1,720,974 research outputs found
Decoding size distribution patterns in marine and transitional water phytoplankton: from community to species level.
Full text linkUnderstanding the mechanisms of phytoplankton community assembly is a fundamental issue of aquatic ecology. Here, we use field data from transitional (e.g. coastal lagoons) and coastal water environments to decode patterns of phytoplankton size distribution into organization and adaptive mechanisms. Transitional waters are characterized by higher resource availability and shallower well-mixed water column than coastal marine environments. Differences in physico-chemical regime between the two environments have been hypothesized to exert contrasting selective pressures on phytoplankton cell morphology (size and shape). We tested the hypothesis focusing on resource availability (nutrients and light) and mixed layer depth as ecological axes that define ecological niches of phytoplankton. We report fundamental differences in size distributions of marine and freshwater diatoms, with transitional water phytoplankton significantly smaller and with higher surface to volume ratio than marine species. Here, we hypothesize that mixing condition affecting size-dependent sinking may drive phytoplankton size and shape distributions. The interplay between shallow mixed layer depth and frequent and complete mixing of transitional waters may likely increase the competitive advantage of small phytoplankton limiting large cell fitness. The nutrient regime appears to explain the size distribution within both marine and transitional water environments, while it seem does not explain the pattern observed across the two environments. In addition, difference in light availability across the two environments appear do not explain the occurrence of asymmetric size distribution at each hierarchical level. We hypothesize that such competitive equilibria and adaptive strategies in resource exploitation may drive by organism's behavior which exploring patch resources in transitional and marine phytoplankton communities
Using null models and species traits to optimize phytoplankton monitoring: An application across oceans and ecosystems
Full text linkPhytoplankton assemblages are privileged descriptors of the ecological status of marine ecosystems regularly included in routine monitoring programmes. The high spatial and temporal variability of phytoplankton and the intrinsic difficulties of species identifications, however, combine in making reiterate assessments of this component of marine biota particularly demanding. Coarse levels of taxonomic resolution (e.g., genus, family) or
morpho-functional categories have been proposed to reduce identification efforts or to ease the analysis of phytoplankton assemblages for monitoring purposes, although with contrasting outcomes. A major issue is that, in the absence of control for the loss of information associated to these alternative approaches, their application may lead to poor representations of genuine spatial and/or temporal patterns of assemblages in relation to natural and anthropogenic sources of variation. We provided a new approach to reduce the efforts required to analyse phytoplankton assemblages that integrate morpho-functional classification of phytoplankton with the use of null models to estimate the consequent loss of information on species-level community patterns. Null models for information loss were built by randomly grouping the original species variables into a progressively decreasing number of groups, in order to identify the minimum number of aggregate variables needed to detect community patters as at species level. Aggregate variables were then defined as morpho-functional groups, by grouping species on the basis of a combination of morpho-functional traits, including general taxonomy, cell size, shape, elongation and complexity. We applied the approach to six case studies investigating the response of phytoplankton assemblages from marine and transitional water ecosystems under different environmental settings in areas spanning the world’s ocean, including coral atolls, mangroves, estuaries, coastal lagoons and inlets. The approach allowed obtaining parsimonious sets of morpho-functional groups, which were suitable to detect changes in phytoplankton assemblage structure as at species level in all case studies. Trait-based approaches to
phytoplankton research and monitoring are crucial to shed light on processes underlying phytoplankton community assembly and dynamics in the face of global change. In this perspective, our framework incorporates cost-effectiveness, instances from traditional monitoring programmes aiming at the detection of community patterns, and the current need for a deeper understanding of functional responses of phytoplankton to environmental
drivers
New data-driven method from 3D confocal microscopy for calculating phytoplankton cell biovolume
No full textConfocal laser scanner microscopy coupled with an image analysis system was used to directly determine the shape and calculate the biovolume of phytoplankton organisms by constructing 3D models of cells. The study was performed on Biceratium furca (Ehrenberg) Vanhoeffen, which is one of the most complex-shaped phytoplankton. Traditionally, biovolume is obtained from a standardized set of geometric models based on linear dimensions measured by light microscopy. However, especially in the case of complex-shaped cells, biovolume is affected by very large errors associated with the numerous manual measurements that this entails. We evaluate the accuracy of these traditional methods by comparing the results obtained using geometric models with direct biovolume measurement by image analysis. Our results show cell biovolume measurement based on decomposition into simple geometrical shapes can be highly inaccurate. Although we assume that the most accurate cell shape is obtained by 3D direct biovolume measurement, which is based on voxel counting, the intrinsic uncertainty of this method is explored and assessed. Finally, we implement a data-driven formula-based approach to the calculation of biovolume of this complex-shaped organism. On one hand, the model is obtained from 3D direct calculation. On the other hand, it is based on just two linear dimensions which can easily be measured by hand. This approach has already been used for investigating the complexities of morphology and for determining the 3D structure of cells. It could also represent a novel way to generalize scaling laws for biovolume calculation
Determination of Coscinodiscus cf. granii biovolume by confocal microscopy: comparison of calculation models
Full text linkBiovolume is commonly used as a size descriptor in the study of phytoplankton ecology. Usually, biovolume is not measured directly but is obtained from a standardized set of geometric models based on linear dimensions measured by light microscopy. This commonly used method allows visualization and measurement in two dimensions (2D) yielding no information at all on the third dimension of phytoplankton cells. Inaccurate biovolume assessment resulting from geometric approximation leads to erroneous interpretation of eco-physiological processes and morpho-functional traits. Here, we use confocal microscopy coupled with an image analysis system (NIS Elements AR software, Nikon) to determine directly shape and biovolume by means a 3D reconstruction of Coscinodiscus cf. granii specimens. We evaluate the accuracy of current methods by comparing the results obtained using geometric models with direct biovolume and shape. We find that calculation of biovolume by approximation to geometric models (cylindrical and complex shapes) leads to a significant overestimation with respect to direct volume. We also propose a data-driven formula for calculating the biovolume of Coscinodiscus cf. granii specimens based on diameter or other linear measurements
Phytoplankton composition in the coastal Magnetic Island lagoon, Western Pacific Ocean (Australia)
Full text link1 - Coastal lagoons have traditionally been considered as transitional systems between continental and marine domains. The phytoplankton plays a key role in these aquatic environments, forming the base of the food web and having a substantial function in nutrient dynamics and in the carbon biogeochemical cycle.2 - Due to their short life cycle, planktonic algae respond quickly to environmental changes and they are thus a valuable indicator of water quality. It is essential to investigate the development of phytoplankton populations to understand the biological functioning and to detect changes in aquatic systems.3 - Phytoplankton studies in the Australian estuaries and lagoons are relatively scarce. This study has provided a broad perspective and preliminary information on taxonomic structure of phytoplankton guilds for the Magnetic Island Lagoon (Queensland, Australia). This work may provide valuable information of interest to later ecological studies.4 - In the whole sampling a total of 143 taxa were identified. In terms of species richness, diatoms (Bacillariophyceae, Coscinodiscophyceae, Fragilariophyceae) and dinoflagellates (Dinophyceae) were the most important groups. In taxonomic terms, diatoms were the major contributor to the phytoplankton composition (~ 70%) whereas Dinophyceae were moderately abundant (~23%). Diatoms are a very important component in estuarine and shallow coastal wetlands and they are increasingly being utilized as indicators of environmental change
Early warning tools for ecotoxicity assessment based on Phaeodactylum tricornutum
No full textPhaeodactylum tricornutum was exposed to various toxic substances (zinc, copper or dodecylbenzenesulfonic acid sodium salt) in accordance with the AlgalToxkit(®) protocol based on the UNI EN ISO 10253 method in order to quantitatively compare the responses obtained by traditional growth-rate inhibition tests with morphological (biovolume) and physiological (chlorophyll-a, phaeophytin ratio) endpoints. A novel approach is proposed for detecting early and sub-lethal effects based on biovolume quantification using confocal microscopy coupled with an image analysis system. The results showed that effects on both biovolume and the photosynthetic complex are sensitive and powerful early warning tools for evaluating sub-lethal effects of exposure. Specifically, biovolume showed significant sensitive and early responses for the tested surfactant. Qualitatively, we also observed structural anomalies and effects on natural auto-fluorescence in exposed cells that also represent potentially useful tools for ecotoxicological studies
Harmful algae and pressure-impact relationship: Noxious blooms and toxic microalgae occurrence from coastal waters of the Apulia region (Adriatic and Ionian Seas, Mediterranean)
Full text linkThe spatial distribution of harmful microalgal taxa along the coasts of the Apulia region (Mediterranean Sea) based on results of eight years (2012-2019) of routine monitoring program and a series of sporadic observations is presented. A total number of 69 potentially harmful taxa were found during the study period. Occurrence, abundance and richness of harmful taxa (toxic, potentially toxic and high biomass producers) varied along the Apulian coasts. The occurrence of harmful species was significantly higher where most of anthropogenic pres-sures overlap than only a few or no pressures existed. The physical alteration of coast is the most important pressure determining this pattern. Despite the variety and the abundances of the harmful microalgae, to our knowledge, no human health problems or risks have been ever recorded, nor were full-blown consequences on marine organisms such as fish kills during algal blooms. However, blooms coupled with water discoloration phenomena could become a big issue to tourism and recreational activities that have locally important socio-economic value
Early warning tools for ecotoxicity assessment based on Phaeodactylum tricornutum
No full textPhaeodactylum tricornutum was exposed to various toxic substances (zinc, copper or dodecylbenzenesulfonic acid sodium salt) in accordance with the AlgalToxkit(®) protocol based on the UNI EN ISO 10253 method in order to quantitatively compare the responses obtained by traditional growth-rate inhibition tests with morphological (biovolume) and physiological (chlorophyll-a, phaeophytin ratio) endpoints. A novel approach is proposed for detecting early and sub-lethal effects based on biovolume quantification using confocal microscopy coupled with an image analysis system. The results showed that effects on both biovolume and the photosynthetic complex are sensitive and powerful early warning tools for evaluating sub-lethal effects of exposure. Specifically, biovolume showed significant sensitive and early responses for the tested surfactant. Qualitatively, we also observed structural anomalies and effects on natural auto-fluorescence in exposed cells that also represent potentially useful tools for ecotoxicological studies
Phytoplankton composition in six Northern Scotland lagoons (Orkney Islands)
Full text link1 - Transitional waters are ecotones between freshwater, marine and terrestrial ecosystems and include a number of different ecosystem types, one of which is constituted by lagoons.2 - Lagoons are important patches in the coastal landscapes, which constitute for their ecological relevance a priority habitat (1150) in the EC Nature 2000 Directive.3 - In the Northern part of Scotland and in the Scottish islands, lagoons are typical coastal ecosystems, while estuaries dominate the Southern Scottish coast.4 - In this study, we investigate the phytoplankton communities in six Scottish lagoons in Orkney Islands (Kirwall, Ouse, Oyce of Isbister, Point of Backaquoy, Skaith and Loch of Stenness), describing their taxonomic composition and abundance.5 - The taxonomic list consists of 9 phyla and 16 classes, including 160 taxa, which are evenly distributed among classes. Generally, the higher taxonomical abundance in the studied lagoons is reached by Bacillariophyceae, Chlorophyceae, Coscinodiscophyceae and Dinophyceae. The dominant groups among all the systems in terms of number of cells are: small undetermined phytoplankton and phytoflagellates, which are numerically abundant in all the six Scottish lagoons, Bacillariophyceae, Chlorophyceae, Coscinodiscophyceae, Cyanophyceae and Fragilariophyceae
Dynamics of phytoplankton guilds under dystrophic pressures in Lesina lagoon
Full text linkWe analyzed the dynamic of phytoplankton guild during an dystrophic crisis observed in an area of Lesina Lagoon from July to September 2008. A two-weekly scale, patterns of variation of phytoplankton biomass (as Chla), numerical abundance, species richness, diversity, taxonomic and size structure were compared in two stations: one within the area affected by the crisis (AT2 station) and one outside, as control (AT3 station). Phytoplankton biomass and cell abundance varied significantly between sampling stations and sampling times. Biomass was on average about 100 time higher in AT2 than AT3 station, with peaks of 180,67±22,12 mgChla/m3 (8 July) and 134,05±47,26 mgChla/m3 (5, September). Cell density was on average about 30 times higher in AT2 station, with values always higher than 20*106 cell/l. Species richness and diversity did not varied significantly between stations and not show a trend with the evolution of anoxic crisis. The taxonomic composition is similar in the two stations (taxonomic similarity among stations was 76,04%), even if the relative abundance of species was significantly different. As regard size structure, in the AT2 station, microphytoplankton dominates at beginning of biomass bloom (dominant taxa: Thalassiosiraceae, average weight (AW) 163,51 pgC), whereas from the end of July until September and in the AT3 station, nanophytoplankton was the dominant fraction (dominant taxa: until the middle of August: Algae indet AW 3,14 pgC and Navicula sp. AW 2,50 pgC)
- …
