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1.
The results of 15 years of monitoring of Posidonia oceanica in the “Cinque Terre” Marine Protected Area (NW Mediterranean) are presented. Seasonal data on meadow characteristics (cover and shoot density), plant phenology (leaf number, leaf length and width, leaf brown portion, undamaged leaves), lepidochronology, leaf epiphyte cover and herbivore pressure collected from three stations at 5, 10 and 17 m depth were compared. Time-series analyses showed both medium-term (5 < years) and long-term cycles (from 5 to more than 20 years). The comparison of annual cycles with sea surface temperatures (SST) and rainfall showed correlations that differed in relation to depth and, in the case of epiphytes, with each side (internal and external) of the leaf blade. Meadow parameters (visual cover, shoot percent cover) and plant parameters (leaf number, number of undamaged leaves, number of scales shoot−1) showed a positive trend in accordance with the rise of air and sea surface temperature recorded over these last decades. Shoot density and leaf width showed exceptions. Leaf length, leaf brown portion length and the number of undamaged leaves shoot−1 showed positive or negative long-term trends, whose variability could not be related to climate data alone. The two major groups of epiphytes (encrusting algae and the bryozoan Electra posidoniae) showed negative trends. Grazing variability could be explained only partially by climate parameters. Epiphyte cover was found to be related to the NAO index.In conclusion, data showed that the effects of the climate change in terms of both sea surface temperature rising and rainfall decreasing may affect the growth cycles of P. oceanica on two levels: on a decadal level, with positive or negative trends in meadow and plant characteristics and in epiphyte cover; on yearly and seasonal levels, influencing endogenous plant growth rhythms, as in the case of leaf production cycle.  相似文献   

2.
Patch dynamics of the Mediterranean slow-growing seagrass Posidonia oceanica was studied in two shallow sites (3–10 m) of the Balearic Archipelago (Spain) through repeated censuses (1–2 year−1). In the sheltered site of Es Port Bay (Cabrera Island), initial patch density (October 2001) was low: 0.05 patches m−2, and the patch size (number of shoots) distribution was bimodal: most of the patches had less than 6 shoots or between 20 and 50 shoots. Mean patch recruitment in Es Port Bay (0.006 ± 0.002 patches m−2 year−1) exceeded mean patch loss (0.001 ± 0.001 patches m−2 year−1), yielding positive net patch recruitment (0.004 ± 0.003 patches m−2 year−1) and a slightly increased patch density 3 years later (July 2004, 0.06 patches m−2). In the exposed site of S’Estanyol, the initial patch density was higher (1.38 patches m−2, August 2003), and patch size frequency decreased exponentially with size. Patch recruitment (0.26 patches m−2 year−1) and loss (0.24 patches m−2 year−1) were high, yielding a slightly increased patch density in the area 1 year later (October 2004, 1.40 patches m−2). Most recruited patches consisted of rooting vegetative fragments of 1–2 shoots. Seedling recruitment was observed in Summer 2004 at both sites. Episodic, seedling recruitment comprised 30% and 25% of total patch recruitment in Es Port Bay and S’Estanyol, respectively. Patch survival increased with patch size and no direct removal was observed among patches of 5 shoots or more. Most patches grew along the study, shifting patch distribution towards larger sizes. Within the size range studied (1–150 shoots), absolute shoot recruitment (shoots year−1) increased linearly with patch size (R2 = 0.64, p < 4 × 10−5, N = 125), while specific shoot recruitment was constant (about 0.25 ± 0.05 year−1), although its variance was large for small patches. Given the slow growth rate and the high survival of patches with 5 or more shoots, even the low patch recruitment rates reported here could play a significant role in the colonisation process of P. oceanica.  相似文献   

3.
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.  相似文献   

4.
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.  相似文献   

5.
The potential of alleviated fishing pressure measures established at the Marine Natural Reserve of Cerbère-Banyuls to affect phenological characters of P. oceanica, the main canopy-forming seagrass, was studied. Our results show differences in some leaf parameters between meadows under fishing prohibition measures compared to those without. In addition shallow P. oceanica meadows inside MPAs had lower non-structural carbohydrate content, yet are able to maintain themselves and, moreover, with an increased density. On the other hand, sexual reproduction was reduced inside protected areas.  相似文献   

6.
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.  相似文献   

7.
In coastal environments, plants are used for phytoremediation of contamination. Organic and inorganic contaminants may be due to natural and/or anthropogenic sources. The aim of this study is to compare inorganic (trace metal) and organic (PAH) contamination in Posidonia oceanica and to analyse the relationship between these types of pollutants indeed very few studies have been interested in their correlations and common sources. P. oceanica leaves were collected in two sites exhibiting different levels of human-induced pressure. Higher values were recorded in the more polluted site (Toulon) for trace metals (Ag, Hg, Pb) as well as for PAHs (Medium Molecular Weight and High Molecular Weight) due to the presence of the city and/or harbour in proximity. For the first time in a coastal environment, correlations were observed between metals and PAHs.  相似文献   

8.
The recovery capacity of meadows of the Mediterranean seagrass Posidonia oceanica (L.) Delile in an area affected by illegal trawling were assessed after protection by anti-trawling reefs. The differences in vegetative growth between two impacted and two undisturbed localities were tested using growth, shoot balance, aborted branches, and leaf and rhizome production of both plagiotropic and orthotropic rhizomes. The organic matter in sediments, silt clay fraction and light intensity incident on the bottom were also measured in order to evaluate the physical conditions. Environmental and plant variables were measured in three sites placed inside each locality. The vegetative growth was positive in both impacted and control meadows but growth rates were lower in impacted than in control meadows. Average growth, production and shoot balance were greater in plagiotropic rhizomes from undisturbed localities (40.7±1.75 vs. 28.4±1.34 mm/year, 1133±0.06 vs. 708±0.04 mg DW/shoot/year, 1.36±0.08 vs. 0.96±0.06 shoots/year, respectively). Significantly greater values were also found in undisturbed localities for orthotropic rhizomes in terms of shoot balance and rhizome production (0.07±0.01 vs. 0.01±0.003 shoots/shoot/year and 155 vs. 124 mg DW/shoot/year, respectively). Of the physical parameters measured, only light intensity differed significantly between impacted and undisturbed localities. This parameter was 15.5% to 67.6% lower in impacted localities than in undisturbed localities, and this is the factor that causes the retardation of vegetative growth. The results show that recovery of P. oceanica meadows is possible after eliminating the cause of the impact. However, the very low rates of vegetative growth may prolong the time to total recuperation to almost 100 years. Therefore, effective management of P. oceanica meadows should aim to prevent meadow loss.  相似文献   

9.
The response of orthotropic rhizome elongation and primary production of Posidonia oceanica to anthropogenic perturbations and potential confounding effects of shoot age were assessed using a Linear Multilevel Model (LMM). This model examined the confounding effect of age by comparing the estimates of impact and variance components obtained by excluding and including Age as an explanatory variable. Age had a negative effect on rhizome elongation and primary production with an annual decrease of 0.6 mm y− 1 and 7 mg dw y− 1 respectively. According to the LMM when age effect was omitted, the differences between disturbed and control locations in rhizome elongation and primary production were 2.62 mm y− 1 and 0.044 g dw y− 1 respectively. These effects were statistically not significant. On the contrary, when age effect was included in the statistical model, impacts became evident for both variables, with significant differences between disturbed and control locations of 5.85 mm y− 1 and 0.081 g dw y− 1 for rhizome elongation and primary production, respectively. Thus, particular attention should be paid to the potential confounding effect of shoots age in analyses of impacts on growth performance of P. oceanica.  相似文献   

10.
Here we studied the effects of adding organic carbon and nutrients to sediment on the physiology and survival of the seagrass Posidonia oceanica in a field experiment in the Medes Islands (NE Spain). Nine randomly selected plots were established at a depth of 10 m; three were enriched with organic carbon (OM treatment), three with organic carbon and nutrients (OMN treatment), and three were kept as controls (CON). The experiment was performed over 5 months and sampling of plants and sediments was done in March, May and July 2002. Sediment sulfide pools and pore water ammonium concentrations increased significantly in OM and OMN plots, both treatments showing increased reducing conditions in the sediment. Plants in these two treatments showed higher mortality and lower biomass compared to plants from CON plots. The greatest effects on seagrass occurred in the OMN plots, indicating a synergistic effect of organic carbon and nutrient additions. Treatments had significant effects on plant nitrogen (N) and phosphorous (P) metabolism, shown by an increase in free amino acid (FAA) content, a change in FAA composition and a lack of increase in N and P tissue content. Treated plants showed higher g-aminobutyric acid (GABA) and malate concentrations and lower concentrations of non-structural carbohydrates compared to CON, indicating that anaerobic respiration in below-ground tissues occurred. Several of the physiological changes shown by P. oceanica can be interpreted as adaptations to anoxia exposure. However, the increased mortality in treated plots demonstrates that this seagrass does not tolerate highly reduced sediments.  相似文献   

11.
Prediction capacity of three main shoot population dynamics methods (age structure, net shoot recruitment per plagiotropic rhizome and shoot census) have been tested for a period of four years (2002-2006) on a Posidonia oceanica meadow. Accuracy of each method was checked by comparing measured and predicted densities at the end of the study period. Predicted densities came from the evolution of initial densities (measured in 2002) by a basic exponential model of population growth. The exponential model used the different net shoot recruitment rate estimates by each population dynamics method on three depths (upper, medium and lower limit) and three localities at each depth. Predictions performed by shoot census and net shoot recruitment per plagiotropic rhizome methods matched with measured densities at the end of the study period. Conversely, age structure method underestimated shoot densities at each depth, indicating an unreal decrease of shoot population in the meadow.  相似文献   

12.
To better understand some basic aspects of the nitrogen economy in Posidonia oceanica and, specifically, the seasonality of the processes of storage, translocation and assimilation, we examined nitrogen speciation into soluble compounds, both inorganic (nitrates, nitrites and ammonium) and organic (free amino acids, FAA, and total soluble protein, TSP), and the nitrogen assimilation potential (through the glutamine synthetase activity measurement) in the leaves, rhizomes and roots of P. oceanica over a 1-year cycle. Only a limited amount of inorganic nitrogen was found, accounting for less than 3.3% of the total nitrogen content, and it was mostly in the form of ammonium. Nitrate and nitrite concentrations were very low, always below 7.2 μmol g−1 dw in annual average. Among the organic soluble fractions, FAAs were the most abundant, accounting for up to 50% of N pools. Rhizomes were the organs in which FAA concentrations reached their maximum value. The leaves showed higher nitrogen assimilation potential than the roots and this assimilation potential was highest during and after the period of maximum leaf growth, probably corresponding to the assimilation of both new and recycled nitrogen. Our results suggest that 5% of the total nitrogen assimilation occurs in roots and 79% in leaves on an annual average. In addition, rhizomes contributed to the total shoot nitrogen assimilation by 32-54% between autumn and spring. Rhizomes appear as key organs in the nitrogen economy of the plant, not only as a major site for nitrogen assimilation but also as an organ for nitrogen storage. This storage, mostly in the form of FAA, occurs during periods of high availability and low demand (winter). This stored nitrogen can supply up to 33% of plant demands during the moment of maximum leaf growth (i.e. late spring).  相似文献   

13.
Seagrasses worldwide are noted for suffering from mechanical damage caused by boat anchoring. This is particularly so in sites highly frequented by boaters (marine protected areas or coastal urbanised areas). In the last decades, different strategies have been put into practice to reduce such impacts on seagrasses (i.e. by anchoring bans or by deploying boat moorings). More recently, in consideration that few marine protected area (MPA) management bodies or local administrations have the resources to enforce their anchorage regulations, the self-regulatory approach based on education and information of boaters has been preferred in several cases. At present, however, very little is known on the correct anchoring practices to ensure the safeguarding of seagrasses. The aim of the present study was to experimentally quantify in the field the damage caused to Posidonia oceanica shoot density by anchoring. A multifactorial experiment was designed to test whether the damage is dependent on (1) different anchor types (Hall, Danforth and Folding grapnel), (2) the use of a chain vs. a rope, (3) the three anchoring stages (anchor fall, dragging/lock-in and weighing), and finally (4) whether the pattern is consistent among different locations of the meadow.As expected, the three anchor types employed in the present study differed in the levels of damage inflicted on the P. oceanica meadows of the Ustica Island MPA. In particular, the use of the Hall type anchor seems to be preferable to minimise this impact in comparison with the other two anchor types. Moreover, the effect on the meadow of the three anchor types is greatly dependent on the anchoring stage. These results confirm that the weighing stage is the critical stage of the anchoring process. The number of damaged shoots of P. oceanica was not affected by the presence of the chain. These patterns were consistent between locations.In the long term, even anchoring on P. oceanica by small boats using low-impact anchors may potentially have detrimental consequences. For this reason, we suggest that in vulnerable sites, it is preferable to implement an educational program based on information of boaters on correct anchoring practices and anchor typology to use, rather than adopting strong restrictions to boat anchoring or deploying mooring buoys. Although the use of these management strategies is still recommended in the case of anchorage frequented by bigger vessels using heavier anchors and chains.  相似文献   

14.
Urban and industrial wastes have been claimed to negatively affect Posidonia oceanica meadows, but few studies have addressed this issue by comparing disturbed locations with replicated reference locations. Here, we examined the general proposition that patterns of growth and morphology of P. oceanica exposed to urban and industrial effluents were different from those observed in reference meadows. Hypotheses were both on differences in mean values of response variables and on variation of these measures at a hierarchy of spatial scales (from centimetres to hundreds of metres). Results indicated a significant reduction in mean number of intermediate leaves at the outfall compared to reference locations, whereas the opposite pattern occurred for juvenile leaves. There were significant, though temporally variable differences in growth of rhizomes between disturbed and reference locations, with reduced growth at the outfall in 2 out of 3 years analysed. Measures of spatial variance in number of juvenile leaves and length of adult leaves at the scale of shoots were significantly larger at the outfall compared to reference locations. At the same scale, measures of spatial variance in length of juvenile and intermediate leaves were significantly lower at the putatively impacted location. Spatial variance in number of intermediate leaves was reduced at the outfall compared to reference locations at the scale of quadrats. Past values of spatial variance in number of leaves per shoot were lower at the outfall than at the two reference locations at the scale of shoots, whereas the opposite occurred at the scale of areas. None of the structural variables examined showed any difference between the putatively impacted location and the two reference locations, either in terms of mean response or as changes in spatial variance. These results indicated that integrating methods to examine present and past events of disturbance, including analyses to detect changes in spatial variance of response variables, may provide a powerful approach to the analysis of environmental impacts on P. oceanica.  相似文献   

15.
Previous studies have shown that most leaf production (>90%) of the seagrass Posidonia oceanica is shed after senescence and that a substantial percentage (up to 80%) may thereafter be exported off the seagrass meadows by waves and currents. It has also been reported that P. oceanica meadows can accumulate large stocks of belowground detritus due to slow decomposition rates. However, the generality of these results across broad spatial scales is poorly known. In this report, we examine the fate of leaf production and the magnitude and dynamics of belowground detritus in 16 P. oceanica meadows distributed along the Spanish Mediterranean. Herbivores removed a small percentage of leaf production in all the meadows (≤13%), with most leaf production (>85%) being shed after senescence. Most shed leaves (>90%) were exported off the meadows by physical agents, such as waves and currents. The amount of belowground detritus stored within 10–15 cm from the sediment surface varied from ca. 70 to 7500 g DW m−2 among the meadows examined, and they accumulated at rates ranging from ca. 65 to 650 g DW m−2 per year. These values are large when compared to other communities of aquatic and terrestrial macrophytes. Our results show that P. oceanica meadows in the Spanish Mediterranean support high values of secondary production in other systems by exporting large amounts of leaf detritus as well as acting as substantial carbon sinks by accumulating large reservoirs of belowground detritus. Therefore, the increasing anthropogenic threats on P. oceanica could entail an important loss of secondary production and carbon storage in Mediterranean coastal ecosystems.  相似文献   

16.
Posidonia oceanica L. (Delile), an endemic species of the Mediterranean, forms extensive meadows which are continuously endangered by anthropic impacts. The availability of up-to-date information about interannual changes in shoot density of meadows and the knowledge of its expansion capabilities are crucial elements for the development of effective protection plans. Conversely, spatial ecology is becoming an increasingly important component of resource management, and the use of quantitative data for constructing prognosis maps of the dynamics of ecosystem degradation and restoration by nonlinear simulation methods is a topical field of landscape ecology. Unfortunately, little is known on spatial patterns of shoot density of P. oceanica on a small scale, despite their increasing use as indicators of the status and/or trends of meadows. The spatial structure of a continuous P. oceanica meadow, extending from 1 to 33 m depth in Lacco Ameno (Gulf of Naples, Italy), is investigated here by the “kriging” technique, a method widely used for geostatistical purposes. The analysis detected peculiar spatial patterns of shoot density and facilitated a small-scale (square meters) model of the distribution of P. oceanica. The highest shoot densities were found at the shallow stand (430 shoots m−2, on the average, with a peak of 1000 shoots m−2 in a relatively small area, at 1 m depth) and the lowest at the deep stand (average density <300 shoots m−2 below 15 m depth). A high degree of patchiness was found in the shallow stand, down to 10 m depth. Nestlike patterns with a rounded shape, characterized by shoot density radially decreasing from the center, were demonstrated mainly in the shallow stand. An opposite trend was detected in one case, where the main nestlike pattern was characterized by a decrease of density towards the center. Nestlike patterns may be generated by the confluence and overlap of stolons expanding from proximal areas. The comparison of density and depth models indicated that the shape of the seafloor influences the density structure of meadows and the growth patterns of P. oceanica.  相似文献   

17.
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.  相似文献   

18.
Between 1981 and 1993 a methane pipeline was deployed between Sicily (Italy) and Tunisia. This involved the construction of a pipeline trench, which damaged the Posidonia oceanica (L.) Delile meadow at Capo Feto (SW Sicily, Italy) and disturbed the surrounding meadow. Seagrass growth and population dynamics were examined at different depth ranges and at increasing distances from the construction site outer limit (5, 15, 30, 50 m). Results showed significant differences between the shallow (10±3.3 m) and the deep (20±4.6 m) meadow as well as differences among distances. The age structure of P. oceanica varied along the distance gradient and with depth. The mortality rate decreased with distance from the trench at all depth ranges, showing that the plants close to the excavation suffered a higher level of disturbance. Turnover and annual gross shoot recruitment rate (Rgross) were higher in the shallow portion of the meadow than in the deep range. Forecast of future meadow development (Rnet) close to the trench indicates that, if present conditions are maintained, shoot density will be reduced by 50% over the next 6 to 17 yrs.  相似文献   

19.
In situ nitrogen uptake by leaves and epiphytes was studied in a Mediterranean seagrass (Posidonia oceanica) meadow impacted from a fish farm and a pristine meadow, using 15NH4 and 15NO3 as tracers. In the impacted meadow both leaves and epiphytes yielded higher N concentrations and showed higher specific N uptake, suggesting a linkage between N uptake and its accumulation. Epiphytes took up N faster than leaves in relation to their corresponding biomass, but when assessed per unit area, N uptake was higher in leaves. Leaf N uptake was negatively correlated with epiphyte N uptake. With increasing epiphyte load on leaves, N leaf uptake decreased while N epiphyte uptake increased, indicating that epiphyte overgrowth hinders N uptake by P. oceanica leaves. Epiphyte contribution to total N uptake increased, while that of leaves decreased at the impacted meadow. However, 2-3 times less N was transferred daily from the water column to the benthic compartment, through seagrass and epiphyte uptake on total, at the impacted meadow. Therefore, it is probably still the loss of the key species - the seagrass - which plays the most important role in N cycling in seagrass ecosystems.  相似文献   

20.
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