Evolution and Vitality of Seagrasses in a Mediterranean Lagoon

International audienceDespite their registration on the list of the Ramsar convention sites, the Mediterranean lagoons rarely beneficiate of an effective protection, and are particularly sensitive to environmental quality. A control of these wetlands needs the creation of an inventory of knowledge for the concerned environment. In this perspective, the seagrass beds were followed up in the coastal lagoon of Urbino (Corse, France) since 1990. A cartographic study was carried out by remote sensing of aerial photography. Temporal evolution of the seagrass beds (Cymodocea nodosa principally) allows to determine the vitality of these structures. A comparison of the surface areas occupied by Cymodocea nodosa, between 1990 and 1999, did not allow seeing any significant evolution. However, some variations appear like biotopes all more fragile and coveted as the Mediterranean coastal fringe is straight and is the privileged site of appear in the localization of the beds, due to the modification of environmental conditions in the lagoon

Chapter Coastal erosion in the Gulf of Follonica and Baratti and coastal defense methods

From 1988 to the present the Institute of Marine Biology and Ecology of Piombino has studied the marine environmental situation of the Gulf of Follonica (Italy), in collaboration with the Universities of Siena, Pisa, Urbino, Sassari, Corte (FR) and the CNR of Pisa. In recent years erosion has drastically changed the sandy beaches mainly as a consequence of the constant retreat of the P. oceanica meadows whose possible causes have been studied. Also in the Gulf of Baratti the methods adopted for the defense of the beach have been inadequate

Continuous mapping of benthic habitats along the coast of Corsica: A tool for the inventory and monitoring of blue carbon ecosystems

Continuous mapping of the benthic marine habitats along the coast of Corsica is based on a synthesis of all available historical data as well as new studies concerning sectors that are poorly taken into account and/or that are of particular interest. The mapped area covers more than 310 000 ha, almost all infralittoral and circalittoral, with a survey up to 150 m deep around the coast of Cap Corse. While within the infralittoral zone, Posidonia oceanica meadows are predominant, with a surface area of about 53 735 ha, in the circalittoral zone, soft bottoms (eg coastal detritic bottoms) are largely dominant, with the rhodolith association particularly well represented (26 493 ha). The coralligenous biocenosis (2 111 ha) covers relatively small areas but includes unique formations at Mediterranean scale: the coralligenous atolls. The reliability scale proposed to assess the accuracy of these maps shows satisfactory results (62% on average), with a higher value for the infralittoral zone (74%). The results confirm that Corsica's coastline is characterized by a significant expansion of the Blue Carbon ecosystems, and in particular the Posidonia oceanica meadows, which regularly reach more than 35 m depth and cover 61% of the of the seabed between 0 and -40m, and free-living coralline algae (8% of the known surfaces in the western Mediterranean basin). The areas covered by Posidonia oceanica in the Mediterranean basin are estimated at between 1.0 and 1.5 million hectares, and show a decreasing pattern along a north-west to southeast gradient

Competition between the invasive macrophyte Caulerpa taxifolia and the seagrass Posidonia oceanica: contrasting strategies

<p>Abstract</p> <p>Background</p> <p>Plant defense strategy is usually a result of trade-offs between growth and differentiation (i.e. Optimal Defense Theory – ODT, Growth Differentiation Balance hypothesis – GDB, Plant Apparency Theory – PAT). Interaction between the introduced green alga <it>Caulerpa taxifolia </it>and the endemic seagrass <it>Posidonia oceanica </it>in the Mediterranean Sea offers the opportunity to investigate the plausibility of these theories. We have accordingly investigated defense metabolite content and growth year-round, on the basis of an interaction gradient.</p> <p>Results</p> <p>When in competition with <it>P. oceanica, C. taxifolia </it>exhibits increased frond length and decreased Caulerpenyne – CYN content (major terpene compound). In contrast, the length of <it>P. oceanica </it>leaves decreases when in competition with <it>C. taxifolia</it>. However, the turnover is faster, resulting in a reduction of leaf longevity and an increase on the number of leaves produced per year. The primary production is therefore enhanced by the presence of <it>C. taxifolia</it>. While the overall concentration of phenolic compounds does not decline, there is an increase in some phenolic compounds (including ferulic acid and a methyl 12-acetoxyricinoleate) and the density of tannin cells.</p> <p>Conclusion</p> <p>Interference between these two species determines the reaction of both, confirming that they compete for space and/or resources. <it>C. taxifolia </it>invests in growth rather than in chemical defense, more or less matching the assumptions of the ODT and/or PAT theories. In contrast, <it>P. oceanica </it>apparently invests in defense rather than growth, as predicted by the GDB hypothesis. However, on the basis of closer scrutiny of our results, the possibility that <it>P. oceanica </it>is successful in finding a compromise between more growth and more defense cannot be ruled out.</p

IS GLUTATHIONE TRANSFERASE (GST) ACTIVITY IN POSIDONIA OCEANICA A STRESS RESPONSE TO MERCURY EXPOSURE?

International audienceToday, efficient monitoring of the environment is increasingly depend on the use of bio-indicator species. Marine phanerogams, and in particular Posidonia oceanica, would appear to be potentially valuable bioindicators of metal pollutants. Although correlations have been found between the mercury levels accumulated in the plant tissue and the concentrations of this metal in the water column, it would be of interest to identify early signs of the stress response induced by this xenobiotic. Thus, mercury concentrations and GST activity in Posidonia oceanica (L.) Delile from contaminated and pristine sites were measured. These results demonstrate that an increase in mercury level is correlated with an increase in GST activity, particularly in the sheaths of P. oceanica shoots. The sites contaminated by mercury were also those sites for which the highest enzyme activity was recorded. An even better correlation was found between the mercury levels and GST activity, if a 2 mo lag in the effect of mercury on GST activity is assumed

Trace metal concentrations in Posidonia oceanica of North Corsica (northwestern Mediterranean Sea): use as a biological monitor?

BACKGROUND: Within semi-closed areas like the Mediterranean Sea, anthropic wastes tend to concentrate in the environment. Metals, in particular, are known to persist in the environment and can affect human health due to accumulation in the food chain. The seagrass Posidonia oceanica, widely found in Mediterranean coastal waters, has been chosen as a "sentinel" to quantify the distribution of such pollutants within the marine environment. Using a technique similar to dendrochronology in trees, it can act as an indicator of pollutant levels over a timeframe of several months to years. In the present study, we measured and compared the levels of eight trace metals (Cr, Ni, Cu, Zn, As, Se, Cd, and Pb) in sheaths dated by lepidochronology and in leaves of shoots sampled from P. oceanica meadows collected from six offshore sites in northern Corsica between 1988 and 2004; in the aim to determine 1) the spatial and 2) temporal variations of these metals in these areas and 3) to compared these two types of tissues. RESULTS: We found low trace metal concentrations with no increase over the last decade, confirming the potential use of Corsican seagrass beds as reference sites for the Mediterranean Sea. Temporal trends of trace metal concentrations in sheaths were not significant for Cr, Ni, Cu, As or Se, but Zn, Cd, and Pb levels decreased, probably due to the reduced anthropic use of these metals. Similar temporal trends between Cu levels in leaves (living tissue) and in sheaths (dead tissue) demonstrated that lepidochronology linked with Cu monitoring is effective for surveying the temporal variability of this metal. CONCLUSION: Leaves of P. oceanica can give an indication of the metal concentration in the environment over a short time period (months) with good accuracy. On the contrary, sheaths, which gave an indication of changes over long time periods (decades), seem to be less sensitive to variations in the metal concentration in the environment. Changes in human consumption of metals (e.g., the reduction of Pb in fuel) are clearly reflected in both organs. These results confirm that P. oceanica is a good bioindicator of metals and a good biomonitor species for assessing Cu in the environment

Patch types in Posidonia oceanica meadows around Corsica. How can we use them in seascape ecology?

The meadows formed by the Mediterranean seagrass Posidonia oceanica are subjected to various natural (e.g., water movement, light availability, sedimentation) and anthropogenic (e.g., anchoring, trawling, fish farms, explosives) phenomena that erode them and create diverse types of patches. The assemblage of the P. oceanica matrix and these patches creates particular seascapes. On the basis of this assessment, we aimed to investigate the importance of the patch type in structuring P. oceanica seascapes and to offer new prospects in the large scale studies of seagrass meadows. Five sites encompassing large P. oceanica meadows ranging from 1.86 km² to 4.42 km² along the Corsican coast (France) were considered. Eleven patch types with different sizes, shapes and origins were identified using side scan sonar images (sonograms). Five were recognized as natural and five as anthropogenic. One can be of both origins. The resolution of the sonograms allowed to detect patches of various sizes ranging from 1 m² to 111 829 m². The relation between structural characteristics of patches and the whole seascape aspect was explored using seven landscape metrics relevant for the study of meadows patchiness (patch area, mean radius of gyration, area-weighted radius of gyration, coefficient of variation of the Euclidean nearest-neighbor distance, area-weighted perimeter-area ratio, landscape division index, number of patches). Only a small number of patch types appears to play the strongest role in the characterization of the P. oceanica seascapes. Furthermore, the use of seascape structures seems to be suitable for the development of new tools like indices for the assessment of human impacts on P. oceanica meadows. In this perspective we propose a new and simple index, the Patchiness Source Index (PaSI), to estimate the origin of the patchiness (natural or anthropogenic) for a given area. A landscape approach, as well as information on patch dynamic, should be integrated in the new indices that aim to assess the state of conservation of the whole P. oceanica ecosystem

Proceedings of the Mediterranean Seagrass Workshop 2006

The Mediterranean Seagrass Workshop 2006 was convened in response to the need to promote a periodic event that would host scientists interested in Mediter- ranean seagrasses, and international scientists who are involved in projects that are focused on the Mediterranean marine environment, to discuss current knowl- edge and present the findings of their latest research. The concept of holding an international meeting originated during the Inter- national Seagrass Biology Workshop (ISBW6) held in 2004 in Queensland, Aus- tralia. In particular, one of the goals of ISBW6 was to identify key ecological issues and environmental trends within a number of geographical regions. This stimulated the idea of taking such topic to a higher level; the Mediterranean scale. The Mediterranean Sea is a rare and vulnerable ecoregion, one of the planet’s biodiversity hot spots, where many of the species present are endemic (around 20%). The Mediterranean Sea also has a millenarian history of human use of its coasts. However, the current exponential increase of human pressure on the coastal zone for living space, transportation, recreation and food production is expected to have dramatic long-term impacts on the Mediterranean marine envi- ronment. Being located in shallow coastal areas close to human settlement, sea- grasses are bearing the brunt of disturbance from such anthropogenic activities, with the result that degradation and loss of seagrass habitats is widespread in the whole Mediterranean Sea. Thus, there is great concern that the functions which seagrasses have performed in the Mediterranean marine ecosystem will be weak- ened or, in some places, lost altogether.peer-reviewe

Posidonia oceanica and Zostera marina as Potential Biomarkers of Heavy Metal Contamination in Coastal Systems

International audienc

Spatially Explicit Seagrass Extent Mapping Across the Entire Mediterranean

The Posidonia oceanica seagrass is the foundation species of the coastal Mediterranean, whose meadows support significant ecosystem services: food security, coastal protection, biodiversity maintenance, carbon sequestration, amongst others. This endemic in the basin seagrass features the largest carbon storage among seagrasses globally, contributing substantially to global blue carbon stocks.  However, climate change, coastal development, and decreasing water quality all render this slow-growing species at risk of area loss, functional extinction, and, hence, its provided services. This risk is further complicated by the current knowledge gaps in its bioregional extent, necessitating accurate, efficient and spatially explicit mapping and accounting of its distribution and trajectories at a high spatial resolution. Here, we leveraged recent Earth Observation advances—cloud computing, open satellite data, and machine learning—with field data via a cloud-based ecosystem accounting framework to map the spatially-explicit ecosystem extent of P. oceanica seagrass across the whole Mediterranean, at 10m resolution.  Employing 279,186 Sentinel-2 satellite images between 2015-2019, and a human-labelled training dataset of 62,928 pixels, we mapped 19,020 km2 of P. oceanica seagrass area in 22 countries across 56,783 km2 of mapped seabed between 0-25 m of depth. Based on 2,480 independent field-based points, we observe an overall accuracy of 72%. Using a Tier 2 assessment, we estimated the bioregional blue carbon storage of P. oceanica beds to be 722.2 million MgC.  As reference data collections, remote sensing technology and biophysical modelling improve and coalesce, such extent accounts could support physical and monetary accounting of seagrass condition and ecosystem services. We envisage that such holistic seagrass ecosystem accounts could enable effective policy uptake in national climate, biodiversity and protection strategies and necessary financing. This in turn could accelerate transparent natural climate solutions and coastal resilience, beyond the physical location of seagrass beds and the 21th century