Two opposite distribution patterns of larval Glyptotendipes paripes in relation to organic carbon content in sediments of some central Florida lakes were discovered. In a majority of studied lakes, G. paripes larvae suddenly declined as the carbon content increased (type 1). However, in one case the opposite was true (type 2). To elucidate the cause, the field-collected sediments from both types of habitats were studied in the laboratory. In type 1 habitats, sediments consisted of fine particles (<0.25 mm), had generally lower dissolved oxygen levels, with relatively low G. paripes larval survival in the laboratory. Whereas, sediments from type 2 habitat consisted of larger aggregates (> 0.25 mm diameter), had higher dissolved oxygen concentrations, and higher larval survival of G. paripes . The dissolved oxygen content and larval survival in the latter type of organic sediment did not differ significantly from mineral sand sediment.
Microscopic examination revealed that prevailing particles in type 2 sediments (organic) were aggregates formed by chironomid faecal pellets. This observation indicates that accumulation of chironomid the aggregates faecal pellets in lake sediments may change physical properties and consequently alter living conditions for chironomid larvae and possibly for other benthic fauna.
Species 1: Diptera Chironomidae Glyptotendipes paripes
Keywords: ecosystem engineers
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