The Mediterranean Sea is the largest enclosed marine environment globally (Coll et al. 2010). A large proportion of its coastline is rocky and mainly made by limestone, a defining characteristic of this marine basin (Gerovasileiou and Voultsiadou 2012). There, marine hard substrates exists which is of great ecological and economic value due to the high structural complexity on which rich marine communities are based. Yet, several goods and services are provided by (Salomidi et al. 2012). Due to the importance of this marine ecosystem, Habitat Directive 92/43/EEC includes it under the code 1170 (Reefs). In the infralittoral zone of the hard substrate, several biocoenoses exist (Pérès and Picard 1964). Among them, the biocoenosis of the photophilic algae is the one that dominates the hard substrates in depths up to 30 meters, depending on the water turbidity, light penetration and availability of nutrients (Coppejans 1980). Macroalgae, the main component of this biocoenosis, provides an excellent host for food and shelter to the taxonomic group of molluscs. This is one of the most important animal groups found in the Mediterranean Sea, and its molluscan fauna is the best known in the world (Sabelli and Taviani 2013) while from the 17,000 marine species that have been found in the Mediterranean, 13% are molluscs (Coll et al. 2010). The biocoenosis of photophilic algae is, however, poorly studied in terms of molluscan biodiversity; few studies examine the species communities in the infralittoral zone. All of them are paper-based, while the detection of them as well as the compilation of the included published information about the species and other associated data (sampling method, depths, location, time period) cannot be retrieved automatically by machine-learning methods and tools.

This study attempts to expand the current knowledge on the rocky infralittoral zone of the Mediterranean Sea by providing occurrence data of molluscan species from two different sources. The first one comes from the sampling campaign of the NAGISA project in the East Mediterranean Sea while the second one comes from the compilation of the available and accessible published material in peer-reviewed journals and grey literature. The present datasets include georeferenced and fully documented information from 22 regions/sampling sites across the Mediterranean Sea, from 1969 to 2012 (Table 1) on 599 species of molluscs (Table 2). Additional information based on the dataset of the NAGISA project about the recorded individuals per species is alsoincluded (127 species, 10326 individuals).