Macrophytes as refuge or risky area for zooplankton: a balance set by littoral predacious macroinvertebrates.

GONZALEZ SAGRARIO M.A.; BALSEIRO, E.G; ITUARTE, R.; SPIVAK, E.

FRESHWATER BIOLOGY (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Año: 2009 vol. 54 p. 1042 - 1054

0046-5070

1. Zooplankton use macrophytes as day-time refuge areas when trying to escape frompelagic predators. But macrophytes can also host a diverse and abundant macroinvertebrateassemblage and zooplankton are also likely to face predacious macroinvertebratesonce they enter the littoral zone. This study aimed to elucidate the role of macroinvertebratesin determining the refuge capacity of macrophytes.2. We conducted a field enclosure experiment using plastic bags and complementarylaboratory feeding trials to test how macroinvertebrates counteract the benefits tozooplankton of the macrophyte refuge. The field experiment consisted of three treatmentswith different macroinvertebrate assemblages: without predators (WP), low abundanceand diversity (LAD) and high abundance and diversity of predators (HAD – whichrepresents lake conditions).3. Populations of Diaphanosoma brachyurum, Bosmina huaronensis and Moina micrura(Cladocera) and of both male and female Notodiaptomus incompositus (Copepoda,Calanoida) declined (by nearly 80%) in the presence of HAD in comparison to WP andLAD treatments.4. Feeding trials revealed that Buenoa sp. (backswimmer), adults of Palaemonetes argentinus(grass shrimp) and Cyanallagma interruptum (damselfly) had a significant negative impacton cladocerans (D. brachyurum, B. huaronensis) and the calanoid copepod population(males, females and copepodites). These predators showed a strong predation effectranging from 75% to 100% reductions of zooplankton populations.5. The refuge effect offered by macrophytes to zooplankton depends on and is balanced bythe predacious macroinvertebrate assemblage that plants host. The risk of confrontinglittoral predators is high and macroinvertebrate presence can turn the macrophytes intorisky areas for zooplankton.