Vertical distribution of fish larvae in the Canaries-African coastal transition zone in summer

This study reports the vertical distribution of fish larvae during the 1999 summer upwelling season in the Canaries-African Coastal Transition Zone (the Canaries-ACTZ). The transition between the African coastal upwelling and the typical subtropical offshore conditions is a region of intense mesoscale activity that supports a larval fish population dominated by African neritic species. During the study, the thermal stratification extended almost to the surface everywhere, and the surface mixed layer was typically shallow or non-existent. Upwelling occurred on the African shelf in a limited coastal sub-area of our sampling. The vertical distributions of the entire larval fish population, as well as of individual species, were independent of the seasonal thermocline. Fish larvae and mesozooplankton were concentrated at intermediate depths regardless of the thermocline position, probably because of its weak signature and spatial and temporal variability. Day/night vertical distributions suggest that some species did not perform diel vertical migration (DVM), whereas others showed either type I DVM or type II DVM. The opposing DVM patterns of different species compensate for each other resulting in no net DVM for the larval fish population as a whole.     

Effects of the toxic dinoflagellate <Emphasis Type="Italic">Gymnodinium catenatum</Emphasis> on uptake and fate of paralytic shellfish poisons in the Pacific giant lions-paw scallop <Emphasis Type="Italic">Nodipecten subnodosus</Emphasis>

Juvenile Pacific giant lions-paw scallops Nodipecten subnodosus were fed the toxic dinoflagellate Gymnodinium catenatum, a producer of paralytic shellfish poison (PSP), supplied with Isochrysis galbana (a nontoxic microalgae). Short-term (<24 h) experiments were performed to determine clearance and ingestion rates of G. catenatum. Kinetics of PSP was examined in longer-term experiments (>2 days). At high food concentrations, juvenile scallops showed production of pseudofeces, partial shell valve closure, and reduction in feeding. According to HPLC analysis, the only toxins present in the dinoflagellate G. catenatum and in the scallops were the gonyautoxins (GTXs), except in the labial palps and digestive gland, where trace amounts of saxitoxin (STX) were present in scallops. These tissues could play an important role in toxin biotransformation. The ranking of toxin concentration in tissues was: digestive gland > labial palps > intestine > gills > mantle > adductor muscle, where the total contribution of viscera was more than 80% of the total toxin body burden. Juvenile scallops exhibited no apparent detrimental physiological responses during the long-term feeding experiment. The dinoflagellate may contribute nutrients to the scallop, in addition to the microalgae I. galbana. The dinoflagellate may enhance cell uptake and byssus production. Once PSP accumulated during the first 12 days, it was slowly eliminated. The limited capacity for accumulating toxins in the adductor muscle favors domestic marketing of scallops.     

Impacts on seafloor geology of drilling disturbance in shallow waters

This paper describes the effects of drilling disturbance on the seafloor of the upper continental slope of the Campos Basin, Brazil, as a result of the project Environmental Monitoring of Offshore Drilling for Petroleum Exploration – MAPEM. Field sampling was carried out surrounding wells, operated by the company PETROBRAS, to compare sediment properties of the seafloor, including grain-size distribution, total organic carbon, and clay mineral composition, prior to drilling with samples obtained 3 and 22 months after drilling. The sampling grid used had 74 stations, 68 of which were located along 7 radials from the well up to a distance of 500 m. The other 6 stations were used as reference, and were located 2,500 m from the well. The results show no significant sedimentological variation in the area affected by drilling activity. The observed sedimentological changes include a fining of grain size, increase in total organic carbon, an increase in gibbsite, illite, and smectite, and a decrease in kaolinite after drilling took place.     

The genetic mating system of a sea spider with male-biased sexual size dimorphism: evidence for paternity skew despite random mating success

Male-biased size dimorphism is usually expected to evolve in taxa with intense male–male competition for mates, and it is hence associated with high variances in male mating success. Most species of pycnogonid sea spiders exhibit female-biased size dimorphism, and are notable among arthropods for having exclusive male parental care of embryos. Relatively little, however, is known about their natural history, breeding ecology, and mating systems. Here we first show that Ammothella biunguiculata, a small intertidal sea spider, exhibits male-biased size dimorphism. Moreover, we combine genetic parentage analysis with quantitative measures of sexual selection to show that male body size does not appear to be under directional selection. Simulations of random mating revealed that mate acquisition in this species is largely driven by chance factors, although actual paternity success is likely non-randomly distributed. Finally, the opportunity for sexual selection (I _s), an indirect metric for the potential strength of sexual selection, in A. biunguiculata males was less than half of that estimated in a sea spider with female-biased size dimorphism, suggesting the direction of size dimorphism may not be a reliable predictor of the intensity of sexual selection in this group. We highlight the suitability of pycnogonids as model systems for addressing questions relating parental investment and sexual selection, as well as the current lack of basic information on their natural history and breeding ecology.     

Surface-enhanced Raman scattering of the adsorption of pesticide endosulfan on gold nanoparticles

The absorption of pesticide endosulfan on the surface of gold nanoparticles results from the formation of micrometric structures (1–10 μm) with irregular shape because of the aggregation of individual particles. Such aggregation of gold nanoparticles after absorption of pesticide shows a surface-enhanced Raman scattering (SERS) spectrum, whose intensity depends on the concentration of endosulfan. In addition, the discoloration of the colloidal solution and a diminishing of the intensity of the surface plasmon resonance absorption from individual particles were observed by UV-visible spectroscopy. At the same time, a second band between 638 and 700 nm confirms the formation of aggregates of gold nanoparticles as the concentration of endosulfan increases. Finally, we used the SERS intensity of the S?O stretching vibration at 1239 cm^?1 from the SO₃ group as a measure of concentration of pesticide endosulfan. This method could be used to estimate the level of pollution in water by endosulfan in a simple and practical form.     

Ecological Correlates of Whooping Crane Use of Fire-Treated Upland Habitats

The only remaining wild population of the endangered Whooping Crane ( Grus americana ) winters in salt marsh habitats of the Texas (U.S.) coast. Whooping Cranes are known to respond and utilize nearby upland habitats after a tire treatment has been applied. We investigated several factors that may attract Whooping Cranes to recently burned sites at Aransas National Wildlife Refuge between 1982 and 1994 and whether cranes utilize upland habitats primarily in response to a recent fire treatment or whether they occur regularly on uplands regardless of burning. We evaluated the effect of different years, burn site location, date of burn, and acorn production on crane use of specific burn sites. Crane use was determined with ground surveys from 1982 through 1985 and from weekly aerial surveys between 1986 and 1994. Whooping Cranes used fire-treated upland habitats to a significantly greater extent than unburned sites. The response of cranes to recently burned sites was greatest immediately after fire treatment and declined with time. No significant difference was found in crane use of burned sites among different years. Similarly, time of burn and acorn production had no significant effect on crane use of fire-treated habitats. Crane use among specific burn units differed significantly. We suggest that Whooping Cranes may be using fire-treated upland habitats to feed on recently killed vertebrates and invertebrates plus recently exposed plant items. Because cranes primarily inhabit salt marsh habitats, the availability of alternate food sources may be of considerable importance, particularly during years when marsh foods are scarce. But because it appears that areas must be burned to facilitate use by Whooping Cranes, we suggest that the extent of prescribed burning be based on reduced availability of marsh food resources and not on acorn production estimates alone.