The 3PP marine cave near Marseille (NW Mediterranean) is at a depth of only 15 m. Nevertheless, the cave is a unique deep-sea-like habitat zone due to total darkness, lack of water circulation, oligotrophy, and cold homothermy, a thermal regime similar to that of the deep Mediterranean. We studied the meiofaunal community composition and diversity at 3 sampling stations in the cave (entrance, middle, and blind end). Major taxon composition, based on presence/absence data, did not vary over the transect; however, significant differences in community were found. Tardigrades were the only major taxon restricted to the inner parts of the cave. Copepod diversity decreased towards the inner parts of the cave. The 3PP Cave was characterized by very low abundances of meiofaunal organisms similar to abyssal sites elsewhere. A total of 405 individual copepods were assigned to 27 families and 90 species (75% of them new to science). Significant differences in copepod communities between stations were found at family, genus, and species level. Some harpacticoid taxa generally known from the deep sea, such as Marsteinia, Ancorabolina, Paranannopus, Nematovorax, and Argestidae, were represented in the 3PP Cave. A naive Bayes model was used for the first time to classify the communities as 'shallow' or 'abyssal'. The meiobenthic communities at the entrance and the end of the cave were unequi vocally classified as 'shallow' and 'abyssal' respectively, while the middle part of the cave presented a mixed community. Our study further highlights the strong faunal and community affinities between marine caves and the deep sea, indicating the existence of dispersal mechanisms from deep waters into the euphotic zone for benthic organisms.
