Seasonal Changes in Soluble Carbohydrates, Starch, and Energy Content in Mediterranean Seagrasses

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.     

Seasonal Changes in Nitrogen, Free Amino Acids, and C/N Ratio in Mediterranean Seagrasses

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.     

The Importance of Posidonia oceanica and Cymodocea nodosa as Contributors of Free Amino Acids in Water and Sediment of Seagrass Beds

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.     

Zonation and Ecology of Epiphytic Hydroids in a Mediterranean Coastal Lagoon: The 'Stagnone' of Marsala (North-West Sicily)

Abstract. Distribution patterns of epiphytic hydroids of seagrass ( Posidonia occanica and Cymodocea nodosa ) beds were studied in the 'Stagnone', a moderately hypcrhaline lagoon in Sicily. The role of water movement in determining the spatial and temporal zonation of epiphytic hydroids and their morpho-physiological variations is evaluated. Remarks on systematics arc also included.     

Effects of mining wastes on a seagrass ecosystem: metal accumulation and bioavailability, seagrass dynamics and associated community structure

Two different Cymodocea nodosa (Ucria) Ascherson beds growing in mining-contaminated sediments were compared with two reference beds in the Mar Menor coastal lagoon. The accumulation of Zn, Pb and Cd in different fractions of the plant, the sediment parameters that regulate the availability of metals, the seabed structure and dynamics of each seagrass bed and its associated macroinvertebrate community were studied. C. nodosa accumulates metals from the sediments and reflects their bioavailability for this seagrass. At each station, the metal content of the rhizomes was lower than that of leaves and roots. The concentration of acid-volatile sulfides does not seem to influence the availability of metals to the seagrass, possibly due to oxygen transport to underground tissues. The highest metal concentration in all the contaminated stations was found in the leaf-biofilm, due to the formation of complexes between metals and the extracellular polymeric substances that form the biofilm. All the seagrass beds were seen to be undergoing expansion, those growing in contaminated sediments accumulating great quantities of metals and showing highest photosynthetic leaf surface area and highest leaf biomass. However, these structural parameters were not seen to be responsible for the differences in the faunal composition observed between contaminated and reference beds. Moreover, the multivariate analysis identified the metal content of leaves, biofilm and sediments as important variables that may be responsible for these differences in faunal composition. In this study we have demonstrated that both the seagrass C. nodosa and the biofilm on the plant leaves may be used as environmental tools in the Mar Menor lagoon. The former is an useful indicator of sediment contamination, whereas the latter seems to be a good sentinel of water quality.     

Comparison between amphipod assemblages associated with Caulerpa racemosa var. cylindracea and those of other Mediterranean habitats on soft substrate

The spread of the invasive alga Caulerpa racemosa var. cylindracea in shallow-water habitats can present different faunal assemblage composition. We compared the amphipod assemblages associated with C. racemosa and natural habitats found on shallow-water Mediterranean soft substrata. Four vegetated habitats were compared: C. racemosa, Caulerpa prolifera, Cymodocea nodosa and Posidonia oceanica with unvegetated substrata. Samples were collected during two sampling periods (September 2004 and March 2005). A total of 63 amphipod species were recorded. The results showed that the vegetated habitats sampled, including C. racemosa stands, supported a higher abundance and species richness of amphipods. Furthermore, the assemblage structure differed between the different habitats, while the abundance of some species was significantly different, depending on habitat. For example, Microdeutopus obtusatus was favoured by C. racemosa habitat; Ampelisca diadema was associated with C. prolifera beds; and Hyale schmidti was more abundant in P. oceanica meadows. Habitat invasion by C. racemosa can exert an important influence on biotic assemblages, modifying habitat structure and associated fauna.     

Growth Dynamics in Posidonia oceanica (L.) Delile

Abstract. Amounts of photosynthate in the rhizomes, in photosynthetically inactive basal parts of the leaves and different old leaf blades were examined. Winter leaf growth was supported by mobilisation of starch in the rhizome. This winter growth enables Posidonia oceanica to utilize the increased energy influx in early spring via the substantial leaf area already developed and to approach highest productivity in spring. During summer and autumn considerable concentrations of soluble carbohydrates were found in the leaves and rhizomes. Starch was stored in the rhizomes in concentrations of up to 6.8 % of dry weight. Levels of nitrogen and free amino acids were correlated with growth rates. The percentage of total nitrogen present as free amino acid-nitrogen decreased from November (35 %) to summer (less than 1 %), by which time leaf growth had stopped. In contrast to this, amounts of organic anions were low in winter and spring and reached their maximum in summer.
Within a shoot, sites of leaf growth were characterized by high amounts of total nitrogen and free amino acids (innermost leaves), while carbon Fixation was highest in the leaves #2–#4. Particularly high concentrations of soluble carbohydrates were found midway along leaf blades.
It is evident that this unusual growth rhythm of Posidonia oceanica was only possible because of the ability to store considerable amounts of carbon and nitrogen in the rhizomes.
The results of this investigation demonstrate on the one hand that the chemical composition of the plant is strongly correlated with growth and production, and on the other hand that it is dependent on environmental factors, such as energy influx and temperature, which change with season.     

Polychaete Depth Distribution in a Posidonia oceanica Bed (Rhizome and Matte Strata) and Neighbouring Soft and Hard Bottoms

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.     

Systematics and Ecology of the Hydroid Population of two Posidonia oceanica Meadows

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.     

Biometric and Genetic Analysis of the Marine Rissoid Rissoa auriscalpium (Gastropoda, Prosobranchia) and its Ecological Implications

Abstract. Two forms of Rissoa auriscalpium were found in Posidonia oceanica beds around the Island of Ischia (Gulf of Naples). In order to investigate their taxonomical value and to quantify the discriminating features found, the radular, conchometric, genetic, and ecological features of the two forms were analyzed. Ecological observations showed that the distribution of the two forms is strongly correlated with hydrodynamic factors.     

Ecological Differences in the Distribution of two Tethya (Porifera, Demospongiae) Species Coexisting in a Mediterranean Coastal Lagoon

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.     

Antioxidant response of the seagrass Posidonia oceanica when epiphytized by the invasive macroalgae Lophocladia lallemandii

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.     

胶州湾水生系统中Pb、Zn 的分布特征及其在生物体中的浓缩

利用在胶州湾采集的47组同站位多介质样品,进行了痕量金属Pb、Zn及其它环境因子的化学成分测试,讨论了胶州湾水-沉积物-生物系统中Pb、Zn的生物地球化学总体特征及其在各介质平面上的分布,揭示了胶州湾水-沉积物-生物系统对陆源物质输入的响应.垂向上表层沉积物是Pb、Zn组分的富集带,该系统中的生物相对于其所处水环境具有显著的富集作用,生物体中Pb、Zn生物浓缩系数分别为36、935;横向上,Pb、Zn在底层水和沉积物介质中的分布主要受控于河口,即高值区分布于胶州湾的各个主要河口区,特别是在沉积物中金属组分浓度的高值区主要集中分布于胶州湾的东部.而孔隙水中Pb、Zn的高值主要分布于水交替较弱的海域,如红岛前缘.但生物体中的痕量金属组分化学场空间分布规律与上述各介质的化学场均不吻合,亦即是生物体中痕量金属组分的浓度与其所处环境中的同名金属组分浓度无关.作者认为,生物对痕量金属组分的富集并不简单地取决于它所处环境介质中同名金属组分的总量,而存在形态上的选择性.通过回归分析揭示了孔隙水对生物体中Pb、Zn的富集贡献较大.     

Feeding of the Sparid Fish Sarpa salpa in a Seagrass Ecosystem: Diet and Carbon Flux

Abstract. In Revellata Bay Gulf of Calvi, Corsica, France, the sparid fish Sarpa salpa L. is the main macro-consumer of Posidonia oceanica L. D elile leaf. Stomach contents were analysed and ¹³C/¹²C isotopic ratios were measured in fish muscle and potential food sources algae, P. oceanica leaf and its epiphytes to determine their relative contribution to the fish diet. S. salpa has an age-related mixed diet: juveniles are plankton feeders, young, sub-adults and adults are herbivorous, and, the older the individuals, the higher the relative contribution of P. oceanica to the diet. Our results and former studies of carbon stocks and fluxes in the P. oceanica bed of Revellata Bay have enabled an estimation of the general impact of S. salpa grazing on infralittoral communities: the studied species consumes 24 g C.m^-2 -a^-1 from P. oceanica leaf, 4.8 from epiphytes and 13 from epilithic algae. The fish net production and biomass turnover in that zone have been estimated to be 1.2gC.m^-2.a^-1 and 1.5 a^-1, respectively.     

Patterns of Posidonia oceanica (L.) Delile Beds around the Island of Ischia (Gulf of Naples) and in Adjacent Waters

Abstract. Posidonia oceanica prairies have been studied and mapped around the Island of Ischia and in adjacent waters. Prairies were found to cover an area of 15.7 km² and to be distributed between 0.5 and 39 m depth. The observed distribution is comparable to those reported by previous authors indicating that prairies have not undergone remarkable regressions in the last 50 years. Patterns recorded within the beds and at their lower limits, as indicated also by their sediments characteristics, are correlated to hydrodynamic energy. Two main types of water motion are responsible for the different types of erosive features: a) steady currents flowing parallel to the coast; b) rip-, wave induced currents flowing normal to the coast.     

Nitrogen Assimilation and Partitioning in the Mediterranean Seagrass Posidonia oceanica

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 H^sat, (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.     

Fragmentation as a Strategy for Caulerpa Species: Fates of Fragments and Implications for Management of an Invasive Weed

Abstract. The successful growth of fragments to full size macroalgal clones is well known for many taxa in mariculture. From an ecological context, however, few studies relate success by invasive species to the ability to fragment readily, disperse widely or re-attach rapidly - obvious hallmarks of weedy species. This study compares morphologically and ecologically distinct species of the green alga Caulerpa : in the Mediterranean, Caulerpa taxifolia is well known as an invasive weed; Caulerpa prolifera grows around or inside seagrass beds and is not apparently invasive; Caulerpa verticillata is among the most diminutive species, with potentially the most restricted reef distribution. We tested three hypotheses: (i) fragment success is independent of size, (ii) fragment success is independent of position within the plant and (iii) fragments from all species will be equally successful in establishing rhizoids, the first step to re-attachment. The success of small fragments (5–40 mm lengths) cut from distinct locations within replicate plants was scored for survival and establishment of rhizoids in bioassays. Additionally, for C. taxifolia , estimates were made of the force needed to puncture upright and prostrate axes, thereby estimating forces required to generate fragments from these two sources. Among the three species, only upright axes of C. taxifolia readily recovered from fragmentation stress for fragment sizes > 10 mm. The forces required to fragment upright axes were substantially less than for comparable rhizome portions. Fragments of C. prolifera were viable only for rhizome portions; fragments of C. verticillata were not viable at any size examined in this study. Estimates of viable fragment size, origin and force required to fragment axes for C. taxifolia support existing field data suggesting that fragmentation is the effective propagation mechanism underlying the spread of this invasive weed.     

Spatio-Temporal Distribution of Algal and Animal Communities in a Posidonia oceanica Meadow

Abstract. Investigations were carried out in a Posidonia oceanica meadow at Ischia (Gulf of Naples) along a depth gradient from 1 to 32 m in November 1979 and May 1981.
In these two months, different discontinuities were found at the sampling stations (1, 5, 10, 20, 30 m) at 10 m for leaf features, between 1 and 5 m for the algal community and the vagile fauna. The leaf features (length, surface, and biomass) along the transects show a delay in leaf production toward the deeper stations, below the thermocline.
The algal community shows in both seasons and in all stations a persistence of an encrusting layer, mostly represented by Corallinaceae and the brown alga Myrionema orbiculare , while at the shallowest station (1 m) the community is characterized by a more developed upright layer.
The vagile fauna of the leaf stratum, mostly represented by Polychaeta, Mollusca , and Crustacea (Peracarida and Decapoda) , shows a consistent zonation in both seasons along the transect. A superficial community at I m, characterized by a low number of species and individuals and specialized for high environmental energy levels, and a deeper community, persistent in time and more strictly related to the Posidonia oceanica meadows, are identified.
The influence of environmental factors and the importance of meadow structure for the zonation of the algal and animal communities are discussed.     

GEOCHEMISTRY OF ABYSSAL SEDIMENT IN THE PACIFIC OCEAN

The contents of Fe, Mn, Cu, Co, Ni, Pb and Zn in the seaiment associated with manganese nodules from the Northern Central Pacific Ocean and in their acid-soluble fractions were determined and correlations among the elements and between the trace metals and environmental parameters were discussed. It has been found that the contents of Mn, Cu and Ni in the sediment are one order of magnitude higher than those in the common sediment. As shown in the manganese nodules, they may mainly derive from seabed. The contents of all trace metals in the sediment are obviously governed by Fe-and Mn-oxides, organic matter, seawater depth, particle size and Eh. Multi-element correlation equations were developed for all trace metals. The trace metals in acid-soluble fraction of the sediment were also much higher than ihose of common sediment and negatively correlated with water depth, implying the possible influence of carbonate speciation.     

Habitat and Microhabitat of Mediterranean Clingfishes (Teleostei: Gobiesociformes: Gobiesocidae)

Abstract. This study addresses the habitat and microhabitat of the seven species of gobiesocid fish in the Mediterranean Sea. It is shown that Lepadogaster lepadogaster is closely adapted to large pebbles and boulder fields of rounded stones with a smooth surface. L. candollei is more euryecious and, in addition to inhabiting boulder fields also, occurs close to seagrass meadows, in small cavities and in association with sea urchins. Diplecogaster bimaculata is also euryecious and extends to greater depths. It lives on sand and muddy bottoms as well as on coralline grounds. At some locations this species is found in high abundance during the spawning season under empty bivalve shells or flat stones. Apletodon dentatus is the rarest species of Gobiesocidae in the Mediterranean Sea. It has a close association with seagrass or large brown algae ( Cystoseira ). Juveniles of A. incognitus are either associated with sea urchins or inhabit Posidonia meadows. Adults prefer the vicinity of seagrass meadows under empty bivalve shells and stones overgrown with red algae. Gouania wildenowi is stenoecious and is restricted to the interstices of roundish coarse gravel near the waterline. Opeatogenys gracilis is also stenoecious and lives only on the leaves of Posidonia and Cymodocea seagrass. The colourations of the different species and their variations are described and discussed.