Use of stable isotope signatures (δ13C & δ15N) in the Black Sea Danubian area – new approach for understanding the influence of terrestrial discharge upon the marine ecosystem

Abstract. Coastal marine zones located in front of large rivers are of major biological interest. In these areas, the origin of the organic matter is complex and highly variable. The continental inputs, added to the nutrients already present in the marine environment, influence considerably the productivity and functioning of the ecosystems. Used for the first time in aquatic ecology on the Romanian coast, the proportion of stable isotopes of carbon (13C/12C) and nitrogen (15N/14N) allowed the identification of the organic material sources (terrestrial and marine) as well as the analysis of the food webs due to the predictable isotopic relation between consumers and their food. Preliminary analyses of stable isotopes of the particulate organic matter POM of the Danube water as well as marine POM, sediments and marine organisms were made on 186 samples collected at 10 stations in October 2004. The identification of the isotopic signatures of the main sources of organic material (terrestrial and marine) was achieved along with those of some groups of marine organisms present in this area (macrophytes, bivalves, polychaetes, amphipods, macrurans, brachyurans and fish). The results obtained in the Black Sea were compared with those of the Mediterranean Sea seawards the Rhone river and showed that the isotopic signatures of the two river POM were close to each other, whereas they largely differed in marine phytoplankton and macrophytes

Catching invasive Chinese mitten crabs whilst releasing the endangered European eel and other fish by-catch:The implications of fyke net design

Modifications of a traditional fyke net design were trialled in 42 hauls over 5 months at 42 locations in the Thames estuary, London. These trials were to determine whether the modified nets could be used to catch invasive mitten crabs while at the same time releasing endangered eels, back into the river. The modifications included rings of different diameters fixed into the netting to provide escape apertures and also a variation in mesh size. A standard, unmodified net was included as a control. Captured mitten crabs, eels and other fish by-catch were measured and recorded for all deployed nets. Mitten crabs and eels were caught in all nets except those of the largest mesh size (70 mm) which caught no eels. This may have been the combined effect of the mesh size and it being set on the square, versus the normal diagonal netting which may become increasingly constricted in one axis, under tension. Such a square mesh net could be used to trap crabs of carapace width > 65 mm, while releasing all eels. The smallest rings, 22 mm internal diameter, inserted into the mesh may have allowed the escape of eels < 35 cm length, but retained larger, market legal, individuals. This suggests that a slightly smaller escape ring could potentially be used to release eels of ≤ 30 cm in length, in line with current regulations

Εκτίμηση της αλιευτικής κατάστασης των ελληνικών αποθεμάτων

Σημείωση: διατίθεται συμπληρωματικό υλικό σε ξεχωριστό αρχείο

Effects of climate change and fishing on demersal ecosystems : an approach to human impacts on North East Atlantic and Spanish Mediterranean communities

Las comunidades marinas están expuestas a ciertas presiones de origen ambiental y antropogénico, entre las cuales destacan el calentamiento global y la presión pesquera. Para conservar el buen funcionamiento de los ecosistemas marinos y facilitar un uso sostenible de los servicios que proveen es necesario que su gestión se realice desde un enfoque ecosistémico. Este tipo de gestión debe apoyarse en estudios científicos que aspiren a entender los procesos que subyacen a las reorganizaciones ecológicas que suceden cuando los impactos de la pesca y el cambio climático actúan de forma combinada. Esta tesis contiene varias aproximaciones en esta línea de investigación, analizando la conexión entre los cambios composicionales observados en las comunidades y el desplazamiento de las especies en busca de sus condiciones ambientales óptimas, atendiendo también otros mecanismos ecológicos que subyacen a estos cambios, en concreto, aquellos relacionados con la sensibilidad y la resiliencia de las comunidades marinas.Global warming is at present an undeniable driver of marine communities’ reorganizations, but marine ecosystems are also exposed to other pressures of environmental and anthropogenic origin, among which the many forms of fishing stand out. In order to protect the functioning of marine ecosystems and allow a sustainable access to the services they provide, a well informed ecosystem-based management depends on the sustained generation of scientific assessments. This thesis aims at a better understanding of the processes that underlie marine communities’ reorganizations related to both warming and fishing, so as to ultimately facilitate the prevention of catastrophic shifts. Through different approaches this thesis analyzes the connection between observed compositional changes and the species tracking of their preferred niche conditions, and also examines the ecological mechanisms behind such changes, in particular those related to the marine communities’ sensitivity and resilience