Charophyte Species Research Articles

Interspecies differences and lake‐specificity in the δ13C and δ18O signatures of charophyte carbonate encrustations

Abstract This study identifies the relationships between the δ13C and δ18O signatures of extant charophyte carbonates (δ13CCARB and δ18OCARB) and the δ13C of dissolved inorganic carbon and δ18O of water (δ13CDIC and δ18OWATER), respectively, and the structure of charophyte beds and the physico‐chemical properties of the ambient water. Inter‐ and intra‐specific differences and lake‐related variability are assessed. Four morphologically different charophyte species (Nitellopsis obtusa, Chara tomentosa, Chara rudis, Chara contraria) were studied in four charophyte‐dominated lakes (Chara‐lakes) in Central Europe. A wide distribution of the species in calcium‐rich freshwater lakes, where they form extensive underwater beds and contribute to the deposition of calcareous sediments, makes the study representative of Chara‐lakes. Charophytes and water above them were sampled monthly (June–September 2008) at permanent study sites. Additionally, three comparative macrophyte‐free pelagic sites were sampled in each lake. For all the charophytes studied, there was a greater variation in the δ13C and δ18O values of the encrustations than of the ambient and pelagic waters. Except for N. obtusa and C. tomentosa, the species differed significantly in the δ13CCARB values. The encrustations were enriched in 13C compared to water DIC. Chara tomentosa encrustations were significantly depleted in 18O compared to N. obtusa and C. contraria. In contrast to Chara species, N. obtusa encrustation was 18O‐enriched compared to surrounding water. The largest isotope differences between carbonate encrustations and surrounding water were found for C. rudis. Considering the δ13CCARB versus δ13CDIC values, only slender species (i.e. N. obtusa and C. contraria) precipitated encrustations close to isotopic equilibrium with water DIC. Based on theoretical δ18OCALCULATED and measured δ18OCARB values, only C. tomentosa precipitated encrustation in equilibrium with the δ18OWATER. Using redundancy analysis, the δ13CCARB values positively correlated with the δ13CDIC and δ18OWATER values and the percent volume of water inhabited by plants. The depth of sites, water mineralisation, alkalinity and fertility were inversely correlated with the δ13CCARB. The redundancy analysis revealed a clear division of samples into species and lakes; lakes were especially distinct. We postulate that the stable C and O isotope compositions of charophyte encrustations are lake‐ rather than species‐specific and that the isotopic signatures of charophyte carbonates are representative of the entire lake epilimnion, not just the vegetated littoral zone. Furthermore, the isotopic signal of bulk sediment can provide environmental information that is as useful as species‐specific isotope values.

Tolypella mongolica (Charophyceae, Characeae): A new dioecious charophyte species from the center of Eurasia and implications for charophyte taxonomy, including the validation of T. porteri and the new combination for T. jwalae

A new dioecious species of Tolypella, T. mongolica sp. nov. from the section Tolypella, was described using an integrative taxonomy. It was found in three distant localities – shallows of a brackish small lake and a channel in the midland steppe in Mongolia and the Altai Mountains, and a small brackish water body in the dry steppe in Southeast Europe. It differs from other species in rbcL and ITS sequences and in distinct complex ornamentation of the oospore surface, varying from sparsely coarsely tuberculate to having the appearance of an aerial view of mountain landscape with acute to mostly sharp edges of elements at probably the ripest stage. Wide intrapopulation variability of expression of this trait, only partly explainable by oospore ripening stage, was found and illustrated for two populations, indicating previous underestimation of this phenomenon in taxonomic research. T. mongolica is richly fertile and appears to be ephemeral as most species of this genus. Only female plants were found in all localities. The absence of male plants could be referred to either their earlier development during the growing season or, less likely, parthenogenesis in this species. The description of the new species suggests taxonomic changes for two dioecious species of charophytes. Tolypella porteri stat. et comb. nov. was validated here. T. jwalae was recognized as a species of Nitella, N. jwalae comb. nov.

Evolutionary and immune-activating character analyses of NLR genes in algae suggest the ancient origin of plant intracellular immune receptors.

Nucleotide-binding leucine-rich repeat (NLR) proteins are crucial intracellular immune receptors in plants, responsible for detecting invading pathogens and initiating defense responses. While previous studies on the evolution and function of NLR genes were mainly limited to land plants, the evolutionary trajectory and immune-activating character of NLR genes in algae remain less explored. In this study, genome-wide NLR gene analysis was conducted on 44 chlorophyte species across seven classes and seven charophyte species across five classes. A few but variable number of NLR genes, ranging from one to 20, were identified in five chlorophytes and three charophytes, whereas no NLR gene was identified from the remaining algal genomes. Compared with land plants, algal genomes possess fewer or usually no NLR genes, implying that the expansion of NLR genes in land plants can be attributed to their adaptation to the more complex terrestrial pathogen environments. Through phylogenetic analysis, domain composition analysis, and conserved motifs profiling of the NBS domain, we detected shared and lineage-specific features between NLR genes in algae and land plants, supporting the common origin and continuous evolution of green plant NLR genes. Immune-activation assays revealed that both TNL and RNL proteins from green algae can elicit hypersensitive responses in Nicotiana benthamiana, indicating the molecular basis for immune activation has emerged in the early evolutionary stage of different types of NLR proteins. In summary, the results from this study suggest that NLR proteins may have taken a role as intracellular immune receptors in the common ancestor of green plants.

Different seasonal dynamics of contrasting aquatic plants and the consequences for the submerged macrophyte biodiversity

Global warming shifts climate zones to the north, resulting in changes in biodiversity. One of the species adaptation strategies to survive is to change their phenology. In temperate climate, most aquatic plants show their peak of biomass in summer. In our study, we hypothesised that the rare charophyte Lychnothamnus barbatus and the partially invasive vascular plant Myriophyllum spicatum may apply a different seasonality and cause a decrease in the biodiversity of submerged macrophytes. The object of our study was a mesotrophic temperate lake in Western Poland with abundant submerged vegetation, where macrophyte seasonality was studied from November 2015 to November 2019 (autumn, spring, summer). Altogether, 29 taxa of plants were recorded, including 13 species of charophytes (40 % of the Polish charophyte flora) but only four species co-dominated, two eutrophic vascular plants, Ceratophyllum demersum and M. spicatum, and two charophytes, the rare mesotrophic L. barbatus and common Nitellopsis obtusa. M. spicatum due to its expansiveness in the shallow littoral decreased biodiversity in the study lake. Moreover, C. demersum negatively affected the endangered L. barbatus by direct competition for habitats in the lake. L. barbatus and M. spicatum dominated in vegetation in autumn while the further two species co-dominated in summer. L. barbartus and M. spicatum seem to avoid high competition in summer, which proves a high adaptive potential with respect to climate warming. However, further study in other lakes is needed to verify the relevance of our findings in terms of the conservation of rare macrophyte species.

Chara squamosa (Characeae, Charophyceae) in Serbia - insights from the taxonomic revision of the BEOU charophyte collection and recent field records

Chara gymnophylla is one of the first charophyte species reported for Serbia during the late 19th and the early 20th centuries, and at that time it was the second in terms of the frequency of its occurrence in the country. General taxonomic misinterpretations in the past resulted in the concealment of another species, C. squamosa, within the findings attributed to C. gymnophylla. In Serbia, Chara gymnophylla was treated as C. vulgaris var. gymnophylla, and as such was not listed as a species inhabiting the country. Recent improvements in the taxonomic concept for C. squamosa prompted a revision of the rich material of C. gymnophylla, C. vulgaris var. gymnophylla, C. vulgaris var. nitelloides, and C. rohlenae, deposited in the BEOU collection. The revision process was conducted concurrently with fieldwork and the collection of new material. Our study confirmed the presence of C. squamosa in Serbia for the first time. Based on numerous revised samples from the BEOU collection, as well as recently collected specimens, the species? continuous presence in Serbia since 1976 was confirmed. Chara squamosa and C. gymnophylla were thus added to the list of Characeae species inhabiting Serbia, and categorised as Critically Endangered according to the criteria outlined by IUCN. An overview of the biogeography, ecology and taxonomy of C. squamosa in Serbia is provided, particularly in relation to C. gymnophylla. The BEOU charophyte collection proved to represent a valuable and relevant resource for critical taxonomic revisions. The results presented in this study strongly encourage further studies on C. squamosa and C. gymnophylla distribution in the Balkan region and wider area in order to gain a deeper understanding of the species? ecology and the further improvement of their taxonomic concepts.

Recycling and deposition of inorganic carbon from calcium carbonate encrustations of charophytes

AbstractMany aquatic primary producers can use bicarbonates as a carbon source for photosynthesis. Charophytes of the two genera: Chara and Nitellopsis are quite efficient in this process. Some species of these macroalgae produce carbonate encrustations, mainly calcium carbonate, constituting up to 86% of the summer maximum dry weight of the standing crop. In this study, we analyzed the fate of inorganic carbon accumulated this way in Chara spp. and Nitellopsis obtusa from six Polish lakes located in two regions (warmer W Poland and cooler NE Poland). Our study distinguished two groups of charophyte species that differed in the way of CaCO3 release from their summer standing crops. On average, the corticate Chara rudis and C. tomentosa belonging to the first group were less efficient in depositing CaCO3 from summer to autumn than the less corticate C. contraria and ecorticate N. obtusa of the second group. The latter two species were more efficient in inorganic carbon burial in sediments. On the contrary, dissolution of encrustation was more typical of the first species group and was facilitated by decreasing the pH and saturation index of calcite in lake water. The final output of CaCO3 loss mainly resulted from combined species‐specific features, lake water properties and overwintering patterns. Our study revealed that inorganic carbon cycling through charophytes involves burial and dissolution and is more complex than previously thought.

Middle to late Eocene charophytes from the Gaize Basin in central Tibet

Charophytes from the middle to late Eocene Kangtuo Formation in the Gaize Basin, central Tibet, are studied from the perspectives of taxonomy, palaeoecology, and biogeography. In the upper member of the Kangtuo Formation of the Mengdangle (MDL) section, southern Gaize Basin, two charophyte species were studied, including Hornichara jianglingensis comb. nov. and Chara cf. wujinensis comb.nov. The flora lives in the temporary pond's depositional environment, based on sedimentological analysis and fossil species occurrence. A palaeobiogeographic analysis of the charophyte assemblage suggests that H. jianglingensis was widely distributed in China basins during the middle to late Eocene, and later as a regional species in the coastal area in the Oligocene. H. jianglingensis and C. cf. wujinensis disappeared during the Oligocene in the interior of the Tibetan Plateau, and it was likely attributed to the rapid uplift of the Central Tibetan Valley.

Charophytes from the Pozo D-129 Formation (lower Aptian, Lower Cretaceous), source rock in the Golfo San Jorge Basin, Patagonia, Argentina

The charophytes studied here are from the uppermost part of the Pozo D-129 Formation in Sierra Silva, which belongs to the Golfo San Jorge Basin. Fructifications from three charophyte species belonging to the families Characeae and Clavatoraceae are described and illustrated. Two charophyte assemblages obtained from the lower part of the section were characterized: Assemblage 1, formed exclusively of characeans, Mesochara stipitata and Lamprothamnium? barcinensis, and Assemblage 2, composed of L.? barcinensis and the clavatoraceans Clavator harrisii var. harrisii and Clavator harrisii var. zavialensis. These differences in the composition of the charophyte floras are related to different paleoecological conditions that changed from the temporary, unstable water bodies represented in the lower assemblage studied to more stable and permanent lake conditions. The charophyte assemblages together with the previously recorded palynological data suggest a late early Aptian age for the succession of the Pozo D-129 Formation studied. Likewise, the charophytes contribute to the paleobiogeographic history of two conspicuous taxa, M. stipitata and C. harrisii var. zavialensis, which are reported here for the first time in the Lower Cretaceous deposits of the basin.

CHAROPHYTES (CHARALES, CHARACEAE) OF THE REPUBLIC OF BASHKORTOSTAN (SOUTH URAL)

Eleven species of charophytes from three genera, Chara, Nitella and Nitellopsis, were found in the Republic Bashkortostan according to herbarium collections and field studies covering the years 1915–2016, among them one newly recorded genus Nitellopsis and four new records of species, namely Chara contraria, C. papillosa, C. subspinosa, and Nitella obtusa. These data allowed re-assessment of few records known from published sources. Biotope and ecoregion preferences of the species were outlined. Most species have been known from the region of study for a long time. Hard water lakes and, especially, water bodies of rich minerotrophic fens are most important regional habitats of charophytes. Some populations of stenobiont species seem to be stable despite significant human transformation of Bashkortostan natural environment. A tentative Red List of charophytes of the Republic of Bashkortostan was suggested.

Do stable carbon and nitrogen isotope values of Nitella flexilis differ between softwater and hardwater lakes?

The composition of stable carbon and nitrogen isotopes (δ13C and δ15N) is widely used for tracking the origin of organic matter (OM) present in lacustrine sediments. These isotopes also define the evolution of OM in food web loops. Charophyte species Nitella flexilis C. Agardh, 1824 can be found in different aquatic environments where it contributes significantly to sediment formation and influences biota function. Therefore, it is crucial to study more about δ13C and δ15N in different lake types. Here, we present the results of the first comprehensive study of N. flexilis δ13C and δ15N, which add to the knowledge of the C and N isotope records of charophytes. We obtained the δ13C and δ15N records of N. flexilis OM from hardwater and softwater lakes and checked for differences between these records. We also analyzed the differences in physical and chemical parameters. Finally, we compared the δ13C and δ15N records with physical and chemical parameters to identify the variables that have the highest influence on N. flexilis δ13C and δ15N values. Our study showed that both δ13C and δ15N did not differ significantly in the two types of lakes, although the lakes had significant differences in several physical and chemical parameters (pH, Ca2+, dissolved inorganic carbon, total phosphorus, conductivity). However, we observed that δ13C values were influenced by light conditions (photosynthetic active radiation, depth, dissolved OM), while δ15N values were influenced by the total nitrogen concentration in water.

Distinct responses in sexual reproduction onset and growth of Chara braunii Gmelin to light level and temperature: evidence from a greenhouse experiment

The importance of oospores in the ecology and life cycle of annual charophyte species is now widely recognized. To elucidate the primary factor that determines the timing (onset) of sexual reproduction, a controlled 3 × 2 factorial experiment with various light levels (100%, 50% and 10% of natural irradiance) and temperatures (25 °C and 20 °C) was conducted to assess their interactive effects on Chara braunii Gmelin under greenhouse conditions. Results revealed that when the light level decreased from 100% to 10% of natural irradiance, the occurrence of gametangia was postponed for 8 days and the proportions of branch whorls with gametangia (PG) and oospores (PO) significantly decreased under high-temperature conditions. Decreased temperature significantly delayed the emergence of gametangia (100% of light levels for 10 days, 50% of light level for 6 days) and decreased PG and PO. Under low-temperature conditions, no gametangia were found at the lowest light level (10/20). This indicated that the combination of low light and low temperature could result in the absence of sexual reproduction in C. braunii. Furthermore, the internode length, dry weight length ratio and pigment pattern of cultured C. braunii were also significantly altered in response to different light levels and temperature treatments. Two-way ANOVA analysis revealed that temperature contributed more to PG and PO than light levels, while light levels contributed more to morphology and pigment ratio than temperature. This might suggest distinct responses of sexual reproduction onset and growth of C. braunii to varied light level and temperature.

Diversity and Ecology of Charophytes from Vojvodina (Serbia) in Relation to Physico-Chemical and Bioclimatic Habitat Properties

In Serbia, almost all charophyte species belong to one of the IUCN categories. This study aimed to gather more knowledge about their floristic richness, distribution and ecology. During the survey, 262 localities were investigated in the Vojvodina province, northern Serbia. Seventeen charophyte species were found, out of which 16 were included in the analyses. The environmental matrix included 38 localities, each characterized by habitat type and 35 environmental parameters. The canonical correspondence analysis (CCA) showed six parameters as being statistically significant: substrate, altitude, depth, water temperature, temperature annual range and precipitation of the driest month. Together, these explain the 32.34% variability in the species composition and abundance data. Altitude and substrate contributed the most to this. Two main types of habitats were outlined by the analysis. Small and shallow temporary habitats in the river floodplains, at lower altitudes, with muddy and clayish substrate, belong to one type. These areas are inhabited by either very tolerant species, such as Chara vulgaris and C. globularis, or the so-called “spring” species of the genera Tolypella and Nitella. Habitats which are located at higher altitudes, when deeper and more permanent with a sandy substrate, such as sandpits and river habitats, belong to the second one. These areas are inhabited by species like Chara papillosa, C. hispida, and Nitellopsis obtusa.

Early Pleistocene charophyte flora from Dursunlu (Ilgın Basin, Turkey): palaeoecological implications

Here, a charophyte assemblage from lower Pleistocene deposits at the coal mine locality of Dursunlu (Ilgın Basin, Turkey) is described and illustrated for the first time. The assemblage is composed of 11 species recovered from 50 samples taken from an 18 m-thick sedimentary sequence. The base of the sequence is dominated by lignites and organic-rich claystones/siltstones with root marks attributed to palustrine facies. The charophyte assemblage in this palustrine interval is dominated by Chara vulgaris and C. globularis. The upper part of the section is constituted by light grey-yellowish marls, siltstones and a limestone bed related to shallow lacustrine deposits. Two charophyte species dominate this lacustrine interval, Chara hispida and Nitellopsis obtusa, which occurred in intervals in association with Chara pappii, Chara molassica var. notata, Chara sp.1, Chara sp.2, Sphaerochara prolifera, Sphaerochara intricata and Lychnothamnus barbatus var. antiquus. The palaeoenvironmental characteristics and evolution of the Ilgın palaeolake during the Early Pleistocene (Günz glaciation) are inferred from a facies analysis and the ecological requirements of the charophyte assemblages. The results suggest that during this glacial period, the Ilgın Basin was occupied by a very shallow eutrophic lake with a dense palustrine vegetation belt, which evolved to a shallow (2–15 m deep), stable, oligotrophic, alkaline and oligohaline lake. The increase in water availability in the palaeolake can be related to climatic oscillation during the Günz glaciation. Finally, the lake depocentre migrated towards the NW due to tectonism, and these deposits were later subjected to intense pedogenic alteration.

Some terrestrial algae on the surface of buildings in Debrecen, Hungary

A total of 19 terrestrial algae were identified from different surfaces of the courtyard of the Hungarian Research Network (HUN-REN) Institute for Nuclear Research in Debrecen. Organisms were identified at the lowest possible taxonomic level. Various species of Cyanobacteria, chlorophytes, charophytes, and diatoms were characteristic components of the studied terrestrial community. Green algae (Klebsormidium sp., Trebouxia sp., and Apatococcus sp.) represent the dominant element in almost all samples mainly on the surfaces of green patches on pavements. Some rare Cyanobacteria species, Hassallia byssoidea, Gloeocapsopsis chroococcoides, Gloeocapsopsis pleurocapsoides, and Gloeocapsa novacekii were found on the old artificial surfaces. A member of the Hungarian Red List, Cylindrocystis brebissonii was also found under an old transformer.

Oospore Features among Morphologically Similar and Closely Related Charophyte Species: Consistency and Variability

Caractéristiques des oospores parmi des espèces de charophytes morphologiquement similaires et étroitement apparentées: cohérence et variabilité. La détermination précise des charophytes au niveau de l'espèce est importante sous de nombreux aspects, mais les caractéristiques taxonomiques morphologiques communes dans certains cas, en particulier entre des taxons morphologiquement similaires, peuvent être insuffisantes ou trompeuses. L'objectif de notre étude était de créer une analyse comparative des paramètres morphométriques des oospores de taxons morphologiquement similaires comme Chara globularis Thuil. et C. “connivens” P.Salzmann ex A.Braun, ou C. braunii C.C.Gmel. et C. baueri A.Braun (Serbie). Le potentiel d'application des caractéristiques des oospores dans la délimitation des espèces a été évalué, ainsi que la variabilité interpopulations des paramètres des oospores dans les populations géographiquement éloignées de C. globularis et C. braunii. Les paramètres courants des oospores (hauteur des oospores, largeur des oospores, nombre de crêtes, largeur du sillon et distance entre le pôle apical de l'oospore et de sa partie la plus large) ont été mesurés et les indices ISI et ANI ont été calculés. La variabilité interpopulations et les différences interspécifiques ont été confirmées en utilisant la morphologie des oospores chez les espèces de charophytes sélectionnées. Bien que la variabilité interpopulations existe effectivement, les paramètres des oospores étaient clairement différents entre les taxons morphologiquement similaires. Ces résultats sont importants du point de vue taxonomique, mais également du point de vue de la caractérisation des banques de diaspores et de son application potentielle dans les projets de restauration. Les résultats obtenus justifient également la nécessité d'élaborer des clés d'identification des oospores au niveau local et régional, en particulier dans les régions où elles font défaut (e.g. Balkans). La collecte de données supplémentaires sur la morphométrie des oospores est nécessaire pour que nos résultats soient plus largement utilisés.

Lamprothamnium sardoum sp. nov. (Characeae, Streptophyta): A new species of Lamprothamnium for Europe

Comprehensive charophyte surveys on the island of Sardinia, Italy revealed a novel species of Lamprothamnium occurring in a salt marsh in the vicinity of San Giovanni Sinis. Most of the discovery and description of charophyte species in Europe took place in the mid–late 1800s, so the discovery of a new species in the region is of note. The species is described and compared with the other species of Lamprothamnium known for the Mediterranean region of Europe and elsewhere. Lamprothamnium sardoum sp. nov. differs from all other species in having antheridia and oogonia clustered internal and external to the axial nodes and on the branchlets, and in the relative absence of sterile whorls, the length and width of its bract cells and decumbent stipulodes, and the persistence of the protonema on mature plants. In addition, data on hydrochemistry and accompanying flora of the Sardinian site of L. sardoum are presented together with proposals for management and conservation.

Late Pliocene-Early Pleistocene Charophyte Gyrogonites from Mudstone Horizon Underlying Volcanic Ash Beds of Northwest Himalaya: Palaeoecological and Palaeoenvironmental Implications

In this paper, a good number of charophyte specimens and angiospermae seeds have been documented from the mudstone horizon underlying the geochronologically dated volcanic ash beds exposed about 0.375 km northwest of Badakhetar village in Samba district of the Jammu region, northwest Himalaya. By using the morphological characteristics (equatorial axis, distance from apical pore to equatorial axis, isopolarity index, anisopolarity index, width of convolution, angle between convolution and equatorial axis, number of convolutions, vertical and oblique line spiral, size, shape, basal pore and apex morphology) of charophytes, these specimens have been identified and tentatively referred as Chara rantzieni, Charaglobularis globularis, Chara globularis aspera (Characontraria), Hornichara maslovi, Lamprothamnium papulosum, Lychnothamnus breviovatus and Boraginocarpus lakhanpalii (Angiospermae seed). The reported species of charophytes are used here in the present study for Palaeoecological and Palaeoenvironmental studies. Keywords: Charophyte Gyrogonites, Mudstone Horizon, Northwest Himalaya, Palaeoecology, Palaeoenvironment

Microalgae Indicators of Charophyte Habitats of South and Southeast Kazakhstan

Charophyte algae is a very sensitive group of organisms occupying Kazakhstan waterbodies. They are distributed throughout the country; however, not enough studies have been conducted, especially in the southern region. Research carried out in 2019–2022 identified 33 habitats of charophyte algae in the south and southeastern regions of Kazakhstan, including 15 new to Kazakhstan. Bioindicators and the statistical analysis of 223 species of nine phyla of microalgae associated with charophytes revealed that the main factors influencing the distribution of algal diversity may be habitat altitude and hydrology. The habitat altitude of about 700 m above sea level was shown to be the boundary between the different diversity distributions. The application of bioindicator methods can expand our knowledge on the ecology of the charophyte species in Kazakhstan. The study of algal diversity in charophyte habitats can serve as a tool for tracking climate change under potential future climate warming.

Charophyte communities in Barremian Iberian wetlands

A combined micropalaeontological, taphonomical and sedimentological study was carried out in the non-marine Barremian of the Maestrat Basin (E Iberian Chain) to elucidate the palaeoecology of Barremian charophytes. Understanding the palaeoecology of fossil charophytes is of prime importance for the accurate application of charophyte biozonations, since most species used as biostratigraphic markers and/or biozone index species are restricted to facies formed in a particular environment. Five charophyte biocoenoses were distinguished. (1) Charophyte association from freshwater alkaline lakes receiving low clastic input, mainly composed of Atopochara trivolvis var. triquetra, Clavator harrisii, Ascidiella stellata, and A. triquetra. The thalli known as Munieria grambastii, corresponding to Clavator utricles, were extremely abundant in the shallowest facies of the lake margins, and Hemiclavator-rich populations were also locally dominant. (2) An association characteristic of freshwater alkaline lakes with high clastic input was mainly composed of Echinochara lazarii, Globator maillardii var. trochiliscoides, A. trivolvis var. triquetra, C. harrisii, Hemiclavator neimongolensis var. neimongolensis, and locally also Clavator calcitrapus. (3) Monospecific populations of Porochara maestratica thrived in brackish settings with little clastic influence, whereas (4) monospecific E. lazarii populations thrived in clastic-influenced brackish settings. (5) A charophyte association grew in lakes that developed in mudflat to floodplain environments and was mainly constituted by E. lazarii, A. trivolvis var. triquetra, and C. harrisii var. harrisii and var. reyi. Accordingly, the palaeoenvironmental conditions inferred indicate that most of the charophyte species were controlled by (i) bathymetry, (ii) clastic content in the sedimentary environment and (iii) salinity. The stratigraphic succession studied shows an upwards increase in clastic content from the base to the top, which is associated with the more humid period recorded along the margins of the Tethys and the Boreal realm during the early Barremian–early late Barremian. In consequence, those species restricted to clastic-poor settings are constrained to the lower part of the section, whereas those taxa that were able to thrive in clastic-rich settings persisted throughout the entire section. This observation establishes a link between the changes observed in the charophyte floras recognized and the environmental changes that occurred during the Barremian in western Europe.

Increases in temperature and freshwater inputs will shift grazing patterns of a coastal mesograzer on foundation species

AbstractFoundation species, and the roles that they play in structuring ecosystems, are threatened by global change. For example, charophytes are a refuge for zooplankton and stabilize sediments, but they are also a food source for various animal species (water birds, fishes, and invertebrates). Particularly, the introduction of new species, such as Gammarus tigrinus, into the Baltic Sea led to yet not understood changes in the food web. Furthermore, future projections point to increased water temperatures and freshwater inputs affecting species capacity to acclimatize to changing abiotic factors. In this study, we investigated the influence of temperature and salinity on the grazing pressure of G. tigrinus on two charophyte species: Chara aspera and Chara tomentosa. The grazing experiments were conducted in a full‐factorial design with the factors salinity (3–13 g kg−1), temperature (5–30°C), and charophyte species. Grazing rates were determined as mass deviation within 48 h considering biomass changes in the presence and absence of gammarids. Grazing rates were further used to calculate charophyte losses in two coastal lagoons with different salinity concentrations for recent and future time periods. Increasing freshwater inputs can buffer charophyte biomass loss at higher temperatures. Gammarids had a higher grazing impact on C. aspera than on C. tomentosa. The potential grazing peak of about 24°C is not yet reached in these coastal waters but may be reached in the near future as shown by our future projection results. However, a temperature increase and decrease in salinity will cause a shift in seasonal individual grazing patterns from summer to spring and autumn. An increase in temperature and freshwater input can lead to a shift in optimal habitats for G. tigrinus in the future. These interactions between abiotic and biotic factors will affect the future spatial distribution that charophytes can exploit as foundation species.