Demography of deep-dwelling red coral populations: Age and reproductive structure of a highly valued marine species

The valuable Mediterranean red coral Corallium rubrum (Octocorallia Gorgonacea) has been harvested for more than 2 thousand years. Although our knowledge on the demographic features of red coral populations living between 10 and 50 m depth has increased considerably in recent years, the main life-history traits of deeper populations (the main target of current harvesting) are still largely unknown. To increase the demographic knowledge of the latter populations, sampling was carried out during early Summer 2010 in the North-Western Mediterranean (Tyrrhenian Sea - Italy), between 50 and 130 m depth. This paper quantifies the main demographic descriptors of this coral population in terms of size/age and sexual structure. Colony age was estimated by counting annual growth rings on thin sections of 69 colonies. A 2-way ANOVA showed no significant difference between the age estimated by three independent observers. The average annual colony growth rate (basal diameter), showing some decrease with colony age increase, was 0.26 mm/yr. The relationship between age and basal diameter derived from a subsample of colonies was then applied to assess the age of a larger sample of the population and showed 38% of the sampled colonies reached the commercial size (>= 7 mm of basal diameter), corresponding to about 30 years in this population and a maximum life span of 93 years; about half of them (51.1%) were in the 21-25 and 26-30 age classes. The analysis of the sexual features revealed a balanced sex ratio, a colony fertility of 90.3% and an average fecundity of 0.83 oocytes or planulae per polyp. The knowledge of these life-history descriptors is needed for our understanding of deep dwelling red coral population dynamics and for matching of harvesting to population growth rate. (c) 2013 Elsevier Ltd. All rights reserved.