Temporal changes in the composition and abundance of the macro-benthic invertebrate communities at dredged material disposal sites in the anse à Beaufils, baie des Chaleurs, eastern Canada

Temporal changes in the composition and abundance of the macro-benthic invertebrate communities were studied at dredged sediment disposal sites located near L'Anse-à-Beaufils, baie des Chaleurs, Québec, Canada, in July and September 1994. A total of 5109 m 3, 2485 m 3 and 6002 m 3 of dredged material from L'Anse-à-Beaufils harbour were damped within the study area in 1992, 1993 and 1994, respectively. Pre-disposal collection of samples was conducted from 4 to 13 July 1994 at five stations located within the targeted dumpsite of 1994 as well as at five nearby control stations. Post-disposal sample collection was carried out from 5 to 16 September 1994. 15 days after the 1994 disposal activities ceased, at five stations in each of the 1994, 1993 and 1992 dumping areas (15 stations total) as well as at five stations in the control zone. The impact was estimated at the community level of the system, using both descriptive statistics and multivariate analytical methods. The surface sediment composition and the benthic community structure were changed drastically shortly after the open-sea deposition of dredged materials. The faunal response may be characterized as a decrease in the density of the less opportunistic families and a major increase in the density of families with the most opportunistic life-style. Both direct burial by dredged sediment discharged in large quantities within a short time interval and an enhanced food supply are the two factors that may explain the changes in density in various families. More than 2 years are required for the disturbed areas to re-establish a sediment composition and a macro-benthic community structure similar to undisturbed areas of the Anse à Beaufils sea bottom.