Life history and secondary production ofHexagenia bilineata(Say) in an embayment of Kentucky Lake

Abstract

Spatial distribution, life history, and secondary production of Hexagenia bilineata (Say) were studied in Ledbetter Embayment of Kentucky Lake, Kentucky, USA. We sampled the naiad population using a PONAR grab based on (1) geographically-referenced random sampling for the whole embayment, and (2) targeted sampling in a known high-density area. Secondary production was calculated with the size-frequency method. Greatest densities of naiads were collected in the shallow area (water depth <2 m) of the embayment with sediments containing gravel and sand. Mean density and biomass in the high-density transect (70.8 m−2, 587.3 mg ash-free dry mass, AFDM/m2) were more than 4× higher than estimates for the whole embayment (16.6 m−2, 121.5 mg AFDM/m2). H. bilineata population in Ledbetter Embayment had a mixed voltinism composed of two major cohorts, 14 and 22 month long with the majority of adult emergence occurring June through August. Annual production of H. bilineata was 333 mg AFDM/m2 for the embayment and 1736 mg AFDM/m2 for the high-density transect. The production of H. bilineata in Ledbetter Embayment was lower than previous estimates from similar reservoirs and lakes in the North America. The unusual spatial distribution pattern and low productivity of H. bilineata in Ledbetter Embayment were attributed to seasonal and spatial variations in water temperature and dissolved oxygen that affected naiad growth and development. H. bilineata population has been relegated from a species often responsible for a large percentage of the benthic macroinvertebrate production and carbon turnover to peripheral importance in total benthic energy flow in Ledbetter Embayment.