Respiratory responses of the salt marsh animals, Fundulus heteroclitus, Leiostomus xanthurus, and Palaemonetes pugio to environmental hypoxia and hypercapnia and to the organophosphate pesticide, azinphosmethyl

Abstract

In tidal saltmarshes in South Carolina hypoxic (low O 2) and hypercapnic (high CO 2) conditions occur frequently. In the summer, water Po 2 was measured in the upper marshes and over a 24-h period ranged from 9 to 170 torr and Pco 2 ranged from 0.3 to 12 torr. These conditions depend on the stage of the tide and the time of day. The respiratory responses to different levels of Po 2 and Pco 2 of the grass shrimp, Palaemonetes pugio, the spot fish, Leiostomus xanthurus, and the killifish or mummichog, Fundulus heteroclitus living and feeding in the saltmarsh were investigated. Mean oxygen uptake in P. pugio, L. xanthurus, and F. heteroclitus at normoxic Po 2 (130–150 torr) and low Pco 2 (< 0.6 torr) was 17.5, 17.1, and 9.5 μmol · g −1 · h −1 and 16.3, 24.5, and 10.5 μmol · g −1 · h −1 at high Pco 2 (= 7 torr), respectively. The critical Po 2 for all species was between 30 and 35 torr. Mean whole body lactate concentrations in P. pugio, L. xanthurus, and F. heteroclitus at Pco 2 < 0.6 torr are 3.5, 2.4, and 2.3 μmol · g −1, respectively, in normoxia and 12.3, 4.5, and 11.0 μmol · g −1 ( p < 0.05; Dunn's pairwise test) in hypoxia and Pco 2 < 0.6 torr. In these saltmarsh animals there appears in general to be no specific effects on oxygen uptake of environmental fluctuations in CO 2 over a wide range of Po 2. The organophosphate pesticide, azinphosmethyl, appears to have no effect on the oxygen uptake of these three species at concentrations of 10 μg · l −1 for fish and 2 μg · l −1 for shrimp.