771 research outputs found
Rocky shore biotic assemblages of the Maltese Islands (Central Mediterranean) : a conservation perspective
No full textLimestone rocky shores constitute ca 90.5% of the 272km coastline of the Maltese islands. Only some 40% of this rocky coastline is gently sloping and easily accessible. Such shores are heavily impacted with 96% of the accessible coastline dominated by tourist-related or by maritime activities. We characterized the biotic assemblages of lowland Maltese rocky shores and tested the popularly held view that given the scarce variation in physical characteristics, such shores form a homogenous habitat. Belt transects were laid perpendicular to the shoreline from biological zero to the adlittoral zone on seven Coralline Limestone and one Globigerina Limestone shores. Cover (for algae and encrusting species) or population density (for animals except sponges) were estimated using 0.5m X 0.05m quadrats placed contiguously for the first few metres and then at regularly spaced intervals. Overall, 19 faunal and 47 floral species, and 10 faunal and 8 floral species were recorded from the Coralline and Globigerina transects respectively, with 60.8% faunal and 25.6% floral species common to the two substrata. Hierarchical clustering showed that the Coralline and Globigerina transects harboured distinct biotic assemblages and identified an upper shore assemblage dominated by the littorinid Melarhaphe neritoides and barnacles, and a lower shore assemblage dominated by algae and molluscs; a mid-shore transition zone where certain species from both assemblages reached peaks of abundance was present in almost all Coralline and the majority of Globigerina transects. Differences in biota between the two types of shore are most likely primarily related to differences in microtopography and, to a lesser degree, to exposure. It is concluded that in spite of gross physical similarity, Maltese lowland rocky shores are biotically inhomogeneous, making conservation of individual sites much more important than previously thought.peer-reviewe
The biogeography and biodiversity of the Namibian intertidal seaweed flora
No full textBibliography: leaves 149-160.There have been very few intertidal studies carried out on the Namibian coast. With respect to seaweeds in particular there have been a number of species lists and shore descriptions, but very little research into the biogeography, diversity or ecology. One of the reasons for the lack of research is probably that much of the 1500 km coast is inaccessible. The coastline is relatively straight with few inlets or bays and comprises mostly sandy beaches, with few rocky shores. Estimates range from 5-16% of rocky shores for the total coast length, and as a result there is relatively little substrate on which seaweed can attach. The dominant current is the northward, slow-flowing Benguela current. Upwelling also occurs here due to long shore winds, which bring cool, nutrient-rich water to the surface. In this study the Namibian coast was divided into three regions, largely governed by accessibility to the coast, viz. southern, central and northern Namibian. Most of the Namibian coast is subject to severe wave action, as a result wave-exposed shores were predominantly chosen. The degree of wave exposure was determined by the degree to which the site was open to the ocean. Sites that were completely or largely protected from incoming swells were not included. Three sites in the southern region were semi-exposed, in that they occurred within relatively large bays and were partially protected from dominant winds, they were however relatively exposed to the open ocean. Two to three transects lines were taken on each shore, along which quadrats were sampled at regular intervals. The material was taken back to the laboratory, sorted and analysed. Multivariate techniques were used as diagnostic tools in the interpretation of the data. Detailed seaweed species data were collected from all samples (biomass of individual species as well as general species collections), while data on major sessile invertebrate groups and amount of sand were also collated
Bioerosion on the small scale – examples from the tropical and subtropical littoral
No full textThe purpose of this paper is to provide a practical guide assisting field workers in identification and interpretation of bioerosional textures created in limestone and other substrates by intertidal organisms. We provide examples of living, dead, and subfossil bioerosional agents and their corresponding traces. The discussion follows taxonomic order of bioerosional agents, rather than morphologic classification of their effects on the rock substrate. Traces left by sponges, molluscs (chiton Acanthopleura, limpets and various gastropods, bivalves Lithophaga and Tridacna, wood-boring bivalves), worms, echinoid Echinometra, and other taxa are illustrated. Features created by a distinct group of organisms but exhibiting excellent, average, and poor levels of preservation are displayed alongside each other to help identification under suboptimal conditions. We also show composite textures resulting from successive or coeval overlapping traces, and offer examples of pseudo-bioerosional features reminiscent of organism traces but created by physical processes
Littoral drift computations on mutual wave and current influence
No full text11th Conference on Coastal Engineering in London 1968, the author presented a method for computing the littoral drift starting from the longshore current velocity as this is generated by the waves and with the assumption that the material is stirred up by the waves. In this paper measurements in a model basin are described by which the procedure is further tested. A comparison with littoral drift rates computed by this procedure and derived from accretion and erosion rates along the coast of Queensland (Australia) are presented. For a hypothetical coast the littoral transports with varying bed roughness are computed. The influence of this roughness on the assumptions forming the basis of the computation procedure is discussed.Hydraulic EngineeringCivil Engineering and Geoscience
Scour underneath submarine pipelines
No full textThis report deals with the physical experiments on scour underneath submarine pipelines, carried out as part of the MaTS project on the stability of submarine pipelines. Moreover, these experiments, which have been carried out in the laboratory for fluid mechanics of the Department of Civil Engineering of the Delft University of Technology, are the topic of the student thesis of the author, who has been joining the Group of Coastal Engineering as a student assistant. His work has been accompanied by ir. W. Leeuwestein. Prof.dr.ir.E.W.Bijker was the supervisor of the entire project on the stability of pipelines. After the introduction in chapter 2, in chapter 3 a summing up is given of the previous research on the subject and the theory needed to approach the problem of the scour process underneath pipelines. In the following chapter a description is given of the way in which the experiments have been carried out. Chapter 5 gives the results of the experiments and using the results a functional relation has been tried to find between the scour depth on the one hand and the flow, pipe and sand parameters on the other hand. In chapter 6 the use of physical experiments to predict prototype scour depths is discussed by studying the concerning scale relations. This thesis ends with some conclusions.Civil Engineering and Geoscience
Sediment concentration and sediment transport due to action of waves and a current
No full textCivil Engineering and Geoscience
Offshore sediment transport and equilibrium beach profiles
No full textCivil Engineering and Geoscience
Zandwinning in de Noordzee
No full textHet hoofdontwerp vormt een studie naar de invloed van een verdieping van de zandbodem op de stabiliteit van de kust. Dit wordt gedaan ter hoogte van IJmuiden.Hydraulic EngineeringCivil Engineering and Geoscience
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