Common Sole Larvae Survive High Levels of Pile-Driving Sound in Controlled Exposure Experiments

In view of the rapid extension of offshore wind farms, there is an urgent need to improve our knowledge on possible adverse effects of underwater sound generated by pile-driving. Mortality and injuries have been observed in fish exposed to loud impulse sounds, but knowledge on the sound levels at which (sub-)lethal effects occur is limited for juvenile and adult fish, and virtually non-existent for fish eggs and larvae. A device was developed in which fish larvae can be exposed to underwater sound. It consists of a rigid-walled cylindrical chamber driven by an electro-dynamical sound projector. Samples of up to 100 larvae can be exposed simultaneously to a homogeneously distributed sound pressure and particle velocity field. Recorded pile-driving sounds could be reproduced accurately in the frequency range between 50 and 1000 Hz, at zero to peak pressure levels up to 210 dB re 1µPa2 (zero to peak pressures up to 32 kPa) and single pulse sound exposure levels up to 186 dB re 1µPa2s. The device was used to examine lethal effects of sound exposure in common sole (Solea solea) larvae. Different developmental stages were exposed to various levels and durations of pile-driving sound. The highest cumulative sound exposure level applied was 206 dB re 1µPa2s, which corresponds to 100 strikes at a distance of 100 m from a typical North Sea pile-driving site. The results showed no statistically significant differences in mortality between exposure and control groups at sound exposure levels which were well above the US interim criteria for non-auditory tissue damage in fish. Although our findings cannot be extrapolated to fish larvae in general, as interspecific differences in vulnerability to sound exposure may occur, they do indicate that previous assumptions and criteria may need to be revised

The great melting pot. Common sole population connectivity assessed by otolith and water fingerprints

Quantifying the scale and importance of individual dispersion between populations and life stages is a key challenge in marine ecology. The common sole (Solea solea), an important commercial flatfish in the North Sea, Atlantic Ocean and the Mediterranean Sea, has a marine pelagic larval stage, a benthic juvenile stage in coastal nurseries (lagoons, estuaries or shallow marine areas) and a benthic adult stage in deeper marine waters on the continental shelf. To date, the ecological connectivity among these life stages has been little assessed in the Mediterranean. Here, such an assessment is provided for the first time for the Gulf of Lions, NW Mediterranean, based on a dataset on otolith microchemistry and stable isotopic composition as indicators of the water masses inhabited by individual fish. Specifically, otolith Ba/Ca and Sr/Ca profiles, and delta C-13 and delta O-18 values of adults collected in four areas of the Gulf of Lions were compared with those of young-of-the-year collected in different coastal nurseries. Results showed that a high proportion of adults (>46%) were influenced by river inputs during their larval stage. Furthermore Sr/Ca ratios and the otolith length at one year of age revealed that most adults (similar to 70%) spent their juvenile stage in nurseries with high salinity, whereas the remainder used brackish environments. In total, data were consistent with the use of six nursery types, three with high salinity (marine areas and two types of highly saline lagoons) and three brackish (coastal areas near river mouths, and two types of brackish environments), all of which contributed to the replenishment of adult populations. These finding implicated panmixia in sole population in the Gulf of Lions and claimed for a habitat integrated management of fisherie

Space and time variations in zooplankton distribution south of Marseilles

The mesozooplankton distribution in the upper water layer (up to 200 m) off Marseilles (NW Mediterranean Sea) was studied during 22 cruises performed between March 1992 and February 1995. Four stations (M1, M3, M5 and M7) were investigated along a coast-open sea transect. Spatial and seasonal variations of zooplankton were described using different quantitative parameters: biomass (dry weight, carbon, nitrogen), displacement volume (biovolume) and abundance of total organisms. C/N ratio, dry weight per individual and volume per individual were also calculated. The seasonal quantitative variations occurring at the four stations were not well synchronized. Annual maximum biomass was observed during spring and summer at M1 but only in early spring at the other stations. Abundance and biovolumes followed the same general pattern of variation. The mean values of the different parameters were maximum near the coast, at M1, and minimum at the most distant station (M7), but the decrease towards the open sea was not regular: the values found at M5 were higher than at M3 and markedly exceeded those at M7. This seems to be related to the presence of the oligotrophic Northern Mediterranean Current flowing parallel to the coast. In most cases M3 was in the core of the current whereas M5 seemed to be frequently influenced by its external boundary. Locally, this frontal situation enhanced the primary production and consequently favoured an increase in zooplankton biomass or production as suggested by the strong temporal correlation between chlorophyll and zooplankton at this station. Comparison between stations demonstrated the specificity of M5 zooplankton which showed the lowest variability in its specific dry weight and biovolume and the highest C\N ratios.La distribution du mésozooplancton dans la couche d'eau superficielle (jusqu'à 200 m) au large de Marseille (Méditerranée nord-occidentale) a été étudiée lors de 22 sorties entre mars 1992 et février 1995. Quatre stations (M 1, M3, M5 et M7) ont été prospectées le long d'une radiale côte-large. Les variations spatiales et saisonnières du zooplancton sont décrites à partir de différents paramètres quantitatifs: la biomasse (poids sec, carbone, azote), le volume déplacé (biovolume) et l'abondance de l'ensemble des organismes. Les rapports carbone/azote, poids sec par individu et volume par individu ont aussi été calculés. Les variations quantitatives saisonnières observées aux quatre stations sont mal synchronisées. Le maximum annuel de biomasse observé au printemps et en été à M1 était limité au début du printemps aux autres stations. L'abondance et le biovolume suivaient le même type de variation. Les biovolumes atteignaient parfois de très hautes valeurs à M l et M3, correspondant à la présence d'animaux gélatineux. Les valeurs moyennes des différents paramètres étaient maximales près de la côte à Ml et minimales à la station la plus éloignée (M7), mais leur décroissance vers le large n'était pas régulière. En effet, les valeurs rencontrées à M5 étaient plus fortes qu'à M3 et surpassaient nettement celles de M7. Cette anomalie positive du gradient est en relation avec la présence des eaux oligotrophes du courant méditerranéen nord occidental parallèle à la côte. Dans la plupart des cas, M3 était au cœur du courant alors que M5 semblait fréquemment influencée par sa limite externe. Localement, cette situation frontale stimule la production primaire et favorise l'accroissement de la biomasse ou de la production zooplanctonique, comme le suggère la forte corrélation entre la chlorophylle et le zooplancton à cette station. Des comparaisons entre les stations montrent le caractère original présenté par le zooplancton de M5: la variabilité de ses valeurs spécifiques de poids sec et de biovolume est la plus faible et il présente les rapports C/N les plus élevés

Effects of the sandbar breaching on hydrobiological parameters and zooplankton communities in the Senegal River Estuary (West Africa)

This study describes the changes in hydrology, zooplankton communities and abundance in the Senegal River Estuary (SRE) before and after the breaching of the sandbar in October 2003. Samples were taken in 2003 at 3 stations located upstream (DI), in mid estuary (HY) and downstream (RM), and in 2005 at the same stations (RM becoming Old River Mouth: ORM), plus the new river mouth (NRM) resulting from the morphological evolution of the SRE. The study showed marked seasonal variations that affected the structure and distribution of zooplankton as well as major changes caused by the sandbar opening: - increased marine influence throughout the whole SRE, - changes in the horizontal gradients, - arrival of euryhaline species and increase in meroplankton, in particular decapod larvae, - transformation of the ORM area into a slackwater area with limited exchanges and the highest zooplankton numbers during high waters