Growth Rates of Chironomids Collected from an Ephemeral Floodplain Wetland

Abstract

Floodplains are dynamic wetlands that are constant- ly alternating between aquatic and terrestrial phases. To survive these conditions, aquatic invertebrates must have life history strategies allowing them to take advantage of inundation periods. One such strategy is growing rapidly and completing development before flood waters recede. We measured daily growth rates and development times of 7 chironomid species during April, June, and August using egg masses collected from the Sipsey River floodplain, west central Alabama, USA. Egg masses and resulting larvae were reared under ambient temperatures (18-27°C) and with a natural food source. All successfully reared chironomids were in the subfamily Chiro- nominae. Mean growth rate was 0.28 d -1 suggesting a biomass turnover time of 3 days. Mean development time was 17 days. Temperature affected chironomid development time, with slower rates occurring at the lowest temperature. While many chironomid species appear capable of rapid growth in flood- plains when temperatures are >18°C, completion of their life cycle seems likely only if inundation persists at least 2- 3 weeks. Longer inundation periods are probably necessary for chironomids to complete their life cycle at colder temper- atures in winter and early spring.