Résumé: Sulphur-oxidising endosymbiont-bearing bivalves often inhabit seagrass meadows, where they can control sulphide levels and variably contribute to carbon cycling, by feeding on endosymbiotic bacteria and/or on particulate organic matter from the water column. The patterns of variability in their feeding mode and their spatial distribution within the seagrass meadows are however poorly studied. Seagrass beds form naturally patchy habitats with seagrass-sand edges that may have variable effects on different organisms. The present study aims at understanding differences in feeding mode and abundance of the endosymbiont-bearing bivalve Loripes lacteus (sensu Poli, 1791) as well as the physiological conditions of its endosymbiotic populations between edge and inner portion of meadows of the eelgrass Nanozostera noltii (Hornemann). In July 2010, Loripes specimens were sampled in 4 eelgrass patches at 2 different locations in the Thau lagoon, South of France. There was a clear negative edge effect on the abundance of small individuals of Loripes, while large individuals were homogeneously distributed between edge and inner part of the meadow. Although Loripes isotopic signatures (delta C-13 and delta N-15) were always closer to those of its symbiotic bacteria than to those of suspension-feeding bivalves, eelgrass edge enhanced mixotrophic behaviour of small animals, which assimilated less bacterial carbon and nitrogen at the edge than in the inner part of the eelgrass meadow. No differences related to eelgrass edges were instead found for the bacterial populations harboured by Loripes. Rather, flow cytometry revealed large variability at small spatial scales. Although bacteria were always important for the nutrition of Loripes, these findings showed that seagrass edges may contribute to regulate feeding mode and population structure of Loripes, which may have implications for seagrass functioning. (C) 2012 Elsevier B.V. All rights reserved.

Résumé: While the global network of marine protected areas (MPAs) has recently been evaluated in the light of bio-geographic targets, there has been no attempt to evaluate the relative conservation efforts made by the different nations with regards to their level of socio-economic development. Using information mostly gathered from the world database on protected areas (WDPA), this paper gives a comparative assessment of MPA progress in countries from different economic categories, ranging from advanced economies to least developed countries (LDCs). Potentially explanatory socio-economic and environmental factors, such as fishing activity and existence of vulnerable marine ecosystems, for variability between nations in the level of MPA implementation are also explored. Existing MPA databases demonstrate a clear gap between developed and developing nations in MPA establishment, with advanced economies accounting for two thirds of the global MPA network. Patterns of MPA use, however, remain extremely heterogeneous between countries within each development group. International agreements on marine conservation, above and beyond the influence of country socioeconomic and environmental profiles, are identified as a stimulating factor to MPA implementation. The level dependence on marine resource extraction appears to impede MPA implementation, though the relationship is not statistically significant due to large heterogeneity among countries. Leading developed nations increasingly use MPAs to designate integrated and adaptive management areas, and implementation of large “no-take” reserves in relatively-pristine overseas areas continues to accelerate. These analyses highlight certain limitations regarding our ability to assess the true conservation effectiveness of the existing global MPA network and the need for improved indicators of MPA restrictions and management efforts.