Size and shape profoundly influence an organism’s ecophysiological performance and evolutionary fitness, suggesting a link between morphology and diversity. However, not much is known about how body ...shape is related to taxonomic richness, especially in microbes. Here we analyse global datasets of unicellular marine phytoplankton, a major group of primary producers with an exceptional diversity of cell sizes and shapes and, additionally, heterotrophic protists. Using two measures of cell shape elongation, we quantify taxonomic diversity as a function of cell size and shape. We find that cells of intermediate volume have the greatest shape variation, from oblate to extremely elongated forms, while small and large cells are mostly compact (e.g. spherical or cubic). Taxonomic diversity is strongly related to cell elongation and cell volume, together explaining up to 92% of total variance. Taxonomic diversity decays exponentially with cell elongation and displays a log‐normal dependence on cell volume, peaking for intermediate‐volume cells with compact shapes. These previously unreported broad patterns in phytoplankton diversity reveal selective pressures and ecophysiological constraints on the geometry of phytoplankton cells which may improve our understanding of marine ecology and the evolutionary rules of life.
Cell shape and size are the result of natural selection, but little is known about how shape depends on size and how they affect biodiversity. Using data on dimensions of unicellular marine algae, we show that shape and volume are interrelated: shapes of intermediate‐volume cells range from flattened to extremely elongated, while shapes of small and large cells are always compact. Taxonomic diversity peaks for intermediate‐volume cells with compact shapes, displays a log‐normal dependence on cell volume and decrease exponentially with cell surface extension for elongated or flattened cells.
Understanding 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.
•Monitoring marine phytoplankton requires intense efforts for species identification.•A new approach based on phytoplankton morpho-functional groups is proposed.•The approach controls for information ...loss associated to species grouping.•Morpho-functional groups detected community patterns as at species level.•The approach could help improving cost-effectiveness of phytoplankton monitoring.
Phytoplankton 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.
Since the first decades of the last century, several hypotheses have been proposed on the role of phytoplankton morphology in maintaining a favorable position in the water column. Here, by an ...extensive review of literature on sinking rate and cell volume, we firstly attempted to explore the dependency of sinking rate on morphological traits using the allometric scaling approach. We found that sinking rate tends to increase with increasing cell volume showing the allometric scaling exponent of 0.43, which is significantly different than the Stokes’ law exponent of 0.66. The violation of the 2/3 power rule clearly indicates that cell shape changes as size increases. Both size and shape affect how phytoplankton sinking drives nutrient acquisition and losses to sinking. Interestingly, from an evolutionary perspective, simple and complex cylindrical shapes can get much larger than spherical and spheroidal shapes and sink at similar rates, but simple and complex cylindrical shapes cannot get small enough to sink slower than small spherical and spheroidal shapes. Cell shape complexity is a morphological attribute resulting from the combination of two or more simple geometric shapes. While the effect of size on sinking rate is well documented, this study deepens the knowledge on how cell shape or geometry affect sinking rates that still needs further consideration.
The 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 pressures 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.
•Harmful microalgae occurrence, abundance and richness varied along the Apulian coasts (Mediterranean Sea).•HABs occurrence along the whole coast increased linearly over time.•HABs occurrence was significantly higher where most of anthropogenic pressures overlap than only a few or no pressures existed.•Physical alteration of coast is the most important pressure determining occurrence pattern.
The emergence of a red tide resulting in yellow-brownish discoloration of waters in Porto Cesareo bay (Italy) during July–August 2018 is reported. The species responsible for the bloom was the ...dinoflagellate Margalefidinium cf. polykrikoides. Cell densities reached 9.1 × 106 cells L−1 during the initial outbreak. A second peak was observed about three weeks later reaching 6.7 × 105 cells L−1. Study of live specimens showed great variation in cell size and shape. Different cyst morphotypes were found in the water samples and in the sediment. For the first time, we followed several stages of the life cycle of M. cf. polykrikoides in natural samples. Fish die-offs in the bay were not observed, however this high-density bloom may have caused consequences on the ecosystem (amount of mucilage on the beach) and in turn, on tourism that is the main activity in the area during the summer season.
Display omitted
•Margalefidinium cf. polykrikoides two - stages blooms in the Mediterranean Sea.•Exceptional yellow-brownish discoloration of the waters in a shallow bay (Northern Ionian Sea)•Morphological observations, cell and cysts density were reported.•Bloom dynamics of Margalefidinium cf. polykrikoides.
Several gymnodinioid dinoflagellates are responsible for blooms in the coastal Mediterranean Sea, coinciding with the greatest tourist arrival in summer. Chain-forming species such as the toxic ...Gymnodinium catenatum and Margalefidinium (Cochlodinium) polykrikoides, and two innocuous species Gymnodinium impudicum and G. litorale are prone to misidentifications. Recurrent yellow-brownish discolorations were observed during summer 2018 and 2019 in touristic areas of Porto Cesareo, Ionian Sea, Italy. The responsible species was identified as Margalefidinium cf. polykrikoides (Roselli et al. 2020, Mar. Pollut. Bull. 151:110825). However, re-examination of the published light micrographs, in addition to the new molecular analyses of samples collected from these blooms (SSU- and LSU rRNA genes and ITS region) pointed to a different gymnodinioid dinoflagellate, Gymnodinium litorale, which was also subsequently identified in the summer of 2021 from the observations of living cells. We provide light micrographs of Margalefidinium polykrikoides, Gymnodinium catenatum and G. impudicum from their type localities in order to facilitate the comparison and to avoid further misidentifications in the future.
Display omitted
•Phytoplankton blooms in the Mediterranean Sea are wrongly attributed to the toxic dinoflagellate Margalefidinium polykrikoides.•Re-examination of the samples and new data reveal that the non-toxic Gymnodinium litorale is the responsible species.•Gymnodinium catenatum, G. impudicum, G. litorale and Margalefidinium polykrikoides are known from the Mediterranean.•We provide a comparative study of these four chain-forming dinoflagellates to prevent further misidentifications.
PDF
