Responses of a Mediterranean soft bottom community to short-term (1993-1996) hydrological changes in the Rhone river.
The polychaete fauna of muddy bottoms off the Rhone delta (NW Mediterranean) was seasonally sampled at two sites at 70 m depth, from 1993 to 1996. During this period, five severe flood events occurred. A clustering analysis (distance coefficient of Whittaker) and three way fixed factor ANOVAs (site x season x year) showed strong year-to-year changes in species density and community structure, changes that masked seasonal variations. Total density increased by a factor of 3 and density of most species significantly increased following the first flooding event. Changes in the community structure were due to the successive dominance of a few species. The opportunistic species, such as Cossura sp., Mediomastus sp. and Polycirrus sp., exhibited peaks in density 1-3 months after the flood. These peaks were followed by a drastic decline. For species with a long life span, such as Sternaspis scutata, a slower but continuous increase in density was observed which was maintained for several months. The density fluctuations of these species exhibited a good correlation with river flow with time lags of 1-2 years. The successional dynamics observed are explained according to the geographical origin of the floods and the biology and feeding ecology of species.
Salen-Picard
Chantal
C
Centre d'Océanologie de Marseille, UMR CNRS 6540, station marine d'Endoume, rue de la Batterie des Lions, 13007 Marseille, France. salen@com.univ-mrs.fr
Arlhac
Denise
D
Alliot
Elisabeth
E
D000818:Animals; D004032:Diet; D004463:Ecology; D004784:Environmental Monitoring; D008136:Longevity; D019083:Mediterranean Region; D011077:Polychaeta; D011157:Population Dynamics; D012098:Reproduction; D012621:Seasons; D014872:Water Movements