The impact of a benthic filter feeder: limitations imposed by physical transport of algae to the benthos

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Abstract:

We used an acoustic Doppler profiler to investigate the hydrodynamics of a nearshore site in western Lake Erie, and we incorporated the measured parameters in numerical simulations of phytoplankton consumption by benthic zebra mussels (Dreissena polymorpha) to examine the link between pelagic production and benthic filter feeders. Daily-averaged eddy diffusivities varied from 10–5 to 10–4 m2·s–1 at our site. Our simulations demonstrate that diffusivities of this order decrease near-bed algal biomass, while algal biomass in the pelagic remains relatively unaffected. Between 8% and 67% of the algal biomass in the water column could be consumed daily, depending on the shape and magnitude of the diffusivity profile. Correspondingly, in situ vertical biomass profiles showed a near-bed zone of algal depletion, but no impact was observed near the surface. The impact of the zebra mussel in nearshore regions is expected to be stronger than in deeper open water. The flow of algal biomass into the benthos was tightly coupled with turbulent mixing, suggesting that open water algal consumption by zebra mussels is small compared with previously published estimates that ignored vertical turbulent mixing processes.

Un courantomètre acoustique à effet Doppler nous a permis d'étudier l'hydrodynamique d'un site près de la berge dans la région occidentale du lac Érié; nous avons incorporé les variables mesurées dans des simulations numériques de la consommation de phytoplancton par des moules zébrées (Dreissena polymorpha) afin d'examiner le lien qui existe entre la production pélagique et les organismes filtreurs benthiques. Les diffusivités turbulentes moyennes varient de 10–5 à 10–4 m2·s–1 à notre site d'étude. Nos simulations montrent que des diffusivités de cet ordre de grandeur diminuent la biomasse des algues près du coussin de moules, alors que la biomasse des algues dans la zone pélagique demeure relativement inchangée. Entre 8 % et 67 % de la biomasse d'algues présente dans la colonne d'eau peut être consommée à chaque jour, selon la forme et l'importance du profil de diffusivité. De la même façon, les profils verticaux de biomasse en place montrent l'existence d'une zone de densité réduite d'algues près du coussin de moules, mais aucun impact près de la surface. L'effet des moules zébrées dans les régions près des berges doit vraisemblablement être plus grand que dans les eaux ouvertes plus profondes. Le flux de la biomasse des algues vers le benthos est étroitement relié au brassage turbulent, ce qui laisse croire que la consommation d'algues d'eaux libres est faible par rapport aux estimations publiées qui ne tiennent pas compte des processus de brassage turbulent vertical.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: January 1, 2005

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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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