Esterases as biomarkers in Nereis (Hediste) diversicolor exposed to temephos and Bacillus thuringiensis var. israelensis used for mosquito control in coastal wetlands of Morbihan (Brittany,France)

Since 1998, a biomonitoring programme has been implemented to assess the potential impact of chemical mosquito control on macroinvertebrates of the coastal wetlands of Morbihan (Brittany, France). Acetylcholinesterase and carboxylesterases were used as biomarkers to assess the effects of Abate 500e (a.i. temephos) and Vectobac 12 AS (a.i. endotoxins of Bacillus thuringiensis var. israelensis, Bti) in Nereis (Hediste) diversicolor. Esterase inhibition revealed a marked impact of temephos, suggesting preferential contamination of the worms through the food. In Bti-exposed N. diversicolor, random variations of esterase activities were observed, that could not be attributed to the larvicide. However, esterases only reflected indirect physiological effects of Bti, and further investigations are needed to identify biomarkers more specific of Bti endotoxins.     

Biomarkers of Exposure and Effects for Assessing Toxicological Risk of Endocrine Disrupters in Top Predators of the Mediterranean Sea

Abstract. Endocrine Disrupting Chemicals (EDCs) have the potential to alter hormone pathways that regulate reproductive processes in wildlife and fisheries. In this research the unexplored hypothesis that Mediterranean top predator species (such as large pelagic fish and marine mammals) are potentially at risk due to EDCs is investigated. In the Mediterranean environment, top predators accumulate high concentrations of polyhalogenated aromatic hydrocarbons (PHAHs) and toxic metals, incurring high toxicological risk. Here we illustrate the need to develop sensitive biomarkers for evaluation of toxicological risk in top marine predators (Xiphias gladius, Thunnus thynnus thynnus) and non-lethal techniques, such as non-destructive biomarkers, for the hazard assessment of threatened species exposed to EDCs, such as marine mammals ( Stenella coeruleoalba, Tursiops truncatus, Delphinus delphis and Balaenoptera physalus ).     

Regeneration of sand waves after dredging

Sand waves are large bed waves on the seabed, being a few metres high and lying hundreds of metres apart. In some cases, these sand waves occur in navigation channels. If these sand waves reduce the water depth to an unacceptable level and hinder navigation, they need to be dredged. It has been observed in the Bisanseto Channel in Japan that the sand waves tend to regain their shape after dredging. In this paper, we address modelling of this regeneration of sand waves, aiming to predict this process. For this purpose, we combine a very simple, yet effective, amplitude-evolution model based on the Landau equation, with measurements in the Bisanseto Channel. The model parameters are tuned to the measured data using a genetic algorithm, a stochastic optimization routine. The results are good. The tuned model accurately reproduces the measured growth of the sand waves. The differences between the measured weave heights and the model results are smaller than the measurement noise. Furthermore, the resulting parameters are surprisingly consistent, given the large variations in the sediment characteristics, the water depth and the flow field. This approach was tested on its predictive capacity using a synthetic test case. The model was tuned based on constructed predredging data and the amplitude evolution as measured for over 2 years. After tuning, the predictions were accurate for about 10 years. Thus, it is shown that the approach could be a useful tool in the optimization of dredging strategies in case of dredging of sand waves.     

Temporal variability in phytodetritus and megabenthic activity at the seabed in the deep Northeast Atlantic

We report a ten-year study of the abundance and activity of megabenthos on the Porcupine Abyssal Plain, northeast Atlantic, together with observations on the occurrence of phytodetritus at the deep-sea floor (4850 m). Using the Southampton Oceanography Centre time-lapse camera system, ‘Bathysnap’, we have recorded a radical change in the abundance and activity of megabenthos between the two periods of study (1991–1994 and 1997–2000). In 1991–1994, the larger megabenthos occurred at an abundance of c. 71.6/ha and were dominated by large holothurians. In addition, there were very substantial populations of smaller megabenthic ophiuroids (c. 4979/ha). Together, the total megabenthos are estimated to track over some 17 cm²/m²/d (exploiting 100% of the surface of the seabed in c. 2.5 years). In 1997–2000, the larger megabenthos increased to an abundance of c. 204/ha and were joined by exceptional numbers of a small holothurian species (Amperima rosea, 6457/ha) and ophiuroids (principally Ophiocten hastatum, 53,539/ha). The total megabenthos population was tracking at an estimnated rate of c. 247 cm²/m²/d (exploiting 100% of seabed in just 6 weeks). Coincident with these increases in the abundance and activity of the megabenthos, there were apparently no mass depositions of aggregated phytodetritus to the seabed in the summers of 1997–1999. Mass occurrences of phytodetritus had been noted during the summer months of the three years previously studied (1991, 1993 and 1994), with covering between 50 and 96% of the sediment surface. There is a statistically significant (p<0.02) negative correlation between maximum extent of this seabed cover of phytodetritus and seabed tracking by megabenthos. Additional studies [Lampitt et al., Progr. Ocean. 50 (2001)], indicate that there were no substantial changes in surface ocean primary productivity, in export flux, or in the composition of the flux that might otherwise account for the apparent absence of observable concentrations of phytodetritus during the summers of 1997–1999. We postulate that the marked increase in megabenthic tracking activity resulted in the removal (via consumption, disaggregation, burial etc.) of the bulk of the incoming phytodetrital flux during these years. A simple conceptual model, based on the apparent phytodetrital fluxes observed in 1991 and 1993, suggests that the megabenthos tracking rates estimated for 1997–1999 are sufficient to account for near-total removal of this flux. However, we are not able to estimate other processes removing phytodetritus (i.e. other elements of the benthos) that may also have increased between 1991–1994 and 1997–1999. Other independent studies [e.g. Ginger et al., Progr. Ocean. 50 (2001)] of flux constituents support the possibility that just a few species of megabenthos (e.g. A. rosea, and O. hastatum) could well have consumed a major proportion of the incoming flux and so substantially modified the composition of the organic matter available to other components of the benthos.     

Modern sediment supply to the lower delta plain of the Ganges-Brahmaputra River in Bangladesh

Vibracores and auger samples collected from the lower (tidal) delta plain of the Ganges-Brahmaputra River in Bangladesh were examined to determine whether the area is a significant sink for riverine sediments. Measurements of ¹³⁷Cs activity and radiocarbon in the sediments indicate sediment accumulation is taking place on decadal and millennial time scales at rates reaching 1.1 cm/year. The sediment of the lower delta plain is primarily derived from an offshore source after having originally been supplied by the Ganges-Brahmaputra river system, carried westward by prevailing currents and advected inland by monsoonal coastal setup and cyclonic events.     

A field-based population model for the sediment toxicity test organism Leptocheirus plumulosus: I. Model development

We describe the development of a stage-structured population matrix model for the estuarine amphipod Leptocheirus plumulosus, a sediment toxicity test organism, based on regular sampling of a natural population for approximately 2 years. Annual population dynamics were characterized by abundance peaks in the spring and fall, and low densities in the summer and winter. We use a sequence of seasonal projection matrices to capture these qualitative patterns in population dynamics. We compare two methods for estimating transition probabilities: multiple regression and truncated singular value decomposition (SVD). Overall, SVD gave more realistic parameter estimates than regression, although fecundity estimation was problematic. There were predictable trends in growth, survival and fecundity within years. The SVD-derived model provides a framework for assessing the population-level effects of contaminants on Leptocheirus.     

Increasing imposex in populations of Bolinus brandaris (Gastropoda: Muricidae) in the northwestern Mediterranean.

The muricid gastropod Bolinus brandaris exhibited imposex, a phenomenon linked to the use of organotin biocides. Several stages of imposex development (1-5) could be distinguished and were documented with SEM-photographs for the first time in this species. Additional alterations of the genital tract in females (blocked vulva preventing copulation and deposition of egg capsules) and males (excrecences on the penis and vas deferens) were shown. Imposex intensity on the Catalan coast was very high. The frequency of imposex off Barcelona and Vilanova i la Geltrú was 100%, with all females showing stage 4. Imposex frequency off Sant Carles de la Ràpita was 99.7% and the VDS index scored 3.9. Despite regulations of TBT-containing antifouling paints in Spain since 1990, the present study revealed that frequency and intensity of imposex have increased on the Catalan coast, at least since 1997. However, at present, imposex does not apparently affect the population dynamics of B. brandaris in the studied area, since no serious consequences on female reproduction (only one case of female sterilization) were detected. Gonadal activity and oogenesis were not suppressed or supplanted by spermatogenesis. Sex ratios were not male-biased. Possible sources of organotin biocides are examined.     

Directional spread parameter at intermediate water depth

The characteristics of directional spread parameters at intermediate water depth are investigated based on a cosine power ‘2s' directional spreading model. This is based on wave measurements carried out using a Datawell directional waverider buoy in 23 m water depth. An empirical equation for the frequency dependent directional spreading parameter is presented. Directional spreading function estimated based on the Maximum Entropy Method is compared with those obtained using a cosine power ‘2s' parameter model. A set of empirical equations relating the directional spreading parameter corresponding to the peak of wave spectrum to other wave parameters like significant wave height and period are obtained. It shows that the wave directional spreading at peak wave frequency can be related to the non-linearity parameter, which allows estimation of directional spreading without reference to wind information.