This study provides the first description of the reproductive features of a red coral Corallium rubrum population. This circum-Mediterranean octocoral has been over-harvested and commercial stocks are depleted. The population we studied was gonochoric at both the colony and polyp levels, and its sex ratio was significantly biased toward females. The minimum age at first reproduction was 2 yr. The percentage of fertile colonies increased with age, reaching 100% fertility for those over 5 yr. Due to the low frequency of older colonies, 2 /3 of the population was unreproductive. The seasonal cycle of oocyte maturation resulted in a rapid increase in diameter after March, corresponding to a significant reduction in fecundity and fertility. Larval release occurred between late July and August, and settlement ended by mid-September. No significant difference was found in fecundity or fertility between colonies living at different depths (25 and 35 m). Both reproductive parameters depended on polyp position on the colony branches, being significantly lower in the tips of 1st order and proximal parts of 2nd order branches. Due to these opposing trends, no significant overall difference was found between branches of different orders. Female polyp fecundity (0.87 gonads per polyp) was considerably lower than fecundity measured in other octocorals, and the larval production depends on the size/age of the colony: while reproductive colonies in Class 2 (diameter 1.82 mm) produce on average 24 planulae, the larger, older colonies in Class 6 (diameter > 4.6 mm) produce 157 planulae on average. This clearly indicates large differences in larval production between populations with different size and/or age structures. A better understanding of red coral reproduction will help to match harvesting levels to recovery rates in overexploited populations.KEY WORDS: Red coral · Octocorallia · Sexual structure · Reproduction · Mediterranean SeaResale or republication not permitted without written consent of the publisher

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A coastal red coral [Corallium rubrum (L.)] population, whose age structure and demographic parameters have been previously analysed, harbours 10 species of endobiotic sponges. This sponge assemblage differs considerably from that inhabiting other calcareous substrata of the surrounding area, suggesting some selectivity for red coral. The two most common endobiotic species, Spiroxya hereroclifa TOPSENT and Cliona sarai MELONE, are described in detail. The percentage of infested coral colonies increases according with colony age, with a sharp increment at four years. An increase in coral colony mortality observed at this age may be related to the increment of endobiotic sponge infestation.