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RESEARCH PRODUCT

Filling gaps: closing the life cycle of the endangered Mediterranean limpet Patella ferruginea Gmelin, 1791 (Gastropoda, Patellidae)

subject

description

Several reproductive issues and the larval development of the ferruginous limpet, Patella ferruginea Gmelin, 1791, an endangered species endemic from the western Mediterranean Sea, were studied to fill gaps in the knowledge of its life cycle. Average diameter of mature oocytes was 141.83 μm and mean oocyte density in the ovary was 283,800 oocytes/gram. No significant correlations were found between both oocyte diameter or density and female shell length. Female fecundity (number of oocytes per gonad) was significantly correlated with shell length and varied between 189,200 oocytes in a 40.0 mm female and 5,019,200 oocytes in an 86.4 mm female. However, there was considerable variability, in particular for the largest females. Spawning induction was not achieved using usual molluscan aquaculture methods. Thus, oocytes obtained after dissection of females were used for fertilisations trials. Alkalinisation treatments of seawater were used to test improvement in oocyte maturation and later fertilisation rates. Treatment at pH 9 during 2 h produced the highest increase in the percentage of mature oocytes and in the fertilisation rate; but these results showed high variability and were mainly significant when the initial degree of maturation was low. Sperm concentration experiments determined that best in vitro fertilisation was performed at 10 and 5×10 spermatozoids/ml. The sequence and timing of the complete larval development of Patella ferruginea in laboratory conditions is described and illustrated here for the first time. At 20 °C, larvae became competent for metamorphosis 3 days after fertilisation, but some crawling pediveliger larvae with a still well-developed velum were found even 7 days after fertilisation. Recruits 1–2 mm in length were achieved in low numbers from two of the assays and were first detected between 131–141 days after fertilisation. The resulting juveniles were monitored for two years and sex determination of five survivors at the end of this period showed that two were mature males, two mature females and one indeterminate. Our results show that the main reproductive traits or larval development of P. ferruginea hardly differ from those of other non-endangered Mediterranean or NE Atlantic limpet species. Therefore, its decline cannot be mainly attributed to constraints of these traits as was previously suggested, but to human impact. On the other hand, it is feasible to complete the life cycle of this species in laboratory conditions, from fertilised eggs to mature individuals. However, an important part of the process like spawning induction was not achieved as gonads needed to be dissected fatally from females, although sperm could be obtained from males through non-lethal biopsies. At present, large-scale aquaculture production for reintroduction, restocking or stock enhancement purposes is neither possible nor an advisable conservation tool yet. Further study is required and meanwhile, the appropriate design of a network of effectively protected marine areas that ensures connectivity among extant populations is necessary.