Continental‐scale patterns of nutrient and fish effects on shallow lakes: synthesis of a pan‐European mesocosm experiment

Abstract

1. Results are analysed from 11 experiments in which effects of fish addition and nutrient loading on shallow lakes were studied in mesocosms. The experiments, five in 1998, six in 1999, were carried out in six lakes, distributed from Finland to southern Spain, according to a standard protocol. 2. Effects of the treatments on 29 standard chemical, phytoplankton and zooplankton variables are examined to assess the relative importance of bottom-up (nutrient enrichment) and top-down (fish predation) effects. For each year, the experiments in different locations are treated as replicates in a meta-analysis. Results of individual experiments are then compared in terms of the patterns of significant influences of nutrient addition and fish predation with these overall results (the baseline), and between years in the same location. 3. The overall meta-analysis gave consistent results across the 2 years, with nutrient loading influencing all of the chemical variables, and on average 31% of primary producer and 39% of zooplankton variables. In contrast, fish influenced none of the chemical variables, 11% of the primary producer and 44% of the zooplankton variables. Nutrient effects on the system were thus about three times greater than fish effects, although fish effects were not inconsiderable. 4. The relative importance of nutrients and fish in individual experiments often differed between years at the same location and effects deviated to varying degrees from the baseline. These deviations were treated as measures of consistency (predictability) of conclusions in repeat experiments. Consistency increased southwards and this is interpreted as a consequence of more variable annual weather northwards. 5. The influence of nutrient loading was greater southwards and this was probably manifested through naturally greater annual macrophyte abundance in warmer locations in consequence of the longer plant growing-season. There was no trend in the relative importance of fish effects with latitude but this may partly be an artefact of the simple fish Correspondence: Brian Moss,

Food web (bio-)manipulation of South African reservoirs – viable eutrophication management prospect or illusory pipe dream? A reflective commentary and position paper

“…In contrast to top-down effects, the bottomup influences of cichlids may be very significant, as documented by Starling et al (2002). Since bottom-up effects of nutrient availability appear to increase with declining latitude (Moss et al, 2004), the role of these cichlids may lie primarily in nutrient regeneration rather than top-down predatory influences.…”

“…Even overseas, its appeal is under scrutiny. Gulati and Van Donk (2002) accede that failures exceeded successes in The Netherlands, while experimental data compiled by Moss et al (2004) demonstrate the increasing importance of bottomup nutrient controls as latitude declines -i.e. as waters become warmer, whereas top-down effects of fish predation remained comparable across latitudes (although this is recognised as a possible experimental artefact).…”

Lakes and society: Mirrors to our past, present and future

“…Fish manipulations may be so rapidly counteracted by natural growth and species substitution that biomanipulation becomes ineffective. In a series of mesocosm experiments carried out along a latitudinal gradient in Europe, the effect of nutrient manipulation on a series of 29 chemical and biological variables was greater than that of fish manipulation with latitude southwards (Moss et al 2004). In warmer lakes, the predation by fish on zooplankton is so intense that the trophic cascade (Carpenter et al 1985) is effectively annulled, and algal growth is dominated from the bottom up by the availability of nutrients.…”

Effects of grass carp introduction on macrophyte communities in a shallow lake

“…In most cases it is caused by intentional or unintentional human activity. Other mechanisms have also been suggested (e. g. Hargeby et al 2004Hargeby et al , 2007Moss et al 2004). Fish grazing is considered as a potential factor that can induce a shift from clear and turbid water, however enclosure experiments on effects of fish introduction in shallow lakes have been performed mostly with the use of zooplanktivorous fish Hietala et al 2004; Van de Bund, Van Donk 2004).…”