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Epiphytic diatoms from Terra Nova Bay (Ross Sea, Antarctica)
No full textIn polar waters, microalgal communities associated with macroalgae exhibit
rates of primary production comparable or even higher than those of
phytoplanktonic ones. These benthic communities are mainly represented by
diatoms. Despite to their crucial ecological role, the biodiversity of Antarctic
epiphytic diatoms is poorly studied and greatly underestimated. In the present
study, the diversity of epiphytic diatom communities from coastal waters of Terra
Nova Bay was investigated and described for the first time. Samplings were
made during the 8 Italian Antarctic expeditions in the space of 15 years. Thalli of
Iridaea cordata, Phyllophora antarctica and Plocamium cartilagineum were
collected during the austral summer. Collections were made from different
depths at 5 sampling sites. Taxonomical identification and counting of diatom
cells has been carried out by scanning electron microscope. According to our
results biomass appears to be inversely related to the diversity. The diatom
community composition varied depending on the sampling site as well as on the
morphology of the macroalgal host. Some differences could be observed along a
depth gradient. In terms of growth form in most cases adnate (e.g. Cocconeis,
Amphora) and mobile forms (e.g. Navicula, Nitzschia) dominated. Erect diatom
taxa tended to be associated with animal macrofouling species
Effect of salinity, temperature, organic and inorganic nutrients on growth of cultured Fibrocapsa japonica (Raphidophyceae) from the northern Adriatic Sea
No full textThe effects of temperature, salinity, inorganic and organic nutrients on the growth and physiological performance of Fibrocapsa japonica have been investigated in strains isolated from the northern Adriatic Sea, where intense and regular blooms have occurred since 1997 in coastal waters during summer. Strains isolated at different times and from different locations appeared homogeneous in terms of both physiological responses and molecular (ITS-5.8S rDNA) characteristics. Growth rates were higher at temperatures between 20 and 26 °C and a salinity range of 30-35 (0.7 div d-1). The temperature of 16°C inhibited growth, more markedly at the lowest and highest salinity values, a result also confirmed by a lower photosynthetic efficiency and by an increase in cell volume due to impaired division. Higher cell concentrations were obtained with macronutrients at f/2 levels than in a five-fold diluted medium. Comparing the utilization of 200 μM nitrate to that of different N sources (inorganic and organic), F. japonica showed an efficient growth with equivalent amounts of ammonia, urea and amino acids, such as glycine and tryptophan; glutamate was less effective, while methionine had toxic effects. Organic phosphate, administered as glycerophosphate, could also sustain F. japonica growth, probably on account of an alkaline phosphatase whose activity was enhanced in the presence of the organic form. Vitamins were necessary for growth, though no further stimulation was observed when a surplus of vitamin B12 (3 nM) was added. The addition of 11.7 μM iron instead of 2.3 μM, as well as that of humic acid, with or without macronutrients, did not enhance algal growth either. These results led us to hypothesise that F. japonica blooms became more frequent due to a general seawater temperature increase and to the availability of organic forms which, in coastal anthropized areas, are especially abundant in summer periods
Effect of salinity, temperature, organic and inorganic nutrients on growth of cultured Fibrocapsa japonica (Raphidophyceae) from the northern Adriatic Sea
Full text linkThe effects of temperature, salinity, inorganic and organic nutrients on the growth and physiological performance of Fibrocapsa japonica have been investigated in strains isolated from the northern Adriatic Sea, where intense and regular blooms have occurred since 1997 in coastal waters during summer. Strains isolated at different times and from different locations appeared homogeneous in terms of both physiological responses and molecular (ITS-5.8S rDNA) characteristics. Growth rates were higher at temperatures between 20 and 26 degrees C and in a salinity range of 30-35 (0.7 div day(-1)). The temperature of 16 degrees C inhibited growth, more markedly at the lowest and highest salinity values, a result also confirmed by a lower photosynthetic efficiency and by an increase in cell volume due to impaircd division. Higher cell concentrations were obtained with macronutrients at f/2 levels than in a fivefold diluted medium. Comparing the utilization of 200 mu M nitrate to that of different N sources (inorganic and organic), F japonica showed an efficient growth with equivalent amounts of ammonia, area and amino acids, such as glycine and tryptophan; glutamate was less effective, while methionine had toxic effects. Organic phosphate, administered as glycerophosphate, could also sustain F japonica growth, probably on account of an alkaline phosphatase whose activity was enhanced in the presence of the organic form. Vitamins were necessary for growth, though no further stimulation was observed when a surplus of vitamin B12 (3 nM) was added. The addition of 11.7 mu M iron instead of 2.3 mu M, as well as that of humic acid, with or without macronutrients, did not enhance algal growth either. These results led us to hypothesise that E japonica blooms became more frequent due to a general seawater temperature increase and to the availability of organic forms which, in coastal anthropized areas, are especially abundant in summer periods
Polyunsaturated aldehydes (PUAS) production and toxicity in a benthic environment: the microphytobenthos community of the Conero Riviera (northern Adriatic Sea).
No full textGrowth and phosphatase activities of ostreopsis cf. Ovata biofilms supplied with diverse dissolved organic phosphorus (DOP) compounds
No full textIt is becoming increasingly evident that the use of organic nutrients is widespread among many aquatic phototrophic organisms. Simultaneously, incidents of eutrophication of coastal waters are becoming more common due to rises in organic nutrient loads deriving from anthropogenic activities and natural terrestrial processes. In the northern Adriatic Sea, blooms of the toxic dinoflagellate Ostreopsis cf. ovata are reported as a frequent phenomenon linked to particular environmental conditions, including increased organic nutrient loads. Ostreopsis blooms typically produce a mucilaginous biofilm that can cover all benthic substrata. In order to clarify the role of dissolved organic phosphorus (DOP) in the onset and maintenance of an O. cf. ovata bloom, we investigated the growth rates in the presence of a range of phosphomonoesters (PMEs) (D-fructose 1, 6-disphosphate, β-glycerophosphate, α-D-glucose 1-phosphate, guanosine 5’-monophos-phate and phytic acid) and phosphodiesters (PDEs) (DNA and RNA). Levels of both phosphomonoesterase (PMEase) and phosphodiesterase (PDEase) activities were assessed in the O. cf. ovata biofilms. The results showed that O. cf. ovata growth is not inhibited in media containing a wide range of DOP and diverse ratios of PME:PDE compared to those containing inorganic phosphorus. Much of the hydrolytic activity was associated with bacteria and with extracellular polymeric substances (EPSs). Our findings suggest that the success of O. cf. ovata stems from the collective participation of all components of the biofilm (O. cf. ovata, EPSs and bacteria) that allows it to thrive in phosphorus-limited environments, but where the main source of phosphorus is organic
Ostreopsis cf. ovata abundances on different benthic substrata: how to compare them?
Full text linkIn the framework of benthic harmful algal bloom monitoring, the most common sampling strategy is based on the collection of macroalgae, and the abundance of epiphytic microalgae are mainly expressed as cells g−1 macroalgal fresh weight (fw). However, this methodology has some inherent problems, due to (i) the thallus-specific weights that markedly differ among algal species, (ii) the thallus architecture, and (iii) the production of allelopathic compounds that affects the epiphyte abundances among macroalgae, irrespective of the available colonizable surface. This study proposes a method to compare the abundances of Ostreopsis cf. ovata cells on different substrata, using a conversion factor that converts the abundances expressed as cells g−1 fw (or dry weight) to cells cm−2. Expressing abundances in terms of cells cm−2, the abundances can be compared (i) among different macroalgal species and (ii) between macroalgae and other substrata (such as rocks, pebbles, or shellfish shells). We also propose to normalize abundances when different macroalgae are sampled throughout the bloom period, considering the different epiphyte loads of different macroalgal species regardless of the available surface area
Symbiosis of Mycale (Mycale) vansoesti sp. nov. (Porifera, Demospongiae) with a coralline alga from North Sulawesi (Indonesia).
No full textEffetto di salinità, temperatura, nutrienti organici ed inorganici sulla crescita di Fibrocapsa japonica (Raphidophyceae) dell’Adriatico settentrionale.
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