THE BIOLOGY OF ASCIDIA NIGRA (SAVIGNY). I. SURVIVAL AND MORTALITY IN AN ADULT POPULATION

Abstract

A marked population of this solitary ascidian has been studied from their 1st appearance 4 weeks after metamorphosis to the time of death. Few animals die until they are 18 months old; all are dead at 22 months. A mass mortality due to fresh-water floods occurred during observation. A corrected survival curve was calculated for a situation in which this did not occur. Survival curves suggest that senescence may occur. This ascidian is a primary colonizer. When colonizing new surfaces, the earliest colonizers survive longer than the later ones, and very few can colonize after the primary sessile community is 3 months old, perhaps due to the climax community of sponges, anemones and ophiurans.