The Life Cycle of Ciona intestinalis (L.) f. typica in Relation to the Environmental Temperature

Abstract

Investigations of Scandinavian populations of Ciona intestinalis f. typica and a survey of the literature concerning other areas evidences a clear relation between age, growth, spawning and embryonic development, on the one hand, and the environmental temperature conditions, on the other. In sub-arctic regions with temperatures constantly below about 50C, the individual Ciona seems to attain an age of several years, in boreal regions an age of about one year and in the Mediterranean, subtropical and tropical regions an age of less than one year. Growth is more rapid at high temperatures than at low and the number of yearly generations which succeed each other in the warmer seas seems to be at least three and possibly four. In boreal regions there are two generations per year in restricted and sheltered water, while populations in more open waters and at somewhat greater depths, about 15-30 m, have one generation per year. In deeper waters (below 50-60 m), in which temperatures of 6-90C prevail all the year round, each generation lives for at least two years and in the colder, sub-arctic waters even longer. The greater the difference between the summer and winter temperatures, the more distinct the spawning periods. In areas with an even temperature all the year round, it seems that reproduction may take place, broadly speaking, throughout the year. Experiments show that on the coasts of Europe embryonic development from the fertilized egg