Effects of salinity on seed germination and early seedling growth of the Mediterranean seagrass Posidonia oceanica (L.) Delile
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Keywords:
Posidonia oceanica
Potamogetonaceae
Posidonia oceanica
Paracentrotus lividus
Epiphyte
Diplodus
Zostera marina
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Techniques for sampling motile macroinvertebrates associated with Posidonia oceanica seagrass meadows have mainly involved the use of hand-nets and suction samplers or collection by hand. These techniques give unreliable quantitative estimates or have practical difficulties. A large cylindrical saw-rimmed corer was designed and used successfully to obtain quantitative samples of macroinvertebrates from both foliage and root-rhizome matrix of a Posidonia oceanica meadow in Malta (central Mediterranean). Choice of the appropriate sample unit size was assessed by comparing the relative accuracy, precision and efficiency of three different core diameters: 25 cm, 35 cm and 45 cm. The results suggest that for comparison of macrofaunal species richness and abundance between different meadows/sites the 25 cm diameter corer is recommended. For surveys aimed at estimating total diversity within a particular site, the 35 cm diameter corer is more appropriate.
Posidonia oceanica
Potamogetonaceae
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The functional importance of herbivory in seagrass beds is highly variable among systems. In Mediterranean seagrass meadows, macroherbivores, such as the fish Sarpa salpa and the sea urchin Paracentrotus lividus, have received most research attention, so published evidence highlights their importance in seagrass consumption. The role of small crustaceans in seagrass consumption remains less studied in the region. Herbivory on Posidonia oceanica seeds has not previously been reported. In turn, crustacean herbivory on P. oceanica leaves is broadly recognized, although the species feeding on the seagrass are mostly unknown (except for Idotea baltica). This work evaluates P. oceanica consumption by two species of amphipod crustaceans commonly found in seagrass meadows. Ampithoe ramondi and Gammarella fucicola actively feed on P. oceanica leaves and seeds. Both species preferred seeds to leaves only when the seed coat was damaged. This study provides the first direct evidence of consumption of P. oceanica seeds by the two named amphipod crustaceans, and confirms that they also consume leaves of this seagrass species.
Posidonia oceanica
Paracentrotus lividus
Potamogetonaceae
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Posidonia oceanica (Linnaeus) Delile 1813 is an endemic and the most widespread seagrass species of the
Mediterranean Sea. Seagrass meadows are one of the most productive ecosystems on Earth, providing habitat to
numerous organisms. Therefore, mapping of seagrass meadows is of crucial importance for conservation and
coastal management purposes. Here we present an integrated geographic information system approach with
SCUBA diving, providing a cost effective method to monitor seagrass beds at shallow coastal habitats. In this
case study P. oceanica meadows were mapped in Ufakdere region of Kaş (Antalya) coastal area between April
– September 2015. A total of 25000 m2
are were screened to create seagrass coverage maps. Results indicate that
P. oceanica meadows cover 21200 m2
and we estimated that 520 m2 of this area is highly damaged. This
integrated approach provided one of the most detailed small-scale Posidonia mapping in Turkey and this time
and cost effective methodology can be applied to any seagrass meadow with great ease to increase our knowledge
on this important habitat.
Posidonia oceanica
Scuba diving
Marine protected area
Marine ecosystem
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Since the seagrass Posidonia oceanica is highly sensitive to environmental changes, a monitoring of the physiognomy, phenology and lepidochronology of the meadows was conducted during 2015-2020 at Tremiti Islands Marine Protected Area (Adriatic Sea). The meadow resulted stressed where anthropogenic disturbances occurred, while the implementation of proper management measures proved to trigger the recovery of the habitat. Our results underlined the importance of P. oceanica as a biological indicator to monitor human activities at local scale.
Posidonia oceanica
Marine protected area
Potamogetonaceae
Marine habitats
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Seagrass meadows are vital coastal habitats that support a wide array of species and provide numerous ecosystem services. The area of seagrass meadow has declined significantly, at a rate of about 5% per year, since 1980. Emerging techniques for seagrass research has the potential to provide new insights to fill knowledge gaps and improve our understanding of seagrass ecological function and ecosystem services. This improved understanding will help us to inform policy makers about protection measures. Using Posidonia oceanica dominated habitats as a case study, this thesis assesses emerging techniques for mapping seagrass habitats, monitoring biodiversity with seagrass habitats and assessing microplastic pollution loads within seagrass sediments.
Kayak-borne down-scan sonar is shown to provide an accurate and cost-effective method for mapping the distribution of seagrass meadows. Sonar-derived data suggested current estimates of seagrass extent in the Aegean, based on analysis of satellite imagery, may contain considerable inaccuracies particularly in areas of complex bathymetry. It is suggested that kayak-borne sonar mapping can provide accurate reference data for larger scale satellite mapping, delivering benefits in terms of our ability to survey seagrass distribution and monitor temporal changes in extent and health.
Environmental DNA is proven to be an effective tool for the non invasive detection of, Pinna nobilis, a culturally important yet Critically Endangered bivalve species associated with P. oceanica habitats. The technique developed in this study is capable of detecting concentrations of DNA as low as 5.50 x 10-10 ng µl-1 from sea water samples. This technique can be used at different spatial scales dependent on the season, allowing eDNA to be a sensitive and precise tool in locating and identifying a key species inhabiting seagrass meadows.
A fine-scale analysis of microplastic distribution within the sediment under a seagrass meadow using recently developed Sediment Microplastic Isolation techniques, indicated that seagrass did not influence the deposition of microplastics to sediment at a semi isolated bay. Microplastics were recovered at relatively low densities across the entire study area. Analysis of sediment patterns suggested that most sediment input was from terrestrial sources immediately adjacent to the seagrass bed and, therefore, that seagrass beds that are closer to terrestrial sources of microplastic pollution are likely to show much greater microplastic loadings.
It is concluded that, emerging techniques such as down-scan sonar, eDNA and microplastic extraction can provide novel insights into the distribution and ecological functioning of seagrass habitats. These insights provide avenues for the development of existing monitoring methods and for conservation policies.
Posidonia oceanica
Marine habitats
Marine protected area
Marine ecosystem
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