Stratigraphic framework of gas accumulations in the Ría de Pontevedra (NW Spain)

Knowledge of marine geological environments in which shallow gas is accumulating is becoming increasingly important in global studies of climate change because a measurable proportion of the total methane source comes from continental margins. Previous studies have revealed that coastal environments represent important geological environments where microbial methane is being generated, is accumulating, and is being released. In the Ría de Pontevedra, at least 4.5 km² of seafloor in the innermost part of the ría is underlain by sediments containing natural gas. Seismic interpretation contributes new findings for the definition of periods and geological environments in which the gas could have been generated, and is accumulating and released in the Ría de Pontevedra. Groundtruthing the seismic data (facies, environments) makes it possible to identify favourable geological environments for gas generation in the sedimentary infill of the Ría de Pontevedra. Sequence stratigraphy based on high-resolution seismic profiles and post-Last Glacial Maximum sea-level records makes it possible to establish the stratigraphic architecture of the ría and to define the periods in which gas could have been generated. The results of this study show that the sedimentary infill is composed of a fifth-order sequence developed since the Last Glacial Maximum. Within this sequence, gas appears to have accumulated in the Holocene deposits associated with the latest transgressive and highstand system tracts. Seismic analysis shows that gas could have been generated in different geological environments in the Ría de Pontevedra. If coastal environments at times of lower sea level were similar to those of the present, organic-rich mud deposits (deposited mainly in lakes, estuaries and floodplains) could have survived transgression and remained buried as potential gas sources in the inner part of the ría.     

Coastal vulnerability in barrier islands: The high risk areas of the Ria Formosa (Portugal) system

Coastal vulnerability in barrier island systems is extremely high. The barrier island shoreline is exposed to many threats, such as storm erosion, reductions in sediment longshore drift and sea level rise. Many of these threats to coastal areas, such as Ria Formosa, are likely to increase in the near future. The main objectives of the present study are to identify the areas in the system that are at most risk by assessing the evolution of the Ria Formosa barrier island system since the 1940s, and determine which interventions would be necessary to protect these areas.The coastal vulnerability of the system was assessed based on current literature, data available from official institutions, and aerial and terrestrial in situ examination. The results obtained for the evolution of the Ria Formosa coastal system reveal that there are several vulnerable areas that have very dynamic processes, such as extremely high evolution rates of islands and inlets. Human actions that affect the whole system, namely the construction of many physical structures, are the main cause of the instability. Moreover, as several stakeholders are involved, efficient management of the coastal system is imperative. Extensive and careful interventions are urgently needed to avoid irreversible negative impacts on the barrier island system. Three types of techniques could be adopted to deal with the threats to barrier islands: hard stabilization, soft techniques, and non-structural alternatives. However, using hard techniques has many negative effects compared to soft techniques, and as a result it is necessary to remove existing structures from the areas at most risk.     

Sediment bioavailable organic matter,deposition rates and mixing intensity in the Setúbal–Lisbon canyon and adjacent slope (Western Iberian Margin)

The role of the Setúbal–Lisbon canyon in accumulation and transport of labile organic matter from the coastal sea and ocean surface water towards the deep sea was assessed by investigating the distribution of organic matter of different quality in sedimentary aggregates and surface sediments of the canyon and adjacent slopes. Total hydrolysable amino acids (THAA) and organic carbon (Corg) were measured from aggregates, and contents of Corg, chlorophyll a (chl a), phaeopigments (phaeo), chloroplastic pigment equivalents (CPE) from sediments. As indices of organic matter (OM) quality THAA:Corg, degradation index (DI), chl a:phaeo, chl a:Corg and C:N ratio were determined. Sediment profiles of chl a and the isotope 210 of lead (²¹⁰Pb) were used as tracers in a transport model to estimate deposition rates and background levels of the tracers, and sediment mixing rates (Db). Whereas bulk Corg contents of canyon and slope sediments were practically similar at all depths, higher contents of THAA, chl a and CPE, as well as higher THAA:Corg, DI and chl a:Corg, in aggregates and sediments from the upper reaches of the canyon indicate that labile organic matter accumulates in the upper canyon. This is confirmed by higher chl a and ²¹⁰Pb deposition and Db calculated from the model. Hence, the Setúbal–Lisbon canyon, specially the upper region, acts as a natural trap of organic matter that is transported to the region via lateral transport and vertical settling from primary productivity. Organic matter might be further transported in downward canyon direction via rebound processes. The chl a and ²¹⁰Pb profiles reveal active sediment mixing by physical processes and/or animal reworking.     

Protein carbonyls and antioxidant defenses in corkwing wrasse (Symphodus melops) from a heavy metal polluted and a PAH polluted site

The use of fish in environmental monitoring has become increasingly important in recent years as anthropogenic substances, many of which function as prooxidants, are accumulating in aquatic environments. We have measured a battery of antioxidant defenses as a measure of oxidative status, as well as protein carbonylation as a measure of oxidative damage, in corkwing wrasse (Symphodus melops) captured near a disused copper mine, where water and sediment are contaminated with heavy metals, and an aluminum smelter, a site contaminated with PAHs. Results were compared to two different reference sites. Fish at the heavy metal site had lower glucose-6-phosphate dehydrogenase activity and elevated protein carbonyls (1.8 times) compared to fish from the reference site. At the PAH site, EROD was increased 2-fold, while total glutathione and methemoglobin reductase concentration, were decreased. No differences were seen in protein carbonyl levels at the PAH site. Measures of both antioxidant defenses and oxidative damage should be used when assessing effects of xenobiotics on oxidative stress in fish species.     

Assessment of dissolved nutrients dispersal derived from offshore fish-farm using nitrogen stable isotope ratios (δ15N) in macroalgal bioassays

In this study, the dispersal of wastes from offshore fish farms was evaluated by analyzing nitrogen stable isotope ratios (δ¹⁵N) in macroalgae incubated in the water column at sites located at an increasing distance from the fish cages. Bioassays were performed at three fish farms situated in separate localities with different nutritional conditions (Canary Islands, Murcia and Catalonia) and varying in size, species of fish reared and annual production. Macroalgal bioassays were carried out in two different directions (DI and DII) and they were replicated at each distance in order to evaluate the effect of small-scale variability on the spatial extent of fish farm wastes. The results obtained with δ¹⁵N contribute to a better understanding of the application of nitrogen stable isotopes ratios in macroalgae as an effective bioindicator for tracing the dispersion of offshore fish farm wastes, and demonstrate that fish farm wastes can be traced even over distances of some km from the pollution source. In the Canary Islands, the maximum distance obtained for detection of fish farm wastes was between 450 and 700 m. Of the three installations studied, Murcia presented the greatest distance for detection of fish farm waste influence, ranging from between 1550 and 2450 m, whilst in Catalonia this distance was less than 120 m. In Catalonia, the results were masked by the influence of other sources of nitrogen, and thus fish farm wastes were detected at more reduced distances than expected. These results confirm that fish farm wastes can be traced using the nitrogen stable isotope ratios of macroalgae and that this method can also be useful for identifying areas of potential risk to some sensitive ecosystems, and as an early signal that changes in the community structure might occur.     

Automatic tracing of the foot of the continental slope

The UNCLOS III (Article 76, Section 4(b)) defines the foot of the continental slope as the point of maximum change in the gradient at its base. It is impossible to locate so defined afoot and thus to trace the foot‐line objectively by eye. In this study we show a method designed automatically to detect and trace the foot‐line of the continental slope from an irregular array of bathymetrical data. Our algorithm first transforms the bathymetric surface to a maximum curvature surface. On this new surface, the foot‐line corresponds to one of the ridges; instead of tracing the foot‐line on the bathymetric surface, we now can trace the ridges on the maximum curvature surface. The tracing of the ridges can be done automatically and objectively and the foot‐line is identified as being one of these ridges. We devote particular attention to the case when the ridge‐line is not defined, i.e., to the case when the point of maximum gradient change becomes a region of maximum gradient change.     

A mass mortality of subtropical intertidal populations of the sea urchin Paracentrotus lividus: analysis of potential links with environmental conditions

An outbreak of bald sea urchin disease was detected affecting intertidal populations of the edible temperate species Paracentrotus lividus at its southernmost geographical limit. The mortality event was detected in three sites (Güímar, Palmar and Alcalá) off Tenerife, Canary Islands (Northeastern Atlantic), in October 2003, coinciding with the highest sea surface temperatures (SST) and the lowest wave heights of the year. The prevalence of infection reached 100% but did not affect equally all studied sites or the different size classes. The disease was more prevalent in large sea urchins (>40 mm). The prevalence appeared to be positively correlated with the environmental variable SST and negatively correlated with wave height. In October 2004, only two infected urchins were found (prevalence 1%) at one of the studied sites. However, during 2004 no such extreme values of temperature and wave height were observed. We conclude that high SSTs and low wave heights such as those observed during 2003 are conditions that may trigger outbreaks of urchin disease.     

Integrative taxonomic description of Plakina kanaky,a new polychromatic sponge species from New Caledonia (Porifera: Homoscleromorpha)

Four similar sponges of different colors, all unknown to science, were collected in submarine caves of New Caledonia. We aimed at determining whether the four chromotypes represented different species or phenotypic variations of a unique new species. We used an integrative taxonomic approach combining morphologic, molecular and metabolomic analyses. The main traits that define these specimens are a skeleton made of monolophose, trilophose and tetralophose calthrops only, high chemical diversity and a high abundance and diversity of prokaryotic symbionts. The symbiotic community includes two unique prokaryote morphotypes, which are described for the first time in Homoscleromorpha, and appeared to be vertically transmitted. Although several features slightly differ among chromotypes, the most parsimonious conclusion was to propose a single new species Plakina kanaky sp. nov. Our phylogenetic analysis indicated the paraphyly of the Plakina genus, with P. kanaky sp. nov. belonging to a clade that includes Plakina jani and Plakina trilopha. The present work demonstrates that integrative taxonomy should be used in order to revise the entire Plakinidae family and especially the non‐monophyletic genus Plakina.     

Concurrent Use of OSCAT and AltiKa to Characterize Antarctic Ice Surface Features

Radar altimetry provides an important geophysical parameter, backscatter coefficient (σ₀), which is useful in studying target surface characteristics. Ku-band (Oceansat-2 scatterometer- OSCAT) and Ka-band (SARAL-AltiKa altimeter) data are concurrently used to characterize polar surface features over the Antarctic region. Maximum-likelihood classification has been employed to classify combined data set (AltiKa and OSCAT) for discrimination among sea ice, open water, and ice sheet (interior and exterior). The sea ice region obtained using the current approach has been compared with sea ice boundary derived from passive microwave data.