The effects of short-term laboratory pH depressions on molting, mortality and major ion concentrations in the mayflies Stenonema femoratum and Leptophlebia cupida

Abstract

Field surveys of the distribution of mayfly nymphs suggest that Stenonema femoratum are more acid-sensitive than Leptophlebia cupida. To assess whether this apparent difference in sensitivity of nymphs is reflected in differences in the degree of whole-body loss of [Na], [Cl], [Ca] or [K] under laboratory conditions, we exposed nymphs of both species to low pH for 96-192 h in soft water ([Ca] = 0.1 mM). Although mortality and loss of whole-body [Na] and [Cl] occurred in both species at pH 3.5, unexpectedly they were considerably greater in L. cupida than in S. femoratum. Ion loss was not size related within the range of nymphal weights used (2-14 mg dry wt) for S. femoratum. Exposure to the environmentally more common pH 4.5 had no effect on whole-body [Na] and [Cl] or on mortality in either species. However, in L. cupida, molting by nymphs increased at both pH 3.5 and 4.5. A decrease in whole-body [Ca] occurred, and the loss of whole-body [Na] and [Ca] at pH 3.5 appeared to cease following the period of molting. In S. femoratum no molting or Ca loss occurred and whole-body [Na] and [Cl] decreased between 96 and 192 h exposures.

Zu den Ursachen der unterschiedlichen pH‐Empfindlichkeit von Gammarus pulex L., G. fossarum KOCH (Amphipoda) und Aselus aquaticus L. (Isopoda)

“…a.) und wurde fur die Eintagsfliegen Stenonema und Leptophlehia durch Neutronenaktivierung indirekt bewiesen (ROWE et al 1989). …”

Effects of aluminum, calcium and low pH on egg hatching and nymphal survival of Cloeon triangulifer McDunnough (Ephemeroptera: Baetidae)

“…However, Rowe et al (1989) found that nymphs within the size range of 2-14 mg dry wt showed no size related ion losses at pH 3.5.…”

Seasonal availability and sensitivity of two field-collected mayflies for the development of a standardized toxicity test

“…Some researchers propose the use of molting, or exuviae production, as a method of determining sublethal responses in laboratory mayfly tests (Henry et al 1986;Pontasch et al 1989;Giesy et al 1990;Diamond et al 1990Diamond et al , 1992, while others have observed molting response to be a poor indicator of dose-dependent responses (Kennedy et al 2004). It is also suggested that molting could be a response to handling stress, temperature change, or a mechanism for shedding certain pollutants which may be absorbed onto the exoskeleton or gill surfaces (Kormonday 1965;Smock 1983;Rowe et al 1989;Diamond et al 1992). The number of exuviae produced by I. bicolor over a 7-day test period was calculated, along with geometric means and incipient response values at the concentration where 25 % of organisms showed inhibited growth (IC 25 ) ( Table 3).…”