Reproductive patterns of the limpet Siphonaria pectinata: influence of microhabitat and seawater temperature

Maria Inês Seabra¹, Stephen J. Hawkins^2,3,4, Joana N. Fernandes¹, Celestino Susana¹, João J. Castro¹, Daniela Nobre¹, Marta Mamede¹, Cristina Espírito-Santo¹, André Costa¹, Teresa Silva¹, Teresa Cruz¹

¹Universidade de Évora, Portugal - ²The Marine Biological Association of the United Kingdom, UK - ³University of Southampton, UK - ⁴University of Plymouth, UK

The limpet Siphonaria pectinata is a subtropical species that inhabits rocky intertidal habitats. The geographical range of this species is spreading northwards in the north-east Atlantic (along the west coast of the Iberian Peninsula) and eastwards in the Mediterranean (both European and African coasts). Its life cycle includes egg mass deposition. In SW Portugal, egg masses are mostly found in spring-summer and abundance of potentially reproductive individuals (shell length > 5 mm, hereafter “adults”) is highly variable at small spatial scales. We studied temporal and spatial variation in the reproductive patterns of S. pectinata in contrasting microhabitats and thermal environments in SW Portugal. Egg masses and adults were counted every month within fixed sampling areas. Monthly estimates of the number of egg masses per adult were analysed as response variables for two comparisons. (1) We compared two microhabitats, open rock vs. rock pools, sampled on two sites over two years. (2) We assessed the potential impact of the discharge of warmed seawater from a local power plant, by sampling 50x50 cm open rock areas in three sites during two periods: one impact site (adjacent to the thermal discharge) vs. two control sites; operational period (power plant in operation: 2013-2014) vs. post-operational period (after closure of the power plant in December 2020: 2021-2024). Temperature was semi-continuously recorded on both microhabitats and in all sites and periods. Monthly estimates of the number of egg masses per adult were significantly higher (15 to 55 times in spring-summer months) in rock pools, where the environmental temperature (all records) was more stable compared to open rock. During the operational period, a temporal shift in the reproductive pattern was found on the impact site: egg masses were absent in July-August; their number per adult was high out of summer months, when the seawater temperature (high tide records) was 3 °C higher than in control sites. During the post-operational period, the abundance of adults declined on the impact site and the seasonal reproductive pattern became synchronous with control sites. Life-history traits and population dynamics of S. pectinata respond to microhabitats and to changes in seawater temperature, with possible implications in the context of climate change.