Colonies of dead man’s fingers actively feed at various times of the day, with the polyps extended (1). They feed on plankton (2) which is brought into the polyps by the generation of a water current caused by the beating of tiny hair-like cilia. This also brings oxygen into the polyp (1). Colonies become inactive from July to December, when they seem to shrink back and develop a brownish or reddish colouration caused by the development of a coating of algae and hydroids. This time of inactivity coincides with the final stages of gonad development (1).
Most colonies are either male or female, although a few hermaphroditic colonies arise (2), in which the polyps develop ova and testes. Colonies reach sexual maturity in the second year, but in some, maturity is delayed for a further year or two (1). Spawning occurs in December and January when the gametes (sex cells) are released into the water. Fertilisation takes place externally, and the embryos float in the water for one week before developing into active free-swimming larvae known as ‘planulae larvae’. These settle, usually after around one or two days, on a suitable substratum and turn into polyps. In some cases, if a suitable site is not found, planulae larvae may survive for a prolonged period in the plankton, enabling them to disperse and eventually find a suitable site on which to settle (2). Colonies of dead man’s fingers are known to live for over 20 years (1).