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1.
Abstract. Seasonal changes in nitrogen, free amino acids, and carbon were investigated in the three Mediterranean seagrasses Posidonia oceanica, Cymodocea nodosa , and Zostera noltii. Leaves, rhizomes, roots, as well as dead plant material were analysed separately. Highest N-concentrations were obtained in the winter months, regardless of species or plant part. In contrast to the other two species, the N-content in Posidonia was higher in the rhizomes than in the leaves.
In the investigated species, marked differences in the free amino acid (FAA) composition were detected between species: Proline, lacking in Posidonia , was the main component in Cymodocea. In Posidonia , FAA decreased from 320umol g-1 (dry wt) in leaf sheaths to 1.5 umol g-1 (dry wt) in the leaf tips. The function of proline as a possible storage and/or stress metabolite is discussed.
High C/N values in dead P. oceanica and C. nodosa rhizomes as well as in P. oceanica wrack seem to be related to considerable resistance to decomposition. Low C/N ratios did not increase in detached C. nodosa and Z. noltii leaves, which began to decompose shortly after detachment from the plants.  相似文献   

2.
Abstract. Leaf sheaths in the seagrass Posidonia oceanica can persist for millcnia and they show, according to their insertion rank, cyclic variations in parameters such as thickness and tissue structure. The principal cycles are always annual, but pluriannual cycles can also be detected. Annual cycles may be changed by environmental parameters such as light, temperature, or water movement. In a fashion analogous to the study of annual tree rings (dendrochronology), the study of cyclic changes in Posidonia oceanica sheaths is thus a technique allowing the study of past yearly changes in the near-shore environment.  相似文献   

3.
The aim was to evaluate the antioxidant defences and the occurrence of oxidative damage in Posidonia oceanica under a stress situation due to the epiphytism of the invasive macroalgae Lophocladia lallemandii. P. oceanica leaves were collected in the absence (control station) and in the presence of the epiphytic algae L. lallemandii and the antioxidant enzyme activities, markers of oxidative damage, and hydrogen peroxide production were determined. Antioxidant enzyme - catalase, glutathione peroxidase and superoxide dismutase - activities were significantly higher in Posidonia epiphytized by L. lallemandii. Malondialdehyde, protein carbonyl derivates, and glutathione levels were also higher in L. lallemandii epiphytized P. oceanica leaves compared to control samples. The production of hydrogen peroxide was also significantly increased when Posidonia was epiphytized by L. lallemandii. The invasion of P. oceanica meadows by L. lallemandii appeared to induce oxidative stress in the seagrass as evidenced by increased levels of oxidative stress markers and antioxidant defences.  相似文献   

4.
P. Francour 《Marine Ecology》1997,18(2):157-173
Abstract. Observations of the fish fauna of Posidonia oceanica (L.) DELILE seagrass beds were undertaken in two shallow stations and one deeper station in Port-Cros National Park, between November 1984 and September 1987. Demographic structure, density and biomass of the 19 most abundant species or taxa were assessed by several non-destructive sampling methods. The fish assemblages studied were dominated in number and biomass by a small number of species (Labridae: Symphodus ocellatus and S. tinca ; Sparidae: Diplodus annularis and Sarpa salpa ). Large individuals were infrequent and small size class fish were dominant especially in sheltered shallow areas. Recruitment and migrations (shortor long-term) have been identified as the most important causes of abundance variations over the year. The four trophic categories were sampled only in the sheltered shallow zone, where the herbivore Sarpa salpa represents a strong proportion of the fish fauna (40–70%) during summer. The fish assemblages differ between the three seagrass beds, and the depth appears as the most important factor affecting the fish assemblages in P. oceanica . The functional difference between shallow and deeper seagrass beds is therefore discussed.  相似文献   

5.
Abstract. A large-scale map of the Posidonia oceanica seagrass beds as well as other benthic substrata and communities was compiled for a cove of a marine reserve free from pollution and man-made disturbance. An extensive diving survey of the cove and the interpretation of aerial colour photographs were used. The greater part of the cove is occupied by the P. oceanica meadow. Patches of dead "matte" were observed at a depth of between 7 and 14 m. They may be the result of a natural hydrodynamic equilibrium between building and erosion.  相似文献   

6.
Abstract On the basis of a detailed cartographic survey carried out by Side Scan Sonar and a towed underwater video camera during 2005, and from a series of historical maps (1959, 1980, 1990), an extensive regression of Posidonia oceanica (L.) Delile beds was evidenced for a vast area of the central Tyrrhenian Sea (Latium coast, Italy). The total loss of P. oceanica surface was assessed through GIS estimate. In 1959, the Posidonia beds extended over 7290 ha, while in the 2005 survey they had regressed to 2899 ha, a loss of about 60% of their coverage. Also the seagrass lower limit showed a general depth decrease in time. Total seagrass coverage loss and lower limit regression were not uniform along the whole investigated areas and three main sub-areas have been identified with different degrees of regression somehow related with coastal potential human-mediated impacts. From different coverage estimates of the present survey and of the previous maps, minimum sampling areas were calculated through bootstrapping simulation routines from small sampling areas (Landscape Units) to reach the nearest estimate of the observed condition in the different periods.  相似文献   

7.
Experimental evaluations about the impact of anchors of small vessels have previously shown that each anchoring can on average damage up to six shoots of Posidonia oceanica, removing small amount of biomass and, at the same time, interrupting continuity among shoots. The aim of the paper was to investigate the response of P. oceanica to different damage intensity at two levels of substrata compactness. Three treatments were considered: control (no damage); low damage (simulated anchor damage by three strokes of a hoe); and high damage (six strokes). Disturbance was higher where the substratum was highly penetrable and after one year significant variation was observed among treatments for both the number of leaves per shoot and shoot density. Conversely, the number of leaves per shoot by the end of the study was similar among all treatment combinations, suggesting that this was the only phenological feature that recovered, and probably the only result that through clonal integration could be achieved. These data strongly highlighted the role that anchoring might have on the slow growing seagrass P. oceanica meadow.  相似文献   

8.
Abstract. Hg, Cd, Pb and Zn concentrations were determined in sediment and in tissues of five species of soft-bottom marine macrophytes ( Posidonia oceanica, Cymodocea nodosa, Zostera noltii, Ruppia cirrhosa and Caulerpa prolifera ) along the Spanish Mediterranean coast. Levels of metals were low in most of the sampling stations and similar to those found by other authors in uncontaminated zones. Certain locations, however, showed some degree of contamination (Cambrils, Almassora, Alacant, Mar Menor and El Portús). In Santa Pola we found high contents of metals in one sample of sediment due to the high proportion of the fine fraction (particules < 63µm) and organic matter, but not in the seagrass species. Mercury and zinc concentrations in the sediment are correlated to those in at least some anatomic fractions of Posidonia oceanica, Cymodocea nodosa and Caulerpa prolifera , suggesting that these species reflect the levels of these metals in the environment. Lead contents in the alga Caulerpa prolifera are also correlated to those in the sediment, while no significant correlations were obtained for cadmium. Among the species studied, Posidonia oceanica and Cymodocea nodosa seem to be better biomonitors than Caulerpa prolifera .  相似文献   

9.
Abstract. The ecosystem associated to the Mediterranean seagrass Posidonia oceanica shows a clear distinction in two subcompartments regarding turnover time: aboveground and belowground. Aboveground parts (leaves) are highly dynamic, and most of the leaf material is decomposed or exported in less than one year, representing a net loss of nutrients. In contrast, belowground biomass (roots and rhizomes) has a turnover time of the order of centuries, with a consequent accumulation of organic matter in the sediment. The accumulation rates for the single elements rank in the order C > N > P. This ecosystem may be considered as a sink for biogenic elements.  相似文献   

10.
Abstract. The study was carried out in a Posidonia oceanica bed and in the neighbouring sandy and rocky bottoms, at Ponza Island (Central Tyrrhenian Sea), in order to investigate the distributional pattern of the polychaete community at different depths. A total of 15232 individuals of polychaetes belonging to 218 species was collected and three new species of Syllidae were found. The polychaete community of the matte can be clearly distinguished from the neighbouring communities; this is due to the high species richness in Posidonia , which is related to the heterogeneity of the biotope. In the Posidonia bed the shallow stations (1 m and 5 m depth) were the richest in terms of species numbers and individuals due to the high shoot density of the seagrass bed. In the shallow waters polychaete community structure changed according to the different exposure to water movement. Rocky bottom species, which preferentially inhabit crevices, were more abundant in the matte exposed to water movement (5–10 m depth). In contrast, soft-bottom species were more abundant in the sheltered zone (1 m depth) as well as in the deeper zone due to the reduction of the Posidonia bed.  相似文献   

11.
Abstract. Respiration in Holothuria tubulosa was investigated in individuals from the Posidonia oceanica meadow off Lacco Ameno (Ischia Island, Italy). Respiratory rates increase with increasing body weight and increasing sea water temperature. Oxygen consumption of an average individual (7g dw body wall) ranges from 0.409 (14 °C) to 1.300 (26 °C) mg O2· h-1. Data on population density, mean size of individuals, and annual sea water temperature variations allow an assessment of holothuroid production. Values of 45.65 and 13.75 kJ · m-2· y-1 were calculated for shallow (3 to 10 m) and deep (25 to 33 m) areas of the Posidonia meadow, respectively. Holothuroid production shows a bathymetric pattern similar to primary production of the Posidonia -epiphytes complex and the production of Posidonia litter.  相似文献   

12.
Abstract. In the Sicilian lagoon Stagnone di Marsala, Tethya aurantium and T. citrina show different ecological distributions, although some overlapping occurs. The first species reaches its highest density where linear currents are maximal, and in this habitat it is particularly frequent on Posidonia oceanica rhizomes. The second species is more abundant in still water locations and is equally common on Posidonia rhizomes and on calcareous concretions. Such distributions can be related to water movement, Posidonia shoot density, and associated factors such as sedimentation and food availability. These observations are consistent with an adaptive interpretation of the morphofunctional features distinguishing the two species.  相似文献   

13.
Abstract. Dissolved free amino acids (DFAA) were measured in sediment porewater and overlying sea water in seagrass beds of Posidonia oceanica and Cymodocea nodosa at a water depth of 8–10 m in Corsica, France. In the sea water, DFAA concentrations from 0.5 to 1.9μM were found. Lowest concentrations occurred in the afternoon in surface water samples, while higher concentrations were measured in morning surface samples and in all bottom samples. The most abundant amino acids were serine, glycine, and alanine. In the sediment, the upper 4cm contained the highest concentrations of DFAA (177nmol cm-3 or 367 μM), while lower concentrations (<50nmol cm-3 or 104 μM) prevailed deeper in the sediment. Glycine, glutamic acid, alanine, and β-alanine were the major components of the DFAA. The photosynthetic activity of the seagrasses influenced sediment porewater pools of DFAA. When a Posidonia bed was covered with a black polyethylene shield, the interstitial amino acids were reduced at a rate of 16nmol cm-2 h-1 (0-10cm depth). Conversely, extended daylight (floodlight) increased the DFAA pool in sediment depths below 4 cm. Free amino acids were released to the overlying sea water from both seagrass sediment and individual shoots, the rates being highest in the dark. The present investigation indicates that a substantial portion of the N-cycling of the seagrass sediment includes free amino acids.  相似文献   

14.
C. Salas  E. Hergueta 《Marine Ecology》1994,15(3-4):255-265
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15.
Abstract. Fishes associated with the seagrass Posidonia oceanica were censused both by skid trawl and visual counts around Ischia Island, Italy. Both sampling procedures were performed during the day in summer and in winter at two sites. Significant differences in the number of species, number of individuals, biomass, and trophic structure of the fish assemblage were observed between sampling methods. Fewer fish species were recorded by visual counts than by trawling. More individuals and a greater biomass, however, were recorded from visual counts. The population of macrocarnivores (Scorpaenidae, Serranidae) were better estimated by trawling, as were canopy-dwellers (Syngnathidae; Symphodus rostratus) and benthic species (Gobiidae; Blenniidae; Bothidae). Conversely, good swimmers ( Sparidae; Coris julis, Symphodus spp.), and planktivorous fishes (Centracanthidae, Pomacentridae) mostly escaped the trawl and were better assessed by visual counts. The importance of methodological biases differed from one season to the other and was higher in summer than in winter. Particular attention should be paid to the biases induced by sampling techniques when interpreting data, and different sampling methods should be used to accurately study the fish assemblages of seagrass meadows.  相似文献   

16.
Abstract. The supply of nitrogen (N) often limits the productivity of marine macrophytes. In vitro and in vivo assays of glutamine synthetase (GS) activity were employed to investigate patterns of N assimilation by the Mediterranean seagrass Posidonia oceanica (L.) DELILE. Biomass-specific GS activity wa measured in root tissue, in leaves within a shoot, in shoots collected at two sites during two season and over a depth range of 5–33 m. Root tissue was less important than shoot tissue in assimilating inorganic N in P. oceanica , due both to the small roots' biomass (ca. 3% of total plant biomass and greatly lower (10- to 50-fold) GS activities. While the GS activity and N assimilatory potentia (biomass × GS activity; μmol N-h--1) were greatest in leaf 2, leaves 1 and 3–5 assimilated N a significant rates. Shoots from a site characterized by elevated N availability in the winter water column and no significant sediment N reservoir exhibited GS activities that were 9-times higher than shoot from a more oligotrophic site. Shoot GS activities in July increased linearly from 5 to 33 m and wer correlated with light availability as defined by Hsat, (daily period during which photosynthetic reaction are light-saturated). This may represent metabolic compensation by P. oceanica to maintain N influx. Factors contributing to the ecological success of P. oceanica include the ability to assimilate N under conditions of severe light limitation (< 35 μmol photons. m-2. s-1), and metabolic plasticity to ensur the de novo generation of N-containing organic compounds.  相似文献   

17.
Abstract. In all scagrass species investigated, rhizomes were the main storage organs for soluble carbohydrate reserves, and the highest levels were found in Cymodocea nodosa (U cria ) A scherson . Sucrose was the primary soluble carbohydrate identified in Posidonia oceanica (L.) D elile , and Zostera noltii H ornem . This disaccharide was dominant in Cymodocea nodosa roots, as well as in its rhizome in winter. Myo-inositol was the main cyclitol in Zostera noltii. In Cymodocea nodosa leaves 1-chiro-inositol was the main sugar component; it was also present to a lesser extent in the roots and rhizomes. The amounts of glucose and fructose were correlated with growth to a certain extent in all species. Higher amounts of starch were stored in the rhizomes of Posidonia oceanica and Zostera noltii. The energy content of Mediterranean scagrasses was significantly higher than in tropical species. No distinct seasonal trend in energy content could be observed.  相似文献   

18.
Gut content examination and trophic markers (fatty acids, stable isotopes of C and N) were combined to delineate the diet of the dominant species of amphipods from Mediterranean Posidonia oceanica seagrass meadows and to highlight trophic diversity among this community. Our results indicate that, although all dominant species heavily relied on macroalgal epiphytes, considerable interspecific dietary differences existed. Carbon stable isotope ratios notably showed that some of the amphipod species favored grazing on epiphytes from leaves or litter fragments (Apherusa chiereghinii, Aora spinicornis, Gammarus aequicauda), while others such as Dexamine spiniventris preferred epiphytes from rhizomes. The remaining amphipods (Caprella acanthifera, Ampithoe helleri and Gammarella fucicola) readily consumed both groups. In addition, SIAR modeling suggested that most species had a mixed diet, and relied on several food items. Fatty acid analysis and gut contents revealed that contributions of microepiphytic diatoms and of benthic and suspended particulate organic matter to the diet of amphipods were anecdotal. None of the examined species seemed to graze on their seagrass host [low 18:2(n‐6) and 18:3(n‐3) fatty acids contents], but Gammarus aequicauda partly relied on seagrass leaf detritus, as demonstrated by the lesser 13C‐depletion of their tissues. Overall, our findings suggest that amphipods, because of their importance in the transfer of organic matter from primary producers and detritus to higher rank consumers, are key items in P. oceanica‐associated food webs.  相似文献   

19.
Ferdinando  Boero 《Marine Ecology》1981,2(3):181-197
Abstract. The ecology and systematics of the hydroid population of Posidonia oceanica meadows have been studied in two different zones of the Western Mediterranean. A new sampling method has been employed and the results obtained have been compared with those of a standard method. The distribution of the species and several morphological variations are pointed out. Depth-related faunistic zones are evidenced. The key-species of the Posidonia hydroid population arc individuated.  相似文献   

20.
Seagrass grazing by fish was measured in a large seagrass-dominated temperate bay (Geographe Bay, Western Australia) to examine whether: (1) seagrass herbivory occurs; (2) the level of herbivory is influenced by nitrogen in seagrass leaves; and (3) how herbivory and herbivorous fish communities vary with water depth and seagrass species. Species and abundance of fish and herbivore bite marks on seagrass leaves were recorded from diver surveys of 23 sites of varying depth ranging from 1 m to 18 m. Posidonia sinuosa, Posidonia coriacea, Amphibolis griffithii, and Amphibolis antarctica seagrass leaves were collected, dried and analysed for total nitrogen. Evidence for low levels of seagrass grazing was found at over half the sites surveyed, though high levels of grazing were recorded at only one site. An east–west pattern was observed in the location of grazed sites and of herbivorous fish species that corresponded with the general prevalence of patch reefs, indicating that reef associated fish assemblages may be responsible for the observed grazing. Total nitrogen was elevated in seagrass leaves associated with drains, although increased nitrogen was not associated with increased grazing. While grazing was recorded in this temperate seagrass meadow, the abundance of herbivorous fish was low and the amount of biomass removed by them was small compared to the balance of the meadow remaining, and to seagrass grazing studies elsewhere.  相似文献   

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