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Continued disappearance of the benthic amphipod Diporeia spp. in Lake Michigan: is there evidence for food limitation?

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Abstract:

Benthic surveys were conducted in the southern basin of Lake Michigan and throughout the lake to assess trends in benthic populations, emphasizing recent changes in densities of the benthic amphipod Diporeia spp. and dreissenid mussels. In the southern basin, Diporeia populations declined 89%, 91%, and 45% between 1993 and 2002 at sites <30, 31–50, and 51–90 m, respectively. Lakewide, the population declined 65% between 1994–1995 and 2000. Over the same time period, dreissenid densities, particularly Dreissena bugensis, increased. Intensive studies at 45 m sites in the southeastern region examined changes in lipid content, age structure, and benthic food inputs relative to the hypothesis that food limitation was a factor in Diporeia's disappearance. As Diporeia densities declined to zero, length–weight remained unchanged, and lipid content generally increased. Recruitment still occurred, but the young did not survive to become adults. Based on organic carbon, biogenic silica, and chlorophyll collected in sediment traps and found in the upper sediments, pelagic inputs to the benthic region still occurred. Our field observations and laboratory experiments did not disprove the hypothesis that food limitation from dreissenid filtering activities was the cause of the decline, but direct relationships between the loss of Diporeia and indicators of food availability were difficult to establish.

Nous avons inventorié le benthos dans le bassin sud du lac Michigan ainsi que dans le lac dans son ensemble afin de déterminer les tendances dans les populations benthiques, en particulier les changements récents de densité de l'amphipode benthique Diporeia spp. et des bivalves dreissénidés. Dans le bassin sud de 1993 à 2002, les populations de Diporeia ont diminué respectivement de 89 %, 91 % et 45 % dans les sites situés à <30, 31–50 et 51–90 m, respectivement. À l'échelle du lac, les populations ont diminué de 65 % entre 1994–1995 et 2000. Durant la même période, les densités des dreissénidés, particulièrement de Dreissena bugensis, ont augmenté. Des études poussées aux sites de 45 m ont évalué les changements du contenu lipidique, de la structure d'âge et des apports de nourriture benthique en relation avec l'hypothèse voulant que la carence de nourriture soit un facteur dans la disparition de Diporeia. Au moment où les densités de Diporeia déclinaient vers zéro, la relation longueur–masse est restée inchangée et le contenu lipidique a en général augmenté. Il y avait encore du recrutement, mais les jeunes ne survivaient pas jusqu'à l'âge adulte. D'après les mesures de carbone organique, de silice biogénique et de chlorophylle effectuées dans les pièges à sédiments et dans les sédiments superficiels, il y avait encore des apports pélagiques vers la région benthique. Nos observations de terrain et nos expériences de laboratoire ne permettent pas de rejeter l'hypothèse d'une limitation alimentaire causée par les activités de filtration des dreissénidés comme cause du déclin, mais il est difficile d'établir des liens directs entre la perte des Diporeia et les indicateurs de disponibilité de nourriture.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: April 1, 2006

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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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