Life History of Potamanthus myops (Walsh) (Ephemeroptera: Potamanthidae) in a Central Michigan Stream

Abstract

The life history of Potamanthus myops (Potamanthidae) was investigated for 1 year in a 4th-order central Michigan stream. Potamanthus myops has a univoltine life cycle with emergence occurring from June until mid-August. Adults averaged 16 mm in length. Fecundity was high, averaging 4559 eggs per female (range 32976498), with females ovipositing over riffle sections from late afternoon until after dark. Eggs hatched in approximately 2 weeks with limited nymphal growth occurring through the summer and autumn. There was no significant growth during the winter months (October to March), with nymphs undergoing accelerated growth (0.99 to 4.7%o dry wt/day) from April to June. A total of 3939 degree-days (base T = 0 C) were required for P myops to develop from the egg stage until emergence 1 year later. INTRODUCTION Potamanthidae is a relatively uncommon mayfly family with most known species occurring in Asia (Edmunds et al., 1976). The genus Potamanthus Pictet has a Holarctic distribution (Edmunds et al., 1976), with eight species recognized in eastern North America (McCafferty, 1975). Potamanthidae are placed within the superfamily Ephemeroidea, known typically as the burrowing mayflies. Although members of most families within this superfamily burrow, Potamanthidae are considered clingers and sprawlers (Edmunds, 1984) on rock substrate in streams. Members of this family are in the collector-gatherer functional group (Merritt and Cummins, 1984), feeding on epilithic material. Earlier studies on Potamanthus myops (Walsh) were taxonomic, yielding little life history information (Ide, 1935; McCafferty, 1975). More recently, studies by Lord (1975) and Meier and Bartholomae (1980) have dealt with the life history and ecology of E myops. Munn (1982) found densities of P myops nymphs to range from 4.6/M2 during July to 68.0/M2 by late August. Population biomass was highest in late June just prior to peak adult emergence with a mean of 67.6 mg/M2, decreasing rapidly to 13.4 mg/M2 by the end of July. This paper presents the life history of Potamanthus myops in a central Michigan fourth-order stream (Strahler, 1957). Life history parameters investigated include emergence period of adults, fecundity and oviposition behavior of females, along with size distribution and growth rates of nymphs for 1 year. DESCRIPTION OF STUDY AREA The Chippewa River is a fourth-order hardwater stream located in Midland Co., Michigan. The area consists of mixed farmland and hardwood forest. The riparian zone consists of dense forest along the river's southern bank and low shrub vegetation on its northern bank. At this site the stream averaged 60 m in width during base flow and was shallow most of the year, with discharge rates varying from 5 m3/sec in August to 18 m3/sec in March. Water temperatures ranged from 1 C during winter when the river was ice-covered, to 31 C during midsummer. Dissolved oxygen during the day varied from 64% saturation (9.1 mg/liter) in mid-winter to 120% saturation (11.2 mg/ 1Present address: Illinois Natural History Survey, Aquatic Biology Section, 607 E. Peabody, Champaign, IL 61820.