Research Document - 2007/018
Distribution of benthic invertebrates in the Estuary and Gulf of St. Lawrence
By Chabot, D., A. Rondeau, B. Sainte-Marie, L. Savard, T. Surette, and P. Archambault
Abstract
This study had two objectives. The first was to gather all the available data from scientific surveys both at the Maurice-Lamontagne Institute (MLI) and the Gulf Fisheries Centre (GFC) in order to establish distribution patterns and relative abundance of benthic invertebrates in the lower estuary and the gulf of St. Lawrence (LEGSL). The second objective was to propose Ecologically and Biologically Significant Areas (EBSAs) for benthic invertebrates of the LEGSL, according to these distribution and relative abundance data.
Surveys from the MLI are mainly conducted in the lower estuary and in the northern gulf of St. Lawrence (nGSL) but some cover Gaspesie, including Chaleurs bay, and the Magdalen Islands. The southern gulf of St. Lawrence (sGSL) is covered by the GFC surveys. The bulk of the information presented here comes from annual scientific surveys carried out by the two regions: the multi-species survey and the mobile gear Sentinel survey by the MLI and the fall survey, snow crab survey, and Northumberland survey by the GFC. Several other surveys by MLI provided useful data, some even with a long time series but with limited geographical coverage (surveys for snow crab, scallop and surf clam), while others were conducted less frequently and at a small geographic scale (surveys for clam and whelk). Cod and Greenland halibut stomach contents have also been used as a sampling device for the distribution on some benthic invertebrates. Despite the large number of surveys considered here, the coastal zone (less than 50 m deep in the Estuary and the nGSL and less than 30 m deep in the sGSL) was not adequately sampled, except for the Northumberland Strait.
In the main section of this document, distributions of 44 taxa are presented and have guided the identification of EBSAs: 4 general groups (soft corals, anemones, sponges, ascidians), 5 echinoderms, 6 molluscs, 1 mysid, 22 shrimps, and 6 crabs. Zones of maximum relative abundance of each taxa, weighted inversely to their surface area of high abundance, were used to calculate an index of benthic invertebrate concentration for each 10 x 10 km square sampled in the study area. This index was the primary tool in the identification of potential EBSAs. As a result, 17 EBSAs for benthic invertebrates are proposed. However, it is important to keep in mind that only a small proportion (approximately 0.02%) of the benthic invertebrate species known to be present in the study area was considered in the process. In particular, the lack of data for the coastal zone is a major gap. We present in appendix to this report the data on 6 coastal species that we were able to obtain.
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