Ecology of an Aquatic Isopod, Lirceus fontinalis Raf., Emphasizing Radiation Effects

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Abstract
The aquatic isopod, Lirceus fontinalis Raflnesque, occurring in granite gneiss weather pools on Mount Arabia, DeKalb Co., Ga., was investigated with respect to behavior patterns, interactions between the isopods and various environmental stresses, and determination of the major factors or combinations of factors that control the distribution and abundance of the isopods. Drought and high temperatures are the 2 major limiting factors controlling the Lirceus population. The capability of individuals to survive drought stress is reduced by acute exposure to high temperatures. Klinokinetic responses to standing water and orthoklnetic responses to moisture contribute to the ability of individuals to survive drought stress by bringing about aggregations in or on top of moist sand under rocks. Rheotactlc responses to rapidly flowing water account for repopulation of weather pools by bringing about emigrations from an intermittent creek to the pools, as confirmed by the movement of Zn-65-labeled isopods. High temperatures have an inhibiting effect on the rheotactic response. Isopods seldom venture from the dark recesses of rocks piled in weather pools because of a negative photokinetic response. Implications of a 43 factorial experiment on the interactions of gamma radiation, high temperature, and drought stresses are that introduction of ionizing gamma radiation into the habitat for even brief periods at 16,400 R/hr would severely lower the ability of the population to withstand high temperatures and drought.