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

Abstract

1. A "marked" population of Ascidia nigra has been followed throughout life from their first appearance to the time of death. 2. Mortality in the first four weeks after metamorphosis has not been studied. Thereafter few animals die until they are 18 months old and all are dead at 22 months old. 3. A mass mortality due to fresh-water floods occurred in the period of observation. A corrected survival curve has been calculated for a situation in which this did not occur. This suggests that senescence may occur. 4. A. nigra is a primary coloniser. When colonising new surfaces, the earliest colonisers survive longer than the later ones. Very few animals can colonise after the primary sessile community is three months old.