The growth, respiration and energetics of Mysidopsis almyra (Crustacea :Mysidacea) in relation to temperature, salinity and hydrocarbon exposure

Abstract

A total of 6,924 individual mysids (Mysidopsis almyra) were divided among 249 combinations of temperature (20, 25 and 30(DEGREES)C), salinity (10, 20 and 30 ppt), South Louisiana crude oil water soluble fraction (WSF) concentration (0, 2, 5, 10 and 20%) at various ages (0, 1, 3, 5, 8, 12, 18 and 24 days) and the respiratory rate and dry weight of mysids were obtained at each of these combinations. Growth was greatest in mysids exposed to temperatures of 25 and 30(DEGREES)C and salinities of 20 and 30 ppt. Growth was sharply reduced at high temperatures at low salinities and at low temperatures at high salinities. Mysid growth was reduced in WSF concentrates of 10 and 20%, corresponding to total dissolved hydrocarbon concentrations of 2.37 and 4.75 ppm. These values are approximately four times lower than the 48 hr LC50 (concentration which caused mortality in 50% of the mysids exposed for 48 hours) concentration of South Louisiana crude oil WSF for M. almyra. The respiratory rate of mysids was highest at 25(DEGREES)C and 30 ppt salinity. Temperature had a greater effect on respiration than salinity. The effect on mysid respiration of the oil WSF varied with the age of the mysids, with a greater effect observed on the younger mysids (less than 8 days of age) than on older organisms. The energetics studies utilizing these data, as well as values from the literature, indicated that M. almyra has a gross ecological efficiency (yield/ingested) of 12.24%. This value was 10.44% for mysids exposed to a 20% WSF concentration. The net ecological efficiency (assimilated/ingested) of unexposed animals was calculated to be 69%. When reared in a 20% WSF concentration, the net ecological efficiency is decreased to 59%. These values are realistic in relation to values in the existing literature, and indicate that the bioenergetics approach may contribute valuable information to studies of environmental pollutants.