ABSTRACT
The populations of Asterina gibbosa and Asterina phylactica which co-exist in a series of mid-shore tide pools in West Wales have undergone massive population changes in recent years. After many years of stable numbers the populations were, in 1996, subjected to severe stress caused by the oil spill from the tanker Sea Empress. The population of A. phylactica fell to very small numbers but the majority of the A. gibbosa survived, however, the juvenile (1995) year class was lost. We have followed the fortunes of these populations from 1996 to date. In 2000 we reported to the Dunedin meeting that A. phylactica was making a gradual return towards pre-spill numbers and that the population of A. gibbosa had undergone some minor fluctuations in numbers but had remained more or less consistent.The absence of a year class (1995) and the very strong recruitment of the following year allowed us to follow that year class through its complete life cycle.This caused us to revise our opinions about the longevity of the species, about the age at which this protandric species becomes functionally female, and hence about the number of opportunities an individual has to contribute to the population.
