Metabolic Imbalance in Coastal Vegetated (Posidonia oceanica) and Unvegetated Benthic Ecosystems

Community metabolism and dissolved organic and inorganic nutrient fluxes were assessed in impacted from fish farm discharges and reference vegetated (Posidonia oceanica) and adjacent unvegetated communities in the Aegean Sea, Greece. Both metabolism and nutrient fluxes significantly differed between impacted and reference communities, but the effect depended on community type and time of year. Net community production (NCP) in the impacted vegetated community decreased by 60%, respiration (R) by 34%, and gross primary production (GPP) by 44%. The GPP:R ratio declined more (35%) in the impacted unvegetated than in the corresponding vegetated community (15%), implying that proximity to the fish farm has a severe impact on the unvegetated community, leading to imbalanced metabolism (GPP < R) and heterotrophic (GPP:R = 0.9) conditions. Higher release of dissolved organic and inorganic carbon, nitrogen, and phosphorous was observed in the impacted vegetated community compared to the corresponding unvegetated one, implying intensification of mineralization in the seagrass community. On an annual scale, the impacted vegetated community supported increased DOC efflux by 204%, DON by 1639%, NH₄ by 122%, and NO₃ by 26%, whereas it supported release of DOP and PO₄ compared to the reference community, which removed these dissolved nutrients from the water column. The impacted unvegetated community supported an annual increase of DOC efflux by 208% and PO₄ by 42% and it released DON, NH₄, NO₃, and DOP, whereas the reference community took up these nutrients. Proximity to the fish farm altered the ecosystem state by lowering the productivity and by enhancing the nutrient release.     

Genetic Polymorphism and Transplantation Success in the Mediterranean Seagrass Posidonia oceanica

We studied the role of genetic variability of donor beds in establishing transplantation criteria for the Mediterranean seagrass Posidonia oceanica. Horizontal rhizomes, collected from three geographically distinct populations, were transplanted into a common bed at a highly human‐impacted locality. The transplantation site was located near one of the donor populations. After three years, the shoots collected in the population adjacent to the transplanting site showed the lowest growth performance. Genetic variability, assessed through the analysis of hypervariable microsatellite regions, and growth performance followed a similar trend. The shoots growing and branching at the highest rate were those collected from populations with the highest heterozygosity values, despite greater geographic distance. No genetic differences were found between the transplanted shoots and shoots from donor meadows, as expected due to the low rate of sexual reproduction in P. oceanica and the short time that had passed since the transplants. The problem of affecting the local gene pool by the introduction of foreign genotypes could arise, but introduction of new alleles could balance the degradation of genetic variability caused by human impact. In general our study suggests that the genetic variability of source material is an important aspect to consider in the development of seagrass restoration strategies.     

Sulfur cycling and seagrass (Posidonia oceanica) status in carbonate sediments

Sulfur cycling was investigated in carbonate-rich and iron-poor sediments vegetated with Posidonia oceanica in oligotrophic Mediterranean around Mallorca Island, Spain, to quantify sulfate reduction and pools of sulfide in seagrass sediments. The oxygen penetration depth was low (< 4.5 mm) and sulfate reduction rates were relatively high (0.7–12 mmol m^–2d^–1). The total pools of reduced sulfides were remarkably low (< 5 mol S m^–2) indicating a fast turnover of reduced sulfides in these iron-poor sediments. The sulfate reduction rates were generally higher in vegetated compared to bare sediments possible due to enhanced sedimentation of sestonic material inside the seagrass meadows. The sulfate reduction rates were positively correlated with the seasonal variation in water temperature and negatively correlated with the shoot density indicating that the microbial activity was controlled by temperature and release of oxygen from the roots. The pools of reduced sulfides were low in these iron-poor sediments leading to high oxygen consumption for reoxidation. The sediments were highly anoxic as shown by relatively low oxygen penetration depths (< 4.5 mm) in these low organic sediments. The net shoot recruitment rate was negative in sediments enriched with organic matter, suggesting that organic matter enrichment may be an important factor for seagrass status in these iron-depleted carbonate sediments.     

Consequences of Mediterranean warming events in seagrass (Posidonia oceanica) flowering records

Posidonia oceanica, a seagrass endemic to the Mediterranean forms extended and extremely persistent meadows. It is a clonal plant with an apparently irregular pattern of flowering events. An extensive bibliographic review allowed the reconstruction of past flowering events of this species around the Mediterranean, with a high degree of confidence for the last 30 years. The data series on annual flowering prevalence (FP, flowering records per total records) and flowering intensity (FI, fraction of flowering shoots) produced have been compared with four series on Sea Surface annual Temperature maxima (SST_max) obtained for the NW Mediterranean (averaged from the local data series of l'Estartit and Villefranche: 1957–2005) and for the Eastern, Western basin and the whole Mediterranean sea (extracted from NCEP Reynolds interpolated SST maps: 1982–2005). Significant warming trends are detected in the Mediterranean SST_max series, at a rate of (mean+SE) 0.04±0.01°C yr⁻¹ (R²=0.24, P<0.01, N=24 years), in the Eastern basin series (0.06±0.01°C yr⁻¹, R²=0.43, P<0.001, N=24 years) and in the long SST_max series of the NW Mediterranean (0.02±0.01 C yr⁻¹, R²=0.12, P<0.02, N=49 years). The magnitudes of the SST_max anomalies around the absolute warming trend do not increase with time in any SST_max series. Peaks of FP and FI in the Mediterranean seem to occur each 9–11 years, and coincide with peaks of annual SST_max. Annual FP and FI increase with the residuals of annual SST_max warming trend in all Mediterranean basins (FP_MED: R²=0.27, P<0.01, N=23; FP_NW: R²=0.34, P<0.01, N=31; FP_E: R²=0.20; P<0.10, N=23). An outstanding event of P. oceanica flowering across the Mediterranean has been registered in Autumn 2003; 1 month after the highest annual SST_max recorded in the series. The hypothesis of flowering induction by thermal stress as the possible cause of this relationship is discussed, as well as the potential use of P. oceanica flowering record as early indicator of biological change induced by global sea warming in Mediterranean marine ecosystems.     

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.     

Distributions and Biomass of Benthic Ciliates,Foraminifera and Amoeboid Protists in Marine,Brackish, and Freshwater Sediments

The quantitative importance of ciliates, foraminifers, and amoebae was investigated in marine, brackish, and freshwater sediments from 15 littoral stations. Total protozoan communities were usually dominated by ciliates in term of abundance, while amoebae often dominated in terms of biomass. Applying the biomass‐metabolic rate equation, ciliates, amoebae, and foraminifera were estimated to contribute 66% of the total abundance and 33% of the biomass, but up to 55% of the combined metabolic rate to the micro‐ and meiobenthos in the 15 sediments. Statistical analyses using ciliate data demonstrated: (1) species composition and community structures represented significant differences between freshwater and marine/brackish sediments, and subsequently between temperate and arctic sampling sites; (2) the occurrence of dominant ciliates and their allocation to feeding types indicated that herbivory was the most common feeding strategy in these sediments; (3) multivariate analyses showed all of the tested environmental factors (temperature, salinity, silt/clay, carbon, nitrogen, and chlorophyll a) to be important to varying degrees, but especially the combination of salinity, temperature, and silt/clay. Multiple factor effects or comprehensive influences might be important in regulating the distribution of protozoa in sediments. The importance of protozoa in sediment systems and the potential ecological significance of cysts are discussed.     

Nutrient Accumulation in the Fruits of Two Species of Seagrass, Posidonia australis and Posidonia sinuosa

The accumulation is described of N, P, K, S, Ca, Mg, Na, Fe,Zn, Mn and Cu in the developing pericarp and seed of two speciesof seagrass. Both species showed essentially the same patterns,which resemble those of herbaceous terrestrial plants. Therewas a close relation between dry matter and nutrient accumulation.N, P, K, Fe, Zn, Mn and Cu accumulated in the fruit againstlarge concentration gradients, with discrimination against Na.Seeds accumulated N, P and trace elements to a greater extentthan pericarps and other plant parts; P was apparently retrievedfrom pericarps to a greater extent than other elements. Calculationswere made of the losses of these elements from seagrass meadowsin shed fruits. Posidonia spp., seagrass, nutrient accumulation in fruits     

Removal of Vanadium(III) and Molybdenum(V) from Wastewater Using Posidonia oceanica (Tracheophyta) Biomass

The use of dried and re-hydrated biomass of the seagrass Posidonia oceanica was investigated as an alternative and –low-cost biomaterial for removal of vanadium(III) and molybdenum(V) from wastewaters. Initial characterisation of this biomaterial identified carboxylic groups on the cuticle as potentially responsible for cation sorption, and confirmed the toxic-metal bioaccumulation. The combined effects on biosorption performance of equilibrium pH and metal concentrations were investigated in an ideal single-metal system and in more real-life multicomponent systems. There were either with one metal (vanadium or molybdenum) and sodium nitrate, as representative of high ionic strength systems, or with the two metals (vanadium and molybdenum). For the single-metal solutions, the optimum was at pH 3, where a significant proportion of vanadium was removed (ca. 70%) while there was ca. 40% adsorption of molybdenum. The data obtained from the more real-life multicomponent systems showed that biosorption of one metal was improved both by the presence of the other metal and by high ionic strength, suggesting a synergistic effect on biosorption rather than competition. There data ware used for the development of a simple multi-metal equilibrium model based on the non-competitive Langmuir approach, which was successfully fitted to experimental data and represents a useful support tool for the prediction of biosorption performance in such real-life systems. Overall, the results suggest that biomass of P. oceanica can be used as an efficient biosorbent for removal of vanadium(III) and molybdenum(V) from aqueous solutions. This process thus offers an eco-compatible solution for the reuse of the waste material of leaves that accumulate on the beach due to both human activities and to storms at sea.     

Genetic variability of Posidonia oceanica (L.) Delile in relation to local factors and biogeographic patterns

To evaluate genetic differences of Posidonia oceanica (L.) Delile both at smaller (within a meadow) and larger scale (Mediterranean basin), plants of P. oceanica were analyzed by PCR technique and compared using random amplified polymorphic DNA (RAPD) markers. Results were associated to known differences in phenology. At the small-scale level, P. oceanica shoots collected in the bay of Monterosso al Mare (Liguria, NW Mediterranean Sea) showed genetic differences among sampling stations, with a decrease in genetic diversity along an anthropogenic disturbance gradient. At basin level, genetic differences were detected among 11 P. oceanica shoots coming from different regions of the Mediterranean, and transplanted to the Port-Cros National Park (France) between 1989 and 1991: Izmir, Turkey; Athens, Greece; Taranto, Italy; Ischia Island, Italy; Lavezzi, France; Port-Cros, France; Banyuls, France; Palma de Majorca, Balearic Islands, Spain; Marsa Bay, Algiers. By cluster analysis two major Mediterranean groups were distinguished, the Eastern Mediterranean Group (EMG) and the Western Mediterranean Group (WMG). This suggests that eastern and western populations of P. oceanica have diverged during the colonization of the Mediterranean (after near extinction of the Mediterranean biota in the Messinian period, approximately 5.6 million years ago), and have experienced little gene flow between them. Cluster analysis also indicated that previously described phenological differences among P. oceanica populations in different sectors of the Mediterranean are not mere phenotypic responses to different climatic and hydrological conditions but may well have a genetic basis.     

Experimental Evaluation of the Restoration Capacity of a Fish‐Farm Impacted Area with Posidonia oceanica (L.) Delile Seedlings

Marine aquaculture is an activity that has induced severe local losses of seagrass meadows along the coastal areas. The purpose of this study was to evaluate the capacity of an area degraded by fish‐farm activities to support Posidonia oceanica seedlings. In the study site, a bay in the southeast coast of Spain where part of a meadow disappeared by fish‐farm activities, seedlings inside mesh‐pots were planted in three areas. Two plots were established in each area, one in P. oceanica dead matte and another inside a P. oceanica meadow. To evaluate if sediment conditions were adequate for the life of the seedlings, half of them were planted in direct contact with the sediment and the other half were planted above the surface of the sediment in each plot. Monitoring during 1 year showed that there were large differences in seedling survival between the dead matte and the P. oceanica meadow. While seedlings planted in dead matte had a high survivorship after 1 year (75%), seedlings planted in P. oceanica progressively died (survivorship of 20% after 1 year). The average leaf length of the seedlings surviving in the two substrata was not different, but the leaf area per seedling was lower in the seedlings growing inside the P. oceanica meadow during most part of the year. Seedling survivorship and vegetative development were not affected by the level of planting and suggest that the sediment conditions are adequate for the life of P. oceanica seedlings.     

Iron Additions Reduce Sulfide Intrusion and Reverse Seagrass (<Emphasis Type="Italic">Posidonia oceanica</Emphasis>) Decline in Carbonate Sediments

Abstract We conducted a 2-year in situ experiment to test the capacity of iron additions to reverse the decline experienced by a Posidonia oceanica meadow colonizing carbonate, iron poor sediment. Iron additions improved the sediment conditions that support seagrass growth by decreasing the sediment sulfide concentration and sulfate reduction rates, and decreased sulfide intrusion into the plants. Iron additions for 2 years did not significantly change survivorship of shoots present at the onset of the experiment, but significantly increased shoot recruitment and survivorship of shoots recruited during the experiment. After 2 years, iron additions reversed seagrass decline and yielded positive growth rates of shoots relative to control populations where seagrass continued to decline. This research demonstrates that seagrass decline in carbonate sediments may be reversed by targeting critical processes such are sediment sulfide pools and seagrass nutritional status, controlling the functioning of the ecosystem.     

Anthesis effects on Posidonia oceanica (L.) Delile phenology in the Bay of Calvi (Corsica,Mediterranean Sea)

In Posidonia oceanica (L.) Delile, anthesis induces a decrease in the number of juvenile leaves resulting in a significant reduction in the number of leaves on the flowering shoots. All the leaves of the flowering shoots are narrower than the leaves of nonflowering shoots. A modification of the leaf growth also appears in flowering shoots: the oldest leaves are longer and the leaves induced during or after anthesis are shorter. At 10 m depth, in the Bay of Calvi, anthesis lasts roughly 3 months and the flowering is induced 7 months before anthesis.     

A biotic index using the seagrass Posidonia oceanica (BiPo), to evaluate ecological status of coastal waters

The development of ecologically based indices that respond to disturbances in a predictable manner has been stressed by the EU Water Framework Directive. The seagrass Posidonia oceanica, given its ecological indicator characteristics, has been identified as one of the elements to determine ecological status under the EU Water Framework Directive. The purpose of this study is therefore to develop a biotic index based on P. oceanica (BiPo), focussing on: (i) the necessity of an index that may be applied over the largest geographical extent possible, (ii) the necessity of a tool for a baseline evaluation of P. oceanica status in the Mediterranean, (iii) the compliance with WFD requirements, (iv) the efficiency of the method in terms of reliability and cost. The BiPo index is developed on the basis of all P. oceanica monitoring data available in the western Mediterranean and on a standard assessment of anthropogenic pressures. The index metrics are selected and evaluated on the basis of this pressures assessment, and are subsequently integrated for the evaluation of ecological status. The index is then tested on 15 sites around Corsica (France). The results show that the BiPo well reflects meadow health status and ecological status. Furthermore it is reliable, standard and cost-effective, and can be applied to a wide array of management and conservation purposes.     

Role of Corollospora maritima in the degradation and bioconversion of leaf material from Posidonia oceanica

Posidonia oceanica supports mainly saprophytic marine flora, comprising predominantly lignicolous fungi. The frequency of occurrence of species recorded on this marine angiosperm, was high, indicating that they play a major role in the biological degradation of the sea grass Posidonia oceanica. In vitro experiments with Corollospora maritima (isolated from leaf material) were conducted in order to evaluate their role in the degradation of leaf material. Corollospora maritima actively degrade leaf material. Biophysical and biochemical changes (particle detritus formation, C and N variation), enzymatic activity involved and sterol production were studied during the transformation process of leaves to mycelial biomass.     

Lulwoana sp., a dark septate endophyte in roots of Posidonia oceanica (L.) Delile seagrass

Posidonia oceanica is the most common, widespread and important monocotyledon seagrass in the Mediterranean Basin, and hosts a large biodiversity of species, including microorganisms with key roles in the marine environment. In this study, we ascertain the presence of a fungal endophyte in the roots of P. oceanica growing on different substrata (rock, sand and matte) in two Sicilian marine meadows. Staining techniques on root fragments and sections, in combination with microscope observations, were used to visualise the fungal presence and determine the percentage of fungal colonisation (FC) in this tissue. In root fragments, statistical analysis of the FC showed a higher mean in roots anchored on rock than on matte and sand. In root sections, an inter‐ and intracellular septate mycelium, producing intracellular microsclerotia, was detected from the rhizodermis to the vascular cylinder. Using isolation techniques, we obtained, from both sampling sites, sterile, slow‐growing fungal colonies, dark in colour, with septate mycelium, belonging to the dark septate endophytes (DSEs). DNA sequencing of the internal transcribed spacer (ITS) region identified these colonies as Lulwoana sp. To our knowledge, this is the first report of Lulwoana sp. as DSE in roots of P. oceanica. Moreover, the highest fungal colonisation, detected in P. oceanica roots growing on rock, suggests that the presence of the DSE may help the host in several ways, particularly in capturing mineral nutrients through lytic activity.     

Unexpected response of the seagrass Posidonia oceanica to a warm-water episode in the north western Mediterranean Sea

The response of Posidonia oceanica (Linnaeus) Delile to the warm-water episode of summer 1999 was studied by means of the technique of lepidochronology. Study sites include three sites affected by the mass mortality event of benthic invertebrates and one not affected. The results showed a significant decline in some parameters (number of leaves and/or rhizome growth) for the three sites affected by the mass mortality event for the year following the warm-water episode (1999-2000). A similar decline was not observed for the unaffected site. The fact that high temperatures could have a negative impact on deep Posidonia oceanica near its cold limit of distribution is an unexpected result.     

Diversity,ecological role and potential biotechnological applications of marine fungi associated to the seagrass Posidonia oceanica

The marine environment is characterized by high salinity and exerts a strong selective pressure on the biota, favouring the development of halo-tolerant microorganisms. Part of this microbial diversity is made up of fungi, important organisms from ecological and biotechnological points of view. In this study, for the first time, the qualitative and quantitative composition of the mycoflora associated to leaves, rhizomes, roots and matte of the seagrass Posidonia oceanica was estimated. A total of 88 fungal taxa, mainly belonging to Ascomycota, were identified by morphological and molecular methods. The most represented genera were Penicillium, Cladosporium and Acremonium. Most of the species (70) were selectively associated with one district; only two species (Penicillium chrysogenum var. chrysogenum and P. janczewskii) were isolated from all the districts. Moreover the capability to produce laccases, peroxidases and tannases by 107 fungal isolated by the different districts of P. oceanica was carried out. These results show that the mycoflora associated to P. oceanica is very rich and characterized by fungi able to produce ligninolytic enzymes and tannases useful to degrade and detoxify lignocellulose residues in presence of high salt concentrations. These fungi, hence, may play important ecological roles in marine environments but can also be very useful in different biotechnological areas.