Biologia 70/3: 372—379, 2015 Section Zoology DOI: 10.1515/biolog-2015-0046 Use of rocky intertidal pools by shrimp species in a temperate area Catarina Vinagre 1 , Marta Dias 1 , Catarina Fonseca 2 , Maria T. Pinto 1 , Henrique N. Cabral 1 & Ana Silva 3 1 MARE – Marine and Environmental Sciences Centre, Faculdade de Ci˛ encias, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal; e-mail: cmvinagre@fc.ul.pt 2 AIMM-Associa¸ c˜ ao para Investiga¸ c˜ao do Meio Marinho, Rua Maestro Frederico de Freitas No. 15-1 ◦ andar, 1500-399 Lisboa, Portugal 3 Centro de Geo-sistemas/CVRM. Instituto Superior Técnico. Av. Rovisco Pais, 1049-001 Lisboa, Portugal Abstract: Rocky shores are among the most-intensively studied ecosystems, however, tidal pools remain relatively under- studied. This study aims to investigate the habitat use and dynamics of the shrimp species that occur in tidal pools of a North-eastern Atlantic coast, the Portuguese coast, in particular species composition, abundance, seasonality and size structure. Shrimps were sampled monthly from six tidal pools for one year, in the west Portuguese coast. Species diversity was much higher than that found in previous studies, in other parts of the world. The shrimp population comprised 8 species: the European rock shrimp, Palaemon elegans, the common prawn, Palaemon serratus, the Atlantic ditch shrimp, Palaemon varians, the Baltic prawn, Palaemon adspersus, the Oriental shrimp, Palaemon macrodactylus and the relatively rare shrimps Eualus sollaudi, Eualus drachi and Caridion gordoni. Shrimp populations varied seasonally and among pools, with peak numbers in spring and summer. The most abundant species was P. elegans. P. elegans was present in all pools, throughout most of the year. Rare and exotic species were present mostly in spring-summer. Lower mean sizes of all shrimp were registered in the beginning of spring, most often in April or May, and gradually increased until winter. New-recruits of the most abundant species, P. elegans, generally entered the pools in spring and formed a high proportion of the population between April and August. They were responsible for the highest abundance peaks of shrimps occurring in the pools. The species richness and high numbers of juveniles occurring in tidal pools suggest that these environments may be nursery areas for coastal shrimp. Key words: Crustacea; intertidal area; rocky reefs; tidal pools; recruitment Introduction Tidal pools in rocky reefs provide highly structured en- vironments, where food and refuge is available for small marine organisms (Menge & Lubchenco 1981; Moore & Seed 1986). Seasonal high densities of fish and inverte- brates can be easily observed in tidal pools; however, studies on the use of tidal pools by juveniles of ma- rine organisms remain scarce. Tidal pools are highly variable in surface area and volume. Additionally, they may be located at different heights in the intertidal and be exposed to different degrees of shading and drainage patterns (Metaxas & Scheibling 1993). This makes each pool unique in environmental characteristics and repli- cates unavailable, and may be the reason why these environments remain understudied (Underwood & Skil- leter 1996; van Tamelen 1996; Nybakken 1997; Trussell et al. 2004; Martins et al. 2007), although rocky shores are among the most-intensively experimentally studied ecosystems globally (e.g., Paine 1994; Benedetti-Cecchi et al. 200; Thompson et al. 1996, 2002). Rocky shores are stressful environments given their sharp environmental gradients, fluctuating conditions and exposure to wave action, yet they offer marine or- ganisms a markedly different environment from their surroundings (Metaxas & Scheibling 1993). The occur- rence of tidal pools allows some organisms to extend their range upward in the intertidal beyond the lev- els to which they would be naturally limited (Metaxas & Scheibling 1993; Paine 1994). They may also act as nursery areas for fish and shrimp, as high densities of juveniles seem to indicate. Coastal ecosystems such as seagrass meadows, marshes, and mangroves have traditionally been re- garded as nursery areas for shrimp and fish (Williams 1955; Costello & Allen 1964; Turner 1977). They of- fer favorable conditions for survival and growth be- cause they provide food resources and refuge (e.g., Un- derwood 1980, McLusky 1981; Kneib 1987; Heck et al. 1997). Densities of juveniles can be very high in these ecosystems and some studies have showed that they are more likely to contribute to the adult popu- lation than juveniles inhabiting adjacent environments (e.g., Gillanders & Kingsford 1996; Dahlgren et al. 2006; Frodie & Herzka 2008). The body of knowledge accumulated on the nurs- ery role of seagrass meadows, marshes, and mangroves for shrimps is not available for rocky reefs. Basic studies c 2015 Institute of Zoology, Slovak Academy of Sciences