Understanding the fundamental laws that govern complex food web networks over large ecosystems presents high costs and oftentimes unsurmountable logistical challenges. This way, it is crucial to find smaller systems that can be used as proxy food webs. Intertidal rock pool environments harbour particularly high biodiversity over small areas. This study aimed to analyse their food web networks to investigate their potential as proxies of larger ecosystems for food web networks research. Highly resolved food webs were compiled for 116 intertidal rock pools from cold, temperate, subtropical and tropical regions, to ensure a wide representation of environmental variability. The network properties of these food webs were compared to that of estuaries, lakes and rivers, as well as marine and terrestrial ecosystems (46 previously published complex food webs). The intertidal rock pool food webs analysed presented properties that were in the same range as the previously published food webs. The niche model predictive success was remarkably high (73–88%) and similar to that previously found for much larger marine and terrestrial food webs. By using a large-scale sampling effort covering 116 intertidal rock pools in several biogeographic regions, this study showed, for the first time, that intertidal rock pools encompass food webs that share fundamental organizational characteristics with food webs from markedly different, larger, open and abiotically stable ecosystems. As small, self-contained habitats, intertidal rock pools are particularly tractable systems and therefore a large number of food webs can be examined with relatively low sampling effort. This study shows, for the first time that they can be useful models for the understanding of universal processes that regulate the complex network organization of food webs, which are harder or impossible to investigate in larger, open ecosystems, due to high costs and logistical difficulties.

Fish were sampled monthly in four tidal pools, for two years, on the west Portuguese coast. Species diversity of transient fish was higher than that found in previous studies, in other parts of the world. The transient fish population comprised six species: the white seabream, Diplodus sargus, sand smelt, Atherina spp., the thinlip grey mullet, Liza ramada, the Baillon's wrasse, Symphodus bailloni, the zebra seabream, Diplodus cervinus and the European pilchard, Sardina pilchardus. Abundance varied seasonally, yearly, and among pools, with peak numbers in spring and summer. The most abundant species in all pools, both as larvae and juveniles, was D. sargus. Diplodus sargus and Atherina spp. were present in most pools, from spring to autumn, while rare species were present mostly in the spring-summer period. Smaller mean sizes of larvae and juveniles were observed at the beginning of spring of 2011 (March–April) and at the end of spring/beginning of summer of 2012 (May–June). Mean size of larvae and juveniles often showed a continuous increase from spring to autumn in both years. The highest density peaks were due to the high number of post-larvae entering the pools in spring. In most pools, the overall condition (Fulton's K) of D. sargus increased throughout the year, in both years. The species richness, the high densities of early stages, and their continuous growth observed in tidal pools strongly emphasize the importance of these environments for larvae and juveniles of several transient marine fishes.