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

Abstract

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.

The Endangered Limpet Patella ferruginea Integrates a Metapopulation across the Species’ Range

“…For instance, Ribeiro [90], in a study on dispersal and connectivity of some European limpet species in relation to the general system of currents, estimated that larval dispersal can exceed 200 km, although the number of larvae decreased sharply with distance, and Sá-Pinto et al [91] pointed out that the duration of the larval stage of related Patella species P. ulyssiponensis and P. rustica can be up to 35.5 days. Furthermore, as Guallart et al [57] noted, some isolated specimens of P. ferruginea have been found more than 200 km away from established populations, such as in the Hormigas Islands (eastern Spain) [28,92] and Liguria (north-western Italy) [30], evidence potential sporadically long-distance dispersal events in this species. Although we report a substantial percentage of self-recruitment in the analysed populations, as also observed by Cossu et al [56], 35.5% of the individuals were recognised as migrants.…”

“…This suggests that relevant differences in larval development and duration of pelagic phase among these species are not expected, and as such, these traits cannot be considered a biological constraint for the ferruginous limpet. Considering a planktonic larval phase of 3 to 7 days in P. ferruginea [31], Guallart et al [57] suggest that the main "hotspots" in the SE Alboran Sea, separated by a distance of about 100 km or less, could facilitate connectivity among the North African populations, depending on the environmental conditions, which may vary from year to year. Interestingly, Ferranti et al [41] found that, in the laboratory, settlement may occur up to 40 days after fertilisation in P. ferruginea.…”

“…Despite the species' relatively short planktonic phase, and therefore assumed limited dispersal capacity and low connectivity among populations, the available information indicates that the larval dispersal capacity of P. ferruginea may be greater than previous thought, probably due to sporadic long-distance dispersal events [57]. Our main objective is to test this hypothesis: if the species has a higher dispersal capacity than previously assumed [21], we expect to observe high connectivity and gene flow among populations and a low level of genetic differentiation among them.…”

Observations on some reproductive features of the threatened limpet Patella ferruginea Gmelin, 1791 in north‐western Mediterranean Italian waters

“…The reproductive mode seems to be even more complex, since Guallart et al (2020) observed that some 2-year-old specimens obtained in the laboratory cultures were first identified by biopsy as females-biopsy was not performed at 1 year old because they were still very small, around 25 mm MSD, and a biopsy could be lethal; and Guallart & Acevedo (2006) have suggested that sexual maturity is reached at 2 years old. These observations, despite being based on a study of P. ferruginea reproduction under controlled conditions, suggest that the species may sometimes sexually mature initially as females.…”