Inhibition of the growth of micro-algae and bacteria by extracts of eelgrass (Zostera marina) leaves

The effects of the water-soluble fraction of dead leaves of the eelgrass Zostera marina L. on the growth of 8 species of micro-algae (pennate and centric diatoms, dinoflagellates, and a green flagellate) and a bacterium were studied on agar plates and in liquid culture. The extracts of leaves which had been dead from a few days to 2 wk inhibited growth and often killed cells in all test organisms. Extracts were lethal even at concentrations equivalent to as little as 0.25 mg dry leaf ml^-1, but inhibition decreased when extracts were prepared from leaves aged in the laboratory for 35 d (loss of anti-bacterial activity) or 90 d (loss of anti-algal activity). Extracts of leaves which had aged and dried several months in the field had no effect, except at very high concentrations (13 mg dry leaf ml^-1) when the lag phase of growth was prolonged several days in a culture of the chlorophyte Platymonas sp. The active fraction in eelgrass leaves may be important in controlling initial growth of micro-organisms on eelgrass detritus, and it could determine the composition and activity of the epiphytic community on living leaves.     

Feeding habits of marine cladocerans in the Inland Sea of Japan

Natural food items of five species of marine cladocerans, Evadne nordmanni, E. tergestina, Penilia avirostris, Podon leuckarti and P. polyphemoides, were investigated in the Inland Sea of Japan between April 1986 and May 1987. Gut content examination with SEM (scanning electron microscopy) revealed that feeding was largely limited to centric diatoms and a few exceptions of pennate diatoms and dinoflagellates. No animal remains were detected, and some unidentified materials were also found. Phytoplankton smaller than 35 m in size (cell diameter in centric diatoms and longest dimension in others) was found most frequently in the gut of cladocerans. The role of grazing of marine cladocerans in trophodynamic pathways of the pelagic realm is discussed.     

Microalgal communities epibiontic on the marine hydroid <Emphasis Type="Italic">Eudendrium racemosum</Emphasis> in the Ligurian Sea during an annual cycle

The microalgal community associated with Eudendrium racemosum, a marine hydroid widely distributed in the Mediterranean Sea, was studied during an annual cycle, at monthly frequency, in a coastal station of the Ligurian Sea. Microalgae were represented mainly by diatoms, which exhibited higher abundance and biomass values between autumn and spring (max 46,752 cells mm⁻² and 1.94 μg C mm⁻², respectively), while during summer a significant decrease was observed (min 917 cells mm⁻² and 0.013 μg C mm⁻²). High levels of abundance of filamentous cyanobacteria were observed in summer. Spatial distribution of epibiontic microalgae showed a markedly increasing gradient from the basal to the apical part of hydroid colonies. Considering the growth forms of diatom communities, motile diatoms (mainly small naviculoid taxa) were the most abundant in all the periods. Adnate (Amphora and Cocconeis spp.) were distributed mainly in the basal and central part of hydroid colonies and showed two peaks (autumn and summer). Erect forms (mainly Tabularia tabulata, Licmophora spp., Cyclophora tenuis) were mainly distributed in the apical part of the colonies and showed their maximum densities in spring–summer. Tube-dwelling (Berkeleya rutilans, Parlibellus sp.) were observed at low densities throughout the study period, without any significant temporal or spatial variability. Comparing the microalgal communities on marine hydroid to those grown on mimic substrata placed in the sampling station during summer, significantly higher values of abundance were observed in the hydroid, suggesting that microalgae may benefit from the polyp catabolites. This fact was particularly evident for the adnate diatoms, whose temporal trend paralleled the cycle of hydroid host.     

Influence of light and temperature on the growth rate of estuarine benthic diatoms in culture

Four species of estuarine benthic diatoms: Amphiprora c. f. paludosa W. Smith, Nitzschia c. f. dissipata (Kützing) Grunow, Navicula arenaria Donkin, and Nitzschia sigma (Kützing) W. Smith were grown in unialgal cultures. The growth rates of the diatoms were determined as the rate of increase of the chlorophyll a content of the cultures. The diatoms were cultured at different combinations of temperture, daylength, and quantum irradiance. The highest growth rates of Navicula arenaria occurred at 16° to 20°C; the other 3 species had their optimum at 25°C or higher. The small-celled species had higher growth rates at their optimum temperature, but at lower temperatures the growth rates of all 4 species became very similar. The minimum daily quantum irradiance that could effect light-saturated growth at 12° and 20°C ranged from 2.5 to 5.0 E.m^-2.day^-1. At 12°C, two species had their highest growth rates under an 8 h daily photoperiod. At 20°C, the three species tested all had highest growth rates under 16 h daily photoperiod. The growth response of the benthic diatoms is comparable to that of several cultures of planktonic diatoms, as described in the literature. The influence of temperature and quantum irradiance on the diatoms in the present investigation was comparable to the influence of temperature and light intensity on the ¹⁴C-fixation of marine benthic diatoms (Colijn and van Buurt, 1975).     

Relative growth of different species of marine algae in wasterwater-seawater mixtures

In recent studies, we developed a combined nutrient removal-marine aquaculture process for the tertiary treatment of wastewater and the production of commercially important shellfish. Part of this process consists of an outdoor mass cultivation system for marine algae. During our previous experiments we observed that marine diatoms almost exclusively are the dominant algal species in our outdoor cultures. To better understand this phenomenon of diatom dominance we grew 16 species of marine algae in continuous monoculture under laboratory conditions simulating to some degree the conditions prevailing in our outdoor experiments. Species such as Skeletonema costatum, Monochrysis lutheri and Tetraselmis sp., which were never dominant in our outdoor cultures, grew as well in monoculture, as Phaeodactylum tricornutum, frequently, the prevalent species outdoors. However, when monocultures of Dunaliella tertiolecta and Thalassiosira pseudonana (3H) were purposely contaminated with P. tricornutum, the latter species quickly became dominant. It is suggested that a complex interaction of environmental factors is usually responsible for the dominance of a particular species; one such factor may be the nitrogen source in the growth media. Under conditions of virtually, complete nitrogen assimilation, the carbon: nitrogen ratio in the algae was high (7 to 8) when NO ₃ ^- –N was the source of nitrogen, and low (4 to 6) when NH ₄ ⁺ –N was the prime form of nitrogen. When algal growth was low, resulting in a large inorganic nitrogen residue, the carbon:nitrogen ratio was low regardless of whether NO ₃ ^- –N or NH ₄ ⁺ –N was the main nitrogen source.Contribution No. 3297 from the Woods Hole Oceanographic Institution.     

Aptamers are an innovative and promising tool for phytoplankton taxonomy and biodiversity research

Nucleic acid aptamers are small-size ligands that selectively bind to molecular segments even when they protrude from cell surfaces. Due to their high specificity, aptamers are widely used in biomedical research and as probes for different applications. Here, we tested whether aptamers can also discriminate among phytoplankton cells. As a proof of concept we focused on the widespread centric diatom Leptocylindrus danicus and generated two aptamers that selectively bind to its cell surface. The aptamers did not bind to other diatoms tested, which included both pennate (Pseudo-nitzschia multistriata) and centric (Skeletonema marinoi, Chaetoceros socialis) species. They also showed negative binding to closely related species (Tenuicylindrus belgicus, Leptocylindrus aporus, Leptocylindrus convexus), which are hardly recognizable with microscopy techniques. In addition, aptamers discriminated also among cells of the same clone, suggesting a potential use of aptamers as clone-specific/stage-specific probes to track phytoplankton life stages in their natural environment. While the method still needs to be tested with natural algal samples, it can complement in a unique way the existing approaches to discriminate among species and possibly life stages of marine phytoplankton. The method can find useful application in taxonomic and ecological studies as well as in environmental monitoring including early warning strategies.     

A new source of dimethylsulfide (DMS) for the arctic atmosphere: ice diatoms

We report the first evidence that pennate diatoms growing within the bottom layer of first-year ice in the Arctic produce significant amounts of particulate dimethylsulfoniopropionate (DMSP_p) and dissolved DMSP+DMS. In 1992 in Resolute Passage, a tributary of Barrow Strait, DMSP_p concentrations within the bottom layer of ice reached 1055 mg S m^-3 at the end of the vernal bloom, a value one order of magnitude higher than the maximum value reported in antarctic ice. Bottom-ice concentrations in DMSP_p and DMSP_d+DMS were significantly correlated with the abundance of the dominant pennate diatom Nitzschia frigida. Intracellular concentration in DMSP of ice algae was very low (0.001 pg cell^-1) at the end of April when algae were light-limited and reached 1.17 pg cell^-1 in mid-May following an increase in light and algal growth. We calculate that the rapid release of the dissolved DMSP+DMS from the ice into surface waters following the ice break-up will generate a sea-to-air DMS flux of 0.7 mg S m^-2 d^-1, a pulse ten times higher than the mean arctic summer flux. We estimate that this 1-d pulse represents up to 5% of the annual DMS emission in the Arctic.     

Diatoms of the microphytobenthic community in a tropical intertidal sand flat influenced by monsoons: spatial and temporal variations

Seasonal variations in the microphytobenthic diatom community were investigated in an intertidal sand flat of a tropical marine environment influenced by monsoons. Cores of sediments were collected along the beach gradient: low tide, mid tide and high tide zone up to a depth of 15 cm.. Diatom abundance was lowest during the monsoons and highest during the post-monsoons and the early pre-monsoon season throughout the intertidal transect. Diatom diversity was highest at the mid tide, followed by the high and low tide zones. Diatoms were viable up to a depth of 15 cm throughout the intertidal transect. The diatom community included the pennates, the permanent residents of this area, centric genera, which lead an attached mode of life and also some planktonic genera, brought in from ambient waters. Among the pennates, Navicula and Amphora were the dominant genera whereas in the case of centrics, Thalassiosira dominated the community throughout the intertidal transect down to a 15 cm depth. . Grain size fractions, which served as predictors of some diatom genera changed with tidal zones. The effect of winds on the resuspension of the pennate diatoms was evident only at the low tide zone down to a depth of 5 cm . Chlorophyll a concentration proved to be a good predictor of both pennate and centric diatom abundance at the low tide zone down to a depth of 10 cm and at the mid tide zone down to a depth of 5 cm.. However, even though chlorophyll a concentrations failed to reveal any positive correlation with the diatom abundance at both the deeper sediment layers and the high tide zone, the fact that viable cells were present at these areas reveal that the diatoms adopt survival strategies, contributing significantly to the carbon budgets of such unstable habitats.     

High recovery of culturable bacteria from the surfaces of marine algae

The culturability of heterotrophic marine bacteria obtained from the surfaces of two species of marine algae (Lobophora variegata andHalimeda copiosa) was assessed by comparing total DAPI-stained cell counts to colony-forming bacterial counts on two agar media. The colony-forming bacterial counts on a low-nutrient medium (LN) consisting of seawater and agar were significantly greater for both algal species than counts obtained on a high-nutrient medium (HN) similar in composition to that typically used for the isolation of heterotrophic marine bacteria. On average, 14 and 58%, respectively, of the total bacteria fromL. variegata andH. copiosa were culturable on LN. These recovery rates far exceed those typically reported for marine bacteria. Of 119 LN strains obtained in pure culture, 55% failed to grow on HN. The yeast extract component of HN (1.5 gl^-1) was responsible for the majority of the observed inhibition, suggesting that this nutrient can be highly toxic to marine bacteria. Eighty-nine percent of the strains inhibited by HN were capable of growth when the nutrients in this medium were diluted by a factor of 100 with seawater. Of 66 epiphytic strains, 30 (45%) initially inhibited by HN showed the ability to adapt to this medium after a period of laboratory handling. The initial inability of low-nutrient-adapted bacteria to grow on high-nutrient media may be due to nutrient shock. The results presented here indicate that the culturability of specific populations of marine bacteria can be dramatically improved by the use of low-nutrient media. Further, the importance of developing new medium formulations that eliminate traditional nutrients, some of which are clearly toxic to bacteria, is demonstrated.     

Growth of marine planktonic diatoms on inorganic and organic nitrogen

A study was conducted to determine if coastal diatoms from eutrophic waters (Werribee, Port Phillip Bay, Australia) are able to grow better than diatoms from oligotrophic waters (Bass Strait, Australia) on organic nitrogen compounds as their principal nitrogen sources. Eight clones of marine planktonic diatoms, belonging to 5 species (Skeletonema costatum, Asterionella japonica, Nitzschia closterium, Coscinodiscus sp., and Fragilaria sp.), were incubated with inorganic (either nitrate or ammonia) or organic (either urea, uric acid, alanine, aspartic acid, glutamic acid, glycine, serine, threonine, or valine) nitrogen sources and growth response was measured under high and low light intensities. All clones grew well on the organic as well as thorganic nitrogen compounds under both light regimes. Intraspecific differences were not great, as no appreciable difference was noted between clones from oligotrophic and eutrophic waters. The two negatively-charged amino acids, aspartic and glutamic acids, were somewhat less effective in supporting growth of some clones than were the other amino acids. Virtually all of the dissolved organic nitrogen (DON) compounds tested were utilizable for algal growth. Further, all clones appeared able to utilize at least some natural DON (uncharacterized) for cell division; in 1980, DON represented 97% of total nitrogen in Bass Strait and 83% of total nitrogen in Werribee waters. The results are consistent with previous findings on algal utilization of certain DON compounds and indicate comparable abilities of cells from oligotrophic and eutrophic coastal waters to assimilate these nutrients.Publication No. 307 in the Ministry for Conservation, Victoria, Environmental Studies Series     

Influence of marine microalgal metabolites on the feeding behavior of the blue mussel Mytilus edulis

Effects of microalgal ectocrines on the feeding behavior of the blue mussel Mytilus edulis L., collected from Delaware Bay, Lewes, USA, were studied. Unialgal cultures of six species of marine microalgae were grown to the end of their exponential growth phase. Cells were removed by gentle filtration, leaving dissolved microalgal ectocrines in culture filtrates. Filtrates were then tested in filtration rate and particle selection bioassays. In filtration rate bioassays, dissolved ectocrines were delivered to mussels in a flow-through apparatus and removal of beads (6 m) used to determine rates. Filtration rates were significantly reduced by dissolved ectocrines from two of the microalgal species tested (Olisthodiscus luteus Carter and Dunaliella tertiolecta Butcher). None of the microalgal filtrates stimulated filtration rates of mussels. In particle selection bioassays, ectocrines were adsorbed onto either reverse phase (lipophilic) or normal phase (hydrophilic) microparticles (10 m) and delivered to mussels with an equal concentration of control treated particles. Mussels showed significant selection, either rejection or preferential ingestion, for ectocrine treated spheres depending upon microalgal species and sphere type used. This research shows that pre-ingestive chemical cues from microalgae can influence mussel feeding behavior. We suggest that epicellular ectocrines are more important in mediating this behavior than dissolved ectocrines.     

Quantitative evidence concerning the stabilization of sediments by marine benthic diatoms

Six species of benthic diatoms and a natural benthic diatom community were cultured in flasks on a variety of sediments. Diatom species which secreted large quantities of mucilage were effective sediment stabilizers. These mucilage-secreting species significantly reduced resuspension and retarded laminar flow of the sediments when the culture flasks were agitated. Diatom species which secreted little or no mucilage were not effective sediment stabilizers. These non-mucilage-secreting species did not significantly effect resuspension or laminar flow of the sediments when the culture flasks were agitated. A sediment stabilizing mechanism based on the secretion of mucilage by pennate benthic diatoms is proposed. The effect such a process may have on distributional patterns of benthic invertebrates in areas where extensive diatom or other microalgal films occur is discussed.This work was supported by the Belle W. Baruch Foundation, and is Contribution No. 68 of the Belle W. Baruch Institute for Marine Biology and Coastal Research.     

Une approche vers l'estimation de la production potentielle du phytoplancton par analyse des cinétiques d'induction de fluorescence

In vivo chlorophyll fluorescence is particularly interesting ot ecologists because of various concepts (biomass, productivity, physiological state) associated with it. Using a modified spectrophotofluorometer, we have studied the kinetics of fluorescence in unialgal cultures and in a natural population of marine phytoplankton. Our apparatus did not achieve satisfactory results with cell suspensions having a chlorophyll concentration less than 10 g l^-1. We have also tested a method for estimating kinetics of diluted cultures and marine phytoplankton using cells collected on glass-fibre filters. For unialgal cultures in the exponential growth phase, the method proved satisfactory, and results obtained from both cell suspensions and filters were in good agreement. However, for aged cultures (principally diatoms) and natural marine phytoplankton the method proved unsuitable. The kinetics of fluorescence induction vary according to taxonomic position of the cells, light intensity of the measuring excitation beam and productiveness of the culture medium. The importance of the kinetics of fluorescence induction for characterization of phytoplankton activity is discussed.     

Phytoplankton in the Weddell Sea,Antarctica: composition,abundance and distribution in water-column assemblages of the marginal ice-edge zone during austral autumn

At the compacted, north-south line of the ice edge, phytoplankton were sampled during early austral autumn of 1986 in the northwestern Weddell Sea. Cells from discrete water bottle samples from 12 stations on two east-west transects were counted to gain quantitative information on the composition, abundance, distribution, and condition of the phytoplankton in water-column assemblages. Over 70 species were found. The highest numbers of total cells (integrated through the top 150 m) were found in open water, well-separated from and to the east of the ice edge on the southern transect, with 6.01×10¹⁰ cells m^-2. The relative abundance of diatoms was low at ice-convered stations (< 35% of the total phytoplankton in preserved samples) and high at open-water stations (> 80%); however, the relative abundance of the prymnesiophyte Phaeocystis sp. was high at ice-covered stations (> 60%) and low at open-water stations (< 16%), with lower absolute abundances than during a previous austral-spring phytoplankton increase. In the open ocean, the dominants were the pennate diatoms Fragilariopsis cylindrus, Pseudonitzschia prolongatoides, F. curta, and a small form of the centric diatom Chaetoceros dichaeta in chains. Although the three pennate diatoms were frequently dominant in number, they represented less biomass than C. dichaeta in open waters. Mean phytoplankton abundance was low (0.2×10⁶ cells l^-1) but, overall, the diatom cell density (0.14×10⁶ cells l^-1) was similar to that found previously during a northward transect from ice-covered to ice-free water at the Weddell-Scotia Sea ice edge (spring 1983). The phytoplankton spatial patterns in the two autumn transects differed, with the more southerly transect exhibiting a higher abundance of diatoms and dinoflagellates. The ratio of full to empty diatoms was higher on the southern transect, indicating a healthy population, while lower ratios of full/empty frustules on the northern transect suggested a generally declining population. However, Phaeocystis sp. was more abundant on the northern transect.     

Larval settlement and metamorphosis of the mussel <Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis> on different macroalgae

Settlement of mussels is commonly associated with macroalgae. The effects of 19 macroalgal species on the settlement and metamorphosis of pediveliger larvae of the mussel Mytilus galloprovincialis were investigated in the laboratory. Settlement and metamorphosis inducing activities of macroalgae Chlorodesmis fastigiata and Ceramium tenerrimum collected each month during the period between January 2005 and April 2006 were also investigated. Furthermore, C. fastigiata and C. tenerrimum were subjected to various treatments to investigate the roles of bacteria and diatoms on the algal surface in the induction of larval settlement and metamorphosis of M. galloprovincialis and the characteristics of the cues in these two macroalgae. Pediveliger larvae of M. galloprovincialis settled and metamorphosed in high percentages on Cladophora sp., Chlorodesmis fastigiata, Centroceras clavulatum, and Ceramium tenerrimum, all of which were filamentous in morphology. Macroalgae that were cylindrical, phylloid, flabellate, palmate and pinnate all showed low (<8%) percentages of post-larvae but four other filamentous macroalgae also had low mussel larval settlement, suggesting that chemical factors may also be involved. Seasonal variation had no effect on inductive activities of C. fastigiata and C. tenerrimum. Treatment of C. fastigiata and C. tenerrimum with formalin, ethanol and heat resulted in the significant decrease or loss of their inductive activities. Survival of algal cells within treated macroalgae also decreased significantly. Treatment of the two macroalgae with antibiotics and GeO₂ reduced the numbers of bacteria and diatoms on their surface but did not affect their inductive activities, indicating that the cue was produced by macroalgae and not by coexisting bacteria and diatoms. However, conditioned water and crude extracts of these two macroalgae did not induce larval settlement and metamorphosis. Thus, larvae of M. galloprovincialis settled and metamorphosed on specific filamentous macroalgae. The chemical cues produced by C. fastigiata and C. tenerrimum were susceptible to ethanol and heat treatments and were not recovered in the conditioned water nor in the extracts. The finding that inactive C. tenerrimum can be produced from culturing its apical segments provides a new tool to elucidate the chemical cue(s) from macroalgae through manipulation of their culture conditions.     

Antimicrobial activities of extracts from tropical Atlantic marine plants against marine pathogens and saprophytes

Studies investigating disease resistance in marine plants have indicated that secondary metabolites may have important defensive functions against harmful marine microorganisms. The goal of this study was to systematically screen extracts from marine plants for antimicrobial effects against marine pathogens and saprophytes. Lipophilic and hydrophilic extracts from species of 49 marine algae and 3 seagrasses collected in the tropical Atlantic were screened for antimicrobial activity against five ecologically relevant marine microorganisms from three separate kingdoms. These assay microbes consisted of the pathogenic fungus Lindra thalassiae, the saprophytic fungus Dendryphiella salina, the saprophytic stramenopiles, Halophytophthora spinosa and Schizochytrium aggregatum, and the pathogenic bacterium Pseudoaltermonas bacteriolytica. Overall, 90% of all species surveyed yielded extracts that were active against one or more, and 77% yielded extracts that were active against two or more assay microorganisms. Broad-spectrum activity against three or four assay microorganisms was observed in the extracts from 48 and 27% of all species, respectively. The green algae Halimeda copiosa and Penicillus capitatus (Chlorophyta) were the only species to yield extracts active against all assay microorganisms. Among all assay microorganisms, both fungi were the most resistant to the extracts tested, with less than 21% of all extracts inhibiting the growth of either L. thalassiae or D. salina. In contrast, over half of all lipophylic extracts were active against the stramenopiles H. spinosa and S. aggregatum, and the bacterium P. bacteriolytica. Growth sensitivity to hydrophilic extracts varied considerably between individual assay microorganisms. While 48% of all hydrophilic extracts were active against H. spinosa, 27% were active against P. bacteriolytica, and only 14% were active against S. aggregatum. Overall, more lipophilic extracts inhibited microbial growth than hydrophilic extracts. The variability observed in the antimicrobial effects of individual extracts against each assay microorganism reflects the importance of choosing appropriate test microbes in assays from which ecologically relevant information is sought. Results from this survey demonstrate that antimicrobial activities are prevalent among extracts from marine algae and seagrasses, suggesting that antimicrobial chemical defenses are widespread among marine plants.     

Responses of echinoid larvae to food patches of different algal densities

High densities of larvae have been found in areas of high primary production, but it remains unclear whether this is the result of hydrodynamics or of larval aggregative behaviour in the presence of food. In this study, we examined changes in the vertical distribution and swimming patterns of four-armed larvae of the sea-urchin Echinometra lucunter (Linnaeus) around food patches of a range of microalgal densities. We reared larvae in the laboratory in a high or low concentration of either single (Isochrysis galbana) or mixed (I. galbana, Dunaliella tertiolecta, Thalassiosira weissflogii) microalgal species. In Plexiglas cylinders, we experimentally constructed haloclines in which the salinity of the bottom water-layer was 33‰ and that of the top water-layer was 24‰. In a thin layer in the middle of the halocline, we inserted a food patch that consisted of 0, 2500, 5000 or 10 000 T. weissflogii cells ml⁻¹. The presence of a food patch had a pronounced effect on the vertical distribution of larvae. This effect depended upon the algal density of the food patch and varied with dietary conditioning. The number of larvae that were above or within the patch decreased with increasing algal density, and was greater if larvae were reared in low-ration or single-species diets than in high-ration or mixed-species diets. Tracking of individual vertical swimming paths showed that within a few minutes, larvae swam into the patches of low algal density, and to positions just below the patches of the two higher algal densities, and remained there until the end of the experimental period. The greater number of algal cells in the digestive tracts of larvae from treatments with a food patch than in those without a patch confirmed that larvae were feeding on the microalgal cells of the patch. To our knowledge, this is the first study to experimentally show an aggregative behavioural response of invertebrate larvae to a food patch. Such a response may reduce the probability of food limitation and therefore enhance larval survival. Received: 14 February 1997 / Accepted: 24 September 1997     

Growth and competition of the marine diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana. II. Light limitation

The marine diatoms Phaeodactylum tricornutum (Bohlin) and Thalassiosira pseudonana (Hasle and Heimdal) were grown under both continous illumination and a 14 h light: 10 h dark cycle at light intensities ranging from 1.53×10^-4 to 2.95×10^-1 ly min^-1. Under both photoperiods, T. pseudonana exhibited higher division rates than P. tricornutum at high light intensities, but the reverse was true at all light intensities <3×10^-3 ly min^-1. Comparison of these results with available data on light-limited growth of other planktonic algae suggests that P. tricornutum may be unusually efficient at maintaining its cell division rate at low light intensity. This efficiency may contribute substantially to its success in turbid, nutrient-enriched mass algal culture systems, the only environments in which it is known to attain great numbers.Contribution No. 4086 from the Woods Hole Oceanographic Institution.     

Water-soluble components of four fuel oils: Chemical characterization and effects on growth of microalgae

Approximately 50% of the compounds in the water solubles from 4 fuel oils have been identified via gas chromatography and mass spectrometry. In addition to the well-described types of compounds (naphthalenes, benzenes) expected in water-soluble extracts we have found phenols, anilines, and indoles. Of these classes of compounds methyl, dimethyl, and trimethyl derivatives are present in relatively high concentrations. The water solubles from the 4 fuel oils showed considerably different inhibitory effects to growth of 6 microalgae, 2 blue-greens, 2 greens, and 2 diatoms. Two of the fuel-oil extracts, Baytown and Montana, were lethal to blue-green algae. This was in part traceable to their content of p-toluidine which was found to be toxic to Agmenellum quadruplicatum, Strain PR-6, 1 g in the algal lawn-pad assay and 100 g/l in liquid culture. The water-soluble fraction from New Jersey fuel oil was lethal to the 2 green algae, with lesser effects on the 2 blue-greens. The 2 estuarine diatoms used as test organisms were not greatly inhibited by Baytown, Montana, or New Jersey fuel-oil water-soluble extracts. However, earlier work with an American Petroleum Institute fuel oil and the diatom Thallassiosira pseudonana (3H) showed that 3H was a very sensitive organism. Water solubles from the Baton Rouge fuel oil were almost without effect on the growth of all 6 microalgae. On the basis of the work herein and earlier work, a very cautious viewpoint is advisable in generalizing on the toxicity or lack thereof of a given fuel oil on the growth of different kinds of microalgae. On the other hand, with water solubles from toxic fuel oils such as Baytown or New Jersey the data clearly suggest that their potential for environmental damage is high, either through selective or enrichment effects on natural populations or through a lowering of total primary production.     

Diel periodicity of photosynthesis in marine phytoplankton

Short-term changes in photosynthesis were documented for 17 of 24 marine phytoplankton species, representing a range of taxonomic groups. Periodicity in phytoplankton photosynthesis on light-dark cycles (diel periodicity) was widespread but not universal for the species studied. The centric diatoms Lauderia borealis, Ditylum brightwellii, Stephanopyxis turris, Coscinodiscus rex, Chaetoceros gracile, and Biddulphia mobiliensis had strong diel periodicity in photosynthetic capacity (P _max). Amplitudes of the daily variations ranged from 2.9 to >50, with maxima in the morning or near midday, and with minima during the dark period, and these variations were not dependent on changes in cell pigmentation. There was some evidence for sustained photosynthetic periodicity in constant conditions in several diatoms, and an endogenous rhythm may have been present. The photosynthesis-irradiance (P-I) relationship was time-dependent for representative marine diatoms, with both the initial slope () and the asymptote (P _max) of P-I curves exhibiting significant synchronous diel oscillations. Moreover, detailed studies of the amplitude and timing of photosynthetic periodicity for the diatoms L. borealis and D. brightwellii demonstrated large temporal variations in photosynthesis with morning maxima. These P-I oscillations are discussed with reference to models of primary production which use the relationship between photosynthesis and light as a component of predictive equations for phytoplankton growth in the sea.