Short communication Temporal asymmetries in the feeding patterns along the tidal cycle in two sympatric littoral blennies C. Faria * , V.C. Almada Unidade de Investigaça ˜o em Eco-Etologia, Instituto Superior de Psicologia Aplicada, R. Jardim doTabaco 34, P-1149-041 Lisboa, Portugal article info Article history: Received 17 February 2008 Accepted 9 May 2008 Available online 18 May 2008 Keywords: Lipophrys pholis Coryphoblennius galerita rocky shore feeding activity tidal rhythms microhabitat shifts abstract The temporal patterns of feeding activity of Lipophrys pholis and Coryphoblennius galerita were studied by snorkelling dives during high-waters. The feeding activity was especially intense during the rising-tide when compared to the ebbing-tide. The relative abundances of C. galerita and small L. pholis observed on rock-walls were higher during the rising- and high-tide. However, L. pholis larger than 7–8 cm showed higher relative abundance on rock-walls during the ebbing phase, apparently because they move up and down with the tide, and many individuals were in their downward movements as the tide ebbs. It is hypothesized that the asymmetry in feeding pattern observed in both species reflects a trade off between two conflicting needs, maximizing feeding time and reaching their low-tide shelters in time, avoiding the risk of getting stranded in unsuitable locations. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction A salient feature of the animals that colonize the intertidal habitat is the prevalence on a wide spectrum of taxa of periodical oscilla- tions, both physiological and behavioural, that are typically driven by internal clocks, and are entrained by external cues that keep them nearly in phase with the tidal cycle (e.g. Williams and Naylor, 1969; Gibson, 1967, 1970, 1973, 1982; Northcott et al., 1990; Northcott, 1991). These ‘‘tidal rhythms’’ seem to enable the organisms to track and anticipate physical, chemical and biotic oscillations that the tide imposes on intertidal organisms (for a review, see Gibson, 1999). Bhikajee and Green (2002) give an interesting extreme example of an amphibious blenny that remains almost constantly emersed, moving up and down with the tide, above the water level. There is still very limited information on the interspecific vari- ation of tidal rhythms that rocky intertidal fish of the same com- munity may display. This is an important gap in our knowledge of the rocky intertidal fish communities. In a given assemblage fish typically vary in size, diet, preferred low-tide shelter and spawning site. They are likely to differ also in the extent of their high-tide excursions away from shelters and in the spatial and temporal patterns of exploitation of the available resources. In Western Europe blennies, namely Lipophrys pholis and Coryphoblennius galerita are major components of the resident icthyofauna of the rocky intertidal habitats (e.g. Gibson, 1972; Milton, 1983; Faria and Almada, 1999, 2001), and there have been attempts to access possible resource partitioning among them (e.g. Milton, 1983; O’Farrell and Fives, 1990; Faria and Almada, 2001). This resource partitioning may be expressed in trophic differences; however, it seems also to be expressed through differences in ontogeny: L. pholis grows faster and reaches a larger size than C. galerita, which leads the two species to use different types of shelter and prey (Milton, 1983; Faria and Almada, 2001; Monteiro et al., 2005). Indeed, L. pholis attains a much larger adult size than C. galerita (Zander, 1986). When they are about 1 year old, L. pholis reach the upper size of adult C. galerita (Faria et al., 1996). At this stage L. pholis leaves the pools that are shared by the juveniles of both species, seeking new shelters in crevices and spaces under boulders, in the lower shore, where they hide in groups (Qasim, 1957; Gibson, 1972; Faria and Almada, 2001). This shift in low-tide shelter is accompanied by a shift in diet, the larger L. pholis now eating larger prey (Monteiro et al., 2005). Most studies on the ecology of these blennies have concentrated on observations made during low-tide, when their activity reached its minimum and fish congregate in shelters (e.g. Qasim, 1957; Gibson, 1972; Milton, 1983; Faria et al., 2001), so little consideration has been given to the possibility that partitioning of resources among the two species may occur through spatial and temporal differences in behaviour during high-tide. Burrows et al. (1999), using underwater TV observations, suggested that the shanny, Lipophrys pholis, shows the highest level of activity during the ris- ing and high-tide periods, and that its feeding movements are concentrated around crevices. Faria and Almada (2006), based on * Corresponding author E-mail address: cfaria@ispa.pt (C. Faria). Contents lists available at ScienceDirect Estuarine, Coastal and Shelf Science journal homepage: www.elsevier.com/locate/ecss 0272-7714/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2008.05.003 Estuarine, Coastal and Shelf Science 79 (2008) 566–568