Limpets (Patella spp.) are marine gastropods that inhabit rocky shores along the coasts of Europe, the Mediterranean, Macaronesia and the north-west coast of Africa. Being considered key species, limpets have an important role regulating algal assemblages in coastal communities. The goal of this work was to evaluate the influence of sea temperature on the respiration rate of four limpet species occurring in mainland Portugal, in line with predictions from the metabolic theory of ecology. The individuals were collected from rocky shores in Portugal and exposed to sea temperatures ranging from 6–28°C for respiration rate assessments. Following the estimation of the relationship between oxygen consumption and temperature the activation energy was calculated. In parallel, low and high thermal thresholds were determined for three of the species. The results indicated that P. ulyssiponensis oxygen consumption increased linearly with sea temperature and the remaining species presented the same tendency. The values of activation energy ranged between 0.33–0.76 eV. For P. ulyssiponensis, the highest activation energy indicated that this species is more sensitive to temperature variations while for the tested temperatures it presented a higher thermal tolerance limit than the other species. Such findings indicate that P. ulyssiponensis is the most susceptible of these species to climate change, in line with the tolerance–plasticity trade-off hypothesis. This work provides a good starting point for understanding the effect of sea temperature on oxygen consumption in Patella spp. and for comprehending sensitivity of limpets to temperature increases under future climate change scenarios.

The limpet Patella vulgata is a key species of northern Atlantic rocky shore-associated communities, and is commonly considered to be important in regulating populations of canopy-forming Ascophyllum nodosum, through consumption of propagules and young recruits. Although P. vulgata is usually regarded as a non-selective epilithic biofilm grazer, a role in the collapse of established A. nodosum through grazing of adult plants has been repeatedly suggested. Factors controlling the preference of P. vulgata for epilithic biofilm or adult algae are still not clearly established. Here, we test the hypothesis that the diet of P. vulgata is mainly driven by the local availability of food sources. Limpets were sampled along the first 6 metres of an A. nodosum bed–bare rock gradient. Stable isotope ratios of their muscle tissue and digestive glands were measured. The contribution of A. nodosum to the diet of limpets was the highest in the immediate vicinity of macroalgae beds, which confirmed our initial hypothesis. However, the contribution of epilithic biofilm did not match our hypothesis, being the lowest for limpets colonizing bare rock. Instead, these limpets relied on a wide array of sources, including ephemeral green algae, biofilm and drifting A. nodosum fragments. Overall, our results indicate that A. nodosum can be readily grazed by limpets, which challenges the hypothesis that these macroalgae dominate rocky shores due to the absence of strong top-down control exerted by herbivores. Our results also highlight the need to consider the small spatial scale to understand the dynamic of herbivore–algae interactions in natural environments.

Intertidal gastropods and bivalves are important hosts for a wide range of metazoan parasites, which may exert a variety of negative effects on their hosts with consequences for mollusc population dynamics and community structure. Although vital for our understanding of the relative importance of parasites in intertidal ecosystems, quantitative information on macroparasite communities in molluscs is still largely missing. We examined the macroparasite community in Littorina littorea, Nucella lapillus, Patella vulgata and Mytilus edulis/galloprovincialis from rocky shore habitats on the south coast of Ireland. In total, twelve macroparasite taxa belonging to four major parasite groups were found in 3900 examined host individuals from sixteen intertidal localities. Digenean trematodes were the dominant parasite group, occurring in all of the investigated mollusc species and at all sampling sites. The macroparasite community in gastropods was largely similar to the species composition reported from other European shore localities, possibly due to a wide distribution of bird final hosts. In contrast, the parasite community composition observed in mussels showed obvious differences when compared to data on macroparasites in mussels from soft sediment habitats, which is probably related to differences in the species composition of gastropods acting as first intermediate hosts on rocky shores. Comparatively low infection rates in molluscs on the south coast of Ireland indicate differences in the abundance of bird final hosts as well as less suitable conditions for parasite transmission. Thus, effects of parasitism on the molluscan hosts can be assumed to be rather low, which is favourable from an economic point of view, since periwinkles and mussels are commercially exploited in Ireland.

Infections of the common limpet, Patella vulgata were investigated along the coast of the Ards Peninsula, Co. Down. Samples were taken from around Portavogie, a small fishing port where seabirds aggregate to feed on fish offal, and from 14 sites along a 15 km transect. A new method of removing larval digeneans from the visceral hump of snails is described. The bulk of the parasite material was rediae of Cercaria patellae. The stage of development of these rediae varied significantly between hosts. Prevalence of infection was substantially greater close to Portavogie. The volume of parasite material recovered was greater for limpets close to rock pools than for those on rocks free from surface water at low tide. Among the latter limpets, the volume of parasite material in the visceral hump increased with increasing height on the shore. The greater part of the variation in parasite volume recovered from snails was determined by the size of the snail. The presence of larval digeneans was associated with progressive deterioration of host gonadal tissue and discolouration of the foot, mantle and digestive gland.

The reproductive cycles of four limpet species, Patella depressa, Patella ulyssiponensis, Patella vulgata and Patella rustica are described for several locations in northern and central Portugal. Patella depressa and P. ulyssiponensis displayed almost continual gonad activity, with two main spawning periods, September–January and March–June, and minor spawning events dispersed throughout the year. Patella vulgata and P. rustica exhibited highly synchronized reproductive cycles, with well-defined breeding and resting periods. Gonad development in P. vulgata started in September and spawning took place from November–December to March. In P. rustica development started in June and spawning occurred from September–October to December–January. Compared to the 1980s these results suggest that breeding periods are becoming longer in southern species and shorter in northern species.