Sandy Sea Bottom Research Articles

Large tsunamis reset growth of massive corals

Corals at Ishigaki Island, Japan, are characterized by their high species diversity. Not only are they struck by storm waves generated annually by typhoons, the corals, especially the massive ones, in the fringing reef were buffeted by huge tsunami waves with a run-up height of ca. 30 m in 1771 Meiwa tsunami and its predecessors at few hundred-year intervals. We present field survey and numerical results demonstrating that such near-field large tsunamis could have reset the growth of massive corals, a phenomenon which large typhoons have not caused. Our field survey revealed that the massive corals in the lagoon are not attached to the bedrock but are instead located on the sandy sea bottom. Therefore, those are movable of sufficiently large wave inundated in the lagoon. Our numerical results further showed that the maximum velocity of the tsunami at the reef edge, calculable as < 21.2 m/s at the study area, is still high in the shallow lagoon, perhaps generating sufficiently strong hydrodynamic force to devastate the massive corals in the shallow lagoon entirely, as well as some presumed damages on tabular and branching corals on the reef crest and reef slope. This numerical result is consistent with the observed fact that even a 9-m long Porites boulder (about 220 t) was cast ashore by the 1771 tsunami. The sizes of the presently living massive corals of Porites spp. are consistent with our hypothesis that they started to grow after the latest 1771 tsunami event. At the coral reefs of high tsunami-risk countries, severe destruction of corals by large tsunami waves should be considered for their growth history because, depending on the bathymetry, coral characteristics, and tsunami hydrodynamic features, tsunamis can radically alter coral habitats.

A thermogenic hydrocarbon seep in shallow Adriatic Sea (Italy): Gas origin, sediment contamination and benthic foraminifera

Gaseous and liquid hydrocarbons are seeping from sandy sea bottom ∼10 m deep, about 2.4 km NNE of Civitanova Marche harbour, in central Adriatic Sea (Italy). We investigated the origin of the gas, the presence of a wide range of aromatic and aliphatic hydrocarbons and trace metals in shallow sediments, as well as the stable carbon and oxygen isotope composition of benthic foraminifera. In absence of detailed seismic images and subsurface geochemical data, we tried to estimate the source rock type and maturity based only on seep gas geochemistry. Molecular and isotopic composition of gas bubbles showed that the CH4-rich gas is thermogenic (δ13CCH4∼ −55‰; δ2HCH4∼ −280‰; C1/(C2 + C3) < 100) with isotopic features that are compatible with low maturity source rocks belonging to the Emma-Scaglia (carbonate source rocks) Petroleum System (Upper Trias to Paleocene). Gas could then be stored in a biodegraded hydrocarbon pool, as suggested by 13C enrichment in propane (δ13C3: −24‰) and CO2 (δ13CCO2: +12‰). Fluid seepage might be due to a local fracture zone corresponding to the intersection of NNW–SSE thrust faults with a NE–SW regional transversal deformation belt. Compared to other shallow marine seeps in Europe, the amount of methane released into the atmosphere is negligible (102–103 kg of CH4 per year); but the seep also releases ethane and propane (103–104 L per year), which are photochemical pollutants and are not emitted by microbial gas seeps. Compared to a reference site one nautical mile far from the seep, the seabed sediments show higher concentrations of various classes of chemicals, such as benzene, toluene and ethylbenzene, semivolatile and non volatile aliphatic hydrocarbons (C10–C40), and phenols (2-methylphenol and 2,4-dichlorophenol). These compounds likely derive from the oil seepage. The sediments at the seepage site and those at the reference site have similar concentrations of trace metals (arsenic, barium, cadmium, chromium, copper, iron, manganese, nickel, lead, vanadium, zinc, mercury), typical of uncontaminated and shallow coastal areas. Finally, we provided the first data on foraminifera associated to thermogenic hydrocarbons. No endemic foraminifera species or authigenic carbonates occur in the sediments. Carbon isotopic composition of Quinqueloculina padana where oil slick prevails is less variable than in the gas bubbling site. However, thermogenic methane and oil do not apparently decrease the δ13C value of foraminifera carbonate shell.

Preservation of hanging aeolian deposits in insular karst depressions: Sediment sources and implications for the Pleistocene palaeogeography of the SE Adriatic archipelago

This study examines how and why the accumulation and preservation of aeolian sands are influenced by the character of karstic basement landforms. The studied examples are Late Pleistocene aeolian sands and underlying karstified carbonates of Southeastern Adriatic islands. To address this issue the spacial relationship between karstified bedrock and aeolian cover, aeolian and associated fluvial facies, as well as the petrography of sands, including heavy minerals and bioclasts (especially foraminifera) have been studied. Specific landforms of the carbonate basement originated as a consequence of deformation, karstification and locally with additional influence of fluvial processes. They are located at different elevations above today’s sea-level, as well as above ancient sand pathways towards the islands, which are now below sea-level. The karst depressions critically influenced the accumulation and preservation of aeolian sands. The depressions represented traps for accumulation and shelters for preservation of these sands. The closed type karst depressions include large examples which contain successions displaying the most complete stratigraphic record, located in the approximate centre of the depression. The open type karst depression is characterised by a partial removal of sands which were exported down-valley. The complex arrangement of the islands and closely located mainland coasts governed the location of primary sand transport paths. They included both aeolian and marine transport depending on the extent of exposed land versus submerged areas related to sea-level fluctuation. Marine settings along the sand pathways included shallow, sandy sea bottoms partly covered by sea-grass, as well as sand beaches and restricted environments. From low inter-island areas which hosted the primary sand pathways, the sands were uplifted and deposited over the islands by wind action thus producing hanging aeolian accumulations. The most influential Pleistocene winds responsible for sand transport over ancient land surfaces were from the SE and E. They were also the main factor for generating marine currents responsible for sand transport in the shallow sea and along the beaches. Only close to the mainland coast, strong N to NE winds dominated.

Optimal dynamics of soft shapes in shallow waters

A sandy sea bottom is seen as a structure with low stiffness which adapts to the motion of water in a shallow domain described by the Saint Venant equations. The coupling is based on the minimization of water wave energy with minimal sand transport. The approach is shown being similar to the use of an original Exner equation for the bottom with non local flux expressions. Also, examples of the applications of the framework to inverse problems in coastal engineering are shown.

Low-frequency sound speed and attenuation in sandy seabottom from long-range broadband acoustic measurements

A joint China-U.S. underwater acoustics experiment was conducted in the Yellow Sea with a very flat bottom and a strong and sharp thermocline. Broadband explosive sources were deployed both above and below the thermocline along two radial lines up to 57.2 km and a quarter circle with a radius of 34 km. Two inversion schemes are used to obtain the seabottom sound speed. One is based on extracting normal mode depth functions from the cross-spectral density matrix. The other is based on the best match between the calculated and measured modal arrival times for different frequencies. The inverted seabottom sound speed is used as a constraint condition to extract the seabottom sound attenuation by three methods. The first method involves measuring the attenuation coefficients of normal modes. In the second method, the seabottom sound attenuation is estimated by minimizing the difference between the theoretical and measured modal amplitude ratios. The third method is based on finding the best match between the measured and modeled transmission losses (TLs). The resultant seabottom attenuation, averaged over three independent methods, can be expressed as alpha=(0.33+/-0.02)f(1.86+/-0.04)(dB/m kHz) over a frequency range of 80-1000 Hz.

Marine electrical resistivity tomography for shipwreck detection in very shallow water: a case study from Agropoli (Salerno, southern Italy)

A marine electric resistivity survey was carried out over a submerged beach along the Agropoli shore (Salerno, Italy) to detect buried objects of archaeological interest below the sandy seabed. We found a shipwreck, a military vessel that probably sunk during the Salerno landing operations of the allied forces in the Second World War. Resistivity data provide information on the vertical and horizontal extension of the shipwreck, which is characterized by very low calculated resistivity values (about 2–5 ohm m). Such values differ significantly from the sand and the bedrock values (5–40 ohm m). Although the presence of the shipwreck is clearly visible from geoelectric data, the joint application of electric, magnetic and multibeam bathymetric techniques reduces the ambiguities inherent in each method. As shown in the Electrical Resistivity Tomography (ERT) and confirmed by the Digital Elevation Model (obtained from the processing of bathymetric data), the shipwreck extends more than 30 m in NE–SW direction and it is about 13 m wide. The global extension of the relic is consistent with the magnetic data, that are characterized by a magnetic anomaly with an amplitude of about 1800 nT and similar dimension, as inferred from the estimation of source boundaries obtained from the computation of the analytic signal. The results of our survey encourage the use of marine geoelectrical methods for the detection of buried archaeological targets, particularly in locations where the use of seismic prospecting is not effective (e.g. very shallow water with sandy sea-bottoms). The integration of different geophysical methods allows to better define the extension, depth and thickness of buried objects, suggesting that such an approach is the most effective for underwater archaeological investigations.

Low-frequency geoacoustic model for the effective properties of sandy seabottoms

The debate on the sound speed dispersion and the frequency dependence of sound attenuation in seabottoms has persisted for decades, mainly due to the lack of sufficient experimental data in the low-frequency (LF) to high-frequency speed/attenuation transition band. This paper analyzes and summarizes a set of LF measurements in shallow water that have resulted in the identification of nonlinear frequency dependence of sound attenuation in the effective media of sandy seabottoms. The long-range acoustic measurements were conducted at 20 locations in different coastal zones around the world. The seabed attenuations, inverted from different acoustic field measurements and characteristics, exhibit similar magnitude and nonlinear frequency dependence below 1000 Hz. The resulting effective sound attenuation can be expressed by alpha(dB/m)=(0.37+/-0.01)(f/1000)((1.80+/-0.02)) for 50-1000 Hz. The corresponding average sound speed ratio at the bottom-water interface in the 50-600 Hz range is 1.061+/-0.009. Both the LF-field-derived sound speed and attenuation can be well described by the Biot-Stoll model with parameters that are consistent with either theoretical considerations or experimental measurements. A combination of the LF-field-inverted data with the SAX99, SAX04, and other high-frequency measurements offers a reference broadband data set in the 50-400 000 Hz range for sonar prediction and sediment acoustics modeling.

Rupert Riedl’s Path of Cognition

In 1944, at the age of 19, Rupert Riedl drafted a plan of the fields of research he intended to address during his future career. The sketch, still in existence today, included hydrobiology, morphology, evolution, theoretical biology, and cultural issues. He then proceeded to implement this plan and became one of Austria’s most influential biologists following WWII. This astonishing feat was based on an understanding of science as adventure and discovery, akin to the arts, that he had derived from adolescent readings of Jules Verne, Humboldt, and Goethe. In defending the holistic reasoning initiated by these early influences he later positioned himself frequently in contrast to the analytical and technology-driven biosciences, in a lifelong rebellion against what he characterized as reductionist and mainstream positions. Uncompromising in every regard, he was able to make genuine and lasting contributions to all the fields he had targeted. Rupert Riedl’s death in September of last year marked the end of a highly successful career as a Humboldtian explorer into multiple fields of biology, from underwater caves and sandy marches to jaw worms and human minds. Owing him a lot, I would like to sketch the most important feats of his “path of cognition,” a term he used for the acquisition of knowledge, especially in scientific discovery. Discovery was to be done at sea, preferably on board of ships that glide over deep-blue waters with elegantly curved sails. In the absence of ships, Riedl’s path took its course in the late 1940s with extensive field trips to the Mediterranean, which, still a student of zoology, he loved to call expeditions. Without any prior training in marine biology, in fact without ever having been to the sea at all, Riedl and his companions set their minds on the uncharted realms of submarine worlds. This was as much a conscious choice of scientifically untrodden (sub)terrain as it was a romantic rebellion against the limited possibilities of a marine biology based on material obtained by fishing and dredging. Using self-tailored diving gear and research equipment, the intrepid explorers of submerged habitats were able to collect new information, specimens, and rare film material, resulting in a large number of publications and eventually a field guide to the Adriatic Sea (1963). Despite being shooed away early on from the most highly reputed European marine biology institution of the time, the Stazione Zoologica di Napoli, Riedl became an internationally renowned marine biologist, equally contributing to marine ecology and to the systematics of marine organisms. Major achievements were his publications on marine caves (1966), sandy sea bottoms (Fenchel and Riedl 1970), and the dynamics of shore water movement (1971; Riedl et al. 1972). Soon Riedl’s attention turned to the exotic organisms living in these habitats, in particular to the fauna of the largely unknown phylum of gnathostomulida and their adaptations to highly specialized environments (e.g., 1969, 1970). The strong morphological tradition of the Zoology Institute at the University of Vienna, where he became an assistant professor in 1953, prompted him to study the detailed anatomy of these organisms. Attempts at classification soon found him pondering classical issues of morphology: bauplans, homology, homoplasy, and the principles of anatomical organization. The pervasive problems associated with the taxonomic use of morphological characters led him to consider the conditions of their evolutionary origins, and during his period as Kenan Professor of Zoology and Marine Sciences at the University of North Carolina, Chapel Hill (1968–1971), he worked out a detailed theory of morphological evolution. Again assuming a stance of rebellion against a dominant view, the sole importance of population genetics in neo-Darwinism, he used an idiosyncratic terminology that led many to disregard the resulting major volume, Order in Living Organisms, first published in German (1975), although the English translation (1978) by the paleontologist Richard Jefferies made it more palatable. This volume, his most seminal publication, summarized the key problems of phenotypic organization in organismal evolution and proposed a systems-theoretical extension to the neo-Darwinian

Broadband sound velocity and attenuation in sandy seabottoms in shallow water

A previous paper analyzed and reviewed low-frequency (LF) field measurements conducted at 17 locations in different coastal zones around the world, and indicated that the effective acoustic attenuation curves for sandy seabottoms, derived from different field characteristics at these locations, exhibited similar magnitude and nonlinear frequency dependence in a frequency range of 50–2000 Hz. [Zhou and Zhang, ‘‘Nonlinear frequency dependence of the effective seabottom acoustic attenuation from low-frequency field measurements in shallow water,’’ J. Acoust. Soc. Am. 117, 2494 (2005)]. This paper aims to report the sound velocity in sandy bottoms, derived from the LF field measurements. The resultant LF velocity ratio in the sandy bottom and in the water (at the water/bottom interface) is in a range of 1.04–1.08. Combining the LF field-derived sound velocity and attenuation with the benchmark data of bottom acoustic parameters at mid- to high frequency, obtained from the SAX99 [Williams et al, IEEE J. Ocean. Eng. 27, 413–428 (2002)], offers a reference data set of sound velocity and attenuation in sandy bottoms for a broadband of 50–300&amp;lt;th&amp;gt;000Hz. The broadband sound velocity data show a significant amount of dispersion. The attenuation data are robust enough to cast doubt on a universal assumption of a linear dependence of attenuation on frequency. [Work supported by ONR and CAS.]

Effects of Habitat Connectivity on the Abundance and Species Richness of Coral Reef Fishes: Comparison of an Experimental Habitat Established at a Rocky Reef Flat and at a Sandy Sea Bottom

Coral reef fish assemblages are widely recognized for the coexistence of numerous species, which are likely governed by both coral diversity and substratum complexity. However, since coral reefs provide diverse habitats due to their physical structure and different spatial arrangements of coral, findings obtained from an isolated habitat cannot necessarily be applied to fish assemblages in other habitats (e.g. continuous habitats). The aim of this study, therefore, was to determine by a field experiment whether habitat connectivity (spatial arrangement of coral colonies) affects abundance and species richness of fishes in an Okinawan coral reef. The experiment consisted of transplanted branching coral colonies at a 4 m×8 m quadrat at both a rocky reef flat and sandy sea bottom. Generally, the abundance of fishes was greater at the sandy sea bottom, especially for three species of pomacentrids, one species of labrids, one species of chaetodontids and two species of apogonids. Species–area curves showed that the species richness of fishes was significantly greater in the quadrat at the sandy sea bottom at 3, 6 and 9 months after the start of the experiment. The rate of increase in abundance of fishes per area was significantly greater in the quadrat at the sandy sea bottom over the study period. The results of rarefaction analyses showed that the rate of increase in species richness per abundance was significantly higher in the quadrat at the sandy sea bottom in the juvenile settlement period, indicating that the magnitude of dominance by particular species was greater at the sandy sea bottom habitat. Our findings suggest that habitat connectivity affects the abundance and species richness of coral reef fishes, i.e. the isolated habitat was significantly more attractive for fishes than was the continuous habitat. Our findings also suggest that the main ecological factors responsible for organization of fish assemblage at a continuous habitat and at an isolated habitat are different.

The Structures and Dynamics of Fish Communities in an Okinawan Coral Reef: Effects of Coral-based Habitat Structures at Sites with Rocky and Sandy Sea Bottoms

Although there have been many studies on ecological factors responsible for the organization of reef fish communities, most of the studies have focused on isolated habitats. However, findings from isolated habitats cannot necessarily be applied to fish communities in other habitats (e.g., a continuous habitat). In this study, therefore, we examined the structures of fish communities (abundance, species richness and species composition), and the dynamics of fish communities (seasonal changes in abundance, species richness and species composition) over a 2-year period in two different habitats (continuous habitat and isolated habitat) in an Okinawan coral reef. We established eight permanent quadrats (8 m × 8 m) on a rocky reef flat (continuous habitat) and rock reef patches surrounded by a sandy sea bottom (isolated habitat). The abundance and species richness of fishes such as pomacentrids, labrids, chaetodontids and acanthurids were greater in quadrats located in the continuous habitat, whereas those of blenniids, gobiids and mullids were greater in quadrats located in the isolated habitat. This caused marked differences between the fish community structure at the two sites. Seasonal and annual changes in fish community structure were relatively small at the continuous habitat site (>0.7 similarity based on Cπ index) but were large at the isolated habitat site (Cπ 0.65 in most sites), but these differences were large at the isolated habitat site (Cπ < 0.4). Our findings suggest that habitat structure (spatial arrangement of habitats) affects both spatial and seasonal differences in the reef fish community structure. The results also suggest that the main mechanisms underlying organization of reef fish communities in continuous and isolated habitats are different.

Distribution and abundance of thraustochytrids in different Mediterranean coastal habitats

Habitat, seasonality and species distribution of the marine fungoid protists, thraus- tochytrids, were investigated in a coastal area of the Ligurian Sea (NW Mediterranean). Three habi- tats (the sandy surf area, the middle of a 5 m seawater column, and its underlying sandy sea bottom) were monitored monthly for 1 yr. Thraustochytrids in the surf and sea-bottom sandy samples yielded average densities of 4.4 ± 4 and 6.1 ± 5.3 × 10 4 cells l -1 , respectively. In both sandy habitats, a similar seasonal trend was observed: the highest densities were recorded in late spring, while a significant drop in densities occurred during the autumn-winter period. In the water column, the density of thraustochytrids was much lower, 1.3 ± 1 × 10 2 cells l -1 and did not show significant seasonal varia- tions. A positive relationship between organic matter and thraustochytrid densities occurred in the sandy sea bottom. Among the nutrients assessed in the water column, only total phosphorus was related to variations of thraustochytrid densities. The 3 habitats analyzed showed marked differences in species number and assemblage. A higher number of species were found in the sandy sea bottom than in the sandy surf area and in the seawater column. The genus Thraustochytrium was the most abundant in the sandy bottom habitat. Among Thraustochytrium species, those characterized by spo- rangia with proliferation bodies were dominant. Species of the genus Schizochytrium, typically form- ing a cluster of sporangia, were dominant in the sandy surf area. Here, the possible ecological signif- icances of these species' features are discussed.

Sediment critical angle estimation via in situ acoustic measurements

The basic physics of sound penetration into ocean sediments is a current area of active research since a good understanding of this phenomenon is essential for designing sonar systems that can detect, localize, classify, and identify buried objects. The sound speed of the sediment is a crucial parameter since the ratio of sound speeds at the water–sediment interface determines the critical angle. Sediment sound speed is typically measured with core samples using high-frequency (100’s of kHz) pulsed travel time measurements. Simulations using Biot theory and taking into account sediment permeability have shown that there may be a significant frequency dependence to sediment sound speed in the range 1–100 kHz. Here, sediment sound speed and critical angle estimation are investigated through the analysis of in situ acoustic measurements. Acoustic energy in the frequency range 2–16 kHz was directed toward a sandy seabottom, and a buried 14-element hydrophone array measured the incoming signals. The critical angle is estimated by analyzing both the variations of the penetration ratios and signal arrival times versus frequency, burial depth, and grazing angle. The influence of bottom roughness and sonar beamwidth on the penetration ratio is also investigated.

Experimental results for detection of buried objects at low grazing angles

Extension of buried object detection sonar system concepts to include low grazing angle geometries (i.e., beyond critical angle) would provide useful gains in coverage rate, provided acceptably high detection probabilities can be maintained for sufficiently low probabilities of false alarm. Several experiments have recently been conducted at shallow water sites with sandy seabottoms near Elba Island, Italy, in order to study the acoustic backscattering characteristics of the seabed and buried targets in a range of grazing angles both above and below the nominal critical angle of the seabed. A parametric sonar with significant secondary frequency source levels in the range 2–16 kHz was used (the size of the targets yielded ka values also in the approximate range 2–16). Modeling results for buried objects have shown that subcritical insonification can produce relatively high monostatic echo levels, especially at lower frequencies where the evanescent field is strongest. Some results of the experiments are discussed which show promising SNR improvements for subcritical cases when the lowest parts of the frequency band are emphasized, in empirical agreement with the models.

Multivariate Analysis of Remains of Molluscan Foods Consumed by Latest Pleistocene and Holocene Humans in Nerja Cave, Málaga, Spain

Nerja Cave is a karstic cavity used by humans from Late Paleolithic to post-Chalcolithic times. Remains of molluscan foods in the uppermost Pleistocene and Holocene sediments were studied with cluster analysis and principal components analysis, in bothQandRmodes. The results from cluster analysis distinguished interval groups mainly in accordance with chronology and distinguished assemblages of species mainly according to habitat. Significant changes in the shellfish diet through time were revealed. In the Late Magdalenian, most molluscs consumed consisted of pulmonate gastropods and species from sandy sea bottoms. The Epipaleolithic diet was more varied and included species from rocky shorelines. From the Neolithic onward most molluscs consumed were from rocky shorelines. From the principal components analysis inQmode, the first factor reflected mainly changes in the predominant capture environment, probably because of major paleogeographic changes. The second factor may reflect selective capture along rocky coastlines during certain times. The third factor correlated well with the sea-surface temperature curve in the western Mediterranean (Alboran Sea) during the late Quaternary.

Sediment characteristics and colonization of soft-bottom benthos: a field manipulation experiment

A field manipulation experiment was carried out to test the effects of sediment characteristics (particle size and organic content) on colonization of soft-bottom benthos. Defaunated mud and sand in experimental trays were exposed at sub-tidal levels of two sites with sandy and muddy sea bottom, and retrieved monthly for examination of benthic composition. Seventy-eight out of the 107 species recorded, and 50% of the dominant species identified in the present study, were common in both the sand and mud trays. Classification analysis revealed higher faunal similarity of benthic composition in both sediment types within each of the two study sites. Results of three-way ANOVA (Sediment, Site and Time) showed that sediment effect was only significant for colonization of bivalves and gastropods, but not for polychaetes, amphipods, total species and individual numbers, or overall benthic diversity and evenness. This suggested that many of the benthic species can colonize both sediment types, and that factors other than sediment particle size and organic content may play a significant role in determining colonization of these species. The faunal composition of the same sediment type between sites was found to be different, indicating that the availability and abundance of benthic larvae/adults may be more important than sediment characteristics in determining benthic settlement. An increase in faunal similarity between mud and sand was observed over the study period, implying that the importance of sediment characteristics to benthic colonization decreased with exposure time.

Experimental Study on Ice Gouging

The pack ice drifts south along the east coast of Sakhalin and occupies completely the Okhotsk coast of Hokkaido. It is carried along by winds and watercurrents and continually reaches and leaves the shores, dependied on the wind direction. Sand beaches of the Okhotsk coast are the habitat of scallops and surf clam. Also, in some parts of the sea live a lot of littleneck clams. When the sea ice moves toward the shores, it gouges part of sandy sea bottom and transports the shells ashore.In addition, there are many shells that are crushed to death by ice floes. This paper clarified the mechanisms of ice gougingby model test.

Present state of the kelp bed creation techniques and an idea of maintenance free kelp bed creation

Social needs are changing from the environmental conservation to the enviroment creation. And the local development and the creation of amenity are desired for the coastal development plans. We are studying on a maintenance free technique for kelp bed creation for this purpose. From the results of litelature survey and interviews with the kelp reserchers, we suggested some ideas related to maintenance free kelp bed creation. Based on three presuppositions, kelp bed creation on sandy sea bottom, setting only kelp bed, and maintenance free, we discussed about how to select the suitable site and time, and also the design of the kelp bed structure in this paper.

Growth of Macro Brown Algae Ecklonia cava on Concrete Brocks Setted in Sandy Sea Bottom

Marine mac rophyte bed, especially, kelp forest consisting of Ecklonia cava is important for production of fishery resources and conservation of marine environmert.1. Populations of E.cava were recognised on no-sand-covered concrete brocks set tedat suitable place in sandy sea bottom.2. At projection on surface of corrcrete brocks, effect for survive of E. cava was observed.3. Adheric power of plants growing at projection was largere than those at flat area.4.Concrete brocks will be advantageous for artificial algal substratum;because of theier processablity, especially, favable size and form.

Réalisation de l'émissaire de la Salie au sud d'Arcachon

The sewage outfall at La Salie, near Arcachon (France), is the first pier of any size to be built on the Bay of Biscay. The pier is owned by S.I.A.C.R.I.B.A. (Syndicat Intercommunal du Bassin d'Arcachon) and was engineered by the Service de l'Equipement de la Gironde. Sea conditions are severe throughout the year and the entire length of the structure is often subjected to strong currents and breaking waves. The offshore part of the 800 m long sewage outfall consist of a 1.50 m diameter overhead steel pipe. The pipe discharges effluent from a paper pulp plant and sewage from neighbouring towns. It is supported every 36 m on steel piles deeply embedded in the sandy sea bottom. The project provides a good example of the use of jack-up barges, which offer a perfectly stable offshore working area and thereby enable construction work to be performed under severe conditions. The works were carried out by G.E.M. Hersent who subcontracted steel structure fabrication and pile driving to C.F.E.M. and Soletanche, respectively.