Population structure of black coral, Antipathes aperta , in the southern fiords of New Zealand

The heights of 2988 colonies of the black coral Antipathes aperta Totton, less than 1 m tall were measured underwater between 5 and 25 m depth in eight of the fiords of New Zealand. The population structure, as given by height frequencies and presented as density traces, showed clear peaks in numbers of individuals in size classes up to 40 cm tall with constant spacing between peaks of 3.9 cm. This is interpreted as a growth rate of 3.9 cm/year. Year classes began to merge after around 7 years, reflecting differences in individual colony growth rates. Growth appeared to be similar throughout all fiords, as did population structure, although one fiord (Preservation Inlet) had a greater proportion of larger colonies. Ninety percent of the total Fiordland population was less than 50 cm tall. Reasons for the high mortality of larger colonies are discussed. The data suggest that recruitment over the 2 years before 1986 had been poor and this is substantiated from site‐monitoring surveys.