Trace element fractionation and distribution in turbidites,homogeneous and pelagic deposits; the Zaire Fan,Southeast Atlantic Ocean

In turbidites, homogeneous and pelagic deposits of the Zaire Fan Th, La, Sm, and Rb and to a lesser extent Yb and Ta correlate strongly. La, Sm, Yb, Rb, Ta, and Th increase two-fold in Te3 turbidite intervals relative to Te 1 due to an increase in clay fraction with which these elements occur associated preferentially.Hf and Zr are anomalously high in Tel and Tel intervals which is probably a result of mineral separation. Zr is absent in Te3 intervals and the homogenous and pelagic deposits. Ba, Br. and U are lowest in turbidites and highest in homogenous continental slope deposits which is probably caused by upwelling. Cc anomalies may be related to the crystallinity of smectite.     

Genetic Relationships Among One Non-Endemic and Two Endemic Mediterranean Triplefin Blennies (Pisces, Blennioidei)

Abstract. Three triplefin blennies occur sympatrically in the Mediterranean Sea; Tripterygion tripteronotus and T. melanurus are endemic, whereas T. delaisi is also found in the Eastern Atlantic. Although very similar in morphology, ecology and behaviour, some striking differences exist among reproductive strategies. Several authors proposed hypotheses on the evolution of these species. In order to enhance insight into the genetic structure of this genus, an enzyme electrophoretic survey was performed. Samples of 40 to 45 specimens of each species were collected near Calvi (Corsica, France). Twenty-four enzyme loci were analysed, of which 17 appeared polymorphic. T. delaisi showed a high level of average observed heterozygosity (H_o) of 0.140, as opposed to very low levels of 0.009 and 0.021 in T. tripteronotus and T. melanurus , respectively. Nei's genetic distance was 0.21 between T. delaisi and T. tripteronotus , 0.35 between T. delaisi and T. melanurus and 0.45 between T. tripteronotus and T. melanurus . We hypothesise that divergence of these species started before the Pleistocene and that the endemic species survived the Pleistocene glaciations in refugia within the Mediterranean. The possibility that T. tripteronotus and T. delaisi diverged through sympatric speciation is discussed.     

A fish hepatocyte model for the investigation of the effects of environmental contaminants

An isolated fish hepatocyte culture system was developed as a models ystem to investigate the mechanisms of action of environmental contaminants. Hepatocytes were isolated from striped bass (Morone saxatilis) by an adaptation of the two stage perfusion technique of Seglen.¹ The system was used to evaluate metal binding protein (MBP) induction in response to cadmium, a primary inducer of metallothionein (MT) in rat hepatocytes. Striped bass hepatocytes appeared to be refractory to the induction of MBP by cadmium, since there was no significant increase in the synthesis of MBP for any of the doses at any of the time points investigated. However, when a similar experiment was performed using rat hepatocytes there was induction of MBP that was related to both dose and time. These comparative experiments indicate that although there are similarities between the hepatocytes of the two species in regard to ³⁵S incorporation into low molecular weight metal-binding proteins, there appear to be significant quantitative differences as well in regard to MBP kinetics. This in vitro model system could potentially be utilized to investigate the toxicological properties of other environmental contaminants.     

Growth and reproduction of the bivalve Spisula subtruncata (da Costa) in Dutch coastal waters

The bivalve Spisula subtruncata is usually abundant in shallow coastal waters along the Dutch coast. However, its biomass has been decreasing since 1995. In order to assess whether reproductive failure may be the cause of the observed decline over the last decades, the energy investment in reproduction of a population of S. subtruncata from central Dutch coastal waters was studied. The population studied consisted of individuals of up to four years old. Shell length reached maximum values of around 32 mm and individual total body, somatic and gonadal ash-free dry mass reached maximum values of about 278 mg AFDM, 252 mg AFDM and 76 mg AFDM, respectively. A clear seasonal cycle in somatic and gonadal mass was observed. Somatic and gonadal mass indices increased in early spring and reached maximum values during summer, followed by a decrease to minimum values at the beginning of the following year. Spawning was in June–July and settlement of spat seems to have occurred in July–August. Mean oocyte diameter was 57.43 ± 0.03 μm, corresponding to a volume of 98972 μm³. These results suggested that reproductive failure was not the cause of the current population decline. Most likely, unsuccessful settlement of spat and/or severe predation during the first months of life were responsible for the observed patterns.     

Upper temperature tolerances of exotic brackish-water mussel, Mytilopsis leucophaeata (Conrad): an experimental study

The dark false mussel, Mytilopsis leucophaeata is an important mussel colonising the brackish-water systems of temperate and subtropical regions. Of late it has earned notoriety as a biofouling species in industrial cooling water systems. However, there are no published data on the temperature tolerance of this species. This paper presents data on the upper temperature tolerance of this mussel from the view point of biofouling control using thermal methods. In addition to mortality, response of physiological activities such as oxygen consumption, filtration rate, foot activity and byssus thread production were also studied at temperatures varying from 5 to 35 degrees C. Experiments were also carried out to understand the effect of mussel size, breeding condition, nutritional status and acclimation conditions (temperature and salinity) on the mortality pattern. The physiological activities were significantly reduced at temperatures beyond 27.5 degrees C and ceased at 35 degrees C. In 20 mm size group mussels exposed to 37 degrees C, 50% mortality was observed after 85 min and 100% mortality after 113 min. The effect of mussel size on mortality at different temperatures was significant, with the larger size group mussels showing greater resistance. M. leucophaeata collected during the non-breeding season (December-April) were more tolerant to temperature than those collected during the breeding season (June-October). Nutritional status of the mussel had no significant influence on the thermal tolerance of the mussel: fed and starved (non-fed) mussels succumbed to temperature at comparable rates. The effect of acclimation temperature and acclimation salinity on M. leucophaeata mortality at different temperatures was significant. Survival time increased with increasing acclimation temperature and decreased with increasing salinity. In comparison with other co-occurring species such as Mytilus edulis and Dreissena polymorpha, M. leucophaeata appears to be more tolerant to high temperature stress.     

A hydropedological approach to simulate streamflow and soil water contents with SWAT+

Reflecting internal catchment hydrological processes in hydrological models is important for accurate predictions of the impact of climate and land-use change on water resources. Characterizing these processes is however difficult and expensive due to their dynamic nature and spatio-temporal variability. Hydropedology is a relatively new discipline focusing on the synergistic integration of hydrology, soil physics and pedology. Hydropedological interpretations of soils and soil distribution can be used to characterize key hydrological processes, especially in areas with no or limited hydrometric measurements. Here we applied a hydropedological approach to reflect flowpaths through detailed routing in SWAT+ for a 157 ha catchment (Weatherley) in South Africa. We compared the hydropedological approach and a standard (no routing) approach against measured streamflow (two weirs) and soil water contents (13 locations). The catchment was treated as ‘ungauged’ and the model was not calibrated against hydrometric measurements in order to determine the direct contribution of hydropedology on modelling efficiency. Streamflow was predicted well without calibration (NSE > 0.8; R² > 0.82) for both approaches at both weirs. The standard approach yielded slightly better streamflow predictions. The hydropedological approach resulted in considerable improvements in the simulation of soil water contents (R² increased from 0.40 to 0.49 and PBIAS decreased from 40% to 20%). The routing capacity of SWAT+ as employed in the hydropedological approach reduced the underestimation of wetland water regimes drastically and resulted in a more accurate representation of the dominant hydrological processes in this catchment. We concluded that hydropedology can be a valuable source of ‘soft data’ to reflect internal catchment structure and processes and, potentially, for realistic calibrations in other studies, especially those conducted in areas with limited hydrometric measurements.