Recruitment of the endangered limpet Patella ferruginea in the Chafarinas Islands (SW Mediterranean)

The recruitment of the endangered limpet Patella ferruginea in the Chafarinas Islands (SW Mediterranean) was studied over a 17-year period (1999-2015). A total of 8115 recruits <20 mm in maximum diameter were counted in 95 transect censuses sampled during the study period. The presence of recruits began at the end of winter or beginning of spring (March-April), when they reached a maximum shell diameter (MD) of at least 4 mm, with a peak in abundance occurring in spring. Smaller recruits were found on the lower infralittoral on the fringe of the vermetid gastropod Dendropoma lebeche and the crustose coralline algae Neogoniolithon brassica-florida, which suggests that settlement occurs at this shore level. Recruits reach 12-27 mm at the end of their first year of life. A regular recruitment was detected for all studied years, with an average of 11.71 recruits m(-1) across the study period. However, recruitment exhibited high interannual variability and did not occur evenly along the coastline of the islands. Higher recruitment was observed in 2001, 2011 and 2012, with a maximum density of 69.07 recruits m(-1) in one transect in 2012. The density of recruits decreased in summer. No significant correlation was found between the density of recruits and adults. Between 1999-2010, 29.29% of recruits were 'phoretic' on the shell of adults (1.81 recruits per host on average). Recruits climbed on to adults sometime after settlement, thus we suggest that 'phoresy' could favour the survival of young limpets instead of being due to selective settlement on adults. To improve and standardize recruitment monitoring in future studies, we propose that recruits are considered as those specimens <20 mm in MD and that recruitment censuses are carried out in spring, with additional censuses after summer to detect juvenile mortality. Additionally, we propose that 1 mm interval size classes are used for growth studies based on size-frequency analyses.

Automated summary

The recruitment patterns of the endangered limpet species Patella ferruginea in the Chafarinas Islands were studied over a 17-year period. The results showed that recruitment occurred during late winter or early spring, with settlement happening at the lower infralittoral on the fringe of certain biological species. The density of recruits varied annually and showed no significant correlation with the density of adults. The presence of 'phoretic' recruits on adult shells may contribute to the survival of young limpets.