The ClimateFish database collates abundance data of 15 fish species proposed as candidate indicators of climate change in the Mediterranean Sea. An initial group of eight Mediterranean indigenous species (Epinephelus marginatus, Thalassoma pavo, Sparisoma cretense, Coris julis, Sarpa salpa, Serranus scriba, Serranus cabrilla and Caranx crysos) with wide distribution, responsiveness to temperature conditions and easy identification were selected by a network of Mediterranean scientists joined under the CIESM programme ‘Tropical Signals’ (https://www.ciesm.org/marine/programs/tropicalization.htm; Azzurro et al. 2010). Soon after, and thanks to the discussion with other expert groups and projects, C. crysos was no longer considered, and Lessepsian fishes (Red Sea species entering the Mediterranean through the Suez Canal) were included, namely: Fistularia commersonii, Siganus luridus, Siganus rivulatus, Pterois miles, Stephanolopis diaspros, Parupeneus forskali, Pempheris rhomboidea and Torquigener flavimaculosus. Considering the trend of increase of these species in the Mediterranean Sea (Golani et al. 2021) and their projected distribution according to climate change scenarios (D’Amen and Azzurro, 2020), more data on these tropical invaders are expected to come in the future implementation of the study. Data were collected according to a simplified visual census methodology (Garrabou et al. 2019) along standard transects of five minutes performed at a constant speed of 10m/min, corresponding approximately to an area of 50x5m. Four different depth layers were surveyed:  0-3m, 5-10 m, 11-20 m, 21-30 m. So far, the ClimateFish database includes fish counts collected along 3142 transects carried out in seven Mediterranean countries between 2009 and 2021, for a total number of 101'771 observed individuals belonging to the 15 fish species. Data were collected by a large team of researchers which joined in a common monitoring strategy supported by different international projects, which are acknowledged below. This database, when associated with climate data, offers new opportunities to investigate spatio-temporal effects of climate change in the Mediterranean Sea and test the effectiveness of each species as a possible climate change indicator.   Contacts: ernesto.azzurro(at)cnr.it   References: Azzurro E., Maynou F., Moschella P. (2010). A simplified visual census methodology to detect variability trends of coastal mediterranean fishes under climate change scenarios. Rapp. Comm. int. Mer Médit., 39. D’Amen, M. and Azzurro, E. (2020). Lessepsian fish invasion in Mediterranean marine protected areas: a risk assessment under climate change scenarios. ICES Journal of Marine Science, 77(1), pp.388-397. Garrabou, J., Bensoussan, N., Azzurro, E. (2019). Monitoring climate-related responses in Mediterranean marine protected areas and beyond: five standard protocols. Golani D.,  Azzurro E.,  Dulčić J.,  Massutí E., Orsi-Relini L.  (2021).  Atlas of Exotic Fishes in the Mediterranean Sea.  2nd edition  [F. Briand, Ed.]  365 pages.  CIESM Publishers, Paris, Monaco. ISBN number  978-92-990003-5-9   

Early-life stages play a key role in the spatio-temporal dynamics of marine populations due to their highly dispersive properties, their sensitivities to environmental factors and their influences on juveniles’ replenishment. However, these stages are difficult to monitor, so that in-situ observations are scarce and disparate, preventing a good understanding of the control they exert on population dynamics. The Mediterranean coastlines have been highly surveyed during the last decades in different sub-regions; yet no effort was made to assemble observations originating from different research projects and countries. Moreover, this sea has been exploited for centuries and is now recognized as a climate-change hotspot, so that it represents an ideal laboratory to address the role of anthropogenic pressures on marine populations. To advance our knowledge, we build an exhaustive compilation of historical data collected over the past decades up to present. From spawning to settlement, it evaluates both egg and larval stages of coastal fishes characterized by bipartite life cycles. This compilation gathers 44 datasets from North-Western Mediterranean countries (including coastlines of Spain, France, Italy, Croatia and Montenegro) over the last three decades (1993-2021) originating from 48 data providers. We consider direct and indirect observations of early-life stages such as otoliths’ data, datasets of settlers and juveniles sampled by underwater visual census, shore seine, hand-nets or light-traps, as well as fish eggs and larvae sampled with plankton nets. All those types of data are harmonized into a uniform dataset that informs on the periods and locations of spawning and settlement. While some sampling techniques directly provide the variables of interests, other methods require a-posteriori estimations based on growth models from the Dynamic Energy Budget (DEB) theory, using taxon-dependent parameters available in the online Add-my-Pet database. Finally, the complete database consists in several taxon, each of them being associated with dates of both spawning and settlement, as well as other information such as the pelagic larval duration, measures of uncertainties and sampling characteristics (location, depth, etc). Statistical analyses of the consolidated database describe the overall coverage of sampling and evaluate the sampling gaps over space and time in order to guide future sampling efforts. In fact, sampling mainly occurs around marine reserves and from May to October. The general coverage of spawning and settlement is then assessed, looking at the differences between observed data (same distribution as sampling) and back-calculated data (nearly uniformly distributed over the year).  Moreover, the overall taxa distribution is described, mainly represented by Sparidae. Thus, this database informs early-life traits and their variability for different coastal fish taxa in the North-Western Mediterranean in order to document their evolution in a changing world. Indeed, this database will be publicly available to help undertake future connectivity and climatic studies.