Ingeborg Soulié-Märsche

Holocene environmental changes in Bangong Co basin (Western Tibet). Part 3: Biogenic remains

Abstract A 12.4 m core collected from the eastern part of Lake Bangong provided a continuous Holocene record. This core was analyzed for diatoms, ostracods, charophytes, content in total organic carbon and identification of organic particles contained in the sediments. The record is remarkable for the abundance and diversity of its microorganisms. An oligo- to mesosaline marsh occupied the core site before 9.5 ka B.P. Bangong was most likely closed. A sudden filling of the lake basin by dilute, nutrient-poor water occurs around 9.4 ka B.P. Maximum lake extent seems to have occurred around 9.4–8.7 ka B.P. Generally freshwater, relatively deep conditions were maintained up to 6.3 ka B.P., although interrupted by short-term regressive events between 8.6 and 7.5 ka B.P. A trend towards palustral conditions begins after 6.3 ka B.P. and the interval 3.9-3.2 ka B.P., rich in detrital organic material, coincides with an extremely low lake level. A last lacustrine episode of minor amplitude is recorded from about 3 to 2 ka B.P., before the closure of the system leading again to slightly saline conditions. The resemblances and synchronism between environmental changes recorded at Bangong and in Lake Sumxi, situated 200 km northwards and 800 m higher in elevation, indicate that regional climatic changes have been the major driving factor on ecological and hydrobiological changes in lakes of western Tibet.

LONG-TERM DYNAMICS OF A MEDITERRANEAN ALKALINE VERNAL POOL (RHONE DELTA, SOUTHERN FRANCE)

Mediterranean vernal pools are threatened habitats that support a number of endangered/ rare plant and invertebrate species. Conservation management of these important habitats is limited by a lack of knowledge, especially concerning their past and present ecological dynamics. A multidisciplinary palaeoecological investigation was conducted on one of the last alkaline vernal pools of the Rhone delta (southern France). Results highlighted the value of a multidisciplinary approach based on several complementary methods, and provide direction for subsequent palaeoecological studies in temporary wetlands. Despite some degradation, fossil assemblages provide an accurate reconstruction of the past ecological dynamics of the vernal pool studied. The pool originated c. 1100 years ago from the infilling of an abandoned palaeochannel and its subsequent fragmentation. It may thus be considered as a legacy of past natural fluvial activity, which ended with the complete channelization and confinement of the River Rhone in 1869 AD. With natural processes disrupted, new pools may need to be artificially constructed in order to preserve the biological communities of alkaline vernal pools of the Rhone delta.

Conservation of Mediterranean wetlands: Interest of historical approach

The wetlands of North Africa are an endangered and invaluable ecological heritage. Some of these wetlands are now protected by various conservation statutes; which actual impact has not yet been reliably evaluated. This article aims to assess the conservation management (Nature Reserve and Ramsar site) of a protected Tunisian lake, Majen Chitane, by using palaeoecological, historical and modern data, and by comparing it with the unprotected lake Majen Choucha. While located in similar environments, these lakes are today home to very different flora. Baseline conditions reconstructed from literature indicate that both lakes were very similar until the 1950s, and comparable to the current state of Majen Choucha, housing rich oligotrophic plant communities. In the 1960s, at the time that cultivation of the adjacent peatland began, Majen Chitane underwent strong ecological changes as the initial oligotrophic plant, diatom and zooplankton communities were replaced by eutrophication-tolerant ones. Eutrophication led to the local extinction of 40-55% of the hydrophytic and temporary-pool plant species, including those characteristic of the Isoetion. Given the damages and despite the recent conservation status of the site, its unlikely that Majen Chitane will undergo any natural regeneration. Restoring it would start with completely protecting the complex lake-peatland and re-introducing the locally extinct species from Majen Choucha. This work exemplifies the usefulness of connecting palaeoecological, historical and modern data for the conservation of Mediterranean wetlands.

Fiabilité des données morphométriquesen micropaleontologie: Exemple des Charophytes

This paper presents the results of a critical study concerning the methods for acquiring morphometrical data, as shown by examples taken from Charophytes, a group of calcareous microfossils. The tests are built up in order to determine the influence of the three elements which may vary between a series of measurements: 1) the optical apparatus (eight different conditions are compared); 2) the observers; 3) the number of specimens measured (tests for ten, one hundred and one thousand specimens are compared). The results are discussed with respect to their practical consequences for the comparison of morphometric data originating from different sources.

Evidence of Chara fibrosa Agardh ex Bruzelius, an alien species in South France

Abstract The paper describes the discovery of a species of genus Chara, hitherto unknown in France. The morphological features of the plants and oospores are shown and identify the plant as Chara fibrosa ssp. benthamii, a tropical taxon, non-native to the European Charophyte flora. The ecological conditions of this particular find correspond to an artificial temporary pond located in the Crau plain, north of the Camargue. In contrast to the normal hydrological cycle ruled by local precipitation during winter, the studied pond is flooded from irrigation water in late spring and during summer. This context allowed C. fibrosa to out-compete the indigenous Chara species, Chara vulgaris and Chara globularis. The accidental introduction of C. fibrosa is attributed to original contamination from rice seed material imported to the nearby Camargue, rather than to dispersal by migratory water birds. Although the species has formed a very large population in that pond within a few years, it might not be classified as “invasive” because this occurrence is linked to a particular man-made habitat. However, spread of the species in the future, as a function of global warming related to climate change, cannot be excluded.

Palaeoenvironmental significance of charophyte gyrogonites from Laguna de Gallocanta (Aragón, Spain)

Abstract At a distance of about 170 km from the Mediterranean, the inland salt lake Laguna de Gallocanta (995 m a.s.l.) is an important stop-over for thousands of migratory water birds and represents an athallasic occurrence of Lamprothamnium papulosum (Wallr.) J. Groves and Chara galioides DC., which were recorded growing in the lake until 1990. These two charophyte species are typically also known from Mediterranean coastal brackish water sites. The material studied here consists of (i) gyrogonites collected from surface sediments in Laguna de Gallocanta and (ii) fossil gyrogonites recovered from the upper 35 cm of a 75 cm core obtained from the lake. Detailed morphological and biometrical analysis of L. papulosum is provided and compared with previous data from South France. The size and shape of the gyrogonites from Laguna de Gallocanta differ greatly from populations growing in coastal sites. These differences are considered to be an adaptive morphological response to the particular hydro-chemical conditions prevailing in Laguna de Gallocanta whose salinity is due to the outwash of sulphate-rich waters from the underground. The distribution and frequency changes of the charophyte species along the core profile allow inferring palaeoecological changes marked by lake-level lowering and increasing salinity.

Helicity of Charophyte gyrogonites through time.

The fossil record of the charophytes or stoneworts is based on the calcified female fructifications, termed gyrogonites. The basic structure of all recent gyrogonites consists of strictly five enveloping cells that twist around the inner egg cell in a clockwise direction. Because the spirals appear in lateral view to climb upwards from right to left, this type is conventionally called sinistral or “sinistrorse”. Dextral gyrogonites, with spiral cells that are counter-clockwise twisted, were restricted to the Palaeozoic. In contrast to the very conservative vegetative structure of the plant’s thallus, the gyrogonites underwent significant changes that are of phylogenetic and biostratigraphical interest. The oldest charophytes are documented from the Late Silurian in Ukraine and in Sweden. The most primitive morphology attributed to the charophytes displayed vertical and even segmented enveloping cells. However, dextral gyrogonites already coexisted with this primitive type. The hitherto oldest sinistral gyrogonites were found in the Middle Devonian of Canada. Although the biogeographical distribution of the Palaeozoic charophytes makes evidence that the clockwise coiled gyrogonites expanded rapidly whereas the counter-clockwise coiled did regress, both types of helicity were present until the Late Permian. The Permian-Triassic Boundary event (250 My ago), which is currently considered the most catastrophic biological crisis of the Earth’s history, also marked the definite extinction of the dextral charophytes. The possible force that caused the selection of only one type of chirality of the gyrogonites remains speculative (Soulie-Marsche, 2004). From the P/T boundary onwards up to Present, all charophyte gyrogonites display the modern coiling pattern composed of five enveloping cells surrounding the egg cell in a clockwise direction. Despite this simple basic structure, the mesozoic charophytes show large patterns of variation, which are classified into four different families and about 50 genera. During the Cretaceous, a very particular group, the Clavatoraceae family, displayed fructifications in the form of a complex utricle composed of an inner gyrogonite with five sinistral spiral cells surrounded by additional calcified vegetative cells. The Cretaceous-Tertiary boundary event (the K/T crisis, 65 My ago) caused the extinction of the Clavatoraceans. Since the beginning of the Tertiary, progressive reduction of the morphological types led to the relatively poor modern flora classified as a single family with seven genera.

Diversity and Distribution of Characeae in the Maghreb (Algeria, Morocco, Tunisia)

Abstract Characeae are macroscopic green algae present in the Maghreb (Morocco, Algeria, Tunisia) that are known since the 19th century works of Desfontaines (1800) and Braun (1868). Feldmann (1946) published the first regional synthesis, and this study provides a new Maghreb-wide synthesis of all collections made since 1784 (570 observations distributed over 464 sites). Each of the 31 reported species is described in detail with its diagnostic features, ecology and distribution in the three Maghrebian countries. Distribution maps distinguish between the three collection periods: 1780–1939, 1940–1979, and 1980–2016. An illustrated key is provided to help botanists working in the Maghreb to identify the taxa. From a biogeographical perspective, the Characean flora of the Maghreb is dominated by elements originating from northern (European) countries (61.3%) that include regionally very rare species such as Chara strigosa and C. tomentosa. The Mediterranean-Atlantic element is also well represented (32.3%), with some Mediterranean endemics (Chara imperfecta, C. oedophylla, C. vulgaris var. gymnophylla). Finally, two taxa that have an affinity for tropical conditions (Chara zeylanica and Lamprothamnium succinctum) extend to the southern Sahara. In North Africa, 14 species (7 Chara, 2 Lamprothamnium, 4 Nitella and 1 Sphaerochara) are threatened and raise issues about their conservation; three of these are particularly endangered: Chara imperfecta, C. oedophylla and Lamprothamnium papulosum.

Ursprung und Evolution der Charophyten

This chapter presents a review of the most significant steps in charophyte evolution and its fossil record, which is amongst the most complete in fossil algae. It provides enough data to document the history of the group from the Silurian until the present. Fossil charophyte remains include mainly their calcified fructifications, i.e. utricles and gyrogonites, but also their fossil thalli. Palaeozoic represents the time when charophytes reached a maximum of diversity in the Bauplan of their fructifications, with the coexistence of three charophyte orders, Sycidiales, Moellerinales and Charales. The extinction of two of these orders at the end of the Palaeozoic led to a single type of fructification, the porocharacean gyrogonite that represents the charalean ancestor of all post-Palaeozoic charophytes. However, this ancestor diverged soon in two evolutionary lines, Polyplacata and Monoplacata, based on the presence of a multicellular vs single basal plate of the gyrogonite. This fundamental difference can be assumed representing two alternative types of female gametogenesis. Charophytes with a composite basal plate, the Polyplacata, developed diverse morphologies at the base of the Mesozoic (Triassic-Jurassic), most of them are traditionally ranged within the porocharaceans, characterised by an apical opening. These polyplacate porocharaceans are considered the ancestors of extant Nitella and Tolypella (sensu stricto), recorded already in the Jurassic and Cretaceous respectively. Monoplacata diversified in several steps, the first in the Upper Jurassic and Lower Cretaceous with the appearance of the utricle-bearing clavatoraceans, and the appearance of the first characean genera with a single basal-plate, including the oldest known Sphaerochara (equivalent to Tolypella sect. Rothia). The Clavatoraceae family dominated the wetlands on the Tethyan islands during the Lower Cretaceous relegating the porocharaceans to brackish environments. At the beginning of the Late Cretaceous (Cenomanian and Turonian) there is a gap in the fossil record. After this gap the monoplacate Characeae underwent an important radiation and expanded with the appearance of many genera including modern Chara, Lamprothamnium, and Lychnothamnus. This radiation occurred in parallel with the extinction of a few last species that remained from clavatoraceans and porocharaceans near the Cretaceous-Tertiary boundary. Genus Nitellopsis is documented since the lowermost Tertiary. Characeans reached their maximum of diversification in the Middle Eocene, with numerous genera whose gyrogonites were quite different from the modern ones. These morphological types regressed during the Late Eocene and the Early Oligocene when a global climatic shift occurred. Afterwards the charophytes were progressively reduced to the morphologies of the seven modern genera. Hence the Neogene to recent flora appears as an impoverished remnant of the flourishing of charophytes in the geological past.

Fossil algae vs Living algae: results from the study of Charophytes

The comparison of fossil Algae with their modern analogues raises a number of questions that are of general interest in palaeontology and are answered in different ways depending on the group studied. On the whole, many organisms become only partly fossilised and often do not contain the significant characters used for the systematics of their living equivalent. The question is: how to obtain a “natural classification” of those fossils ? In the case of the charophytes, sensu Charales, the palaeobotaical systematics is based on the gyrogonites, that is the calcified female fructifications, which provide the only determinable fossil remains for this order. However the living charophytes are classified according to characters of the plant which are not preserved in the fossil state. Study at the interface Extant/Fossil has shown that the living genera display very distinctive fructifications and can be accurately determined from their gyrogonites even in absence of plant remains (Soulie-Marsche, 1989). At species level, the parallelism is more difficult to establish because the gyrogonites display morphological variation in response to environmental differences. In order to determine correctly the subfossil and quaternary gyrogonites that are related to still living taxa, the range of ecological variation has to be calibrated through the study of abundant gyrogonite populations from modern lakes and ponds with various physico-chemical conditions. These investigations should help limiting the number of fossil morpho-species simply based on minor morphological differences. The knowledge of the range of inter-population variation that a given modern species is able to produce shows that many fossil morphologies distinguished as separate species potentially could have belonged to one species and should be grouped. Better understanding of the relationship between environmental factors and morphology of the gyrogonites also increases the significance of fossil charophytes in terms of environmental change and contributes to reconstructing former aquatic habitats. The aim of this presentation is to give rise to discussion about the different nomenclatural solutions adopted in various groups of fossil algae in order to correlate the fossil representatives to their modern analogues.