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Population decline and life‐cycle changes in a phantom midge ( C haoborus flavicans ) after introduction of planktivorous fish
Author(s) -
Regmi Bishnu P.,
Wivegh Jan S.,
Hobæk Anders
Publication year - 2013
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/fwb.12141
Subject(s) - perch , voltinism , biology , midge , zooplankton , larva , predation , ecology , population , zoology , fishery , fish <actinopterygii> , demography , sociology
Summary Eurasian perch ( P erca fluviatilis ), a non‐native planktivorous fish species in western Norway, has been released into L ake M yravatn, which previously lacked planktivorous fish. Prior to the introduction, the zooplankton community was structured by predation by larvae of the phantom midge ( C haoborus flavicans ), which maintained a bivoltine life cycle in the lake. We hypothesised that the perch introduction would diminish the density and alter the bivoltine life‐cycle pattern of C haoborus . To assess this, we used time series data from before (1983) and after (2007–10) the perch introduction. The perch appears to have effectively exterminated the previously dominant predator C . flavicans within 4–5 years of introduction into the lake. The density of the larvae in the water column was high in 1983 as well as in 2007, with maximum levels recorded in August (up to 15 400 individuals m −2 ). In 2008, larval density was lower than in previous years, but the most dramatic decline occurred in 2009 (maximum 212 individuals m −2 ). In 2010, the density was very low (maximum 11 individuals m −2 ), and after July 2010, no larvae were found in the water column. The number of larvae residing in the sediments also declined quickly after the perch introduction. In 1983 and 2007, C . flavicans produced two generations per year. Following the first emergence and reproduction in May, young larvae appeared in June and developed rapidly to emergence and reproduced again in August. Young larvae appeared again in August–September. In 2008, young larvae appeared only in June with no second emergence and reproduction. In 2009, young larvae did not appear until July, and again no further reproduction took place. Only a few instar IV larvae were recorded in 2010. The collapse in life cycle into a univoltine pattern occurred prior to the main population decline. We conclude that direct predation by perch on C haoborus larvae is the most likely explanation for the observed changes in their life cycle and density. It appears that the C . flavicans population of L ake M yravatn is approaching extinction.