Simplified food webs lead to energetic bottlenecks in polluted lakes

Abstract

Very little is known about the consequence of human activities on the flow of energy through natural ecosystems. Here, we present a trophic-based approach to describing energy relationships in pollutant-disturbed lakes, emphasizing the importance of prey diversity in maintaining energy transfer to growing fish. Both diet and community analysis indicated that the food web leading to yellow perch (Perca flavescens) in metal-polluted lakes was extremely simplified compared with reference lakes. Through the application of an in situ marker for fish activity costs (muscle lactate dehydrogenase activity) and through bioenergetic modelling, we show how this has severe consequences on the efficiency of energy transfer to perch from their prey; premature energetic bottlenecks (zero conversion efficiency) occur when successively larger prey types are not available to growing perch. These observations provide a much needed ecological and physiological framework for assessing how energy transfer can be affected in polluted systems. Our approach need not be limited therein but should be applicable to any aquatic system where food web structure is variable and (or) disrupted.Résumé : Très peu est connu au sujet de la conséquence des activités humaines sur le transfert énergétique dans les écosystèmes. Cette étude présente une nouvelle approche pour décrire des relations énergétiques dans les lacs pollués, soulignant l'importance d'une diversité de proies pour la croissance des poissons. Les analyses de contenus stomacaux et de la communauté ont indiqué que la base de nourriture disponible aux perchaudes (Perca flavescens) provenant de lacs pollués par les métaux lourds a été extrêmement simplifiée comparativement aux lacs références. Par l'application d'un indicateur enzymatique pour les coûts d'activité (natation) chez les poissons, et par l'application d'un modèle bioénergétique, cette étude démontre que ceci a des conséquences graves sur l'efficacité du transfert énergétique de proies aux perchaudes; des entonnoirs énergétiques (aucune croissance) se produisent quand des proies de différentes tailles ne sont pas disponibles successivement aux perchaudes en croissance. Ces observations fournissent un cadre écologique et physiologique important pour évaluer comment le transfert énergétique peut être affecté dans les systèmes pollués. Cette approche n'a pas besoin d'être limitée spécifiquement aux systèmes pollués, mais pourrait être aussi appliquée à tous systèmes aquatiques où la chaîne alimentaire est variable et (ou) dérangée. Rapid communication / Communication rapide 5

Live Fast and Die Young: Metal Effects on Condition and Physiology of Wild Yellow Perch from along Two Metal Contamination Gradients

“…2000; Sherwood et al 2002), intermediary metabolism (Levesque et al 2002), aerobic metabolism (Rajotte and Couture 2002;Audet and Couture 2003;Couture and Kumar 2003), and even basic morphometric condition indicators (Laflamme et al 2000;Levesque et al 2002;Pyle et al 2005;Couture et al 2008b). Although this substantial literature leaves little doubt that metals affect the condition of wild yellow perch, natural variations in fish condition likely confound interpretation of most indicators of yellow perch health.…”

“…In contrast, RN fish exceeding tissue Cd and Cu concentration thresholds generally expressed higher liver and muscle LDH activities, but exceeding Ni thresholds led to lower liver and muscle LDH activity. Muscle LDH activity in yellow perch has been used as an indicator of activity cost (Sherwood et al 2002;Kaufman et al 2006). Our data indicate that, at least for RN fish, metal contamination must be considered when LDH activity is used as an indicator of locomotion in contaminated yellow perch.…”

Recolonization of Acid-damaged Lakes by the Benthic Invertebrates Stenacron interpunctatum, Stenonema femoratum and Hyalella azteca

“…Post and Cucin (1984) showed that predation pressure on littoral benthic invertebrates by introduced yellow perch decreased biomass and body size in benthic invertebrate communities. Many other studies have shown the important interactions between fish and littoral benthic invertebrate communities (Diehl 1992, Carbone et al 1998, Sherwood et al 2002. Fish can be efficient predators and are important in structuring invertebrate communities in aquatic ecosystems ranging from streams (Wooster 1994, Nilsson et al 2008) to tropical reefs (Ayal andSafriel 1982, Dulvy et al 2004).…”

Food web of a SW Atlantic shallow coastal lagoon: spatial environmental variability does not impose substantial changes in the trophic structure

“…The structure of the assemblage of intermediate consumers that link basal OM sources and higher predators can be very relevant for food web processes and ecosystem functioning. For instance, disappearance of specific intermediate consumers may result in a simplification of the food web that compromises the efficiency of energy transfers ('energetic bottlenecks', sensu Heath & Roff 1996, Sherwood et al 2002, Iles & Rasmussen 2005. The assemblage of consumers can be modulated by food availability and environmental conditions, i.e.…”