Rock-pools as nurseries for co-existing limpets: spatial and temporal patterns of limpet recruitment.

Abstract

Rock-pools are considered to be important habitats for early shore-life of intertidal limpets. We investigated recruitment patterns of three co-existing limpet species in the region of Sines (SW Portugal): the patellids Patella depressa and Patella ulyssiponensis, and the siphonariid Siphonaria pectinata. Juvenile limpets (shell length ≤ 10 mm for P. depressa and ≤ 5 mm for S. pectinata) were counted in summer 2007 and winter 2009, in a wide range of intertidal habitats, on three natural shores (one shore inside the Port of Sines and two shores outside the Port, 4 and 9 km away). Temporal and among-shore patterns of abundance of recruits (shell length < 5 mm for all species) into mid-shore rock-pools were examined over quarterly periods, from May 2005 to July 2008. Despite a widespread distribution of P. depressa and S. pectinata juveniles, significantly higher juvenile abundance was mostly found in habitats of rock-pools (maxima of 94 and 92 juveniles in 15x15 cm, respectively, both in rock-pools at mid-shore). All species were found to recruit into mid-shore rock-pools year-round. Recruitment of both patellid species followed a similar seasonal pattern, being consistently low during all summer periods (maxima of 64 recruits of P. depressa during spring 2008 and 45 recruits of P. ulyssiponensis during spring 2007, both in 15x15 cm). High inter-annual variation was found in the intensity of recruitment of S. pectinata, with the yearly highest densities of recruits during summer or autumn periods (maximum of 134 recruits in 15x15 cm during summer 2005). Recruitment of all species was highest on the farthest shore from the Port. This study suggests the primacy of rockpools as nurseries for both patellogastropod and pulmonate limpets and the value of these habitats for sustaining limpet populations on this coast, where rocky-shores have been gradually replaced by artificial structures with scarcity of rock-pools.