The spatial distribution of the muddy fine sand community from the Bay of Veys (western English Channel) were investigated during spring and autumn 1997. A grid of 55 and 54 sites was sampled in ...March and October, respectively, using two replicates per site of a Hamon grab (0.25 m
2) for macrofauna collection and an additional one for sediment analysis. A total of 172 species were sampled with a dominance of polychaetes, followed by crustaceans and bivalves. The species richness and abundance show low temporal changes despite higher values in October than in March. In March, the mean abundance was 165 ind. 0.5 m
−2; in October, the mean abundance was 212 ind. 0.5 m
−2. Four assemblages from the
Abra alba–
Pectinaria koreni community were identified corresponding to a bathymetric and sedimentary gradient from muddy fine sands with high levels of fine particles in shallow water to fine sands in deeper water. The discussion focuses on factors prevailing on the spatial structure of sandy communities in the English Channel.
Along the coast of France in the English Channel, muddy fine-sand communities are restricted to bays and estuaries, but in the southern North Sea they stretch out to larger areas (mesoscale ...continuum). We studied three regions containing these communities, each subject to different hydrological conditions and contrasting trophic structures of the water column. The Bay of Morlaix was strongly affected by the “Amoco Cadiz” oil spill of 1978 and recovered slowly. The Bay of Seine is influenced by high levels of nutrient input from the River Seine. A retention structure exists in the eastern part ensuring recruitment stability. The Gravelines area in the southern North Sea was invaded by the American jackknife clam (Ensis directus), which became a key species several years after its accidental introduction. These areas are important nursery grounds for demersal fish species. The distribution and evolution in trophic structure and diversity of macrofauna were analysed in each region, permitting the identification of the roles of disturbance and natural factors in the organization and long-term evolution (including recovery after an event) of the communities. The effects of different spatial scales of observation on the resulting image of macrobenthic community evolution are discussed.
Data from samples of the macrobenthic
Abra alba–
Pectinaria koreni community of the eastern Bay of Seine (English Channel) collected in winter 1986 are analysed to illustrate the advantages of a ...novel method of multivariate analysis of spatial patterns described by Thioulouse et al. (Environ. Ecol. Stat., 2 (1995) 1–14), consisting of local and global approaches. Multivariate ordination procedures are applied that take spatial components into account explicitly through the construction of a neighbourhood graph between closely placed sampling sites, which is then used to weight the data. The result is a decomposition of spatial structure on local and global scales. This method is for the first time applied to macrobenthic data of this region. It shows the underlying importance of spatial scaling in analysis and proves to offer more information than classical ordination methods such as correspondence analysis, which may confuse the two different spatial scales. Global analysis is proposed as a powerful tool to define species assemblages and local analysis as an additional instrument to define partitions resulting from biological interactions. Additionally, this method appears capable of incorporating rare species (which influence classical analyses, often resulting in their elimination from datasets) by minimising their effects on the global scale and conversely maximising them on the local scale. This analysis demonstrates the importance of explicitly incorporating spatial information into the detection and interpretation of patterns in a macrobenthic community.
Thèse de doctorat : Océanologie biologique : Lille 1 : 2002.
N° d'ordre (Lille) : 3160. Résumé en français et en anglais. Textes en français et en anglais. Bibliogr. p. 120-129. Notes bibliogr.
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