Complex size-dependent habitat associations in potamodromous fish species

Knowledge of the distribution of species life stages at multiple spatial scales is fundamental to both a proper assessment of species management and conservation programmes and the ability to predict the consequences of human disturbances for river systems. The habitat requirements of three native cyprinid species—the Iberian barbel Barbus bocagei Steindachner, the Iberian straight-mouth nase Pseudochondrostoma polylepis (Steindachner), and the Northern straight-mouth nase Pseudochondrostoma duriense (Coelho)—were examined at 174 undisturbed or minimally disturbed sites in 8 river catchments across western Iberia, by modelling occurrence and counts of species life stages at two spatial scales—large (regional) and instream (local)—using hurdle models. All the life stages of the barbel showed a negative association with upstream high-gradient river reaches, whereas juvenile P. duriense favoured such areas. Stream width and openness were negatively related with the occurrence of juvenile and small adult barbel, but not with large adults. Juvenile nase, on the other hand, were found to be mainly confined to fast-flowing habitats with high instream cover and coarser substrata. Advanced life stages of the barbel were mainly associated with the “pure” regional and shared components, whereas the purely local attributes accounted for much of the model variation among nases, in particular juveniles, and juvenile barbel. The results of this study are useful for setting or refining management goals, and highlight the need to separately consider life stages when performing conservation-related studies of species distribution.     

Potential Use of Biomarkers in Zooplankton as Early Warning Signals of Ecotoxicological Risk in the Marine Food Chain

Abstract. Zooplankton is an essential component of the marine and brackish food chains. The ecotoxicological risk of zooplanktonic communities, estimated by the modern methodological approach of biomarkers, can be used as an early warning signal of ecosystem health. The aim of this project is to estimate the potential use of several biomarkers (esterases, mixed function oxidases, porphyrins) in zooplanktonic organisms. Studies were carried out with different zooplanktonic crustaceans: the copepods Acartia margalefi and Acartia latisetosa collected in Ganzirri Lake (Messina); the mysid Siriella clausi collected in Faro Lake (Messina); the mysids Diamysis bahirensis, Siriella armata and Mysidopsis gibbosa collected in Stagnone di Marsala (Palermo); the Antarctic euphausiids Euphausia crystallorophias and Euphausia superba; the am-phipod Streetsia challengeri and the euphausiid Meganycthiphanes norvegica collected after a shore-stranding along Messina's Ionian coast. Moreover, experiments were carried out with the benthic decapods Eriphia verrucosa and Pachygrapsus marmoratus from a rocky shore of Messina's Ionian coast. Acetylcholinesterase activity (AChE) was determined in homogenates of whole organisms. The key result of this project concerns the different AChE activity basal values of different crustacean species. Particular attention should be paid to the difference in basal activity found between the Antarctic and the Mediterranean species.     

Bioaccumulation and depuration of Zn and Cd in mangrove oysters (Crassostrea rhizophorae, Guilding, 1828) transplanted to and from a contaminated tropical coastal lagoon

In order to study Zn and Cd accumulation and depuration, a set of oysters, Crassostrea rhizophorae, were transplanted to a metal contaminated coastal lagoon and another one was harvested there and transplanted to a non-polluted site. C. rhizophorae oysters and Perna perna mussels native from both sites were collected in order to monitor variability of metal concentration in resident populations. After three months exposure, oysters transplanted to the polluted site accumulated fourfold Zn (307-1319 microgg(-1)) without reaching the concentration level of resident oysters (9770 microgg(-1)). Cadmium concentrations had a slight but significant decrease during the same period (1.25-0.54 microgg(-1)). Oysters transplanted to the non-polluted site, showed threefold Zn depuration (6727-2404 microgg(-1)), while Cd had no significant variation (0.90-1.45 microgg(-1)). Results showed that transplanted oysters do not reach heavy metal concentrations in indigenous populations suggesting transplanted organisms would be better used to evaluate bioavailability instead of environmental concentrations.     

Multi-level assessment of chronic toxicity of estuarine sediments with the amphipod Gammarus locusta: I. Biochemical endpoints

We report on biomarker responses conducted as part of a multi-level assessment of the chronic toxicity of estuarine sediments to the amphipod Gammarus locusta. A companion article accounts for organism and population-level effects. Five moderately contaminated sediments from two Portuguese estuaries, Sado and Tagus, were assessed. Three of them were muddy and two were sandy sediments. The objective was to assess sediments that were not acutely toxic. Three of the sediments met this criterion, the other two were diluted (50% and 75%) with clean sediment until acute toxicity was absent. Following 28-d exposures, the amphipods were analysed for whole-body metal bioaccumulation, metallothionein induction (MT), DNA strand breakage (SB) and lipid peroxidation (LP). Two of the muddy sediments did not cause chronic toxicity. These findings were consistent with responses at organism and population levels that showed higher growth rates and improvement of reproductive traits for amphipods exposed to these two sediments. Two other sediments, one muddy and one sandy, exhibited pronounced chronic toxicity, affecting SB, MT induction (in muddy sediment), survival and reproduction. Potential toxicants involved in these effects were identified. The last sandy sediment exhibited some loss of DNA integrity, however growth was also enhanced. Present results, together with the organism/population-level data, and also benthic communities information, were analysed under a weight-of-evidence approach. By providing evidence of exposure (or lack of it) to contaminants in sediments, the biomarkers here applied assisted in distinguishing toxicants' impacts in test organisms from the confounding influence of other geochemical features of the sediments.     

Physical forcing of onshore transport of crab megalopae in the northern Portuguese upwelling system

Wind-driven circulation is a mechanism that may be involved in the shoreward transport of invertebrate larvae. This study investigated the temporal variability of the supply of crab megalopae to an estuary located in the northwest coast of Portugal, which is affected by seasonal upwelling, and related variations in supply to several upwelling indices. Megalopae of the European common shore crab Carcinus maenas (L.). were collected daily, using artificial settlement substrates, during a 3-month period, from March 15 to June 15, 2000. Two settlement episodes were detected, which were consistent with the variation in abundance and size of juvenile crabs. Variations in subtidal sea level and sea surface temperature anomaly were correlated with the strength of along-shore wind stress and consistent with upwelling theory. Contingency analyses showed positive significant associations between increasing intensity of southerly winds and megalopal supply, for time lags of 0–6 d, indicating that shoreward transport occurred during relaxation or reversal of upwelling favourable winds. Associations between megalopal supply and tidal range or the duration of nocturnal flood were not detected. Compared to other studies of the supply of crab megalopae to coastal habitats that used a similar methodology, very low numbers of megalopae were collected during this study. The paucity of C. maenas megalopae in the Ria de Aveiro is in agreement with the low densities of this larval stage in the plankton, and indicates that maintenance of the population is achieved despite a low supply of megalopae.     

Facies analysis of Pleistocene sediments from the Bannock Basin area: A key to the reconstruction of its tectonic evolution

Facies analysis was carried out on 21 selected cores from the Bannock area in order to investigate the relationships between sedimentation and tectonism. Bannock Basin is a large, > 3500 m (uncorrected) deep subcircular depression near the deformation front of the Mediterranean Ridge facing the Sirte Abyssal Plain. The basin is divided into several sub-basins aligned along a rim-syncline surrounding a central elevated area (salt dome?). High-density brines and anoxic sediments occupy the deepest part of the depressions.

The facies distribution is controlled by the bottom configuration in that pelagic facies typically occur on plateaus and domes, debris-flow deposits in base-of-slope settings, and turbidites in basinal settings. The facies distribution may therefore be used to reconstruct the evolution of the various parts of the rim-syncline.

Erosional gaps may be related to tectonism or may be features created by the passage of major turbiditic events.

The results of our study of the facies associations, and of the rates of sediment accumulation, indicate that the collapse of the eastern part of the rim-syncline pre-dates the collapse of the western part. The western basins are deeper and larger than the eastern ones and (unlike the latter) are aligned at the foot of a strike-slip fault with a vertical offset of at least 700 m.     

Progressive deformation of an evaporite-bearing accretionary complex: SeaMARC I,SeaBeam and piston-core observations from the Mediterranean Ridge

The Mediterranean Ridge is an arcuate ridge of deformed sediment caught up in the convergent plate margin between the African plate and the Aegean. An intensive campaign of SeaMARC I and SeaBeam surveys followed by piston coring has been conducted along the contact between undeformed turbidites of the Sirte Abyssal Plain and folded and faulted sediments of the Mediterranean Ridge. Along the outer edge of the Ridge, surficial sediments have been deformed into sinusoidal ridges and troughs (wavelengths 0.5–2 km, amplitude 20–150 m), which we interpret as folds. In plan view, the ridge and the trough fabric parallels the NW-SE trending regional contours, suggesting that the folds formed in response to compression orthogonal to the Mediterranean Ridge. The outermost ridge is shedding a debris apron out onto the abyssal plain, implying that uplift and deformation are ongoing. We show that the geometry of the outermost folds can be produced by elastic bending of a packet of 5–10 relatively strong layers, each 10–20 m thick, interbedded between weaker layers; we equate the strong layers with gypsum beds in the Messinian upper evaporites. Folding the seafloor from a flat layer into the observed ridge and trough topography would shorten the layer by less than 2%. Two percent shortening (equals two percent thickening) is insufficient to create the observed relief of the Mediterranean Ridge even if the entire sediment column down to basement were involved; we infer that additional shortening/thickening is accommodated by thrust faulting above a decollement at the top of the Messinian salt layer. At distances > 15 km from the deformation front and more than 500 m from the abyssal plain, sharp-edged, fine-grained side-scan lineations with very little vertical relief cut across the kilometer-scale ridge and trough topography. These fine-grained lineations fall in two groups trending N/S to NNE/SSW and ~ENE. We interpret these lineaments as traces of conjugate strike-slip faults formed in the same compressional regime which formed the NW/SE trending folds. The onset of strike-slip faulting may coincide with the cessation of imbricate thrust fan development above the initial salt-controlled decollement surface. The following characteristics of the Mediterranean Ridge are attributed to the presence of evaporites in the incoming sedimentary section: (1) initial deformation by folding rather than thrust faulting; (2) narrow taper; (3) rapid rate of outward growth; (4) karstification.