**3. Anthropogenic impact on Patellid limpets**

Patellid limpets are common gastropods of intertidal rocky shores; however, some species are in serious decline mainly as a consequence of overexploitation [94]. These intertidal and shallow-water grazers are highly vulnerable because of their restricted habitat and its accessibility to human activity [26]. Worldwide, shellfish exploitation has often been shown to lead to decreased biomass and species richness and cause shifts in community composition [95–98]. These effects are driven by the increase of human population density along the coast, the replacement of subsistence by commercial exploitation, and technological advances in methods of collection, processing, storage, and transport [99, 100]. As a result, the effects of human exploitation add to those of natural processes that influence population size of exploited limpets and are a concern in conservation biology [101]. Limpets have been exploited by human populations since the Palaeolithic period [102] at a subsistence level and used as food and bait in several parts of the world, including Mexico, the United States of America [101], Hawaii [103], Australia [104], South Africa [105], Chile [106], and Macaronesia [53, 107, 108]. More recently, this subsistence activity has been replaced, in many parts of the world, by heavy and highly profitable commercial exploitation, increasing the pressure on these species' stocks. Limpet harvest results in reductions in density and shifts toward smaller individuals and can decrease reproductive output since individual fecundity is greater in larger individuals [44, 109, 110]. Thus, harvesting has both direct and indirect effects on these species. There are also effects on the overall community composition as removal of grazing limpets facilitates the growth of algae [20, 111, 112], leading to further changes within the rocky shore communities [16, 17].

The direct effects of limpet exploitation are the decline of the exploited species' abundance and a shift in size composition of their populations that results from the size-selective nature of limpet harvest [100]. This is a result of larger individuals being more visible, thus more prone to be caught, and due to their greater commercial value [22, 113, 114]. The loss of older and larger individuals results in cascading effects on the biology of these species and the affected populations, including changes in life-history parameters, demographics, reproductive success, and ecological interactions [98].

For instance, the decline of larger individuals in an exploited population of limpets might lead to the complete disappearance of the population's viable size as a consequence of a seriously diminished reproductive success, affecting different species in a differentiated manner, as observed by Martins et al. [115] in the Azores. Protandrous hermaphrodite species are particularly susceptible to changes in their population size composition that promote a decline of frequency of larger individuals, since it directly affects the sex ratio of the population resulting in a decrease in female specimens that in natural conditions occur with higher frequency in the larger size classes. Also, larger individuals represent a greater contribution to the reproductive effort in limpets [104], thus the harvest of larger individuals contributes to a decrease in the reproductive success of marine invertebrates such as reported for *P. ferruginea* [33] and may eventually result in the collapse of exploited populations [86, 116, 117].

Reduction of sizes and abundance of larger individuals in exploited populations of limpets have been reported for *Patella candei* d'Orbigny, 1840 [116] and *Patella candei crenata* [114] in the Canaries, *P. candei* e *P. aspera* in the Azores [115], *Helcion concolor* (Krauss, 1848) [44], and *P. ferruginea* in Algeria [118] and Spain [86], as well as for the species *C. oculus* in Southern Africa [88]. The overexploitation of limpets has prompted the implementation of management strategies in order to protect the exploited populations and mitigate human impacts in several parts of the world [26, 53]. The establishment of species-specific total allowable catch, minimum size of capture, closed seasons, and closed areas has been the most common measures ensued with this objective. These strategies are thought to maintain sex ratios, preserve age structure, prevent sperm limitation, enhance yield, and restrict evolutionary changes in response to fishing, such as shifts to early maturation [119–122]. When considering limpets, due to the phenomenon of protandrous hermaphroditism, in addition to minimum size limits used to prevent recruitment overfishing, management policies should also consider minimum and maximum size limits [122].

to lead to decreased biomass and species richness and cause shifts in community composition [95–98]. These effects are driven by the increase of human population density along the coast, the replacement of subsistence by commercial exploitation, and technological advances in methods of collection, processing, storage, and transport [99, 100]. As a result, the effects of human exploitation add to those of natural processes that influence population size of exploited limpets and are a concern in conservation biology [101]. Limpets have been exploited by human populations since the Palaeolithic period [102] at a subsistence level and used as food and bait in several parts of the world, including Mexico, the United States of America [101], Hawaii [103], Australia [104], South Africa [105], Chile [106], and Macaronesia [53, 107, 108]. More recently, this subsistence activity has been replaced, in many parts of the world, by heavy and highly profitable commercial exploitation, increasing the pressure on these species' stocks. Limpet harvest results in reductions in density and shifts toward smaller individuals and can decrease reproductive output since individual fecundity is greater in larger individuals [44, 109, 110]. Thus, harvesting has both direct and indirect effects on these species. There are also effects on the overall community composition as removal of grazing limpets facilitates the growth of algae [20, 111, 112], leading to

The direct effects of limpet exploitation are the decline of the exploited species' abundance and a shift in size composition of their populations that results from the size-selective nature of limpet harvest [100]. This is a result of larger individuals being more visible, thus more prone to be caught, and due to their greater commercial value [22, 113, 114]. The loss of older and larger individuals results in cascading effects on the biology of these species and the affected populations, including changes in life-history parameters, demographics, reproductive success,

For instance, the decline of larger individuals in an exploited population of limpets might lead to the complete disappearance of the population's viable size as a consequence of a seriously diminished reproductive success, affecting different species in a differentiated manner, as observed by Martins et al. [115] in the Azores. Protandrous hermaphrodite species are particularly susceptible to changes in their population size composition that promote a decline of frequency of larger individuals, since it directly affects the sex ratio of the population resulting in a decrease in female specimens that in natural conditions occur with higher frequency in the larger size classes. Also, larger individuals represent a greater contribution to the reproductive effort in limpets [104], thus the harvest of larger individuals contributes to a decrease in the reproductive success of marine invertebrates such as reported for *P. ferruginea* [33] and may

Reduction of sizes and abundance of larger individuals in exploited populations of limpets have been reported for *Patella candei* d'Orbigny, 1840 [116] and *Patella candei crenata* [114] in the Canaries, *P. candei* e *P. aspera* in the Azores [115], *Helcion concolor* (Krauss, 1848) [44], and *P. ferruginea* in Algeria [118] and Spain [86], as well as for the species *C. oculus* in Southern Africa [88]. The overexploitation of limpets has prompted the implementation of management strategies in order to protect the exploited populations and mitigate human impacts in several parts of the world [26, 53]. The establishment of species-specific total allowable catch,

further changes within the rocky shore communities [16, 17].

eventually result in the collapse of exploited populations [86, 116, 117].

and ecological interactions [98].

78 Organismal and Molecular Malacology

For instance, in Madeira archipelago the harvest of *Patella candei* sensu lato and *P. aspera* is regulated since 2006, enforcing the maximum allowable commercial catch of 15 kg/person/ day or 200 kg/boat/day and a minimum capture size of 40 mm. Additionally, the competent authorities became responsible for issuing harvest licenses, limiting the number of active fishermen involved in limpet harvest. A closed season was also implemented between November and February in order to prevent limpet harvest during the reproductive season. More recently, the closed season was modified in order to more effectively provide protection to these heavily exploited species, now lasting from December to March. In the Azores, the overexploitation of limpets resulted in a drastic decline in population density and abundance of limpet populations, and in order to prevent a complete collapse of the stocks, regulation was implemented through the establishment of limpet protected zones that comprise stretches of coast of a few kilometers where the collection of limpets is strictly prohibited throughout the year, seasonal fishing closures, and minimum legal catch sizes [123].

Martins et al. [123] studied the effect of regulation on the recovery of the exploited populations of limpets in the Azores and concluded that the legislation and current levels of enforcement were insufficient to protect the exploited populations and greater levels of enforcement, such as the establishment of physical barriers and other protective strategies should be considered to protect limpet populations. The authors further elaborate that in the absence of adequate enforcement, a complementary approach that has had positive results is co-management [124], due to increasing awareness of the need to increase ownership of conservation areas and to involve all interested parties in the development of management schemes [125, 126].
