Effects of temperature on the swimming of salps (Tunicata, Thaliacea): Implications for vertical migration1

Abstract

Salps swim by means of rhythmic contractions of the circular body muscles. In most species, these contractions are regular. At constant temperature, the pulsation rate is inversely related to body length for hand‐collected animals. Such a relationship is not seen with trawl‐collected salps. When temperature is lowered experimentally, marked differences are seen in the response of individual species. The pulsation rates of Pegea confederata, Cyclosalpa polae, and Salpa cylindrica are greatly depressed and cease altogether at low temperatures (response type I). For Pegea socia, Cyclosalpa pinnata, Cyclosalpa affinis, and Salpa maxima, the pulsation rates are usually greatly depressed, but do not cease, even at extremely low temperatures (response type II). The pulsation rates of Salpa fusiformis and Salpa aspera are largely insensitive to changes in temperature (response type III). Evidence from net sampling suggests a relationship between these response types and vertical and horizontal distribution patterns. Salps showing response type I are found only in tropical and subtropical surface waters; those showing response type II are more widely distributed or are found in temperate waters; and those showing response type III are vertical migrators. Thus, differences in the temperature response provide clues as to the differing modes of life available to salps in the open sea.