Some effects of temperature, desiccation, and light on the intertidal anemone, Actinia tenebrosa Farquhar (Cnidaria: Anthozoa)

The upper limit of the zone occupied by Actinia tenebrosa is determined primarily by the effects of desiccation on the juvenile stages after settling. Juveniles are especially prone to death from these effects at relative humidities lower than about 70%. This susceptibility is mainly a consequence of high surface area to volume ratios in juveniles, and is further enhanced by a higher rate of evaporation from the column walls of juveniles as compared with adults. A rapid rate of evaporation will cause the anemones to show decreased responses, but within the usual range of environmental conditions death probably results from a net loss of water from the ectoderm and mesogloea. Normally the effects of temperature are unimportant, although adult anemones may move away from areas of unfavourably high temperatures. During emergence evaporation from the ectoderm may decrease the surface temperature of adult anemones by over 5°C from that of the surface of the adjacent substratum. Dark-adapted A. tenebrosa show responses to light stimuli of high intensity after 20-40 sec, but these are immediate responses and there is no evidence either of phototaxis or that light affects the intertidal zonation of the anemones.