Distribution,structure and phenology of Posidonia oceanica meadows along sicilian coasts

Abstract

Distribution, structure and phenology of Posidonia oceanica meadows along Sicilian coasts are reported. Posidonia beds are frequently found in Sicily, especially along the south-eastern, north-western and western coasts. Leaf surface per shoot is identified as the most important variable among the phenological parameters. The rhizomes annual mean primary production turned out to be among the highest values observed in the Mediterranean Sea. Flowering and fruiting of Posidonia oceanica are frequent and can occur every year.     

The effect of nutrient additions on bacterial activity in seagrass (Posidonia oceanica) sediments

The influence of nutrient additions on benthic bacterial activity under seagrass meadows was tested by enriching five seagrass (Posidonia oceanica) meadows with nutrients over one year. We found a highly significant response of benthic bacterial activity to nutrient additions, which was reflected in greater (about two-fold) ammonification rates and, to a smaller extent, a significant tendency for a greater exoenzymatic activity. Nutrient additions significantly raised bacterial activity, without altering the seasonal changes in bacterial activity. As a result of the increased bacterial activity, the organic content of the sediments declined significantly, by about 33%, after one year of nutrient addition. Hence, nutrient additions to the seagrass meadows enhance seagrass production but also accelerate bacterial decomposition of seagrass carbon, thereby reducing the capacity of the sediments to store organic carbon. These results demonstrate that sediment nutrient availability limits bacterial activity in these Posidonia oceanica meadows, and identify bacteria as important nutrient consumers in these systems.     

Posidonia oceanica in the Marmara Sea

The seagrass Posidonia oceanica is a stenohaline species endemic to the Mediterranean Sea, where it normally lives at a salinity of between 36.5 and 39.5 ppt. Surveys carried out at the North-eastern distribution limits revealed large beds in the Dardanelles Strait and isolated beds in the Marmara Sea, where the salinity ranges between 21.5 and 28 ppt. Microsatellite analysis of these low-salinity tolerant P. oceanica beds, show different signs of genetic isolation: excess of heterozygosity and a presence of fixed alleles. These particularities are rarely found in the whole distributional range of the species. Moreover, all the populations considered in the analysis have a very low genetic diversity in comparison with most of the meadows sampled throughout the Mediterranean Sea. Taking into consideration the genetic data, rhizome expansion rate and the actual extent of the isolated beds in the Marmara Sea and knowing the reproductive rate and dissemination characteristics of P. oceanica, we hypothesize that the isolated population of the Marmara Sea has been established since the Middle Holocene, before the catastrophic intrusion of brackish water into the Marmara Sea and the strong and persistent flow coming from the Black Sea.     

Illegal trawling and induced invasive algal spread as collaborative factors in a Posidonia oceanica meadow degradation

Posidonia oceanica, a key seagrass species of the Mediterranean Sea, shows clear signs of regression throughout the Mediterranean and illegal trawling is recognized as one of the main causes. We examined the condition of a P. oceanica meadow in Alykes Bay (Zakynthos Island, western Greece), a typical Mediterranean littoral area where illegal trawling is common practice, in respect to the total area affected, and in terms of possible ecological substitution. A side scan sonar (SSS) survey of the seafloor provided an image of the condition of the meadow and biological sampling evaluated the ecological status in affected meadow areas. SSS images revealed that trawling has a serious effect on the meadow, with 11% of the vegetated area being abraded, and the affected areas were also found to be fully colonized by the invasive alga Caulerpa racemosa. Moreover, unusually high densities of the polychaete Sabella pavonina were detected in the affected areas among C. racemosa fronds. Recolonization by P. oceanica of the affected meadow areas that have been colonized by C. racemosa seems improbable considering the allelopathic interactions between the species, with the alga displaying phytotoxic properties through caulerpenyne production and deterioration of the sediment quality.     

Molecular Characterization of a Variable Tandem Repeat Sequence Determined during RAPD Analysis among Posidonia oceanica Insular and Coastline Populations

The seagrass Posidonia oceanica plays a multifunctional role in the coastal area as an important and productive component of ecosystems in the Mediterranean Sea. We detected by RAPD analysis with two arbitrary primers genetic differences in P. oceanica collected from several sites in the Southern Mediterranean. By AMOVA analysis we observed a level of about 20% genetic difference among individuals within a population and 80% among populations. A common band of 200 bp was found in all the amplified samples. Cloning and sequencing analysis of this band revealed the presence of a simple tandem repeat sequence (minisatellite) that we called PoTR (Posidonia oceanica tandem repeat). Finally, the ability of PoTR to detect genetic variability inP. oceanica genome was demonstrated by the presence of amplification products of different lengths utilizing primers internal to this sequence.     

A new species of Caprella (Crustacea: Amphipoda) from the Mediterranean Sea

A new caprellid amphipod, Caprella tavolarensis n. sp., is described based on specimens collected from a Posidonia oceanica seagrass meadow at the Tavolara-Punta Coda Cavallo Marine Protected Area (Sardinia, Mediterranean Sea). The species is close to Caprella liparotensis, but can be clearly distinguished by smaller size, presence of a short rostrum, body elongate and dorsally smooth, absence of serrate carina on the basis of gnathopod 2 and pereopods, mouthparts scarcely setose, absence of fine setae on peduncle of antenna 1 and absence of swimming setae on antenna 2. The number of caprellid species reported from the Mediterranean Sea has increased from 23 (1993) to 41 (2010), consequently, further taxonomical studies should be addressed to properly estimate the total amphipod diversity in the Mediterranean Sea.     

Isolation of putative type 2 metallothionein encoding sequences and spatial expression pattern in the seagrass Posidonia oceanica

Metallothioneins (MTs) are a group of proteins with low molecular mass and high cysteine content that bind to heavy metals and are thought to play a role in their metabolism and detoxification. Genes encoding MT-like proteins have been isolated in a number of plants. In this work we isolated nine MT-like sequences from copper- or cadmium-exposed plants of the seagrass Posidonia oceanica, a marine Angiosperm playing a major role in maintaining infralittoral ecosystems in the Mediterranean sea. These sequences, together with two other MT genes previously isolated from this species, show high similarities with genes encoding type 2 MTs. Neighbour-joining analysis, at both deduced protein and 3′-UTR sequence level, indicates that at least two subgroups occur within Posidonia type 2 MTs, showing, however, a strong sequence uniformity. Southern analysis of two type 2 MT-encoding sequences (Pomt2b and Pomt2f) belonging to the two different subgroups showed distinct hybridisation patterns. For both type 2 MTs, we have determined, by in situ technique, the expression domain in Posidonia plants. The members of these two MT subgroups show differences in their histological expression, with Pomt2b associated with proliferative tissues whereas Pomt2f is associated with lignified or suberized cell wall.     

The necromass of the <Emphasis Type="Italic">Posidonia oceanica</Emphasis> seagrass meadow: fate,role, ecosystem services and vulnerability

Posidonia oceanica is a seagrass endemic to the Mediterranean Sea. Most of the primary production of the P. oceanica meadow is not directly consumed by herbivores and plays a role as dead rhizomes and roots, dead leaves and drift epibionts (hereafter necromass). The fate of this necromass is (i) sequestration within the matte, (ii) consumption by detritus-feeders within the meadow, (iii) export towards other marine ecosystems, where it constitutes a source for food webs, (iv) export towards beaches, where it constitutes banquettes, reduces the impact of waves and contributes to the beach ecosystem, and (v) export towards the terrestrial dune ecosystem. These five stocks can exchange necromass. The ecosystem services of the P. oceanica necromass are pivotal. For example, the role of P. oceanica banquettes is fundamental in protecting beaches from erosion, and the carbon sequestration within the matte contributes to the mitigation of emissions of CO₂. Human impact on each of these stocks can affect the other stocks and their ecosystem services. The removal of banquettes from beaches can have a dramatic negative impact on P. oceanica ecosystem services, including the sustaining of beaches. The erosion of matte due to trawling and anchoring can remobilize the sequestrated carbon stock.     

Properties of ion channels in the protoplasts of the Mediterranean seagrass Posidonia oceanica

Posidonia oceanica (L) Delile, a seagrass endemic of the Mediterranean sea, provides food and shelter to marine organisms. As environment contamination and variation in physico‐chemical parameters may compromise the survival of the few Posidonia genotypes living in the Mediterranean, comprehending the molecular mechanisms controlling Posidonia growth and development is increasingly important. In the present study the properties of ion channels in P. oceanica plasma membranes studied by the patch‐clamp technique in protoplasts obtained from the young non‐photosynthetic leaves were investigated. In protoplasts that were presumably originated from sheath cells surrounding the vascular bundles of the leaves, an outward‐rectifying time‐dependent channel with a single channel conductance of 58 ± 2 pS which did not inactivate, was selective for potassium and impermeable to monovalent cations such as Na⁺, Li⁺ and Cs⁺ was identified. In the same protoplasts, an inward‐rectifying channel that has a time‐dependent component with single channel conductance of the order of 10 pS, a marked selectivity for potassium and no permeation to sodium was also identified, as was a third type of channel that did not display any ionic selectivity and was reversibly inhibited by tetraethylammonium and lanthanum. A comparison of Posidonia channel characteristics with channels identified in terrestrial plants and other halophytic plants is included.     

Comparison of the epifauna spatial distribution in Posidonia oceanica,Cymodocea nodosa and unvegetated bottoms: Importance of meadow edges

In order to detect the influence of seagrass, the most important habitats of shallow soft-bottom along the Mediterranean coast, on spatial distribution of epifauna, four different types of habitat were sampled: Posidonia oceanica, Cymodocea nodosa, edge of Posidonia meadow and sandy bottoms. Sampling was carried out, using the hand net method, in various random sites and at different times (April 95, August 95 and February 96) on the Alicante coast (SE Spain). A double taxonomic approach was used in order to detect spatial and temporal changes in the abundance of the main taxonomic groups and amphipod species. The differences among habitats were detected by non-parametric multidimensional scaling (MDS) for community structure and by analysis of variance for groups and amphipod populations. The community structure defined by the abundance of taxonomic groups was not significantly modified by the habitats. Single abundance of taxonomic groups also had no significant preference for the type of habitat except in the case of Acari, a group linked to Posidonia. However, certain trends of preference, such as mysids on Posidonia edge and isopods on Cymodocea, were detectable. On other hand, the amphipod assemblage showed important differences among habitats. Some species changed significantly in abundance depending on the habitat considered, e.g. Dexamine spiniventris and Perioculodes longimanus. It was possible to conclude that there is an important influence of Posidonia and Cymodocea on epifauna distribution by diversification of habitat structure on sandy bottoms, but it was more important at the species level than when considering taxonomic groups. Furthermore, sandy bottoms and the meadow edges had a relatively high importance on fauna distribution, depending on taxa and the period of the year.     

FIELD MEASUREMENTS OF INORGANIC NITROGEN UPTAKE BY EPIFLORA COMPONENTS OF THE SEAGRASS POSIDONIA OCEANICA (MONOCOTYLEDONS,POSIDONIACEAE)1

Crustose corallines, crustose and erect brown algae, and sessile animals are major components of the epiphytic community of the Mediterranean seagrass Posidonia oceanica (L.) Delile. Production, biomass, and specific composition of this epiphyte–seagrass association are impacted by anthropogenic increase of nutrient load in this oligotrophic area. In this context, nitrogen uptake by P. oceanica and its epiflora was measured using the isotope ¹⁵N at a 10 m depth in the Revellata Bay (Corsica, Mediterranean Sea). Epiflora components showed various seasonal patterns of biomass and abundance. The epiphytic brown algae appeared at the end of spring, later than the crustose corallines, and after the nitrate peak in the bay. Because of their later development in the season, epiphytic brown algae mostly rely on ammonium for their N needs. We hypothesize that the temporal succession of epiphytic organisms plays a crucial role in the N dynamics of this community under natural conditions. The epiphytic brown algae, which have a growth rate one order of magnitude greater than that of crustose corallines, showed lower N‐uptake rates. The greater N‐uptake rates of crustose corallines probably reflect the greater N requirements (i.e., lower C/N ratios) of red algae. We determined that the epiflora incorporated ammonium and nitrate more rapidly than their host. Nevertheless, when biomass was taken into account, P. oceanica was the most important contributor to N uptake from the water column by benthic macrophytes in this seagrass bed.     

Effects of Posidonia Oceanica Beach-Cast on Germination,Growth and Nutrient Uptake of Coastal Dune Plants

Seagrass meadows play an important role in marine ecosystems. A part of seagrass production is also exported to adjacent coastal terrestrial systems, possibly influencing their functioning. In this work we experimentally analyzed the effect of Posidonia oceanica beach-cast on plant germination, growth, and nutrient uptake of two plant species (Cakile maritima and Elymus farctus) that grow on upper beaches and fore dunes along the Mediterranean coasts. We compared plants growing in simple sand (control) with those growing in a substrate enriched with P. oceanica wrack (treatment) in laboratory. P. oceanica wrack doubled the N substrate pool and kept the substrate humid. Plants growing in the treated substrate grew faster, were twice as large as those growing in the control substrate, while tissues were enriched in N and P (Cakile by the 1.3 fold in N and 2.5 fold in P; Elymus by 1.5 fold in N and 2 fold in P). Our results suggest a positive effect of seagrass litter for the enhancing of dune species, highlighting its role for the conservation of coastal dune ecosystems.     

Secondary metabolites of Posidonia oceanica (Posidoniaceae)

Posidonia oceanica Delile is an endemic of the Mediterranean Sea. P. oceanica is one of the few marine higher plants of the Mediterranean and plays a significant role in coastal ecosystems of the Mediterranean Sea. In the past, a number of phytochemical investigations with different focus were carried out. The results of these investigations are summarized and appraised here. A total of 51 natural products was reported from P. oceanica, including phenols, phenylmethane derivatives, phenylethane derivatives, phenylpropane derivatives and their esters, chalkones, flavonols, 5α-cholestanes, and cholest-5-enes. Many of the compounds reported for P. oceanica were, however, not detected by appropriate phytochemical methods and some most probably represent artifacts and are no genuine natural products.     

Spatial,temporal and structural variations of a Posidonia oceanica seagrass meadow facing human activities

The Bay of Saint-Cyr (Provence, France, Mediterranean Sea) is the site of two harbours, coastal urban development, trawling, boat anchoring and a sewage outfall. The Posidonia oceanica seagrass distribution was mapped with the help of aerial photographs, side scan sonar and GIS. In addition, the temporal variations of its distribution were studied by aerial photographs and GIS from 1955 to 2000. Finally, coverage and shoot density were measured via scuba-diving. This work reveals (i) the regression of the P. oceanica meadow at sites where harbours have been built, (ii) the occurrence of spaces within the meadow free of live P. oceanica (“intermattes”), which account for 8% of its surface area, (iii) a deep area where P. oceanica coverage and shoot density are low and (iv) evidence of regression, although modest, of the meadow at its lower limit. Nevertheless, the study site also exhibits an extensive and on the whole relatively healthy meadow whose limits have changed little over time.     

New microsatellite markers for the endemic Mediterranean seagrass Posidonia oceanica

The seagrass Posidonia oceanica is endemic to the Mediterranean Sea, where it plays an important role in coastal ecosystem dynamics. Because of this important role and concerns about the observed regression of some meadows, population genetic studies of this species have been promoted. However, the markers used until now were not polymorphic enough to efficiently assess the level and spatial pattern of genetic variability. Hypervariable molecular markers were obtained by screening a genomic library enriched for microsatellite dinucleotide repeats. Among 25 primer pairs defined, eight amplified polymorphic microsatellites with an encouraging level of variability at the two geographical scales sampled.     

Modelling the spatial distribution of the seagrass Posidonia oceanica along the North African coast: Implications for the assessment of Good Environmental Status

Posidonia oceanica (L.) Delile, 1813 is a seagrass species endemic to the Mediterranean Sea, which is considered as an indicator of environment quality in coastal areas. This species forms large meadows, which are sensitive to several anthropogenic pressures and the decrease in their extension is considered a priority issue for the Mediterranean Sea. The aim of this study was to develop a Species Distribution Model for P. oceanica, to be applied to the Mediterranean North African coast, in order to obtain an estimation of the potential distribution of this species in the region. The Species Distribution Model was calibrated using high resolution data from 4 Mediterranean sites, located in Italy and Spain, as the study area is a data-poor zone with regard to seagrass distribution (i.e. only for some areas detailed distribution maps are available). The model was then validated using available data concerning the North African coast. The probability of presence of the species in a given area was modelled using a binomial generalized linear model as a function of the bathymetry and water transparency, dissolved organic matter, sea surface temperature and salinity, mainly obtained from satellite data. Model selection procedure suggests that water transparency plays a major role, but also other variables, such as salinity and sea surface temperature, are important at larger spatial scales in explaining meadows distribution. The availability of high resolution time-series of input data allowed us to apply the validated model to the whole North African coast. Suitable areas are strongly related to the coastal realm, and cover a large portion of North African coasts, with Tunisian and Lybian ones being the most relevant zones for this species. In particular, the shelf of the Gulf of Gabes includes large areas with environmental conditions suitable for the species. Based on model predictions, we developed a robust indicator of potential habitat suitability, which could be used for the assessment of Good Environmental Status, as requested by the Ecosystem Based Approach, to be implemented at the scale of the whole Mediterranean basin in the framework of the Barcelona Convention.     

Invasion of alien macroalgae in different Mediterranean habitats

The study evaluated different macroalgal invasions in the main Mediterranean coastal habitats on hard bottom. Biodiversity, species composition and structure of macroalgal assemblages were compared among non-invaded areas and areas invaded by the Chlorophyta Caulerpa racemosa var. cylindracea and by the turf-forming Rhodophyta Womersleyella setacea in three different habitats: shallow rocky bottom, deep rocky bottom and dead matte of the seagrass Posidonia oceanica. Results showed that alien macroalgae constituted a relevant component of benthic assemblages in invaded areas of the Mediterranean Sea. Assemblages invaded by Womersleyella setacea and Caulerpa racemosa showed lower values of diversity and large differences in the structure and species composition related to non-nvaded assemblages. The species that mostly suffered from invasion were erect species reproducing sexually; moreover, the dominance of W. setacea led to low abundance of native filamentous algae, while C. racemosa colonization seemed particularly threatening for encrusting algae. All the studied habitats appeared highly invasible by alien macroalgae, even if W. setacea appeared more invasive in deeper habitats, while colonization of C. racemosa seemed more serious in shallower habitats; the dead matte of P. oceanica represented a suitable substrate for the spread of both species. Differences among assemblages in different habitats were reduced in invaded areas.     

Weight–length relationships for selected fish species of the western Mediterranean Sea

Weight–length relationships are presented for 24 species of the western Mediterranean Sea (Spain). These species were selected from samplings made during November 1995. The captures were made by beam trawl in Posidonia oceanica meadows up to depths of 20–22 m.     

Seagrass light acclimation: 2-DE protein analysis in Posidonia leaves grown in chronic low light conditions

Posidonia oceanica meadows are among the most valuable coastal systems in the Mediterranean basin. They provide nursery and forage areas for many commercially important species, including juvenile mollusc, finfish, and crustaceans. In the Mediterranean Sea, P. oceanica beds have recently suffered from progressive die-offs attributed to lower light availability from elevated water turbidity. In order to understand adaptive low-light responses of this seagrass, we compared the protein expression in plants collected from turbid waters (low-light) with plants collected from pristine-clear waters (high-light). More than 2600 proteins were detected in leaves from both sites. Among them, 26 proteins were differentially expressed in low-light conditions, 12 of which were identified through MASCOT analyses. The remaining 14 proteins, did not receive significant identity scores due to a lack of genomic and proteomic information in available databases. Nevertheless, we observed a 30% down-regulation of RuBisCo large subunit in low-light acclimated leaves. Whereas, enzymes involved in carbohydrate cleavage (1-fructose-bisphosphate aldolase, nucleoside diphosphate kinase, and beta-amylase) were upregulated in low-light conditions. Electron microscopy studies also revealed substantial changes in the stroma lamellae/grana ratios in chloroplasts receiving low-light, possibly as a mechanism for re-establishing optimal PSI/PSII ratios. Furthermore, under low-light conditions, four components of the ubiquitin/mediated proteolysis pathway (26 S proteasome regulatory, proteasome beta type 1, proteasome 7 D beta type, and proteasome alpha 7), and the perchloric acid soluble translation inhibitor protein, were upregulated. This suggests that, in P. oceanica leaves, enhanced protein turnover mediates acclimation to low-light conditions. Also, enzymes involved in defending against cellular stress (superoxide dismutase, pyridoxine, and 2-caffeic-acido-methyl transferase) were differentially expressed in low-light regime. Subsequent aquaria studies involving P. oceanica transplants maintained in low- and high-light conditions, also demonstrate RuBisCo down-regulation and proteasomes upregulation in low-light acclimated plants.