Giulia Margaritelli

Biodiversity trends of the meiofaunal and foraminiferal assemblages of Lake Varano (southern Italy)

Abstract In this study, the meiofaunal diversity in Lake Varano (southern Italy) is investigated in detail. Using a statistical approach, these data were coupled with the physicochemical parameters of the bottom water and the sediment characteristics in order to understand the factors influencing meiofaunal biodiversity distribution. The lake is selectively influenced by different factors, namely: organic matter and grain-size, as well as water salinity. Although these assemblages appear to be poorly diversified, the diversity index values are similar to those generally reported in other transitional environments. Relatively higher values of both meiofaunal and benthic foraminiferal diversity were found in front of the Capoiale channel and in the inner part of the lake. The meiofaunal assemblages are mainly dominated by nematodes, copepods, and turbellarians. The benthic foraminiferal assemblages comprise 18 taxa and are mainly represented by calcareous forms, suggesting a relatively low degree of confinement and, consequently, moderately restricted conditions. These assemblages are comparable to the Ammonia assemblages with Haynesina germanica that are characteristic of lagoons along the Mediterranean coasts. On the basis of these findings, coupled with the biotic data, the lake can be regarded as an oligo-mesotrophic environment.

Environmental control on a land–sea transitional setting: integrated sedimentological, geochemical and faunal approaches

Because of their location at the interface between sea and emerged lands, so-called transitional environments are characterized by strong spatial and temporal variability in terms of sedimentological, physicochemical, and geochemical parameters. An increasing number of studies put forward the use of bioindicators as a tool for environmental monitoring. However, the sensitivity to these environmental parameters is commonly tested separately, even though it is known that interactions are numerous within this complex ecosystem. An integrated methodological study was conducted in Lake Varano (Italy). On the basis of 45 spatially distributed samples throughout the area and selected environmental parameters (trace elements, organic matter, clay mineral assemblages, grain size of sediment, and water characteristics), four factors are identified. The Lake Varano ecosystem is predominantly influenced by terrigenous inputs (first-order factor). The clastic fractions of the sediments supply a large range of trace elements, occasionally in relatively high concentrations. Under such circumstances, despite occasionally exceeding of threshold limits, the trace element pollution can generally be ruled out. The organic content combined with depth is the second key factor. In Lake Varano, the organic content is high and may lead to seasonal eutrophication. As a third-order factor, although only analyzed once, oxygen, ORP, salinity, and pH gradients show that foraminiferal diversity is positively influenced by more saline conditions. The fourth-order factor is the sediment size. To conclude, this paper illustrates the interest in and need to conduct a detailed, integrated, sedimentological study of a site prior to any examination of its ecological status (possible occurrences of sources of pollution).

Holocene forest dynamics in central and western Mediterranean: periodicity, spatio-temporal patterns and climate influence

It is well-known that the Holocene exhibits a millennial-scale climate variability. However, its periodicity, spatio-temporal patterns and underlying processes are not fully deciphered yet. Here we focus on the central and western Mediterranean. We show that recurrent forest declines from the Gulf of Gaeta (central Tyrrhenian Sea) reveal a 1860-yr periodicity, consistent with a ca. 1800-yr climate fluctuation induced by large-scale changes in climate modes, linked to solar activity and/or AMOC intensity. We show that recurrent forest declines and dry events are also recorded in several pollen and palaeohydrological proxy-records in the south-central Mediterranean. We found coeval events also in several palaeohydrological records from the south-western Mediterranean, which however show generally wet climate conditions, indicating a spatio-temporal hydrological pattern opposite to the south-central Mediterranean and suggesting that different expressions of climate modes occurred in the two regions at the same time. We propose that these opposite hydroclimate regimes point to a complex interplay of the prevailing or predominant phases of NAO-like circulation, East Atlantic pattern, and extension and location of the North African anticyclone. At a larger geographical scale, displacements of the ITCZ, modulated by solar activity and/or AMOC intensity, may have also indirectly influenced the observed pattern.