Phototoxicity of pyrene and benzo[a]pyrene to embryo-larval stages of the Pacific oyster Crassostrea gigas

There is a growing body of evidence to suggest that certain polycyclic aromatic hydrocarbons (PAHs) pose a greater hazard to aquatic organisms than previously demonstrated, due to their potential to cause photo-induced toxicity when exposed to ultraviolet (UV) radiation. The consequences of photo-induced toxicity are reported here for embryo-larval stages of the pacific oyster Crassostrea gigas, following exposure to pyrene and benzo[a]pyrene. During laboratory investigations, significant increases in toxicity were observed in the presence of environmentally attainable levels of UV-radiation, compared with embryos exposed to PAH alone, at levels previously deemed to have little acute biological effect. The phototoxicity of pyrene and benzo[a]pyrene completely inhibited the development to the D-shell larval stage when embryos were simultaneously exposed to 5 microg l(-1) PAH and ultraviolet light (UVB = 6.3 +/- 0.1 microW/cm2 and UVA = 456.2 +/- 55 microW/cm2). A linear relationship was also demonstrated for benzo[a]pyrene phototoxicity with decreasing UV light intensity.     

Uncertainty in predictions of oil spill trajectories in open sea

A method is introduced to calculate and to account for the uncertainties in the predictions of oil spill trajectories using a classic oil spill model. The method considers the output of the oil spill model as a function of random variables, which are the input parameters, and calculates the standard deviation of the output results which gives a measure of the uncertainty of the model given the uncertainties of the input parameters.Instead of a single trajectory that is calculated by the oil spill model using the mean values of the parameters, a band of trajectories can be defined when various simulations are done taking into account the uncertainties of the input parameters. This band of trajectories defines envelopes of the trajectories that are likely to be followed by the spill given the uncertainties of the input.The method is applied to an oil spill that occurred in open sea near Madeira Islands, in the Atlantic Ocean, in December 1989. The simulations allow the understanding of how a change in the wind direction drove the spill towards the Islands.The envelope of likely trajectories that is obtained with the uncertainty modelling shows a band of trajectories that is in better agreement with the observations than the single trajectory simulated by the oil spill model, based on mean parameters.     

GEBCO Centennial Special Issue – Charting the Secret World of the Ocean Floor: The GEBCO Project 1903–2003

This special issue of Marine Geophysical Researches presents five papers dealing with GEBCO, the General Bathymetric Chart of the Oceans, which celebrated its Centennial in April 2003, hosted by the International Hydrographic Bureau and the Principality of Monaco. Over the past 103 years GEBCO has been the sole body dedicated to compiling all available data to produce standardized maps of the oceans and seas covering 71% of planet Earth. Over time GEBCO has undergone a complete transformation as sparse 500 m contours on paper charts were replaced by digital grids with ever-increasing resolution. The 2003 Centennial saw the release on two CDROMS with the first global 1′ grid, produced by methods unheard of in 1984, when GEBCO’s last 6th Edition paper chart set was published. In GEBCO’s second century, the thrust is towards global grids that will capture the resolutions available with evolving deep-water swath mapping technologies, as well as vast improvement in the details of the shallow continental shelves that have traditionally been the preserve of the hydrographic community. As little more than 10% of the oceans have been mapped to the desired level of detail, there is much to be done. However refinements in satellite altimetry appear to offer an interim stop-gap as more multi-beam sonars ply the oceans and as the littoral countries of the world map their adjacent marine areas for submission under Article 76 of UNCLOS (United Nations, 1983, 1999). In addition GEBCO is becoming increasingly proactive, with outreach to the public via the internet and a new GEBCO Map of the World, active data-scrounging, and encouraging development of the first drifting buoys for acquiring data in the inaccessible areas of the Antarctic, SW Pacific, and Arctic Oceans.     

A 15-month study of zooplankton ingestion by farmed mussels (Mytilus edulis) in Bantry Bay, Southwest Ireland

There is a growing body of evidence to suggest that bivalve molluscs routinely ingest zooplankton. To elucidate further these observations, a 15-month study of zooplankton ingestion by farmed mussels was conducted using mussel long-lines in Bantry Bay, Ireland. Stomach content analysis of the mussels showed that there was evidence of zooplankton ingestion throughout the sampling period, but that highest mean numbers of zooplankters were ingested by mussels in the spring and summer months. Various zooplankton species were present in mussel stomachs. Harpacticoid copepods were found more often in stomach contents than calanoid copepods, probably due to their proximity to the bivalves' inhalent siphons. Barnacle cyprids featured in large numbers in stomach contents, but only for a period of 3 months which broadly corresponded with their pelagic phase. Sizes of ingested zooplankton ranged from 126 μm to 6 mm, but more of the smaller zooplankters (e.g. crustacean nauplii) were ingested. When lengths of ingested copepods were compared with those found in plankton net samples, it was found that the net-sampled copepods were significantly larger than those found in mussel stomachs, suggesting that mussels select for smaller categories within the zooplankton available to them. Soft bodied zooplankton was rarely found in mussel stomachs but their absence may be due to rapid digestion or they may have been destroyed in the preservation process. Ingestion of zooplankton by bivalves is discussed in the context of the impacts mussel farms have on resident zooplankton populations.     

Impact of urban stormwater runoff on estuarine environmental quality

Urban stormwater runoff could contribute to the deterioration of water quality of a receiving water body. In this research, field studies and laboratory experiments were conducted to assess the microbial contamination resulting from urban stormwater runoff into the Lake Pontchartrain estuary. Fecal coliform, Escherichia coli and enterococci were used as indicator organisms. The specific objectives of the research were to examine the distribution of the indicator organisms in different environmental elements (water column, suspended particles and sediment) and to further investigate the mechanisms related to their fate. Results of the research indicated satisfactory water quality at the study sites during dry weather periods. However, a significant increase was observed in the concentrations of the indicator organisms in the water columns and sediment at specific study sites following a given stormwater event. Three to seven days were needed for the elevated indicator organisms to return back to their background levels in the water column and sediment, respectively. The mechanism of sedimentation contributed to a reduction in the microbial concentration in the water column, as the indicator organisms were found to attach to the suspended particles in the stormwater. The percentage of fecal coliform, E. coli and enterococci attached to the suspended particles was found to be within the range of 9.8–27.5%, 21.8–30.4%, and 8.4–11.5% of the total indicator organisms in the stormwater loaded into the estuary, respectively. About 75–80% of the total indicator organisms remained free-floating for some distance in the water column before dying off.     

Path following control system for a tanker ship model

A two-dimensional path following control system for autonomous marine surface vessels is presented. The guidance system is obtained through a way-point guidance scheme based on line-of-sight projection algorithm and the speed controller is achieved through state feedback linearization. A new approach concerning the calculation of a dynamic line-of-sight vector norm is presented which main idea is to improve the speed of the convergence of the vehicle to the desired path. The results obtained are compared with the traditional line-of-sight scheme. It is intended that the complete system will be tested and implemented in a model of the “Esso Osaka” tanker. The results of simulations are presented here showing the effectiveness of the system aiming in to be robust enough to perform tests either in tanks or lakes.     

Time domain modelling of the transient asymmetric flooding of Ro-Ro ships

This work aims at contributing to improve knowledge on transient asymmetric flooding through theoretical and experimental research. First, a time domain theoretical model of ship motions and flooding is described. Results from experimental work are presented evidencing that transient asymmetric flooding may cause the capsizing of a Ro-Ro shaped barge. The theoretical model is used to predict the capsize of the Ro-Ro shaped barge. Reasonable agreement between experimental and theoretical results was found. Finally, a review of the European Gateway accident is given and the theoretical model is applied to the study of this type of accident. The conclusion is that this theoretical model, together with an accurate modelling of the flooding of machinery compartments, reproduces successfully the capsizing of the European Gateway due to transient asymmetric flooding. Therefore, the internal arrangement of Ro-Ro ships should be carefully studied at the design stage in order to avoid this phenomenon.