Nutrient Limitation in Macroalgae (Ulva and Enteromorpha) from the Rías Baixas (NW Spain)

Abstract.  Photosynthesis and growth rates in samples of two green seaweeds ( Ulva and Enteromorpha ) were monitored in the laboratory. The macroalgae were collected every 15 days from four coastal embayments in Galicia (NW Spain). Ulva samples were found to be nutritionally limited, particularly in summer. The physiological activity of Enteromorpha did not appear to be as affected by nutrient scarcity, although it may have suffered from phosphorus limitation. The subsistence quotas, critical concentrations and storage capacity for N and P in Ulva were comparable to those obtained by other investigators in similar studies. The trace metals analysed apparently did not negatively affect the macroalgae at the measured concentrations; one explanation is that many of these metals function as essential micronutrients. The complex physiological interactions between metals and nutrients, however, may complicate interpretation of the results.     

The S reflector west of Galicia: the seismic signature of a detachment fault

The so-called S reflector is a group of bright, continuous reflections underlying the landward-tilted fault blocks of the west Galicia rifted margin, S has been interpreted as the brittle-ductile transition, the lop of an intrusion, a detachment fault, and the crust-mantle boundary. To constrain the internal structure of the reflector, we have carried out detailed analyses of these reflections. We compare the waveforms of the seafloor reflection and its first multiple, both to determine the amplitude of the seafloor reflection and to show (hat the seafloor is in effect a spike in the reflectivity series so that the seafloor reflection can be used as the far-field wavelet, including both source and receiver ghosts. We compare (he waveform of the seafloor and 5 and show that, within the resolution of our data, S is a reflection from a step increase in acoustic impedance. This result is confirmed through complex trace analysis, and in particular the determination of the apparent polarity of S, and the examination of the instantaneous frequency function: S is consistently positive polarity, and shows no significant frequency anomaly. Simple modelling shows that S is very unlikely to be a reflection from a thin layer. We thus conclude that S is probably a single steplike interface. From the varying frequency content of the data, we determine a value for the effective Q between S and the seafloor, and use this to assess the amplitude loss due to attenuation and scattering. We use a comparison between the seafloor and the S reflection to constrain the amplitude of S, and estimate a reflection coefficient for S of at least 0.2 in places, decreasing landwards. By analogy with structures developed in the highly extended regions of the western United States, we consider that the most likely interpretation of S is as a sharp west-dipping detachment fault separating a 'granitic' upper plate from a higher-velocity lower plate, locally probably serpentinized mantle.     

Characterization of fisheries dependence in Galicia (Spain)

The management of marine ecosystems requires adequate knowledge of both environmental and human dimensions, as well as their interrelationships. In this study, the aquaculture and fisheries activities are analyzed in one of most important fishing regions in Europe, Galicia (NW Spain). In particular, the intensity and characteristics of the fishing dependency are evaluated in terms of income and employment. Thus, nine marine economic activities for nine Maritime Zones have been defined, considering the social and economic relevance of the provided ecosystem services to these communities. This paper highlights the entire Galician coast as fishing-dependent, independently of the urbanization level. Furthermore, the contribution of different fishery segments to the income and employment of these coastal communities is reviewed, including fluctuations on whether the activity is small or large-scale. Finally, this study establishes a strong relationship among the marine activities, which generate most employment, and the regulatory framework of the Regional Government. Therefore, the conclusions are relevant to design and implement policies that affect Galicia׳s Region and all its related marine ecosystems.     

“GALICIA'S HURRICANE”: ACTOR NETWORKS AND ICONIC CONSTRUCTIONS*

Monumental constructions are created for a purpose, often as a symbolic representation of a particular vision of a people or a place. Spain's Cidade da Cultura, a museum conceptualized by Galicia's former president with the hubristic goal of creating a world icon, is one such example. Like many iconic constructions, the Cidade da Cultura project was highly contentious and sparked a regionwide political debate, vastly overran its projected cost, and years later remains controversial and incomplete. An actor‐network theory analysis of why the project failed reveals the different roles played by individual components in the vast network of actors, including the monument itself, which came to exercise influence over the outcome of the project. Because the former president could not fully control this expanding network of actors, events soon spun out of control in what became popularly known as “Galicia's Hurricane.”     

Rifting and early evolution of ancient ocean basins: the record of the Mesozoic Tethys and of the Galicia-Newfoundland margins

Although of different age, the undeformed Cretaceous Iberia/Newfoundland margins and the relics of the Jurassic Briançonnais/Adriatic margins preserved in the Alps document a similar spatial and temporal evolution of rifting suggesting that the evolution of both pairs of margins was controlled by the same processes. Rifting appears to depend strongly on the thermal history of the lithosphere, which controls the rheology and consequently also the structural evolution of the margin. The tectonic evolution of non-volcanic margins appears to be distinctly different from that of volcanic ones.     

Effect of a simulated oil spill on natural assemblages of marine phytoplankton enclosed in microcosms

Two microcosm experiments were carried out to simulate the effect of sporadic oil spills derived from tanker accidents on oceanic and coastal marine phytoplankton assemblages. Treatments were designed to reproduce the spill from the Prestige, which took place in Galician coastal waters (NW Iberia) in November 2002. Two different concentrations of the water soluble fraction of oil were used: low (8.6 ± 0.7 μg l⁻¹ of chrysene equivalents) and high (23 ± 5 μg l⁻¹ of chrysene equivalents l⁻¹). Photosynthetic activity and chlorophyll a concentration decreased in both assemblages after 24–72 h of exposure to the two oil concentrations, even though the effect was more severe on the oceanic assemblage. These variables progressively recovered up to values close or higher than those in the controls, but the short-term negative effect of oil, which was generally stronger at the high concentration, also induced changes in the structure of the plankton community. While the biomass of nanoflagellates increased in both assemblages, oceanic picophytoplankton was drastically reduced by the addition of oil. Effects on diatoms were also observed, particularly in the coastal assemblage. The response of coastal diatoms to oil addition showed a clear dependence on size. Small diatoms (<20 μm) were apparently stimulated by oil, whereas diatoms >20 μm were only negatively affected by the high oil concentration. These differences, which could be partially due to indirect trophic interactions, might also be related to different sensitivity of species to PAHs. These results, in agreement with previous observations, additionally show that the negative effect of the water soluble fraction of oil on oceanic phytoplankton was stronger than on coastal phytoplankton.     

Trophic ecology of the swimming crab Polybius henslowii Leach, 1820 in Galician and Cantabrian Seas: Influences of natural variability and the Prestige oil spill

Diet and feeding intensity of the portunid crab Polybius henslowii were studied during the spring of 2004 along Galician and Cantabrian continental shelves (NW Iberian Peninsula) between 78 and 287 m. The area had been affected by the Prestige oil spill in November 2002, with different sectors at different levels of pollution: highest in between Miño River and Cape Finisterre (MF) and from there to Estaca de Bares Point (FE) and lowest from Estaca to Cape Peñas (EP). From 37272 specimens collected in 59 bottom hauls, 342 were analysed for stomach fullness and diet composition. Stomach fullness was lower in FE, but with no significant differences among sectors. Diet was a mixture of pelagic and benthic prey: cephalopods (Ilex coindetti), brachyurans (P. henslowii) and polychaetes (Glycera sp.). Other prey were beloniform eggs and fish remains. Two stress markers were also studied in some specimens: Acetylcholinesterase (a neurotoxicity marker) varied among sampled areas, while lipid peroxidation (an oxidative stress marker) did not. Changes in trophic variables, distribution and density were analysed in relation to depth, surface and bottom T, surface Chl a from satellite imagery and tar aggregate concentration in sediments. Along Galician and Cantabrian coasts prey availability, linked to productivity level, seems to be the main factor affecting P. henslowii diet and distribution. Interannual abundance variability seems to be controlled by large-scale climatic conditions (NAO index). This natural variability masks possible effects induced by the oil spill.     

Influence of point sources on trace metal contamination and distribution in a semi-enclosed industrial embayment: the Ferrol Ria (NW Spain)

Concentrations of heavy metals (Co, Cr, Cu, Fe, Ni, Pb and Zn), particulate organic (POC) and nitrogen (PON), particulate inorganic carbon (PIC) and opal content were measured in 35 surface sediment samples taken in the Ferrol Ria (Galicia, NW Spain). This ria is a semi-enclosed embayment receiving inputs from industrial and urban effluents. The restricted water exchange between the ria and the shelf has led to a significant accumulation of contaminants within the embayment. Two main factors controlled the metal distribution and concentrations in the bay: (1) contamination point sources and (2) distribution of the organic-rich sediments. Zn, Cu and, to a lesser extent Pb, were the metals most contaminated in the bay, with average enrichment factors (AEF)—defined as the mean metal concentration in the bay divided by the background value reported for this ria—of 4.7, 5.5 and 2.7, respectively. The highest concentrations for these metals were observed in the vicinity of the point sources. Values found for Zn, Cu and Pb are comparable to other industrialized coastal areas in the world. For Ni, Fe, Cr and Co a negligible to low contamination was found (AEF = 1–2), with the highest concentrations found in the organic-rich sediments.