Development of sustainable strategies for conservation and management of Posidonia oceanica, (Linneo) Delile 1813, meadow: a case study within a Site of Community Importance
Author(s)
Dante, Giovanna
Date Issued
March 15, 2010
Type
Doctoral Thesis
Abstract
This research starts considering that Posidonia oceanica, seagrass endemic in
the Mediterranean Sea, has a fundamental role in coastal marine ecosystems;
it is responsible for forming underwater meadows with high ecological value
as a climax community of Mediterranean Sea. Meadows protect the coastline from erosion by reducing the waves’ energy. This seagrass is also responsible for oxygen production, it is involved in the hydro-sedimentological coastal dynamic, hosts several invertebrates species and it is nursery of a number of
fish species. These are the main reasons for which this ecosystem has been defined as priority habitat (sensu Directive 92/43/CE), for which is foreseen the designation of Site of Community Importance (SCI).
The conservation status of Posidonia meadows today is seriously threatened by the increasing level of anthropication of the landscape and by humans’ activities, which can relevantly affect this ecosystem even at high distance from the source of impact due to the continuity of the sea.
The ultimate aim of this study is to identify a way for defining management
guidelines for Posidonia oceanica meadows (habitat 1120* sensu Directive
92/43/CE). A case study has been chosen for this purpose: Santa Marinella
meadow, which is located within a Site of Community Importance (code: IT000007, “Fondali antistanti S. Marinella”).
Through an integrated and multidisciplinary approach it has been verified the perimeter of the site, it has been done the mapping of the biocenosys, it has been assessed the conservation status of the Posidonia meadow, it has been identified the humans activities and their impacts on the meadow, it has been
developed the strategic management priorities and it has been defined the
guidelines for the Management Plan implementation.
The processed map of the Posidonia at the site allowed the identification of
the real distribution of the ecosystem and showed how the perimeter of the
SCI (IT000007, “Fondali antistanti S. Marinella) and the Standard Data Form
of the N2000 site should be updated. It also allowed the identification of high
surface of dead matte below 17 m depth and highlighted the regression of the lower limit of the meadow.
The assessment of the conservation status of the meadow was performed analyzing data on coverage, density and rhizomes production, collected on 20 sample station points located within 2 areas of the meadow, during a three years campaigns (2006-2007-2008).
In every sample station, depth, area and bottom types have been recorded;
also sediment samples were collected ones in every station, during the three
year. Statistical processing has shown how absolute density and coverage
(relative density) are inversely correlated with depth. Correlation has not been
found between density or production and sedimentogical data. Following the
Pergent et al. (1995) classification, the meadow resulted disturbed.
Thanks’ to the use of a predictive model (PosiPred), expected absolute density and expected rhizome production have been calculated for each sampling station, comparisons have been performed. Real density was lower then the predicted one and rhizomes production was higher then the predicted one, showing an anomalous behaviour of the meadow.
Human activities map has been processed using, as baseline CLC2000, the database of Lazio Region (SIRA), the interpretation of aerial image and sites visiting; the results of the map have been used to calculate the Index of Conservation Landscape of the whole water basin which was classified as medium.
The analysis of data related to marine water quality and ephemeral streams,
collected from the Regional Body for environmental protection (ARPAL),
showed that the streams are highly polluted, highlighted by the BOD5 values and the high turbidity level.
There have not been recorded high significant differences between nitrogen
suspended sediment in the targeted area and near Tevere mouth; this can be
assumed as an evidence of high level of nutrients in Santa Marinella sea area.
This equality is unexpected considering how distant is the study site from the
source of impact (mouth of Tevere).
The collection of these data and the analysis of the literature on Posidonia
meadow allowed the identification of the effects that human activities can
have on the meadow. Considering the area occupied by each activity, the
influences of them on the site have been assessed. This has shown that SDF
needs to be updated on this issue too.
With the aim of identifying possible management solutions to reduce the
impacts described, also other biological features characteristic of the site have
been considered as suggested by the Guidelines of EC to marine N2000 sites
management.
Besides, in collaboration with the Human Computer Studies Department of
Amsterdam University, an original qualitative model has been developed
(within Garp3 software) with aim of representing the dynamics determining
the meadow fragmentation and net growth in the study site in relation with
anchoring impact. The model implemented can be a useful tool to transfer knowledge to stakeholders when decision-making process starts for planning and managing the N2000 site. Overall the model can help in simulating the change of the conservation status caused by unregulated anchoring.
Operational proposes facing this problem, have been thus developed.
Qualitative reasoning can also help in deepen the dynamic processes that
characterized structure and function of this complex ecosystem. Moreover the use of generic standard ecological and physical concepts in the model implementation makes the model re-usable in areas with similar problems and values.
More valuable tools for meadows’ monitoring (e.g. sediment traps) and supporting identification of early indicators for nutrients over-enrichment are described as priorities actions when managing the site, together with the designation of areas where anchoring would be temporary forbidden.
In general Tevere (which waters move mainly north outside the mouth) and ephemeral streams polluted waters are the main cause of high turbidity and of high values of nitrogen particulate substance recorded. Sediments and nutrients cause low levels of transparency, which are responsible of the
regression of the lower limit of the meadow and therefore they are the main
limiting factors for seagrasses growing below certain depth.
High levels of total nitrogen and nitrogen particulate substance recorded (although they are not enough to determine eutrophic water), can be assumed as the cause of high values of rhizomes production and primary production
per shoots recorded. These values have been assumed as mainly linked with
the level of anthropication of the terrestrial area southern to the site (where is the city of Rome) and to the intensive agricultural activities around the site.
Therefore, it is clear how an integrated management strategy of land and sea
is the only way to reduce the threats now affecting the study site in particular
and, in general, all marine Natura 2000 sites with similar threats and
conditions.
In this way Member States will be able to identify and undertake appropriate
steps to avoid the deterioration of natural habitats for which the SCIs have
been designated and thus respect the commitment signed with ratification of
the Habitat Directive.
The involvement in the decision making process through “concerting table”
of the regional and local administrations responsible for both sea and water
basin area and, thus, the developments of tools useful to communicate and
“teach” scientific concepts to stakeholders, administrators and population is a
fundamental step to help implementing protection of Posidonia oceanica
meadow for future generations.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
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