Legal protection is not enough: Posidoniaoceanica meadows in marine protected areas are not healthier than those in unprotected areas of the northwest Mediterranean Sea

Using the Conservation Index, which measures the proportional amount of dead matte relative to live Posidonia oceanica, we assessed the health of 15 P. oceanica meadows at a regional scale along the coast of Liguria (NW Mediterranean). These areas were characterized by different degrees of anthropization, from highly urbanized sites to marine protected areas. Two different scenarios were identified according to depth: in shallow zones, the health of P. oceanica meadows was related to the degree of anthropization along the coastline. In contrast, in deep zones, most meadows exhibited poor health, independent of both the degree of disturbance and the legal measures protecting the area. Working synergistically with the regional impact of increased water turbidity, local impacts from the coast were recognized as the main causes of the severe regression of most Ligurian P. oceanica meadows. We conclude that marine protected areas alone are not sufficient to guarantee the protection of P. oceanica meadows. We emphasize the need for a management network involving the Sites of Community Interest (SCIs) containing P. oceanica meadows.     

Algal blooms and climate anomalies in north‐east New Zealand,August ‐December 1992

A raphidophyte‐dominated phytoplankton bloom extended discontinuously along the northeastern coastline of New Zealand, from Bream Tail, north of Leigh, to the western coast of the Coromandel Peninsula from late August until December 1992. The bloom was associated with an “El‐Niño” phase of the Southern Oscillation, resulting in unusually cold sea temperatures. The dominant bloom species in the north was Fibrocapsa japonica and in the south Heterosigma akashiwo. Associated species included the coccolithophorid Gephyrocapsa oceanica and the naked form of the silicoflagellate Dictyocha speculum. By December, numbers of the armoured form of D. speculum had increased, as those of raphidophytes and coccolithophorids declined. Bioassays to test for shellfish biotoxins were negative and Artemia salina bioassays, indicators of ichthyotoxicity, were negative except for Heterosigma akashiwo cultures, isolated from Coromandel water samples.     

Temporal and depth distribution of microepiphytes on Posidonia oceanica (L.) Delile leaves in a meadow off Tunisia

A survey on the epiphytic microorganisms growing on Posidonia oceanica leaves was conducted along a depth transect along the coast of Eastern Tunisia (Mahdia). Samples were collected by SCUBA diving at depths of 3, 5, 10 and 12 m in July 2008 and January 2009. A total of 58 microepiphyte taxa were identified. Multivariate analyses revealed temporal and spatial variation of the abundance of epiphytic microalgae. Water motion, light availability, temperature and motility of species seem to be responsible of temporal and bathymetric variations of epiphytic microalgae. Unlike diatoms, dinoflagellates were more abundant in deep waters, suggesting that they are more vulnerable to hydrodynamics. The significant correlation between leaf area index and abundance of epiphytic species indicates that the phenological parameters of the host plant influence the abundance of the epiphytic microorganisms. Among the epiphytic dinoflagellates, our data showed a great number of potentially toxic species (Alexandrium minitum, Amphidinium carterae, Karenia selliformis, Coolia monatis, Karlodinium veneficum, Ostreopsis siamensis, Prorocentrum concavum, Prorocentrum minimum, Prorocentrum rathymum and Prorocentrum lima). These species were more abundant in the deep station under more sheltered conditions than found at inshore shallower stations, which are subjected to high water motion.     

夏季南海西部今生颗石藻

首次报道了南海西部上层水体今生颗石藻的物种组成、群落结构和分布。根据2007年9月在南海西部海域（11°—15°N,110°—114°E）32个站位采集的200m以浅208个颗石藻样品在偏光显微镜下的分析结果,研究了该海域颗石藻群落特征,并进行了颗石藻与环境因子的典范对应分析（CCA）。调查区共发现20种今生颗石藻,其...     

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.     

Modelling the cross-shore profiles of sand beaches using artificial neural networks

Abstract

Artificial neural networks (ANN) have been widely used successfully to solve coastal engineering problems. In this article, they are used to model the cross-shore profile of sandy beaches taking into account the possible effect of marine vegetation (Posidonia oceanica). Sixty ANNs were generated by modifying both the inputs and the number of neurons in the hidden layer. The best results were obtained with the following inputs: wave height perpendicular to the coast and the associated period and probability of occurrence, median sediment size, profile slope, and energy reduction factor due to P. oceanica. With these inputs and 10 neurons in the hidden layer, a mean absolute error of 0.22?m during training and 0.21?m during the test was obtained, which represents an improvement of 81.2% and 55.5% compared to models without and with P. oceanica.     

Geological history and petroleum system of the Mittelplate oil field, Northern Germany

The geological history of Germany’s largest and most productive petroleum accumulation, the Mittelplate oil field in Schleswig-Holstein (Northern Germany), is reconstructed by simulating the structural and thermal evolution along a 2D cross-section. The Mittelplate field is located at the western flank of the Büsum salt dome at the transition from the Schleswig-Holstein mainland to the German North Sea Sector. Organic geochemical data confirm the Lower Jurassic Posidonia Shale to be the predominant oil source rock in the Schleswig-Holstein area. The studied section is characterized by salt walls and salt domes built up by Permian evaporites. Reconstruction of the structural and thermal evolution of the Mittelplate field by means of basin modelling reveals the dominating influence of salt dynamics on the entire petroleum system: The development of secondary rim-synclines during salt rise provided accommodation space for the deposition of the Posidonia Shale as well as the deltaic Middle Jurassic reservoir sandstones. The rise of the nearby Oldenswort salt wall controlled the timing of maturation and petroleum generation during Cenozoic times. Hydrocarbon migration from the Posidonia Shale into the reservoirs occurred up-dip from the deeper subsiding rim-syncline into the structural trap with the Middle Jurassic reservoir sandstones pinching out at the flank of the Büsum salt dome. Along the modelled 2D section the field’s recent temperature field and its complex reservoir architecture are reconstructed.     

Experimental transplanting of Posidonia australis seagrass in Port Hacking, Australia, to assess the feasibility of restoration

Over the last 50 years, about one-third of the original area of the seagrass Posidonia australis has been lost from Port Hacking (Australia) due to anthropogenic impacts. To assess the feasibility of restoring these seagrass meadows, healthy Posidonia rhizomes were transplanted to four impact sites and one control site. Survival rates of transplanted shoots were monitored in situ bi-monthly for 16 months and, at the end of the experiment, rhizome growth, shoot growth, shoot production and growth architecture were assessed by harvesting tagged rhizomes. A total of 575 shoots were transplanted and after 16 months 650 shoots were present. Four of the five sites exhibited high survival rates in the short term (less than six months) but only two impact sites, Burraneer Bay (BB) and Red Jacks Point (RJP), and the control site (CS) survived to the end of the experiment. Total number of shoots increased by 61% at CS, tripled at BB, but decreased by 22% at RJP. Rhizome growth varied significantly between site, from 22.3 +/- 1.4 cm yr(-1) at BB to 9.1 +/- 1.0 cm yr(-1) at RJP. Shoot growth did not vary significantly between sites and was approximately 2-3 cm yr(-1). At BB and CS there was substantial colonisation of the surrounding substrate, with new rhizomes, orthotropic shoots and transitional shoots produced. Survival of transplants appeared to depend on whether the factors that had caused the original loss of Posidonia were still operating in the study area.     

Evolution of porosity and pore types in organic-rich,calcareous, Lower Toarcian Posidonia Shale

Low and high resolution petrographic studies have been combined with mineralogical, TOC, RockEval and porosity data to investigate controls on the evolution of porosity in stratigraphically equivalent immature, oil-window and gas-window samples from the Lower Toarcian Posidonia Shale formation. A series of 26 samples from three boreholes (Wickensen, Harderode and Haddessen) in the Hils syncline was investigated. The main primary components of the shales are microfossiferous calcite (30–50%), clay minerals (20–30%) and Type II organic matter (TOC = 7–15%, HI = 630–720 mg/gC in immature samples). Characteristic sub-centimetric light and dark lamination reflects rapid changes in the relative supply of these components. Total porosities decrease from 10 to 14% at Ro = 0.5% to 3–5% at Ro = 0.9% and then increase to 9–12% at Ro = 1.45%. These maturity-related porosity changes can be explained by (a) the primary composition of the shales, (b) carbonate diagenesis, (c) compaction and (d) the maturation, micro-migration, local trapping and gasification of heterogeneous organic phases. Calcite undergoes dissolution and reprecipitation reactions throughout the maturation sequence. Pores quantifiable in SEM (>ca. 50 nm) account for 14–25% of total porosity. At Ro = 0.5%, SEM-visible macropores¹ are associated mainly with biogenic calcite. At this maturity, clays and organic matter are not visibly porous but nevertheless hold most of the shale porosity. Porosity loss into the oil window reflects (a) compaction, (b) carbonate cementation and (c) perhaps the swelling of kerogen by retained oil. In addition, porosity is occluded by a range of bituminous phases, especially in microfossil macropores and microfractures. In the gas window, mineral-hosted porosity is still the primary form of macroporosity, most commonly observed at the organic-inorganic interface. Increasing porosity into the gas window also coincides with the formation of isolated, spongy and complex meso- and macropores within organic particles, related to thermal cracking and gas generation. This intraorganic porosity is highly heterogeneous: point-counted macroporosity of individual organic particles ranges from 0 to 40%, with 65% of organic particles containing no macropores. We suggest that this reflects the physicochemical heterogeneity of the organic phases plus the variable mechanical protection afforded by the mineral matrix to allow macroporosity to be retained. The development of organic macroporosity cannot alone account for the porosity increase observed from oil to gas window; major contributions also come from the increased volume of organic micro- and meso-porosity, and perhaps by kerogen shrinkage.