The role of patellid limpets as omnivorous grazers: a new insight into intertidal ecology

Abstract

Although patellid limpets are influential grazers on many shores, few studies have characterised their diets in detail. These key species can be found as dominant grazers on rocky shores, but this ecosystem is being transformed due to the increase in infrastructures such as jetties, breakwaters or seawalls by commercial, residential and tourist activities. Increasing knowledge about the ecological effects of these artificial substrates on marine environments is available, and many papers have reported that urban infrastructures support different biota and assemblages and do not act as a surrogate for natural rocky shores. However, little is known about the effect of artificial substrata on marine trophic ecology. The aim of the study was to explore the influence of artificial substrata (breakwaters) on the dietary composition of the common grazer Patella caerulea, to provide data about food resource availability, and its influence on the trophic ecology of limpets. A nested design was used to explore potential differences between natural and artificial shores in Algeciras Bay (Strait of Gibraltar). Additionally, the dietary composition of the endangered limpets Cymbula safiana and Patella ferruginea was studied in a single site. Analyses of the chlorophyll a concentration of the substrate did not show differences between substrata. The analysis of the rock surface by SEM indicated a general prevalence of diatoms and cyanoprokaryotes on all of the substrata. P. caerulea specimens collected from artificial substrata showed a lower number of consumed taxa than those collected from natural rocky shores, whereas the assemblages found in the gut contents also differed between artificial and natural substrata. The diet richness of the three species might be due to the differences in the position of the species on the shore. Our results suggest that limpets are a key group in the top-down control of meiofaunal and macrofaunal populations, due to the presence of several animal taxa in their gut contents in this study, despite the fact that they have traditionally been considered herbivorous grazers that regulate only algal populations in the intertidal regions.