The inverted trophic cascade in tropical plankton communities: impacts of exotic fish in the Middle Rio Doce lake district, Minas Gerais, Brazil

Abstract

The present study deals with the ecological impacts of the introduction of two alien species of piscivorous fish in several lakes of the Middle Rio Doce lake district in Minas Gerais, Brazil. It was demonstrated that these effects were not restricted only to the fish community. The introduction of the predatory red piranha Pygocentrus nattereri and the tucunaré Cichla cf. ocellaris caused not only a sharp decrease in the number of native fish species, but also major shifts in other trophic levels. Just after the fish were introduced, most lakes began to show conspicuous changes in phytoplankton species composition, in which Cyanophyceae gradually came to dominate. The zooplankton community lost several species, and in some cases, such as Lake Carioca, all the cladoceran species disappeared. On the other hand, invertebrate predators, represented by the dipteran Chaoboridae, boomed in the lake, with higher densities of exotic species, probably as a result of the "ecological release" by reduction of the original fish fauna. There was a general trend of species loss in different trophic levels. All these changes are apparently associated with decreases in water quality. The present situation in these lakes demands new approaches to the management and conservation of these ecosystems.Keywords: exotic species, eutrophication, trophic cascade, zooplankton, introductions.A cascata trófica invertida em comunidades planctônicas tropicais: Impactos da introdução de peixes exóticos no distrito de lagos do médio rio Doce, MG Resumo O presente estudo trata dos impactos ecológicos da introdução de duas espécies invasoras de peixes piscívoros em diversos lagos da região lacustre do médio rio Doce em Minas Gerais, Brasil. Demonstrou-se que estes efeitos não se restringiram às comunidade de peixes. A introdução dos predadores Pygocentrus nattereri (piranha-vermelha) e Cichla cf. ocelaris (tucunaré) não só causou uma forte redução no número de espécies de peixes nativos, como também mudanças nos níveis tróficos inferiores. Pouco depois das introduções, a maioria dos lagos começou a mostrar alterações na comunidade fitoplanctônica, tais como o aparecimento da dominância de Cyanophyceae. A comunidade zooplanctônica perdeu diversas espécies e, em alguns casos, houve o desaparecimento de todas as espécies de cladóceros limnéticos, como é o caso da lagoa Carioca. Por outro lado, predadores invertebrados, representados pelos dípteros da família Chaoboridae, floresceram nos lagos com maiores densidades de espécies exóticas de peixes, provavelmente como resultado da "liberação ecológica" causada pela redução da ictiofauna original. Além de uma Pinto-Coelho, RM. et al. 1026 Braz. J. Biol., 68(4, Suppl.): [1025][1026][1027][1028][1029][1030][1031][1032][1033][1034][1035][1036][1037] 2008 tendência geral de perda de espécies em diferentes níveis tróficos, outras mudanças estão aparentemente associadas com a redução da qualidade de água. Dessa forma, esses ecossistemas estão necessitando urgentemente de novas abordagens nas est...

Fluctuations of the population of Daphnia laevis Birge 1878: a six-year study in a tropical lake

“…Introduced piscivorous fishes, such as the Piranha Pygocentrus nattereri and the Tucunaré Cichla spp., can exert different pressures on the zooplankton: directly predating as larvae, and indirectly by disrupting other links of the food chain. However, predation by larvae in the limnetic zone is highly unlikely, since the larvae are much more numerous near-shore., In a study on the lakes of the middle River Doce valley, Pinto-Coelho et al (2008) observed an increase in Chaoborus density caused by the introduction of exotic piscivorous fish species into the lakes. According to the authors, the introduction of these species led to the collapse of the native planktivorous fish species and to the reduction of predation pressure on invertebrates, causing an increase in their density and, thus, an increase in the pressure on other zooplankton organisms by chaoborids.…”

A long-term study on crustacean plankton of a shallow tropical lake: the role of invertebrate predation

“…In addition, young and smallsized fish species that could potentially exploit zooplankton are mostly associated with the littoral zone in warm lakes (Fernando, 1994;Arcifa and Northcote, 1997;Meschiatti and Arcifa, 2002;Agostinho et al, 2003;Teixeira-de Mello et al, 2009), and are, therefore, segregated from the limnetic zooplankton. Predatory invertebrates can exert greater pressure on zooplankton if they are not strongly controlled by fish (Lampert and Sommer, 2007;Pinto-Coelho et al, 2008). However, when other factors, such as turbidity and dissolved oxygen, reduce the spatial overlap between fish and Chaoborus, prey consumption by the dipteran larvae can exceed that of fish, becoming the major predatory force even when planktivores are abundant (Liljendahl-Nurminen et al, 2003).…”

Pleistocene karyotypic divergence in Hoplias malabaricus (Bloch, 1794) (Teleostei: Erythrinidae) populations in southeastern Brazil

“…In 2005 an extensive survey indicated that invasive species had found their way to 90% of the lakes in the rio Doce State Park (Latini, 2005). As a long term-effect, exotics have apparently caused inverted cascade processes that affect the lowest trophic levels (Pinto-Coelho et al, 2008).…”