Enhancing stocks of the exploited limpet Patella candei d’Orbigny via modifications in coastal engineering

It is widely recognised that microhabitats are important for a variety of marine organisms, yet this knowledge has rarely been applied in the construction of engineered structures as a means of enhancing biodiversity or populations of species at risk. Here we examined the influence of microhabitats on the distribution and survival of the exploited limpet Patella candei on natural shores before determining the effect of introducing such habitats to an artificial seawall. On natural shores individuals were associated with pits (a natural feature of volcanic rocky shores). Animals inhabiting pits showed reduced mortality and were smaller than those on open rock. Microhabitat utilisation was similar over the vertical range of distribution of P. candei. Following observation of natural patterns, we applied this knowledge by experimentally drilling pits at varying densities and sizes in a seawall that had been constructed with simple topographical complexity. Overall, the number of animals increased in areas with experimentally increased microhabitat area. There was evidence that this was the result of immigration (larger animals) but also of increased recruitment. This study demonstrates one cost-effective way of conciliating the need to protect our coastlines while promoting the conservation and stock enhancement of over-exploited species.