Demography, Reproductive Biology and Trophic Ecology of Red Coral (Corallium rubrum L.) at the Costa Brava (NW Mediterranean): Ecological Data as a Tool for Management

Abstract

The precious Mediterranean red coral (Corallium rubrum, L. 1758) is an overexploited gorgonian coral whoose red calcium carbonate skeleton is used in the jewelery industry. This work studies the demography, reproductive ecology and trophic ecology of red coral, and used the data to provide recomendations for its fishery managment and conservation. Five harvested populations at the Costa Brava, Spain, showed a population structure that is significantly shifted towards small/young colonies, compared to a protected population at the Medas Islands Marine Park. Average size and age of colonies in the harvested populations were estimated at 5 cm height and 7.5 years, whereas the species is capable of reaching 50 cm and 100 years. Only a small part of the colonies found show a well developed branching pattern, indicating overexploitation. The reproductive output significantly depends on colony size, with 100 % fertility being reached by colonies of 4 � 6 cm height. Mesoscale geographic variation however had no significant effect on reproductive output. Colonies in deep water spawned slightly earlier than shallow ones, when temperature stratification in summer was particularly pronounced. The main proportion of the diet of corallium rubrum is particulate organic matter (POM), while crustaceans such as copepods played a smaller role due to their infrequent capture. No clear seasonal pattern of the ingestion rate was found, due to the high variablity that may be linked to variability in watermovement. It appears that red coral is a flexible omnivore, able to exploit various trophic situations. Maximum sustainable yield, calculated using the Beverton and Holt model, show an optimal age at first capture of 98 years, while current fishing regulations permit harvesting of colonies that are 11 years old. This results in only a fraction of the calculated maximum yield. Poaching and illegal capture of small colonies appear to be a major problem at the Costa Brava.