The life history, secondary production and microdistribution of Ephemera spp. (Ephemeroptera: Ephemeridae) in a tropical forest stream

Abstract

The ecology of ephemerid mayflies was investigated in Tai Po Kau Forest Stream (TPKFS), New Territories, Hong Kong, over a two-year period. Quantitative benthic samples of larvae were taken from different microhabitats within stream riffles on 45 occasions, and combined with light-trap captures of adults, were used as a basis for investigating life-history patterns and estimating secondary production. Two species, Ephemera (Ephemera) spilosa and E. (Aethephemera) pictipennis were collected, of which the former was more abundant (mean densities ± 95 % confidence limits = 11.06 ± 1.48 versus 0.48 ± 0.26 indiv. m -2 ). Larvae of E. (E.) spilosa were patchily distributed. Mean densities in microhabitats close to the stream banks, where sediments were relatively fine grained, were >50 % greater than those in midstream ; however, this difference was not statistically significant. Both ephemerids were univoltine in TPKFS, but emergence of adult E. (A.) pictipennis was highly synchronized (in April), while E. (E.) spilosa emerged later over a more extended period (mainly May-July). Annual production of E. (E.) spilosa (in terms of ash-free dry weight, AFDW) in the study reach was estimated at 24.26 mg AFDW m -2 using the size-frequency method ; the dry-weight (DW) annual production estimate was 37.28 mg DW m -2 . Densities of E. (A.) pictipennis were too low to allow reliable production estimates. Production : biomass ratios for E. (E.) spilosa were 3.79 (AFDW) and 3.67 (DW), and within the range of values reported for ephemerids elsewhere.