Epiphytic Diatom Communities on Sub-Fossil Leaves of Posidonia oceanica Delile in the Graeco-Roman Harbor of Neapolis: A Tool to Explore the Past (original) (raw)
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the lack of carbonate mud production. The rate of epiphytic carbonate production obtained by two of the investigated meadows averages 400 g m −2 year −1. This value is in the range of temperate Mediterranean as well as of tropical and subtropical seagrasses. The epiphytic carbonate production plus the calcareous biota living on seagrass substrate contributes to form mixed siliciclastic-carbonate sediments of the nearshore environment of the Mediterranean. Lastly, the carbonate production associated with seagrass was derived by biota belonging to the heterozoan assemblage, where aphotic organisms are dominant, together with oligophotic biota such as coralline algae and symbiont-bearing foraminifera. Consequently, in the well-illuminated seagrass settings, the prevalent skeletal assemblages is represented by the heterozoan association while the components of the photozoan assemblages are absent or subordinate. This a key point for the paleoenvironmental reconstruction of the photic zone in the fossil record. Because the skeletal components of many seagrass dwellers greatly contribute to the carbonate sediment production of photic shallow-water environments, the seagrass meadows became substantial places of carbonate production and C (organic and inorganic) sequestration during the Cenozoic.
The Diversity of Epizoic Diatoms: Relationships Between Diatoms and Marine Invertebrates
is currently a Senior Researcher at the Department of Marine Sciences, Polytechnical University of the Marche (Italy). She obtained her Ph.D. in 1999 from the Polytechnical University of the Marche. Her research activity is focused on ecology and taxonomy of marine microalgae: phytoplankton long time series, mucilage aggregates, harmful microalgae, and microphytobenthic communities (epipelic, epilithic, epiphytic, and epizoic) particularly deepening the relationships occurring between microalgae and marine invertebrates.
The bryozoan Electra posidoniae Gautier is found solely on the leaves of the Neptune grass Posidonia oceanica (L.) Delile, dominating the leaf epifauna of this seagrass. Epiphytes of marine angiosperms (or seagrasses) often play an important role in ecosystem functioning, for example as food web suppliers. As dysfunction of the epiphytic component is often implied in human-induced seagrass decline, it is important to understand the dynamics and life traits of this community in pristine areas. This study involved the monthly assessment of colonization dynamics, biomass seasonality, and diet composition through measurements of stable isotopes, in E. posidoniae at a depth of 10 m in the Revellata Bay (Corsica, Mediterranean Sea). Ancestrulae (i.e. colony founders) appeared towards the end of winter and were very selective in their settlement position along the leaves of P. oceanica. A maximum of 100,000 colonies per square meter was recorded. Colonies of E. posidoniae dominated the epiphytic community biomass in early spring, but were overtaken by epiphytic algae in June. Food shortage could be involved in this reduction in dominance. Although stable isotope ratios of C, N and S showed that this suspension feeder mainly relies on the water column for its food, other food sources such as re-suspended epiphytic diatoms could be important in late spring (i.e. after the phytoplanktonic bloom). Additionally, a contribution of seagrass phytodetritus to the diet of this species cannot be excluded. The species was almost absent in winter, raising the question of its recruitment in spring. This study confirms the quantitative importance of this species in the seagrass meadow and explores its role in the relationship between the water column and this seagrass ecosystem.
Ancient DNA in the seagrass Posidonia oceanica
Marine Ecology Progress Series, 2002
Posidonia oceanica is a seagrass endemic to the Mediterranean, characterized by low genetic polymorphism, with potential effects on its survival and expansion. In the last 2 decades, a progressive decline of P. oceanica meadows was recorded. This could derive either from intrinsic characteristics of the plant or from habitat fragmentation and isolation induced by external sources of impact. P. oceanica forms large meadows whose remains can persist in the matte and in the sediment for thousands of years. In this paper we illustrate a protocol for the extraction of DNA from old remains of P. oceanica (between 300 and 1100 yr old) collected in the matte and in marine sediments in order to gather information on the evolution of genetic diversity over time. We also report a first genetic analysis of old seagrass DNA using species-specific microsatellite markers.
Frontiers in Marine Science, 2023
Against the accelerating pace of worldwide species extinction, reliable biodiversity assessments are critical, both as baselines and to track potential declines. DNA metabarcoding techniques allow for fast and comprehensive assessment of biodiversity in both terrestrial and marine habitats. However, these methods need to be adapted and standardised for each ecosystem in order to be effective. Seagrass meadows are among the most diverse marine habitats and are irreplaceable in terms of the ecosystem services they provide, yet metabarcoding has never been implemented for these systems. In this study, we developed and tested a protocol for metabarcoding the eukaryotic community of meadows of the iconic species, Posidonia oceanica L. (Delile). This seagrass is the main habitat-forming species in Mediterranean coastal waters and is known for its high diversity due to the structural complexity of its canopy and rhizome structures. This habitat is experiencing a range-wide retreat, and there is an urgent need for fast and efficient methods for its biomonitoring and detection of early changes. Our proposed method involves direct sampling of the community, collecting and processing the leaves and rhizome strata separately. To test the utility of the method in distinguishing between different meadow conditions, we sampled two distinct meadows that differ in their prevailing wind and surge conditions, and a nearby rocky reef for comparison. We then adapted a method and pipeline for COI metabarcoding using generalist primers that target the eukaryote diversity present. We detected a high diversity in the two meadows analysed (3,350 molecular operational taxonomic units, dominated by Metazoa and Archaeplastida) and a clear differentiation of the seagrass samples from those of the nearby rocky reefs. The leaves and rhizomes harboured clearly distinct assemblages, and differences were also detected Frontiers in Marine Science frontiersin.org 01
Evolutionary history of the seagrass genus Posidonia
Marine Ecology Progress Series, 2011
Seagrasses are the structural species of one of the most important coastal ecosystems worldwide and support high levels of biodiversity and biomass production. Posidonia is one of the most ancient seagrass genera and displays a contrasting disjunct biogeographic pattern. It contains one single species in the Northern Hemisphere, P. oceanica, which is endemic to the Mediterranean Sea, and has up to 8 recognized taxa in the Southern Hemisphere, which in Australia are divided into 2 complexes, P. ostenfeldii and P. australis. A phylogeny based on a nuclear marker (rRNA-ITS) revealed an ancient split between the northern (i.e. Mediterranean) and southern (i.e. Australian) taxa, followed by a separation of the 2 recognized Australian complexes. However, the species belonging to the P. ostenfeldii complex were indistinguishable, suggesting an ecotypic origin or a recent speciation. Therefore, among the 7 morphologically described Australian species only 4 species lineages can be discriminated. The organelle markers nad 7 intron, trnL-F and mat K/trnK intron were not informative for reconstructing the phylogeny of this genus, and the mitochondrial markers exhibited a strikingly slow evolutionary rate relative to other genome regions.
Marine Ecology, 2011
A survey on the epiphytic microorganisms growing on Posidonia oceanica leaves was conducted along a depth transect along the coast of Eastern Tunisia (Mahdia). Samples were collected by SCUBA diving at depths of 3, 5, 10 and 12 m in July 2008 and January 2009. A total of 58 microepiphyte taxa were identified. Multivariate analyses revealed temporal and spatial variation of the abundance of epiphytic microalgae. Water motion, light availability, temperature and motility of species seem to be responsible of temporal and bathymetric variations of epiphytic microalgae. Unlike diatoms, dinoflagellates were more abundant in deep waters, suggesting that they are more vulnerable to hydrodynamics. The significant correlation between leaf area index and abundance of epiphytic species indicates that the phenological parameters of the host plant influence the abundance of the epiphytic microorganisms. Among the epiphytic dinoflagellates, our data showed a great number of potentially toxic species (Alexandrium minitum, Amphidinium carterae, Karenia selliformis, Coolia monatis, Karlodinium veneficum, Ostreopsis siamensis, Prorocentrum concavum, Prorocentrum minimum, Prorocentrum rathymum and Prorocentrum lima). These species were more abundant in the deep station under more sheltered conditions than found at inshore shallower stations, which are subjected to high water motion.