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Effects of cell density, temperature, and light intensity on growth and stalk production in the biofouling diatom Achnanthes longipes (Bacillariophyceae)
Abstract
Achnanthes longipes Ag. is a marine stalk-forming diatom that grows in dense biofilms. The effects of cell density, temperature, and light on growth and stalk production were examined in the laboratory to determine how they affected the ability of this diatom to form a biofilm. Stalk production abruptly increased when A. longipes was cultured at a density of 5.4 × 103 cells·mL−†, with a lag before stalk production occurring in cultures initiated at lower densities. Growth occurred at all temperatures from 8 to 32° C, with maximum growth at 26° C. Growth rate was light saturated at 60 μmol photons·m−2·s−†. Stalk production was determined as the proportion of cells producing stalks and stalk length in response to various temperatures and light intensities at high (5000 cells·mL−†) and low (500 cells·mL−†) densities. More cells formed stalks at high density, with no difference in stalk length. The proportion of cells producing stalks was maximal at 20° C, with little change at 17–32° C. Stalk length was at a maximum between 14 and 26° C. Stalk production showed little change in response to varying light intensity. The results of an earlier investigation on the effects of bromide concentration on stalk formation were expressed as the proportion of cells forming stalks and the lengths of the stalks. Both measures of stalk production varied with bromide concentration, with maximum values at 30 mM bromide. The increased stalk production at higher densities may be a means of elevating cells above the substrate to avoid competition in the dense biofilm.
... A. longipes relies on production of highly organized extracellular adhesive biocomposites for cell motility and permanent adhesion to submerged surfaces (Wang et al., 1997). Studies on its adhesion focused on factors that affect the production of stalks both in field and experiments (Johnson et al., 1995;Wang et al., 1997;Lewis et al., 2002). A. longipes may provide a continuous food source for grazing abalone juveniles (Kawamura et al., 1995;Takami et al., 2003). ...
... However, the increasing in temperature to 20-25 o C exerted a strong influence on the growth causing a noticeable development in Chl. a content by days, particularly at 10 salinity. Lewis et al. (2002) reported the growth ability of A. longipes to a wide temperature range between 8 to 32°C, with maximum growth at 26°C. A decline in its density with a drop in temperature from 20 to 16 o C was observed (Parker et al., 2007). ...
... At continuous light, cultures grown under 10-15 o C&30-40 salinity reached the stationary phase slowly (day 6), and the increased temperature accelerated the development of the stationary phase faster (day 2). Temperature also seems affecting the stalk formation, shorter stalks were seen in the lowest temperature (10 o C) in agreement with the results of Lewis et al. (2002). At 12/12 LD cycle, the start of the stationary phase exhibited much delaying at 15 o C and 30-40 salinity (days 8-10), indicating another impact of light duration on the growth. ...
... Diatoms are among the earliest autotrophic colonisers in running waters following bed-clearing events because they can attach to substrata by means of extracellular polymeric substances (EPS) (Hoagland et al. 1993, Wustman et al. 1997, Wetherbee et al. 1998. Laboratory studies of marine biofouling diatoms have identified factors influencing diatom attachment such as the presence of calcium and temperature (Cooksey & Wigglesworth-Cooksey 1995, Lewis et al. 2002, but information on the responses of individual species in situ is scarce. Insight into the colonisation stages of stream diatoms has been gained using scanning electron microscopy techniques (Hudon & Bourget 1981, Wu et al. 1999 or whole assemblage analyses (Peterson & Stevenson 1989, Roberts et al. 2004). ...
... Differences between treatments were either not significant or very small (e.g., 0.52 vs. 0.59 in the presence and absence of UVR in Experiment 7). Lewis et al. (2002) reported a steep increase in stalk formation in the marine biofouling diatom Achnanthes longipes Agardh between ∼ 8 and 20 • C, but only when cell densities were high. The limited data from our experiments do not indicate similar a link between stalk production and cell densities in D. geminata because the highest proportions of stalks occurred in Experiment 4, when attachment densities were lowest. ...
... In laboratory studies of stalk length in A. longipes at relatively low light levels, there was a unimodal effect of temperature, with maximum stalk length occurring between 15 and 25 • C (Lewis et al. 2002). Temperatures in our experiments on D. geminata ranged between 11 and 17 • C and may represent the rising limb of such a relationship between stalk length and temperature. ...
We measured cell attachments and stalk lengths of the stalked diatom Didymosphenia geminata in situ, using in vivo staining, under different nutrient (phosphorus and nitrogen) and light treatments. Our aims were: (1) to investigate the effects of light and temperature (season) on attachment and stalk growth, including the effect of ultraviolet radiation (UVR), which has been suggested as a possible factor favouring D. geminata proliferation; and (2) to test the hypothesis that enrichment with dissolved phosphorus (DRP) inhibits the initial attachment of D. geminata cells. Although low concentrations (below ∼ 2 mg m−3) of DRP appear to be responsible for D. geminata proliferation, its general absence where DRP>2 mg m−3 is not understood. The experiments were conducted in outdoor channels over 14 months, spanning a range of water temperatures and light intensities. Increasing visible light intensity usually had a positive effect on attachment densities and stalk length, but both were depressed by very high intensities. Exposure to UVR generally led to lower attachment rates and shorter stalks. Increasing water temperature with season had a positive influence on the proportion of cell attachments producing stalks. Elevated nutrients (up to 6.6 mg m−3 P, and up to 115 mg m−3 N above ambient) did not affect D. geminata cell attachment unless the treatment channels contained previously colonised substrata. Nutrient enrichment negatively affected stalk length. Earlier findings of a positive role of light and a negative effect of nutrients on stalk length in D. geminata were corroborated, except that photoinhibition was demonstrated at very high visible light intensities. There was no evidence of a positive effect of UVR on D. geminata proliferation at the initial stages of attachment and growth. The results indicated that the absence of D. geminata from rivers with high DRP concentrations is not the result of nutrient interference with initial cell attachment.
... For example, EPS are central to adhesion to surfaces by benthic species (Wetherbee et al. 1998) and to motility in raphe-bearing diatoms (Lind et al. 1997), and they are the primary constituent of diatom stalks (Hoagland et al. 1993). Much of our understanding of the environmental drivers of EPS production has been gained from studies on marine planktonic diatoms (Myklestad and Haug 1972, Myklestad 1977, Granum et al. 2002, benthic intertidal diatoms (Smith and Underwood 1998, Underwood et al. 2004), or marine biofouling species (Wang et al. 1997, Lewis et al. 2002. Only recently has attention been paid to environmental aspects of EPS production by freshwater diatoms (Cyr andMorton 2006, Gerbersdorf et al. 2009), although the structure and composition of EPS-related structures has been relatively well studied (see review by Hoagland et al. 1993). ...
... There appear to have been few, if any, previous studies on freshwater diatom EPS production (including stalks) under nutrient limitation. Stalk occurrence and length in Achnanthes longipes were found to be generally unrelated to light intensity and more dependent on cell density and temperature, but this was in nutrient-replete culture medium (Lewis et al. 2002). However, photosynthesis as the driving process in EPS production in the marine benthic diatom Cylindrotheca closterium was highlighted by Staats et al. (2000). ...
... Nevertheless, the option of studying D. geminata in a mixed algal community colonizing outdoor channels has proved successful, because, as has been pointed out previously (Whitton et al. 2009), the large size of D. geminata makes it an ideal model organism. Direct measurements of diatom stalk length have rarely been employed in previous studies on species-environment relationships, exceptions being studies on A. longipes (Johnson et al. 1995, Lewis et al. 2002. In the present experiments, our ability to accurately measure lengths of individual stalk segments was facilitated by the reaction of methylene blue with anionic polysaccharides providing contrast between the stalks and the non-staining polystyrene (Styrofoam TM ) substratum. ...
Blooms of the freshwater stalked diatom Didymosphenia geminata (Lyngb.) M. Schmidt in A. Schmidt typically occur in oligotrophic, unshaded streams and rivers. Observations that proliferations comprise primarily stalk material composed of extracellular polymeric substances (EPS) led us to ask whether or not the production of excessive EPS is favored under nutrient-limited, high-light conditions. We conducted experiments in outdoor flumes colonized by D. geminata using water from the oligotrophic, D. geminata–affected Waitaki River, South Island, New Zealand, to determine the relationship between D. geminata stalk length, cell division rates, and light intensity under ambient and nutrient-enriched conditions. Stalk lengths were measured in situ, and cell division rates were estimated as the frequency of dividing cells (FDC). FDC responded positively to increasing light intensity and to nutrient additions (N+P and P). Under ambient conditions, stalk length increased as light level increased except at low ambient light levels and temperature. Nutrient enrichment resulted in decreased stalk length and negative correlations with FDC, with this effect most evident under high light. Our results are consistent with the hypothesis that extensive stalk production in D. geminata occurs when cell division rates are nutrient limited and light levels are high. Thus, photosynthetically driven EPS production in the form of stalks, under nutrient-limited conditions, may explain the development of very high biomass in this species in oligotrophic rivers. The responses of FDC and stalk length under nutrient-replete conditions are also consistent with occurrences of D. geminata as a nondominant component of mixed periphyton communities in high-nutrient streams.
... Very few studies (Johnson et al. 1995, Lewis et al. 2002, Kilroy & Bothwell 2011 have been conducted to define the conditions promoting stalk formation in fouling diatoms. However, EPS production has been extensively investigated in several marine benthic and planktonic diatoms (see review by Hoagland et al. 1993). ...
... In comparison with other marine and freshwater stalkforming diatoms, such as Achnanthes subconstricta (Meister) Toyoda, Didymosphenia geminata (Lyngbye) M.Schmidt and Gomphonema gracile Ehrenberg, our test organism L. flabellata exhibited a different growth and stalk-formation response to environmental conditions (Table 3). In their study on nutrient-replete A. subconstricta (as A. longipes C.Agardh), Lewis et al. (2002) observed that although growth rate increased with increasing light and temperature (maximum at 60 μmol photons m −2 s −1 and 26°C, respectively), cell density had an overriding stimulatory effect on stalk production. At high cell density, temperature influenced stalk production (but Downloaded by [University of Tasmania] at 19:21 08 June 2015 ...
Submerged natural and artificial marine substrata can rapidly become covered by biofouling organisms, of which diatoms are the early algal colonisers. Licmophora flabellata is an estuarine stalk-forming diatom that strongly adheres to substrata via a compound-branching polysaccharide stalk. In the present study, the effects of light, nutrients, temperature and turbulence were examined in laboratory cultures to determine how they affected stalk formation and growth rates. Growth rates in multiwell plates were estimated using in vivo fluorescence in a plate reader. Low light intensities (50, 100 and 150 µmol photons m−2 s−1) produced no or poor growth, whereas growth rates of 0.24-0.42 divisions per day were achieved at 233 µmol photons m−2 s−1. High growth rates coincided with long stationary growth periods (21-36 days) and long branching stalks (800-3500 µm). N, P and Si nutrients had no effect on growth or stalks, whereas high turbulence (from an orbital shaker) reduced stalk length but not growth. The results call for species-specific approaches towards mitigating the impact of fouling diatoms.
... Culturing microalgae under optimal conditions is advantageous to achieve high nutritional values that are beneficial for shrimp larvae. Among other things, light intensity, day length, and nutrient concentrations are important factors regulating microalgae growth in culture and also affect the nutritional content (Renaud et al. 1991;Lewis et al. 2002;Meseck et al. 2005;Sheng et al. 2011;Huang et al. 2013). Several researchers also have shown that salinity, pH, and temperature are important factors determining the growth of microalgae and controlling the nutritional quality (Goldman et al. 1982;Schmidt and Hansen 2001;Lewis et al. 2002;Renaud et al. 2002;Khatoon et al. 2010;Gu et al. 2012). ...
... Among other things, light intensity, day length, and nutrient concentrations are important factors regulating microalgae growth in culture and also affect the nutritional content (Renaud et al. 1991;Lewis et al. 2002;Meseck et al. 2005;Sheng et al. 2011;Huang et al. 2013). Several researchers also have shown that salinity, pH, and temperature are important factors determining the growth of microalgae and controlling the nutritional quality (Goldman et al. 1982;Schmidt and Hansen 2001;Lewis et al. 2002;Renaud et al. 2002;Khatoon et al. 2010;Gu et al. 2012). Table 3 summarises the optimal culture condition for microalgae species commonly used in shrimp aquaculture. ...
Demand for shrimp, particularly the eastern Pacific white shrimp Litopenaeus vannamei (Boone 1931), will continue to increase in Asian and worldwide seafood markets. Providing shrimp farms with a robust, healthy, and continuous supply of shrimp seed is a challenge that must be addressed to meet the demand. Shrimp feed during hatchery production still relies on live microalgae, despite many years of effort to find suitable full or partial-replacement diet alternatives. Successful mass production of microalgae for hatchery feed to obtain good quality shrimp seedstock depends on a number of environmental factors that determine the growth and nutritional values of various microalgal species. These factors include nutrients in the culture medium, light intensity, temperature, salinity, and pH. An overview of the use and the culture of microalgae in shrimp hatcheries is also presented and outlines the need for research for optimisation of algal diets for the rearing of L. vannamei seedstock in Asian hatcheries. Finally, the possibilities of using local isolates for hatchery operation are also highlighted.
... In this case stalk formation was essentially stimulated by high light intensity (233 μmol photons m -2 s -1 , similarly to our study), whereas nutrients or temperature did not influence growth rates or stalk formation/length. These results did not match the responses of L. colosalis and other marine and freshwater stalked-diatoms (Lewis et al., 2002;Perkins, 2010;. ...
... However, as far as we know the nutrient and stalk production relation in marine systems has been investigated only in Licmophora flabellata, and stalk formation in this species was essentially stimulated by high light intensity (233 μmol m À 2 s À 1 ), whereas nutrients or temperature influenced neither growth rates nor stalk formation/length (Ravizza and Hallegraeff, 2015). These results did not match the responses of L. colosalis and other marine and freshwater stalked-diatoms (Lewis et al., 2002;Perkins, 2010;Bothwell and Kilroy, 2011). ...
... Moreover, temperature is an important basic abiotic factors affecting the bacterial production and growth. Lewis et al. reported that the growth rate of Achnanthes longipes increased significantly (P < 0.0001) with increasing temperature until the maximum growth rate was reached at 26 °C, above which growth rate dropped sharply 48 . The suitable temperature for the cell growth of S. avermitilis is 28 °C in this study, below which the increasing temperature could improve the cell growth rate. ...
Avermectins, a group of anthelmintic and insecticidal agents produced from Streptomyces avermitilis, are widely used in agricultural, veterinary, and medical fields. This study presents the first report on the potential of using nanosecond pulsed electric fields (nsPEFs) to improve avermectin production in S. avermitilis. The results of colony forming units showed that 20 pulses of nsPEFs at 10 kV/cm and 20 kV/cm had a significant effect on proliferation, while 100 pulses of nsPEFs at 30 kV/cm exhibited an obvious effect on inhibition of agents. Ultraviolet spectrophotometry assay revealed that 20 pulses of nsPEFs at 15 kV/cm increased avermectin production by 42% and reduced the time for reaching a plateau in fermentation process from 7 days to 5 days. In addition, the decreased oxidation reduction potential (ORP) and increased temperature of nsPEFs-treated liquid were evidenced to be closely associated with the improved cell growth and fermentation efficiency of avermectins in S. avermitilis. More importantly, the real-time RT-PCR analysis showed that nsPEFs could remarkably enhance the expression of aveR and malE in S. avermitilis during fermentation, which are positive regulator for avermectin biosynthesis. Therefore, the nsPEFs technology presents an alternative strategy to be developed to increase avermectin output in fermentation industry.
... Not surprisingly, light intensity affects the growth rate of epiphytic algae (e.g. Lewis et al., 2002); however, epiphyte cover also affects seagrass photosynthesis. Dixon (1999) examined the role of epiphytic growth on attenuating light available to leaves of T. testudinum and concluded that epiphyte growth attenuated some 33% of PAR at depth. ...
... Sekar et al. (2004) reported that attachment by N. amphibia was directly proportional to culture density. Furthermore, culture density has been found to be a key stimulator for stalk production in Achnanthes longipes C. Agardh 1824 (Lewis et al. 2002). A further possibility is that other organisms present in the multiple-cell experiments influence survival. ...
Didymosphenia geminata is a freshwater diatom that can form extensive nuisance mats in rivers and streams.
First detected in New Zealand in 2004, D. geminata has been found in over 150 rivers throughout the South Island. The
diatom exhibited interesting distribution patterns in New Zealand, where it has remained absent from several apparently
suitable habitats. The aim of this study was to investigate the role of New Zealand river water chemistry in the establishment
of D. geminata. Water was collected from 16 North Island and four South Island rivers, and four South Island
groundwater-fed creeks where D. geminata was absent, and from seven South Island rivers with low to medium levels of D.
geminata and six South Island rivers with high levels of D. geminata. Water chemistry parameters were measured for these
sites. The survival and attachment of D. geminata cells to the surface of culture plates were monitored in the laboratory
under controlled conditions. Cells survived, attached and underwent cell division in waters with a wide range of chemistries,
including water where D. geminata was absent. No correlation was found between cell survival, attachment, or division and
any of the individual elements, compounds, or nutrient ratios tested. Findings in this study suggested that water chemistry,
in isolation of other environmental parameters, was unlikely to be the sole variable responsible for D. geminata distribution
in New Zealand. The attachment of free D. geminata cells to a substrate was a prerequisite for cell division, indicating that
substrate composition may play an important role in D. geminata establishment.
... The stalks of some bacteria and multicellular hairs of cyanobacteria and eukaryotic algae increase in length in response to P limitation (Schmidt & Stanier, 1966; Whitton et al., 2005). The stalks may represent a means of elevating cells above the substrate to avoid competition in dense biofilm (Lewis et al., 2002) and to have at the same time a better exposure to current speeds enhancing gas exchange and nutrient uptake (Whitford, 1960). Frequently , the stalked colonies of D. geminata are located near the water surface and may eventually be emerged without suffering any damage probably because they are protected by the huge amount of polysaccharides they produce. ...
One of the most striking features of the diatom Didymosphenia geminata, which has increased markedly in abundance in a number of countries in recent years, is the very large branched stalks. In order to help understanding their role, an ultrastructural study was carried out on two populations, one from a stream in northern England and the other from a river on Vancouver Island, Canada. In both cases, the main part of the stalk had a central reticulate core surrounded by an outer region with dense fibres. A longitudinal structure in the uppermost part of the stalk just under the collar surrounding the base of the cell may perhaps correspond to a tube. The structure of the septa formed where branches divide is also described. Phosphomonoesterase activity known to be present in the stalks was shown to occur in the inner peripheral layers of the stalks and especially in the collar area. The results show that stalks have a complex structure suggesting their importance for their phosphatase activity to overcome low inorganic phosphate concentrations. Their large surface may function in herbivory avoidance, a better exposure of cells to turbulent conditions to increase nutrient uptake, adsorption of limiting elements and gas exchange.
... This includes the widespread species A. brevipes C. Agardh and A. longipes C. Agardh, which are very common in coastal microphytobenthic communities (McIntire & Moore, 1977), together with the marine A. javanica Grunow and A. septata A. Cleve, and several terrestrial species, e.g. A. coarctata (Bre´bisson in W. Smith) Grunow in Cleve et Grunow and A. inflata (Ku¨tzing) Grunow. Achnanthes species are easy to cultivate and extensive experience has accumulated about how to manipulate the life cycle experimentally, through rapid alteration of cell size (von Stosch, 1942(von Stosch, , 1965Roshchin, 1982Roshchin, , 1984aRoshchin, ,b, 1994aRoshchin & Chepurnov, 1992, 1993, 1999Mizuno, 1994;Chepurnov & Roshchin, 1995;Mann, 1999;Lewis et al., 2002). Crucially, remarkable variation in breeding behaviour has been discovered within the genus, at both intra-and interspecific levels (Roshchin, 1994b;Chepurnov & Mann, 1997, 1999, 2000Mann, 1999;Mann & Chepurnov (unpublished observations)). ...
The availability of extensive experimental data and remarkable intra- and interspecific variation in breeding behaviour make Achnanthes Bory sensu stricto an especially good model for studying the reproductive and population biology of pennate diatoms. In most Achnanthes species studied, auxospore formation is accompanied by biparental sexual reproduction, but we found uniparental auxosporulation in Achnanthes cf. subsessilis. Auxosporulation appears to be apomictic and follows contraction of the contents of unpaired cells and then a mitotic division, which is normally acytokinetic: one nucleus aborts before the cell develops into an auxospore. Rarely, both daughter nuclei survive and cytokinesis produces two auxospores (two auxospores per mother cell is highly unusual in pennate diatoms); one may abort. Expansion of auxospores is not accompanied by deposition of a transverse perizonium, but a longitudinal perizonium is produced and consists of a wide central strip (structurally similar to the araphid valve) and at least one narrow lateral strip. This newly discovered asexual lineage in Achnanthes is discussed in relation to other reproductive systems found in the genus, and also in relation to the ‘sex clock’ hypothesis concerning the adaptive significance of the diatom life cycle. Brief information on chloroplast division and nuclear dynamics over the cell cycle is also presented.
... In Part B, the density of A. longipes in the high temperature unshaded treatment decreased after 15 days (Fig. 3) suggesting that A. longipes may have been light saturated or nutrient limited. Lewis et al. (2002) found growth of A. longipes to be light saturated at 60 mmol photons m -2 s -1 . This is equivalent to 4,440 lux, using the conversion factor provided in Langhans and Tibbitts (1997). ...
A series of trials was conducted to investigate the optimal temperature and light conditions for the culture of 3 benthic diatoms (Cocconeis sublittoralis, Achnanthes longipes and Navicula cf. jeffreyi), their biochemical composition as well as their suitability as a feed source for juvenile greenlip abalone (Haliotis laevigata) (4.07 ± 0.08 mm shell length) in commercial scale nursery culture over 24 wk. C. sublittoralis can grow well in a range of light intensities (830–1,217 lux) and is thus suited for the changing light conditions in a commercial abalone nursery. Achnanthes longipes grows well under high light conditions (1,412–4,400 lux) at low (18°C) and high (25°C) temperatures indicating that this species is more suited to culture in unshaded tanks and higher in the water column, on plates closer to the water surface. Cocconeis sublittoralis and Navicula cf. jeffreyi were cultured together to investigate competitive interactions between the two species. Throughout the experiment Navicula cf. jeffreyi was significantly higher in cell density when grown separately compared with the combined culture with C. sublittoralis. However when considering cell volume C. sublittoralis is substantially larger with a cell volume of 20,183 μm3 compared with 367 μm3 for N. cf. jeffreyi. Thus the cell density of N. cf. jeffreyi must be around 4 times higher than C. sublittoralis to achieve similar biomass, which was only the case at the start of the experiment. Hence N. cf. jeffreyi is a pioneer species (early colonizer) whereas C. sublittoralis is likely to eventually out compete N. cf. jeffreyi. Cocconeis sublittoralis is a suitable diatom species for commercial abalone nurseries, particularly when larger photophobic juveniles (+5 mm shell length) are cultured and shading is often necessary. The percentage of protein was significantly higher in N. cf. jeffreyi in comparison with the other two species whereas A. longipes contained significantly higher percentage lipid. At a commercial scale juvenile abalone were successfully maintained on diatom diets for at least 18 wk (to ca. 8 mm in SL) after which growth slowed. All diatom species declined in density after week 18 coinciding with a drop in temperature from 20.38 ± 0.09°C at the beginning of the experiment to 16.23 ± 0.11°C. Juveniles feeding on N. cf. jeffreyi and A. longipes reached only 9.99 ± 3.52 and 9.49 ± 3.21 mm, respectively, in nursery tanks after 24 wk. The biomass of these later two species was lowest overall because of the small cell volume of N. cf. jeffreyi and low cell density of A. longipes. Shell length reached 10.71 ± 3.58 and 10.42 ± 3.71 mm in the C. sublittoralis and mixed diatom treatments, respectively. Specific growth rates and weight gain were highest in the mixed treatment and biomass was highest in this treatment from week four onwards. This indicates that differences in food biomass are more important for the growth of these animals than differences in biochemical composition.
... These low light intensities are in accordance with the results obtained by Parker et al. (2007) for Cocconeis sublittoralis and confirm that most Cocconeis species grow preferentially in shaded environments. In addition, this irradiance range has been shown to be suitable for most epibenthic diatoms (Lewis et al. 2002, Mouget et al. 2005, and Cocconeis spp. are FIG. ...
The optimal conditions for the growth of two conspecific benthic diatoms were defined through factorial experimentation. We investigated the roles of light spectrum, nutrient availability, and culture conditions on the laboratory production of Cocconeis scutellum scutellum Ehrenb. and C. scutellum parva Grunow. Diatoms were cultivated in petri dishes, and inverted optical microscopy was used to periodically record their abundance. Growth curves were constructed from these data for each culture condition. In addition, at the end of the experiment we performed weight measurements to determine the total production for each of the considered conditions. We found that cultivation in nonsealed (NS) petri dishes (permitting gas exchange) represented the most productive technique. Cell density and biomass varied among light spectra, although this effect was inconsistent. For example, the Sylvania Gro‐Lux lamp (GL) produced the lowest cell density but highest biomass, suggesting that it may promote the production of larger cells. Surprisingly, of the culture media tested, f/2 (a media commonly used for the culture of diatoms) was the least productive. Diatom density and biomass were variably dependent on the combination of experimental culture conditions and strain used. These physical and chemical factors act mainly on given features of the diatom growth curve. These results permitted us to devise adequate culture protocols, to produce a biotechnologically important substance: a proapoptotic compound that specifically destroys the androgenic gland of a shrimp and could find novel applications in human medicine.
... Not surprisingly, light intensity affects the growth rate of epiphytic algae (e.g. Lewis et al., 2002); however, epiphyte cover also affects seagrass photosynthesis. Dixon (1999) examined the role of epiphytic growth on attenuating light available to leaves of T. testudinum and concluded that epiphyte growth attenuated some 33% of PAR at depth. ...
... species may even regulate the length of their stalks (Lewis et al. 2002), growing over the underlying mat and becoming competitors for light in conditions of dense mat development. The growth of epiphyte microalgae is generally favoured by a nutrient increase in the water column, and the response of epiphytes to the nutrient supply may depend on their position in the matrix (Burkholder et al. 1990; Hillebrand et al. 2000). ...
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 46,752cellsmm−2 and 1.94μg Cmm−2, respectively), while during summer a significant decrease was observed (min 917cellsmm−2 and 0.013μg Cmm−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.
... Other species able to attach to the wall, such as Navicula, Cymbella and Tabellaria were also present on the experimental Tarraleah slides, but they never remained in significant numbers in older fouling. The ability of G. tarraleahae to produce stalks may also have aided its longer term survival and dominance, increasing its access to light and nutrients by pushing cells above a crowded, partially shaded, substratum (Lewis et al. 2002). Cymbella also produced stalks which pushed it away from the wall, but cells of this species were rare in older fouling. ...
Freshwater microalgal biofouling in hydropower canals in Tarraleah, Tasmania, is dominated by a single diatom species, Gomphonema tarraleahae. The microfouling community is under investigation with the aim of reducing its impact on electricity generation. Species succession was investigated using removable glass slides. Fouled slides were examined microscopically and for chlorophyll a biomass. Chl a biomass increased steeply after 8 weeks (0.09-0.87 mg m(-2)), but increased much earlier on slides surrounded by a biofouled inoculum. Succession began with low profile diatoms such as Tabellaria flocculosa, progressing to stalked diatoms such as Gomphonema spp. and Cymbella aspera. Few chlorophytes and no filamentous algae were present. Pulse amplitude modulated fluorometry was used to measure the physiological health of fouling on the canal wall. Maximum quantum yield (F(v)/F(m)) measurements were consistently <0.18, indicating that the fouling mat consisted of dead or dying algae. The succession and physiological health of cells in the fouling community has broad implications for mitigation techniques used.
Despite two decades of research, the cause of blooms of the diatom Didymosphenia geminata remains uncertain. Blooms have been associated with low nutrient, oligotrophic streams. In this study, we used available data from across the globe and conducted experiments to determine how D. geminata responds to soluble reactive phosphorus (SRP) concentrations. Globally, D. geminata blooms have been found in streams with SRP below 11 μg P l−1. In North America, blooms only occurred at high equivalent latitudes when SRP was very low, whereas at lower latitudes blooms were observed under higher SRP concentrations. Using an in situ experiment, we found that following physical removal of D. geminata from stones, regrowth did not occur despite low SRP concentrations. In a second experiment, we found that there were no differences in D. geminata growth between a treatment which depleted SRP and a treatment which maintained elevated springtime SRP levels. These findings indicate that D. geminata blooms do not always form when SRP is low, even when cells are present. Bloom formation that is not exclusively related to low SRP suggests additional chemical or biotic factors, specific physical conditions, a seasonal timing requirement, or some combination of these with low P that are necessary to produce blooms.
Diatoms are an incredibly diverse group of microalgae that are primarily characterized by their highly ornamented siliceous cell wall. Diatoms have long been a source of interest in the field of bioadhesion due to their ability to adhere and glide upon surfaces, as well as construct extracellular adhesive structures that can enable temporary or permanent adhesion to a surface. This chapter introduces the various adhesion and motility strategies employed by a number of benthic diatom species, describing the mechanisms that facilitate these processes. We review the chemical, molecular, and physical characterization of extracellular polymeric substances resident on the cell surface, as well as those secreted specifically for adhesion and motility from various structures in the cell wall. We highlight the significant work undertaken using atomic force microscopy to understand the nanomechanical properties of these adhesives, allowing sub-molecular structures to be identified that have allowed new insights into their role in enhancing diatom adhesion to surfaces even in high-energy aquatic environments. Finally we look at how new technological advances, such as the recent sequencing of several diatom genomes, together with an integrative research approach, will facilitate the further identification and characterization of diatom adhesives.
The epibiotic communities (diatoms and metazoans) on the outer surfaces of
the shell of the barnacle
Balanus amphitrite
(BSh) and its opercular valves (the
scutum and tergum; BST) were investigated on a monthly basis for 1 year in a
tropical monsoon-influenced estuary and compared with that of the surround-
ing rock biofilm. BSh and BST were rich in the diatoms
Achnanthes longipes
and
Melosira nummuloides
and amongst the invertebrates, nematodes and
tardigrades were abundant. To the best of our knowledge, this is the first
report of epibiosis on the acorn barnacle. Diatom abundance was at its maxi-
mum during the monsoon season on all the inter-tidal substrata
i.e
. BSh, BST
and rock. A significant correlation was found between the density of diatoms
and invertebrates associated with the BSh and BST, possibly because of the
trophic relationship between them or the suitability of the physical environ-
ment. The possible role of these epibionts on the settlement of this barnacle
species is currently unknown and needs further investigation.
The relationship between ecological impact and ecosystem structure is often strongly nonlinear, so that small increases in impact levels can cause a disproportionately large response in ecosystem structure. Nonlinear ecosystem responses can be difficult to predict because locally relevant data sets can be difficult or impossible to obtain. Bayesian networks (BN) are an emerging tool that can help managers to define ecosystem relationships using a range of data types from comprehensive quantitative data sets to expert opinion. We show how a simple BN can reveal nonlinear dynamics in seagrass ecosystems using ecological relationships sourced from the literature. We first developed a conceptual diagram by cataloguing the ecological responses of seagrasses to a range of drivers and impacts. We used the conceptual diagram to develop a BN populated with values sourced from published studies. We then applied the BN to show that the amount of initial seagrass biomass has a mitigating effect on the level of impact a meadow can withstand without loss, and that meadow recovery can often require disproportionately large improvements in impact levels. This mitigating effect resulted in the middle ranges of impact levels having a wide likelihood of seagrass presence, a situation known as bistability. Finally, we applied the model in a case study to identify the risk of loss and the likelihood of recovery for the conservation and management of seagrass meadows in Moreton Bay, Queensland, Australia. We used the model to predict the likelihood of bistability in 23 locations in the Bay. The model predicted bistability in seven locations, most of which have experienced seagrass loss at some stage in the past 25 years providing essential information for potential future restoration efforts. Our results demonstrate the capacity of simple, flexible modeling tools to facilitate collation and synthesis of disparate information. This approach can be adopted in the initial stages of conservation programs as a low-cost and relatively straightforward way to provide preliminary assessments of.nonlinear dynamics in ecosystems.
The availability of rapid and effective methodologies for assessing lotic systems with microphytobenthos is still quite scarce. Hence, the primary goal of this study was to optimize the growth conditions of the sensitive and ubiquous benthic diatom Navicula libonensis for laboratorial and field assessments. The effect of different conditions of temperature, photoperiod, initial cell density, test duration and cell encapsulation into calcium alginate beads was evaluated in a first set of experiments. There was a slight increase in the growth of free and immobilized cells at 23 °C, at lower initial cell densities and at the shortest experimental period (6 days). Through all the conditions, the growth profiles of free versus immobilized were fairly variable. A second experimental trial involved the validation of selected conditions, applied to the ecotoxicological testing of N. libonensis to two reference chemicals-3,5-dichlorophenol and potassium dichromate. A similar response of free and immobilized cells was observed between exposures to spiked stream water and synthetic medium, and through the conditions tested. This outcome suggests that N. libonensis may potentially provide reliable responses under direct in situ exposures.
Intra- and interspecific competition of clonal populations of Achnanthidium minutissimum and two potential competitors (Cocconeis Placentula var. lineata and Cymbella cistula) were examined in laboratory experiments. Growth rate of A. minutissimum was compared at low and high initial population densities and when in competition with C. p.lineata or C. cistula. In addition, four treatment combinations of nutrients and light were used. Intraspecific rather than interspecific competitive effects regulated A. minutissimum growth rates. C. p. lineata grew very slowly in cultures. C. cistula grew well in culture, formed stalks, and overgrew A. minutissimum. Facilitation by C. cistula stalks, providing substratum for colonization, may have countered interspecific competition on A. minutissimum.
The first laboratory cultures of diatoms were made in the mid nineteenth century and involved incubating samples of mixed natural populations. Clonal cultures were first reported in 1892. Since then, rough, clonal and axenic cultures have provided many insights into taxonomically relevant aspects of diatom biology, although diatom taxonomy has remained obstinately linked to the study of cleaned silica valves. Relevant discoveries using cultures include diplonty, control of sexuality by cell size, specific and generalized patterns of shape change during size reduction, mechanisms of sexual reproduction (e. g. oogamy v. isogamy), heterothally (dioecy), reproductive isolation between morphologically similar demes (semicryptic species), aspects of phenotypic plasticity, patterns of cell wall and protoplast ontogeny, evolutionary relationships (from molecular sequence data), and population genetics. There is considerable scope for further contributions by culture-based studies in each of these subject areas but we suggest that increased attention should be paid to examining mechanisms of dispersal and gene flow, intrinsic reproductive isolation between allopatric demes, discovery of cryptic species, mate choice, evolution of the karyotype, 'evo-devo' (using molecular phylogenies to reveal how changes in wall morphology and protoplast structure have been brought about through modifications of developmental pathways), and girdle development and function. In addition, there is a great need for simple observations ('natural history') of e. g. growth form, motility, secretions, protoplast structure and dynamics, and mechanisms of sexual reproduction. Without such basic information about diatom structure and function, molecular phylogenies will be largely bald and uninteresting. Major impediments to the development and maintenance of diatom culture collections are (1) the finite life of clones (which has consequences for validation of research) because of size reduction and obligate sexual reproduction, (2) absence of dormant stages and lack of cryopreservation methods, and (3) recalcitrance in culture of many medium- and large-celled benthic species.
Open air freshwater hydrocanals in Tarraleah, Tasmania, Australia, exhibit significant diatom biofouling which leads to economic losses in hydroelectricity generation. These fast-flowing (flow velocity 2 m s−1) canals produce between 2 and 18 tonnes dry weight of fouling and 1–5 mg chlorophyll a/m 2 over a 20 km long course, with the canal surface area being 192,000 m2. Mostly monospecific diatom communities of Tabellaria flocculosa occur in canal sections with reduced flow, whereas a stalk-forming (up to 200 μm long) Gomphonema species dominates the majority of canal fouling in fast flowing areas. Gomphonema tarraleahae Perkins et Hallegraeff is newly described, the species differing from its close relative, G. angustatum (Kützing) Rabenhorst in its extreme stalking habit and distinctive head and footpoles. Low numbers of G. subclavatum (Grunow) Grunow and two other undescribed Gomphonema species were also present in fouling. Seasonal changes in biofouling are most likely related to temperature (5–15°C annually) and light intensity variation, with shaded, south-facing walls exhibiting higher fouling densities. Implications for fouling mitigation strategies are discussed.
Soft-sediment habitats in intertidal and shallow subtidal marine ecosystems frequently support extensive populations of benthic microalgae (microphytobenthos). These algal assemblages are dominated by species of motile benthic diatoms and form biofilms, a matrix of cells, sediments and extracellular polymeric substances (EPS), that create a complex microhabitat and act to stabilise sediments. Diatom EPS consists of a relatively undefined complex mixture of proteins, proteoglycans and carbohydrates. This complexity causes problems in extracting and analysing EPS and in the intercomparison of studies. This chapter reviews our current knowledge on the production rates, patterns and composition of benthic diatom EPS in culture and field studies. Production patterns are dynamic, changing with cell growth phase, photosynthesis and irradiance, nutrient conditions, and are also linked to endogenous cell rhythms. Meta-analysis of published monosaccharide composition data identified at least four major types of EPS produced by benthic diatoms, with varying patterns of production and composition. It is clear that more detailed research on the structural and physical properties of EPS are needed to understand its role in the environment. The natural occurrence of EPS is closely linked to diatom biomass, a pattern consistent over both macro (km) and micro (μm) scales. EPS is lost from sediments by various routes, solubilisation and removal by overlying water, bacterial degradation and consumption by deposit-feeding invertebrates. Work is needed to quantify these pathways and clarify the importance of EPS in coastal carbon cycles. Diatom EPS is a widely cited mechanism for increasing sediment stability and stabilisation by biofilms is well described. However, data are not consistent and developments in our knowledge of the structure and function of EPS are needed to explain how EPS binds and interacts within the sediment- biofilm matrix and affects the theology of sediment.
In all aquatic environments, available surfaces are rapidly colonized by a variety of organisms. If these organisms grow on
plants they are called epiphytes. Seagrasses provide an excellent substratum for epiphytic organisms and these organisms are
an integral component of seagrass ecosystems. The ecology and physiology of seagrass epiphytes have been reviewed previously
(Harlin, 1980; Borowitzka and Lethbridge, 1989) and this chapter focuses primarily on new developments in our understanding
of seagrass epiphyte biology and ecology that have occurred since then.
Seasonal fouling by diatoms was studied in the heavily polluted and eutrofied area near Piran in the Gulf of Trieste. Concrete plates (50 x 50 cm) were placed at l m, 3 m and 7 m depths, with the fouling observed monthly for one year, from March to October. Two plates were used at each level: one was scratched clean monthly to get an insight into the seasonality of fouling, while from the other only representative samples were taken in order to follow the fouling succession. In the eulittoral two quadrats of the same dimension were scratched clean on a vertical concrete wall. Diatoms proved to be the main fouling component sublittorally, while in the eulittoral green algae determined the physiognomy of the experi mental surfaces during spring. The present contribution deals only with the diatoms. Peaks of diatom colonization were found in April and August in the eulittoral, and sublittorally in July. Regarding the depth distribution, maxima in the number of recorded species were found at 3 m in spring, and at 7 m in autumn. The fouling populations were heterogenous, including epilithic, epipsammic and epipelic species with different affinities (marine, brackish and even freshwater). Colonial forms belonging to the genera Berkeleya, Navicula and Licmophora were outstanding and covered most of the experimental surfaces. Achnanthes species were among the primary colonizers, while Nitzschia species joined the fouling communities in autumn, along with several epipelic species. Seasonal recolonization on the monthly denuded plates was usual for species found sublittorally, either the whole year around, or only in autumn. Species found during spring did not recolonize monthly, and the same was true of the eulittoral ones.
Epipelic diatoms are important constituents of estuarine microphytobenthic biofilms. Field-based investigations have shown that the production of carbohydrates by such taxa is ecologically important. However, limited information exists on the dynamics of carbohydrate production by individual species of epipelic diatoms. The production of low and high molecular weight extracellular carbohydrates in axenic cultures of five species of benthic estuarine diatoms, Cylindrotheca closterium (Ehrenberg), Navicula perminuta (Grun.) in Van Heurck, Nitzschia frustulum (Kütz.) Grunow, Nitzschia sigma (Kütz.) Grunow, and Surirella ovata (Kütz.) Grunow, were investigated. All species produced colloidal (water-soluble) carbohydrates during growth, with maximal production occurring during stationary phase. During logarithmic growth, approximately 20% of extracellular carbohydrates consisted of polymeric material (extracellular polymeric substances [EPS]), but during stationary phase, EPS content increased to 34%–50%. Pyrolysis–mass spectrophotometry analysis showed differences in the composition of EPS produced during logarithmic and stationary phase. All species synthesized glucan as a storage carbohydrate, with maximum glucan accumulation during the transition from log to stationary phase. Short-term labeling with 14C-bicarbonate found that between 30 and 60% of photoassimilates were released as colloidal carbohydrate, with EPS consisting of approximately 16% of this colloidal fraction. When cells were placed in darkness, EPS production increased, and between 85 and 99% of extracellular carbohydrate produced was polymeric. Glucan reserves were utilized in dark conditions, with significant negative correlations between EPS and glucan for N. perminuta and S. ovata. Under dark conditions, cells continued to produce EPS for up to 3 days, although release of low molecular weight carbohydrates rapidly ceased when cells were dark treated. Three aspects of EPS production have been identified during this investigation: (1) production during rapid growth, which differs in composition from (2) EPS directly produced as a result of photosynthetic overflow during growth limiting conditions and (3) EPS produced for up to 3 days in the dark using intracellular storage reserves (glucans). The ecological implications of these patterns of production and utilization are discussed.
This paper evaluates the utilisation of space by epibenthic diatom cells, as a response to environmental variations. The aggregation pattern of five species of epibenthic diatoms was quantified and compared to provide evidence for the significance of cell motility as an adaptive mechanism for space occupation and monopoly. The epibenthic diatoms included (1) non-mobile colonial species forming either fan-shaped (Synedra tabulata (Ag)Kz.) or arborescent (Gomphonema kamtschaticum var. californicum Grun.) colonies; (2) slow-moving (Cocconeis costata Greg, and Amphora pusio Cl.), and (3) fast-moving (Navicula direct a (W. Sm.) Ra.) non-colonial species. The aggregation pattern of S. tabulata did not vary significantly among six different light intensities manipulated in nature. The major patterns of aggregation were identified using analysis of covariance and dummy-variable regression. Highly mobile N. directa are significantly less aggregated than the four other diatom species. Non-mobile and slow-moving species show a similar, highly aggregated pattern. The occurrence of two patterns of spatial dispersion indicates that growth forms bear far-ranging ecological implications with respect to colonization strategies, immigration, and possibly impact by grazers. An integrated model of growth form characteristics, biological properties, and ecological implications is presented for epibenthic diatoms.
Diatoms are a key component of marine ecosystems and are extremely important for the biogeochemical cycling of silica and as contributors to global fixed carbon. However, the answers to fundamental questions such as what diatoms can sense in their environment, how they respond to external signals, and what factors control their life strategies are largely unknown. We generated transgenic diatom cells containing the calcium-sensitive photoprotein aequorin to determine whether changes in calcium homeostasis are used to respond to relevant environmental stimuli. Our results reveal sensing systems for detecting and responding to fluid motion (shear stress), osmotic stress, and iron, a key nutrient that controls diatom abundance in the ocean.
Extracellular adhesives from the diatoms Achnanthes longipes, Amphora coffeaeformis, Cymbella cistula, and Cymbella mexicana were characterized by monosaccharide and methylation analysis, lectin-fluorescein isothiocyanate localization, and cytochemical staining. Polysaccharide was the major component of adhesives formed during cell motility, synthesis of a basal pad, and/or production of a highly organized shaft. Hot water-insoluble/hot 0.5 M NaHCO3-soluble anionic polysaccharides from A. longipes and A. coffeaeformis adhesives were primarily composed of galactosyl (64-70%) and fucosyl (32-42%) residues. In A. longipes polymers, 2,3-, t-, 3-, and 4-linked/substituted galactosyl, t-, 3-, 4-, and 2-linked fucosyl, and t- and 2-linked glucuronic acid residues predominated. Adhesive polysaccharides from C. cistula were EDTA-soluble, sulfated, consisted of 83% galactosyl (4-, 4,6-, and 3,4-linked/substituted) and 13% xylosyl (t-, 4f/5p-, and 3p-linked/substituted) residues, and contained no uronosyl residues. Ulex europaeus agglutinin uniformly localized [alpha](1,2)-L-fucose units in C. cistula and Achnanthes adhesives formed during motility and in the pads of A. longipes. D-Galactose residues were localized throughout the shafts of C. cistula and capsules of A. coffeaeformis. D-Mannose and/or D-glucose, D-galactose, and [alpha](t)-L-fucose residues were uniformly localized in the outer layers of A. longipes shafts by Cancavalia ensiformis, Abrus precatorius, and Lotus tetragonolobus agglutinin, respectively. A model for diatom cell adhesive structure was developed from chemical characterization, localization, and microscopic observation of extracellular adhesive components formed during the diatom cell-attachment process.
Examination of the three-dimensional structure of periphyton communities through time indicated that their microsuccession is analogous to higher plant succession. The development of attached diatom communities in two reservoirs was studied using artificial substrates, and the morphology of dominant organisms, patterns of spatial heterogeneity, and community interactions were documented with scanning electron microscopy. Of 93 taxa found, Gomphonema parvulum, G. olivaceum, Navicula graciloides, Nitzschia palea, and N. dissipata were dominant, depending upon season and reservoir. Comparisons of community diversity (SIMI) between reservoirs within seasons ranged from 0.023–0.843 (median = 0.254), indicating that the reservoirs were quite different with respect to diatoms present and their apportionments. Colonization was slow the first 2 wk in spring and fall, and throughout winter, but rapid during summer. Shifts in numerical dominance between certain species occurred in fall, spring, and summer. These inverse correlations of abundances and the functional dominance of overgrowth suggested competition for substrate surface area in the periphyton. The colonization sequence was often predictable—a presumably organic coating and a variety of bacteria, followed by low profile diatoms, and finally an upperstory of long-stalked and large-rosette diatoms and filamentous green algae. Periphyton microsuccession is similar to higher plant succession in the consistent change in vertical community structure from low to high physical stature, in the association of numerical dominance with large stature (via cell size or long mucilaginous stalks), and in the progressive slow-down in the rate of succession. Diatom mucilage also contributed to community structure by binding particulates and entrapping other algae and serving as the mechanism for substrate attachment.
This chapter explains the world-wide survey of slime formation of antifouling paints. Microbial slime films have been shown to increase significantly the drag of objects in contact with moving seawater. Small growths of Tubularla indivisa were found on the organotin varnishes and during 1984 patches of Achanthes subsessilis were also present. Fouling growth on nontoxic submerged surfaces can be immense even within two months as seen at certain sites in the present study. Although the test areas employed were very small, fouling development was consistent from one year to the next and followed the same pattern as that observed on large test areas immersed at certain sites. Laboratory studies on biocide resistance (particularly using mixed combinations of biocides) are needed on those diatoms found to flourish on antifouling paint surfaces. Such data combined with the analysis of paint leachates will improve theunderstanding of the biology of fouling organisms.
Heavy shade presents serious challenges for primary producers and food-limited herbivores in forest streams. This study examines the response of periphyton and grazing snails (Elimia clavaeformis) to summer shade in White Oak Creek (WOC) in a Tennessee deciduous forest. Three experiments were performed: (1) in situ manipulation of light and snail density to test the effects of light limitation and grazing; (2) construction of photosynthesis-irradiance (P-I) curves to test for shade adaptation by periphyton; and (3) measurements of snail growth vs. irradiance. In the first experiment, light and snail densities were manipulated in a 2 x 2 factorial design. Snails at normal densities cropped periphyton biomass to low levels regardless of light regime, but periphyton productivity was higher at the open sites where snails grew faster and accumulated more lipid. Snail growth and lipid accumulation were strongly affected by intraspecific competition in both light regimes. In the second experiment, photosynthesis-irradiance curves for periphyton from shaded and open sites illustrated considerable shade adaptation: shaded periphyton was 2 times more efficient at low irradiance than with periphyton from open sites. Despite the greater efficiency of shaded periphyton at low irradiance, integrated primary production estimated with photosynthetic models was 4 times greater in the open because shade adaptation provided only partial compensation for the shade. In the third experiment, in situ snail growth again increased with decreasing shade. Bottom-up effects of light limitation were propagated very strongly in WOC, where the vertebrate fauna is dominated by a grazer that appears to escape top-down control. 68 refs., 4 figs., 3 tabs.
These pages describe relatively simple and reliable methods for the culture of marine phytoplankton species useful for feeding marine invertebrates. The methods suffice for the most fastidious algae now routinely cultivable, and simplifications indicated for less demanding species are easily made; for example, omission of silicate for plants other than diatoms. Certain modifications of techniques, ancillary methods, and precautions will be treated briefly because questions often arise concerning them, but documentation will be minimal and hopefully restricted to publications readily available.
The general arrangement of cytoplasmic organelles in Achnanthes subsessilis is similar to that of other pennate diatoms so far investigated. The central nucleus is surrounded by perinuclear Golgi bodies which are believed to produce vesicles containing stalk material. The stalk is composed of four layers, is secreted from the raphe and in this region is surrounded by a mucilaginous collar. At the point of attachment the stalk spreads out over the surface and the outer layer terminates. The stalk is composed of polysaccharide without any associated protein, and the centre is more sulphated than the periphery. The stalk raises the cell well above the boundary layer on an antifouling-treated surface, thus permitting its continued growth and multiplication.
We examined the energetic dependency of the biochemical and physiological responses of Thalassiosira pseudonana Hasle and Heimdal. Chaetoceros gracilis Schütt, Dunaliella tertiolecta Butcher, and Gymnodinium sanguineum Hirasaka to NH4+, NO3−, and urea by growing them at subsaturating and saturating photon flux (PF). At subsaturating PF, when energy was limiting, NO3− and NH4+ grown cells had similar growth rates and C and X quotas. Therefore, NO3− grown cells used up to 48% more energy than NH4+ grown cells to assimilate carbon and nitrogen. Based on our measurements of pigments, chlorophyll-a-specific in vivo absorption cross-section, and fluorescence-chlorophyll a−1, we suggest that NO3−, grown cells do not compensate for the greater energy requirements of NO3− reduction by trapping more light energy. At saturating PF, when energy is not limiting, the utilization of NO3−, compared to NH4+ resulted in lower growth rates and N quotas in Thalassiosira pseudonana and lower N quotas in Chaetoceros gracilis, suggesting enzymatic rather than energetic limitations to growth. The utilization of urea compared to Nh4+ resulted in lower growth rates in Chaetoceros gracilis and Gymnodinium sanguineum (saturating PF) and in lower N quotas in all species tested at both subsaturating and saturating PF. The high C:N ratios observed in all urea-grown species suggest that nitrogen assimilation may be limited by urea uptake or deamination and that symptoms of N limitation in microalgae may be induced by the nature of the N source in addition to the N supply rate. Our results provide new eridence that the maximum growth rates of microalgae may be limited by enzymatic processes associated with the assimilation of NO3−, or urea.
Four species of estuarine benthic diatoms: Amphiprora c. f. paludosa W. Smith, Nitzschia c. f. dissipata (Ktzing) Grunow, Navicula arenaria Donkin, and Nitzschia sigma (Ktzing) 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 20C; the other 3 species had their optimum at 25C 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 20C ranged from 2.5 to 5.0 E.m-2.day-1. At 12C, two species had their highest growth rates under an 8 h daily photoperiod. At 20C, 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).
The importance of accurate demographic information is reflected in the United States Constitution, Article 1, which provides for a decennial census of this country's human population. Bacteria also conduct a census of their population and do so more frequently, more efficiently, and as far we know, with little if any of the political contentiousness caused by human demographers. Many examples have been found of particular bacterial genes, operons, or regulons that are expressed preferentially at high cell densities. Many of these are regulated by proteins related to the LuxR and LuxI proteins of Vibrio fischeri, and by a diffusible pheromone called an autoinducer. LuxR and LuxI and their cognate autoinducer (3-oxohexanoyl homoserine lactone, designated VAI-1) provide an important model to describe the functions of this family of proteins. LuxR is a VAI-1 receptor and a VAI-1-dependent transcriptional activator, and LuxI directs the synthesis of VAI-1. VAI-1 diffuses across the bacterial envelope, and intracellular concentrations of it are therefore strongly increased by nearby VAI-1-producing bacteria. Similar systems regulate pathogenesis factors in Pseudomonas aeruginosa and Erwinia spp., as well as T1 plasmid conjugal transfer in Agrobacterium tumefaciens, and many other genes in numerous genera of gram-negative bacteria. Genetic analyses of these systems have revealed a high degree of functional conservation, while also uncovering features that are unique to each.
The cellulose synthesis inhibitor 2,6-dichlorobenzonitrile (DCB) and the DCB analogs 2-chloro-6-fluorobenzonitrile, 3-amino-2,6-dichlorobenzonitrile, and 5-dimethylamino-naphthalene-1-sulfonyl-(3-cyano-2, 4-dichloro)aniline (DCBF) inhibited extracellular adhesive production in the marine diatom Achnanthes longipes, resulting in a loss of motility and a lack of permanent adhesion. The effect was fully reversible upon removal of the inhibitor, and cell growth was not affected at concentrations of inhibitors adequate to effectively interrupt the adhesion sequence. Video microscopy revealed that the adhesion sequence was mediated by the export and assembly of polymers, and consisted of initial attachment followed by cell motility and eventual production of permanent adhesive structures in the form of stalks that elevated the diatom above the substratum. A. longipes adhesive polymers are primarily composed of noncellulosic polysaccharides (B.A. Wustman, M.R. Gretz, and K.D. Hoagland [1997] Plant Physiol 113: 1059-1069). These results, together with the discovery of DCB inhibition of extracellular matrix assembly in noncellulosic red algal unicells (S.M. Arad, O. Dubinsky, and B. Simon [1994] Phycologia 33: 158-162), indicate that DCB inhibits synthesis of noncellulosic extracellular polysaccharides. A fluorescent probe, DCBF, was synthesized and shown to inhibit adhesive polymer production in the same manner as DCB. DCBF specifically labeled an 18-kD polypeptide isolated from a membrane fraction. Inhibition of adhesion by DCB and its analogs provides evidence of a direct relationship between polysaccharide synthesis and motility and permanent adhesion.
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Division rates Handbook of Phycological Methods Culture Methods and Growth Measurements
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Guillard, R. R. L. 1973. Division rates. In Stein, J. R. [Ed.] Handbook of Phycological Methods. Volume 1: Culture Methods and Growth Measurements. Cambridge University Press, Cambridge, pp. 289– 312.
Diatom fouling of in-service shipping with particular reference to the influ-ence of hydrodynamic forces
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Woods, D. C., Fletcher, R. L. & Jones, E. B. G. 1988. Diatom fouling of in-service shipping with particular reference to the influ-ence of hydrodynamic forces. In Round, F. E. [Ed.] Proceedings of the Ninth International Diatom Symposium. Biopress, Bristol, pp. 49–59.
Periphyton responses to temperature at dif-ferent ecological levels Algal Ecology: Freshwater Benthic Ecosystems
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DeNicola, D. M. 1996. Periphyton responses to temperature at dif-ferent ecological levels. In Stevenson, R. J., Bothwell, M. L. & Lowe, R. L. [Eds.] Algal Ecology: Freshwater Benthic Ecosystems. Ac-ademic Press, San Diego, pp. 149–81.
Marine littoral diatoms: eco-logical considerations The Biology of Dia-toms
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McIntire, C. D. & Moore, W. W. 1977. Marine littoral diatoms: eco-logical considerations. In Werner, D. [Ed.] The Biology of Dia-toms, Botanical Monographs. Vol. 13. Blackwell Scientific, Ox-ford, pp. 333–71.
A broad spectrum artificial seawater medium for coastal and open ocean phytoplankton.
- Harrison