Depth and Seasonal Distribution of Some Groups of the Vagile Fauna of the Posidonia oceanica Leaf Stratum: Structural and Trophic Analyses

Abstract. The taxonomical and trophic structures of the vagile fauna communities of the leaf stratum in a Posidonia oceanica meadow at Ischia (Gulf of Naples, Italy) were investigated at five stations along a depth gradient (1 to 25 m). Sampling was performed in July, November, February, and May. The analyzed groups - polychaetes, molluscs, tanaids, isopods, amphipods, and decapods - exhibited similar distributional trends in all seasons, with coenotic discontinuities occurring at well-defined depths. The same zonation pattern was produced by feeding-guild analysis. Eleven trophic groups were identified. The most abundant groups were: Herbivores, which were found mainly at the shallow stations; Herbivores-deposit feeders, which were widely distributed along the transect; Deposit feeders-carnivores, found mainly at the deep stations.
This study suggests that in the Posidonia leaf stratum, herbivores and herbivores-deposit feeders, as consumers of epiphytic micro- and macroflora and deposited particulate organic matter, play an important role in the energy transfer from producers to higher trophic levels of the system.     

Structure of the Epiphytic Community of Posidonia oceanica Leaves in a Shallow Meadow

Abstract. The structure of the epiphytic community (hydroids, bryozoans, and the most abundant macrophytes) of Posidonia oceanica leaves in a shallow meadow near Lacco Ameno, Ischia was studied. The structure of the community changed along an age gradient that extended from the inner to the outer leaves and from the basis to the apex of each leaf. This structure was also affected by microclimatic factors. The dynamics of community "maturation" is described.     

The Zonation of Epiphytic Hydroids on the Leaves of Some Posidonia oceanica (L.) DELILE Beds in the Central Mediterranean

Abstract. The vertical zonation of the hydroid fauna associated with Posidonia oceanica leaves in three different localities of the central Mediterranean reveals the presence of two distinct communities. This depth-related zonation shows patterns that are independent on the geographic area.     

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.     

Occurrence of Spadella cephaloptera During One Year at Ischia Island (Gulf of Naples)

Abstract. The life cycle of the benthic arrowworm, Spadella cephaloptera , which inhabits the Posidonia meadow at Ischia (Gulf of Naples, Italy), was examined by a one-year systematic sampling survey and by laboratory culture. The seasonal fluctuations in abundance and the reproductive characteristics indicate that there were two generations of S. cephaloptera in one year; these generations have a different life span. The habitat of S. cephaloptera depends on the growth of the Posidonia meadow; the influence of different factors on the S. cephaloptera population, especially of the Posidonia vagile fauna, is discussed.     

Fish Assemblages of Posidonia oceanica Beds at Port-Cros (France, NW Mediterranean): Assessment of Composition and Long-Term Fluctuations by Visual Census

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.     

Study of a Crustacea Decapoda Taxocoenosis of Posidonia oceanica Beds from the Southeast of Spain

Abstract. During 1986 and 1987 a decapod crustacean taxocoenosis of Posidonia oceanica beds from the southeast of Spain has been studied.
Data on abundance-dominance of the 50 species found and other information such as reproduction and the selective use of gastropod shells by the dominant hermit crabs arc given.
Differences in richness and cquitability between shallow (3–4 m) and deeper (5–7 m) samples arc also shown.
The taxocoenosis presents a geometrical distribution in which only 9 species have a relative abundance higher than 1 % and in which the structure is basically controlled by the two dominant hermit crabs, Cestopagitius limidus and Calcium tubularis , and hydrodynamic conditions.     

Heavy Metal Contents in Soft-Bottom Marine Macrophytes and Sediments Along the Mediterranean Coast of Spain

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 .     

A Map of the Posidonia oceanica Beds of Marina ďElbu (Corsica, Mediterranean)

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.     

Respiratory Rate and Assessment of Secondary Production in the Holothuroid Holothuria tubulosa (Echinodermata) from Mediterranean Seagrass Beds

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.     

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.     

Primary Production and Growth Dynamics in Posidonia oceanica

Abstract. Studies on leaf growth and production were performed in two stands, at depths of 5 m and 22m, in the Posidonia oceanica (L.) D elile bed off Lacco Ameno, Ischia (Gulf of Naples). Experiments were carried out in situ from May 1988 to August 1989 at monthly intervals.
Leaf growth and production profiles differed in the two stands investigated. Growth rates were higher at 5 m, with a peak in autumn (5.8 mg · shoot^-1· d^-1) and another in March (3.8 mg · shoot^-1· d^-1). At 22 m the maximum rate occurred in May (3.9 mg · shoot^-1· d^-1). These differential growth rates resulted in a delayed maximum leaf surface and biomass at the deep stand, where lower irradiance values and different temperature patterns were also found. The biomass of epiphytic algae showed trends similar to those of leaves; however, there were remarkable differences in the values between the two stations and for the two investigated years.
The production data of the present study are compared with those of other reports, and it is shown that growth processes are greatly influenced by physical factors.     

Biometry, Bathymetric Distribution, and Reproductive Cycle of the Holothuroid Holothuria tubulosa (Echinodermata) from Mediterranean Sea grass Beds

Abstract. Holothuria tubulosa individuals were sampled regularly at three different depths (6, 19, and 33m) over a 20-month period in a Posidonia oceanica meadow off Ischia Island (Italy). Biometrical analysis demonstrated that holothuroids have a well-marked size-related distribution according to depth, with the smallest individuals in the shallowest part of the meadow and the large ones in its deepest part. The observed distributions reflect the ability of H. tubulosa to grow more efficiently in areas of low water turbulence where Posidonia shoots are scattered and detrital food is more easily accessible. Recruitment takes place in the shallow meadow, and holothuroids with high reproductive potential only occur in the deep meadow. Small holothuroids (shallow individuals of similar sizes) may be either juveniles or sexually mature individuals; environmental constraints apparently restrict the growth of individuals and their gonads. There is a progressive downward migration of growing individuals when the whole population is considered, although at the level of the individual the migration occurs randomly. Accordingly, the size of a sexually mature individual is more a function of its past history in the meadow than of its real age.     

Study and Cartography of the Benthic Communities of Medes Islands (NE Spain)

Abstract. A bionomic study and cartography of the benthos of Medes Islands (NE Spanish coast, Catalan Costa Brava) is presented. From 1977 to 1980 the fauna and flora of the meso- and macrobenthos were sampled by a triple sampling procedure: standard, visual and photographic samples were simultaneously taken along underwater transects, yielding 124 punctual inventories, 176 visual inventories and some 1000 photographic "samples". These, together with the floristic and faunistic study of each algal and invertebrate group, served as the basis for the bionomic survey of the islands' bottoms. In a first approach, the hard substrata of the infra- and circalittoral Stages were studied, along with the Posidonia meadows, and their communities diagrammatically sketched along representative transects. Further work focused on the submarine caves and tunnels of the area, the supra- and mediolittoral communities and the coastal detritic soft bottoms. The bionomic survey of the Medes Islands has emphasized, with minor differences, the basic similarity between the archipelago's benthic communities and those described elsewhere in the Northwestern Mediterranean. The identified communities or groups of communities are the trottoir, the photophilic algae, the sciaphilic algae (precoralligenous), the coralligenous and cave communities on hard substrata, as well as the Posidonia meadow and the coastal detritic community on soft substrata. These have been used as the basic macro-units in the bionomic cartography of the islands, which has been plotted on a 1:2000 map. Their distribution, over a surface area of some 2 km² and to a depth of up to 60–70 m, follows that of the heterogeneous substrate, its slope and the hydrodynamical and illumination conditions of the area.     

Spatio-temporal variation in the structure of a deep water Posidonia oceanica meadow assessed using non-destructive techniques

The Malta‐Comino Channel (Maltese islands, central Mediterranean), supports extensive meadows of the seagrass Posidonia oceanica that in some places extend to a depth of around 43 m, which is rare for this seagrass. To assess spatial and temporal variation in the state of the deeper parts of the P. oceanica meadow with time, data on the structural characteristics of the seagrass meadow at its lower bathymetric limit were collected during the summers of 2001, 2003 and 2004 from four stations (two stations within each of two sites) located at a similar depth, over a spatial extent of 500 m. Shoot density was estimated in situ, while data on plant architecture (number of leaves, mean leaf length, and epiphyte load) were successfully obtained using an underwater photographic technique that was specifically designed to avoid destructive sampling of the seagrass. Results indicated that P. oceanica shoot density was lower than that recorded from the same meadow during a study undertaken in 1995; the observed decrease was attributed to the activities of an offshore aquaculture farm that operated during the period 1995–2000 in the vicinity of the meadow. ANOVA indicated significant spatial and temporal variations in meadow structural attributes at both sites during the 3‐year study; for example, shoot density values increased overall with time at site A; a indication of potential recovery of the meadow following cessation of the aquaculture operations. Lower shoot density values recorded from site B (compared with site A) were attributed to higher epiphyte loads on the seagrass, relative to those at site A. The findings, which include new data on the structural characteristics of P. oceanica occurring at depths >40 m, are discussed with reference to the use of the non‐destructive photographic technique to monitor the state of health of deep water seagrass meadows.     

Use of Posidonia Oceanica Ash in Stabilization of Expansive Soils

Posidonia oceanica (PO) is the most plentiful seaweed of the Mediterranean Sea, which grows all along the coastal areas, forming widespread meadows. The leaf rejuvenation process of Posidonia oceanica typically occurs in fall when an increase in wave action causes the dead seaweeds to be transported and usually piled up along the coastal areas. This paper investigates the effect of PO ash stabilization on behaviour of an expansive clay. The ash was obtained by combustion of crushed PO pieces in a muffle furnace at 550°C. Atterberg limits, linear shrinkage, particle size distribution, one-dimensional swell, and unconfined compression tests have been carried out on natural soil as well as soil mixtures with 5% and 10% PO ash. There has been no significant improvement in the soil properties with 5% ash inclusion, whereas 10% ash has noticeably reduced the swell amount and increased the compressive strength. It is therefore concluded that there is a potential for the use of PO ash in geotechnical engineering applications.     

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.     

Spatial scale variability in shoot density and epiphytic leaves of Posidonia oceanica on Kerkennah Island (Tunisia) in relation to current tide effects

A study was undertaken of the patterns of spatial variability, epiphytic biomass and distribution of epiphytic fauna and flora of Posidonia oceanica. Samples were taken at four stations located approximately 4 km apart, exposed to different current conditions. Stations A and B, situated near the Oued Mimoun tidal channel with its relatively strong bi‐directional flows, were affected by high current tide. The other two stations, North Oued Mimoun (L1) and South Oued Mimoun (L2), were located further from the channel, in low current tide conditions. Sampling was conducted in the Attaya area of Kerkennah Island (Tunisia) in August 2009 at depths between 2 and 3 m, with the results indicating differences among the stations. Shoot density decreased when exposed to high levels of hydrodynamic activity generated by current tides whereas the epiphytic biomass of P. oceanica leaves decreased at sheltered stations located far from the channel. Epiphytic algae such as Heterokontophyta, Rhodophyta and Chlorophyta, and epiphytic fauna represented by Bryozoa, Hydrozoa, Annelida, Porifera and Tunicata, dominated the epiphytic assemblages and were abundant at the station most exposed to high current tide hydrodynamics. Cyanobacteria, however, were dominant in stations exposed to low current tide.     

Seasonal variations in faunal distribution and activity across the continental slope of the goban spur area (NE Atlantic)

Density, biomass and community structure of macrofauna were estimated together with several sediment characteristics at seven stations ranging from 208 m to 4460 m water depth along the OMEX transect in the Goban Spur area (NE Atlantic) during three seasons (October 1993, May 1994, and August 1995). Median grain size decreased with increasing water depth and showed no differences between the seasons. The percentages of organic carbon and total nitrogen were highest at mid-slope depths (1000 to 1500 m), and were significantly higher in August at the upper part of the slope to a depth of 1500 m. The C:N ratio in the surface layer amounted to 7 to 8 in May, 10 to 12 in August and 14 to 17 in October at all stations (except the deepest at 4460 m, where it was 11 in May and August), indicating arrival of fresh phytodetritus in May, and therefore seasonality in food input to the benthos. Densities of macrofauna decreased exponentially with increasing water depth. Significantly higher densities of macrofauna were found in May at the upper part of the slope to a depth of 1500 m. These differences were mainly due to high numbers of postlarvae of echinoids at the shallowest station and ophiuroids at the deeper stations. Biomass values also decreased with increasing water depth, but biomass was relatively high at the 1000 m station and low at 1500 m, due to relatively high and low mean weights of the individual macrofaunal specimens. No significant differences in biomass were found between the seasons. Respiration was high (15 to 20 mgC·m⁻²·d⁻¹) in May at the upper part of the slope to a depth of 1000 m and low (1–3 mg C·m⁻²·d⁻¹) at the deeper part. At the shallowest stations to a depth of 1000 m respiration was highest in May, at the mid-slope stations (1400–2200 m) it was highest in August, whereas the deepest stations (3600 to 4500 m) did not show any differences in respiration rates. In conclusion; seasonal variation in organic input is reflected in denstiy, community structure and activity of the macrofauna along the continental slope in the NE Atlantic.     

Short-term response of the slow growing seagrass Posidonia oceanica to simulated anchor impact

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.