Variation and resilience of rocky intertidal fish in western Portugal

A monthly census of resident fishes in tide pools was made at 3 sites on th e Portuguese west coast, from 1993 to 1997. A total of 43 tide pools was mo nitored. Results of manipulation (addition and removal) experiments are pre sented. There is a very high level of consistency in the numbers of species at 1 site. Experiments on removal and addition show that the number of fis h in the pools returns to normal in a few weeks. The inter-annual fluctuati ons of recruitment are less pronounced as the fish grow, possibly due to de nsity dependent mortality. At the other 2 sites, where the pools are distur bed by storms that reshape their contents and move large quantities of sand , there is a less consistent pattern. The agonistic behaviour of tide pool fishes is strongly related to the priority of access to holes and crevices and this may place Limits on the number of fishes of a given size that can exist in each pool as a function of topographic complexity.