Pautas de distribución espacial y modelización mediante SIG del habitat de Larvas de Solea solea, Pleuronectes flesus y limanda en la parte oriental del Canal de la Mancha durante la primavera

The spring distribution of larval fish stages of flatfishes in the Dover Strait (eastern English Channel) was studied in 1995 and 1999. Fish larvae were identified and sorted according to developmental stages in order to study their ontogenic distribution. The French coastal waters are characterised by an unstable tide-dependent front, which influences larval dispersion. In spring, the French coastal waters have a high phytoplanktonic production. They have higher temperatures, lower salinities and differences in current intensity compared with the central English Channel waters. Generalised Additive Models (GAM) combined with Geographic Information Systems (GIS) were used to model the potential habitats of life stages considering data from three major surveys in this area. The models were developed by coupling presence-absence models with non-null abundance models. The potential habitat of larval stages was then mapped using a geostatistical method (kriging). This revealed different species strategies in which young stages were abundant in central waters and older ones were distributed mainly along the French and Belgian coasts. It is concluded that the central English waters are important for young stages after hatching and that coastal waters are essential nurseries for future juveniles. The models of three flatfish species having similar life cycle strategies are presented here: Limanda limanda, Platichthys flesus and Solea solea.Durante 1995 y 1999 se estudió la distribución primaveral de los estadios larvarios de peces planos en el Estrecho de Dover (parte oriental del Canal de la Mancha).Las larvas de peces fueron identificadas y separadas en función de su estadio de desarrollo con objeto de estudiar su distribución ontogénica. Las aguas costeras francesas se caracterizan por un frente de marea inestable, que influencia la dispersión larvaria. Durante la primavera, dichas aguas presentan una elevada producción fitoplanctónica. Asimismo, presentan altas temperaturas, bajas salinidades y diferencias en la intensidad de la corriente, comparado con las aguas centrales del Canal de la Mancha. A partir de datos obtenidos en tres amplias campañas en este área, se utilizaron Modelos Aditivos Generalizados (GAM) con Sistemas de Información Geográfica (SIG) para modelizar los hábitats potenciales de los estadios larvarios. Los modelos se desarrollaron uniendo modelos de “presencia-ausencia” con modelos de “abundancia no nula”. A continuación, usando métodos geoestadísticos (kriging) se representó el mapa del hábitat potencial de los estadios larvarios. Esto reveló diferencias en las estrategias de aquellas especies cuyos primeros estadios son abundantes en las aguas centrales y cuyos estadios más avanzados están distribuidos principalmente a lo largo de la costa francesa y belga. Se mostró la importancia de las aguas centrales del Canal de la Mancha para las larvas lecitotróficas, y como las aguas costeras son áreas de cría esenciales para los futuros juveniles. Aquí se presentan los modelos para tres especies de peces planos que tienen estrategias de vida similares: Limanda limanda, Platichthys flesus and Solea solea

Introductions of fish and crabs in the Schelde estuary

Since 1991, we have systematically recorded the fish and crab fauna of the Schelde estuary in samples of power plants cooling water and of fyke nets. In this period, we found 71 species of which eight were introduced (table 1). Additionally, one native and three non indigenous crab speices were observed. All non native marine species recorded in the estuary arrived from North America. Probably, their presence is due to transport via the ballast water of ships docking at the port of Antwerp. All non native freshwater species in the estuary arrived from eastern Europe and Asia. The occurrence of these species in the estuary is almost invariably due to deliberate introductions. The most recent observations of non-indigenous species in the Schelde estuary date from October 2001 when two young Vimba vimba and an adult Micropogonias undulatus were caught nearby the Dutch-Belgian border (Stevens et al., submitted). These species have not been recorded yet in Belgium

Host records and geographical distribution of Corynosoma magdaleni, C. semerme and C. strumosum (Acanthocephala: Polymorphidae).

A literature survey was conducted to investigate the host and geographical distribution patterns of three Corynosoma species (Acanthocephala: Polymorphidae), viz. C. magdaleni, C. semerme and C. strumosum. All three species appear to be restricted to the Northern Hemisphere. Occurrence records of C. magdaleni are limited to the Northern Atlantic coasts, while C. semerme has a circumpolar distribution. The geographical range of Corynosoma strumosum encompasses the distributions of the other two species, but also extends into warmer southern regions. Some Corynosoma populations are living with their definitive hosts in very isolated locations, such as in the brackish Baltic Sea or different freshwater lakes (e.g. Lake Saimaa). All three species have a heteroxenous life cycle, comprising a peracaridan intermediate host, a fish paratenic host and a mammalian definitive host. Occasionally, an acanthocephalan may enter an accidental host, from which it is unable to complete its life cycle. The host records reported here are categorised by type, i.e. intermediate, paratenic, definitive or accidental. While most of the definitive hosts are shared amongst the three Corynosoma species, C. strumosum showed the broadest range of paratenic hosts, which reflects its more extensive geographical distribution. One aim of this study and extensive literature summary is to guide future sampling efforts and therewith contribute to throw more light on the on-going species and morphotype discussion for this interesting parasite species

Protozoa parasitic in fish

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Managing ichthyophonus in multi-species exhibits at the two oceans aquarium

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol)Ichthyophonus hoferi has been diagnosed in multiple species at the Two Oceans Aquarium, this study focuses on Rhabdosargus globiceps (White stumpnose). I. hoferi is a mesomycetozoan parasite that multiplies in blood rich organs in the fish hosts causing a wide range of clinical signs resulting in organ dysfunction. I. hoferi can be diagnosed from microscopic examination of tissue squash preparations, culture, polymerase chain reaction (PCR) and histopathology. In the literature only lethal methods of diagnosis are described. The development of a non-lethal diagnostic tool for disease monitoring is vital for collections where euthanasia of specimens is not possible

The ecology of the benthos in Liverpool Docks.

A broadscale survey of the benthos was carried out in the docks around Liverpool and the results indicated that the walls of the majority of the South Docks were dominated by Mytilus edulis. This species tended to be less abundant in docks close to the intake from the Mersey while Molgula manmattensis tended to be more abundant at these sites. These differences may be due to a combination of either increased suspended solids or decreased phytoplankton. The walls of Albert, Queens and Princes Docks were surveyed over a three year period. The results indicated that the abundance of Mytilus was relatively constant between years. Other more ephemeral species, such as Ciona, showed considerable variation both within and between years. Closer examination of the Mytilus population structure has indicated that it was dominated by one or two cohorts which had settled in 1988 - 1989. Much less recruitment has occurred subsequently. Reasons for this lack of recruitment are examined, however, the most likely explanations are increased predation from Carcinus and/or intraspecific interactions from the adult bed, either filtering out Mytilus larvae or reducing food supply to new settlers. Monitoring of the zooplankton indicated considerable temporal and spatial variation, despite the fact that the docks are effectively a closed ecosystem. The observed variations are attributed to either adult or larval behaviour or changes in primary production affecting secondary production. Tiles have been used to follow the pattern of annual succession and the effect of timing of available space on this pattern of succession. Results were integrated with changes observed in the wall benthos and variations in larval supply. Considerable differences were observed in the community that developed on suspended tiles, tiles fixed to the dock wall and cleared areas of the dock wall. One of the primary factors affecting this was thought to be reduced food supply on the wall due to the dense filter feeding assemblage there. No evidence was found of any strong interspecific interactions in the successional sequence. Rather, the community composition was typical for the time of year. The community development is described with regard to the life-history strategies of the species in the fouling assemblage. Tiles were also used to look at the annual pattern of algal settlement. This indicated that diatoms were the principal settlers early in the year, brown ephemerals such as Giffordia and Punctaria during spring and green ephemerals such as Enteromorpha and Cladophora over the summer period. Amphipods were the dominant grazers of this assemblage. Tiles left in place for two to three months initially developed dense algal growth but this was subsequently replaced by a cover of Botryllus. This change was thought to be accelerated by the grazing amphipods. No perennial algae were recorded in the docks; reasons for this are proposed. Finally, an assessment is made of the overall stability of the benthic ecosystem found in the docks around Liverpool and a number of possible management options, which could be used to improve the stability, are suggested

The impact of multiple stressors on coastal biodiversity and associated ecosystem services

Marine and coastal ecosystems are subject to diverse and increasingly intensive anthropogenic activities, making understanding cumulative effects critically important. However, accurately accounting for the cumulative effects of human impacts can be difficult, with the possibility of multiple stressors interacting and having greater impacts than expected, compounding direct and indirect effects on individuals, populations, communities and ecosystems. Assessment of multiple stressors therefore requires extensive scientific research that directly tests how single or multiple ecological components are affected by stressors, both singly and when combined, and as a consequence, cumulative effects assessments are now increasingly included in environmental assessments. Currently, there is a need to assess these at larger spatial scales, with additional research also urgently needed on the responses of ecological components, processes and functions to single and cumulative stressors. As cumulative environmental impacts could be better addressed by regional stressor effects assessments that combine methods for predicting multiple pressures on ecosystem recovery alongside degradation, this study used several separate approaches that can be used in parallel to give support for local management measures. I tested four completely different methods – a range of multi-metric indices, a food web model (Ecopath), a predictive model (Ecosim) and a Bayesian Belief Network model. Each approach was tested and compared in two shallow water estuarine systems, in Scotland and England, initially concerning the impact of nutrient enrichment and subsequent recovery and was followed by an investigation of how the addition of multiple stressors (nutrient levels, temperature and river-flow rates) would impact the future state of each system. The response to stressors was highly context dependent, varying between and within geographic locations. Overall, each of the four different approaches complemented each other and gave strong support for the need to make big reductions in the pressures and to consider trade-offs between impacting pressures. The models and tools also indicate that in order to reach an improved overall environmental state of each ecosystem, a focus on nutrient reductions are likely to be the most effective of the controls on stressors explored and that cumulative effects of the management of nutrient inputs and increased water temperatures and river-flow are likely to exist