Population Ecology of the Intertidal Anemone Actinia tenebrosa I. Pedal Locomotion and Intraspecific Aggression

Abstract

Some 80 adult and over 250 juvenile A. tenebrosa, the total natural population on 2.5 m² of a stable rock substratum, were tracked for up to 738 days. In this period 24% of adults and 10% of juveniles moved > 250 mm, Some adults and many juveniles showed no discernible locomotion at all, although most juveniles survived less than 20 days. Large, directed movements of up to 1.6 m were sometimes associated with such external factors as impact injuries from moving rocks or logs, physical shocks, repeated desiccation, interference from molluscs, or wounding from intraspecific aggression.

Acrorhagi are the nematocyst-bearing structures, present in most A. tenebrosa larger than about 10 mm column diameter, which are used in intraspecific conflicts. Some 44 % of adults were involved in fights with other adults over the 2 years of observations. None of those fights was fatal. Contact of two adult A. tenebrosa did not always result in an aggressive conflict, but after intraspecific aggression, in both field and laboratory situations, the wounded anemone moved directly away from the site of wounding.