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Recent declines in benthic macroinvertebrate densities in Lake Ontario

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Abstract:

Surveys of benthic macroinvertebrates conducted in Lake Ontario during 1994 and 1997 revealed recent declines in populations of three major taxonomic groups: Oligochaeta, Sphaeriidae, and Diporeia spp. (Amphipoda), with the most drastic reductions occurring in the latter. Results from sediment measurements were used to classify deepwater sediments into three habitat zones. Densities of all three taxa declined in the shallowest (12–88 m) of the sediment zones between 1994 and 1997; the greatest changes in density were observed for Diporeia, which declined from 3011 to 145 individuals·m–2, and for total benthic macroinvertebrates, which declined from 5831 to 1376 individuals· m–2. Mean densities of Dreissena spp. in 1997 were highest in the shallowest zone, and the areas of greatest densities corresponded to areas of largest reductions in Diporeia populations. We believe that dreissenids are competing with Diporeia by intercepting the supply of fresh algae essential for Diporeia survival. A decline in macroinvertebrate densities, especially populations of an important food item such as Diporeia, in Lake Ontario sediments at depths of 12–88 m may have a detrimental impact on the benthic food web.

Des inventaires des macroinvertébrés benthiques du lac Ontario en 1994 et 1997 ont révélé des déclins récents dans les peuplements de trois importants groupes taxonomiques, les oligochètes, les sphaeriidés et, de façon encore plus marquée, les amphipodes Diporeia spp. Des analyses de sédiments ont permis de classifier les substrats de la zone profonde en trois types d'habitats. Les densités des trois taxons ont diminué dans la zone la moins profonde (12–88 m) de 1994 à 1997; les déclins les plus importants se sont manifestés chez les Diporeia, don't les densités sont passées de 3011 à 145 individus·m–2, et dans le peuplement total de macroinvertébrés qui a baissé de 5831 à 1376 individus·m–2. Les densités moyen nes les plus élevées de Dreissena spp. en 1997 ont été retrouvées dans la zone la moins profonde, leurs densités maximales correspondant aux régions des plus forts déclins des peuplements de Diporeia. Nous croyons que les dreissénidés font compétition aux Diporeia en leur bloquant l'accès aux algues fraîches nécessaires à leur survie. Un déclin des densités des macroinvertébrés, particulièrement celui d'une ressource alimentaire importante comme les peuplements de Diporeia, dans les sédiments du lac Ontario aux profondeurs 12–88 m peut avoir un effet néfaste sur le réseau alimentaire benthique.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2001

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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