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Benthic grazing and functional compensation in stressed and recovered lakes

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Abstract:

During ecosystem recovery, grazing pressure is expected to increase as larger herbivores become reestablished. Alternatively, grazing pressure may remain unchanged during recovery as large consumers replace and functionally compensate for more abundant populations of smaller, tolerant herbivores. We tested these hypotheses by conducting a 90-day experiment in which three size categories of benthic consumers were excluded from producers in three chemically stressed and three recovered lakes. Our findings showed that consumers did not significantly affect producer biomass in either type of lake. However, exposure to larger and more abundant grazers did induce a physiognomic shift towards less edible producers in the recovered lakes. In comparison, recovered lakes contained significantly greater producer biomass and diversity. Comparison of the observed subtle effects of consumers and pronounced negative impact of ecosystem stress on benthic producers suggest that they can compensate for natural disturbances (e.g., grazing), but not for the other multiple stressors associated with anthropogenic acidification of the Killarney lakes.

Durant la restauration des écosystèmes, on s'attend à ce que la pression de broutement augmente, à cause du retour des grands herbivores. D'un autre côté, la pression de broutement peut rester inchangée durant la restauration, parce que les consommateurs de grande taille remplacent les populations plus abondantes d'herbivores tolérants plus petits et compensent fonctionnellement pour eux. Nous avons testé ces hypothèses lors d'une expérience de 90 jours durant laquelle trois tailles de consommateurs benthiques ont été séparées des producteurs dans trois lacs en stress chimique et trois lacs restaurés. Nos résultats montrent que les consommateurs n'affectent pas significativement la biomasse des producteurs dans les deux types de lacs. Cependant, une exposition à des brouteurs plus abondants et de plus grande taille induit un changement physionomique qui favorise les producteurs moins comestibles dans les lacs restaurés. En comparaison, les lacs restaurés possèdent une biomasse et une diversité de producteurs significativement plus importantes. La comparaison des effets subtils des consommateurs que nous observons et l'important impact négatif du stress de l'écosystème sur les producteurs benthiques indiquent que ces derniers peuvent compenser pour les perturbations naturelles (par ex., le broutement), mais pas pour les autres multiples facteurs de stress reliés à l'acidification anthropique des lacs de Killarney.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: September 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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