N-starved, N-deficient, and N-sufficient Skeletonema costatum (Grev.) Cleve and in N-deficient Chaetoceros debilis Cleve and Thalassiosira gravida Cleve, both before and after the addition of a pulse of nitrogen.N-sufficient Skeletonema costatum contains high concentrations of protein, large persistent pools of amino acids, and, if it is growing on nitrate, sizeable amounts of nitrate. As it becomes N-starved, the total cellular nitrogen decreases, the internal nitrate and amino acids become entirely depleted, and the protein content is drastically reduced. After nitrogen additions to N-deficient and N-starved cultures, transient pools of unassimilated nitrogen form which can account for a large fraction of newly taken up nitrogen. The size and kind of pool which accumulates is determined by the preconditioning of the cells, the nitrogen compound which is added, and the species identity. The pools which form in S. costatum indicate that nitrate reduction is the slowest step in nitrogen assimilation, the synthesis of protein from amino acids is the next slowest, and the incorporation of ammonium into amino acid is the fastest. However, the rate limiting steps may vary between diatom species.For the first time, measurements of the variation in cellular nitrogen compounds over a wide range of environmental conditions reveal the ability of some phytoplankton to buffer the effects of a changing, and sometimes growth-limiting, nitrogen supply. They accomplish this by utilizing stored internal nitrogen for growth when the external supply is low and by quickly storing unassimilated nitrogen when the external supply is suddenly increased beyond their ability to immediately assimilate it. The accumulation of large pools of unassimilated nitrogen compounds can explain the often observed difference between nitrogen uptake rates and growth rates.     

Occurrence and distribution of plankton-associated and free-living toxigenic Vibrio cholerae in a tropical estuary of a cholera endemic zone

Cholera epidemics are thought to be influenced by changes in populations of estuarine Vibrio cholerae. We investigated the abundance and distribution of this bacterium, as ??free-living?? (<20???m fraction) and associated with microphytoplankton (>20???m) or zooplankton (>60???m), in the Karnaphuli estuary of Bangladesh during pre- and post-monsoon seasons. Cultivable Vibrio populations were ~10²?C10⁴ colony forming units (CFU) ml^?1 in the high saline zone (19?C23 practical salinity unit, PSU) and declined in freshwater (<10¹?CFU?ml^?1). Culture independent detection of toxigenic V. cholerae O1 and O139 serogroups revealed a higher abundance of ??free-living?? (10⁴?C10⁵ cells?l^?1) than those attached to plankton (10¹?C10³ cells?l^?1). However, ??free-living?? O1 and O139 cells were sometimes absent in the medium saline and freshwater areas (0.0?C11 practical salinity unit [PSU]). In contrast, plankton samples always harbored these serogroups despite changes in salinity and other physico-chemical properties. Microphytoplankton and zooplankton were dominated by diatoms and blue-green algae, and copepods and rotifers, respectively. Toxigenic V. cholerae abundance did not correlate with plankton abundance or species but had a positive correlation with chitin in the <20???m fraction, where suspended particulate matter (SPM), V. cholerae and chitin concentrations were highest. C:N ratios indicated that organic matter in SPM originated predominantly from plankton. The differential occurrence of ??free-living?? and attached V. cholerae suggests a pivotal function of plankton in V. cholerae spreading into freshwater areas. The probable association of this pathogen with organisms and particles in the nanoplankton (<20???m) fraction requires validation of the concept of the ??free living?? state of V. cholerae in aquatic habitats.     

Reduction of marine phytoplankton reproduction rates by copper and cadmium

The reproduction rates of 38 clones of marine phytoplankton were measured in media in which free cupric ion activity was controlled at different levels using a NTA-cupric ion buffer system. The major trend among species in their resistance to copper toxicity was a phylogenetic one, with cyanobacteria being the most sensitive, diatoms the least sensitive, and coccolithophores and dinoflagellates intermediate in sensitivity. The reproduction rates of most of the cyanobacteria were reduced at cupric ion activities above 10⁻¹² M, while most eukaryotic algae still had maximum reproduction rates at 10⁻¹¹ M. Four species, Emiliana huxleyi (Lohm.) Hay & Mohler, Skeletonema costatum (Grev.) Cleve, Thalassiosira pseudonana (Hustedt) Hasle & Heimdal and Thalassiosira oceanica (Hustedt) Hasle were particularly resistant to copper, being able to reproduce well at the highest cupric ion activities tested, 10^−9.5 M and 10^−9.2 M. There was no major difference, however, between neritic and oceanic species in their sensitivity to copper.The sensitivity of 20 species of marine phytoplankton to free cadmium ion activity was measured in a similar manner using an NTA-cadmium ion buffer system. As observed with copper, the prokaryotic cyanobacteria were the most sensitive to cadmium toxicity, diatoms were the least sensitive, and coccolithophores and dinoflagellates were intermediate. All cyanobacteria tested were dead at a cadmium ion activity of 10^−9.3 M whereas the reproduction rates of most of the eukaryotic algae were not reduced significantly until 10^−8.3 M.Comparison of these data with natural concentrations in sea water implies that cadmium is not an important ecological factor in unpolluted waters but natural copper concentrations may inhibit the reproduction of some phytoplankton species, especially cyanobacteria, in upwelled sea water. Copper may influence the seasonal succession of species.     

Phytoplankton of four rivers,the Tyne,Wear, Tees and Swale

An account is given of the phytoplankton in four relatively fast-flowing rivers in north-east England associated with a water transfer scheme. The total number of live cells (or units) ranged from 2 × 10² to 2 × 10⁴ cells ml^–1. Input of plankton from a reservoir did not appear to influence densities at a site 25 km downstream. Diatoms formed the majority of cells in most samples, with green algae second and cryptomonads third in importance. Among the diatoms, centrics were relatively more abundant at downstream sites. The ratios of live versus dead diatoms showed marked differences with season and between centric and pennate forms.     

Lysine biosynthesis and the evolution-of pennate marine diatoms

The classification of lysine biosynthetic pathways in various organisms have been used to investigate their descent in evolution. We have attempted these determinations in the diatoms Amphora coffeaeformis var:perpusilla (Grunow Cleve.) and Phaeodactylum tricornutum (Bohlin). Additionally, we have verified earlier results of Vogel in a green alga, Chlorella pyrenoidosa strain Tx 71105 (Texas Culture Collection). Our research indicates that the diaminopimelic acid route is involved in all three organisms. While these studies do not exclude the possible co-existence of the α-aminoadipic acid route, the results imply a closer evolutionary relationship of pennate diatoms to bacteria and “classical” photosynthetic plants rather than to heterotrophic or mixotrophic fungi and atypical algal strains such as the Euglenophyta.