13 pages, 3 figures, 3 tables, supporting Information https://dx.doi.org/10.1111/fog.12464, We investigated the effects of three sea surface oceanographic variables (temperature, salinity and chlorophyll a) on the abundance of eggs and larvae of two summer-spawning species in the NW Mediterranean sea, the anchovy Engraulis encrasicolus and the round sardinella Sardinella aurita, based on data from ichthyoplankton surveys carried out in the 1980s, 2000s and 2010s. The environmental data showed an increase in sea water temperature and salinity along time, coupled with a decrease in chlorophyll a (proxy for primary production). These long-term directional changes in environmental conditions helped explain the important reduction observed in the abundance of eggs and larvae of anchovy, as well as shrinking of spawning habitat in this species. At the same time, the probability of occurrence of round sardinella has increased from practically zero in the 1980s to probabilities near 1 along the coastal area of the study region in the two decades of the 21st century. Given that the trends observed in the environmental variables along the three decades of study are expected to continue during the 21st century, as a consequence of climate change, the spawning habitat of anchovy is expected to continue decreasing, while round sardinella habitat can expand. Considering that anchovy is of high commercial importance in NW Mediterranean fisheries, while round sardinella has very low commercial interest, our results show that the viability of small pelagic fisheries in the area may be compromised, This research is partially supported by the CERES project (H2020, EU 678193) and by the Spanish Ministry of Economy and Competitiveness (CTM2010-18874 and CTM2015-68543-R), With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI), Peer reviewed

23 pages, 8 figures, 1 table, supplementary material https://doi.org/10.1007/s10584-020-02723-4, We studied the effect of climate change on the potential spawning habitats of two marine small pelagic fishes. We examined the projected changes in the potential spawning habitat of the summer-spawning anchovy (Engraulis encrasicolus) and round sardinella (Sardinella aurita) in the northwestern Mediterranean by combining the regionalized projections of RCP scenarios with an existing species distribution model (SDM). The SDM was based on a separate generalized additive model for the eggs and larvae of the two species computed from ichthyoplankton sampling that was conducted with simultaneous readings of surface temperature, salinity and chlorophyll-a values as predictor variables. The SDM was projected for the 2010 decade, which represented the present-day conditions, with these environmental variables obtained from the regionalized POLCOMS-ERSEM biogeochemical model forced by the RCP 4.5 and RCP 8.5 scenarios. The comparison of the present-day projection results with the projections for the middle and final decades of the twenty-first century showed that the suitability of the spawning habitat as defined by the anchovy eggs model was likely to increase over time under RCP4.5 or decrease slightly under RCP8.5, but the habitat for anchovy larvae was likely to decrease in all cases. Loss of habitat was projected to be particularly important in the south of the study area on the Ebre River delta continental shelf. Conversely, the probability of round sardinella occurrence will significantly increase under both scenarios. The potential habitat of this species, which is of subtropical origin, is likely to shift northwards. The limitations of the existing models to extrapolate the current results to future scenarios are discussed regarding (i) the uncertainty in the projections of driving environmental variables (e.g., chlorophyll-a), (ii) the simplified nature of the projection models, which did not capture the dynamics of the early life stages of the fish at a small scale, and (iii) insufficient consideration of important drivers, such as larval transport or retention by mesoscale hydrographic phenomena, This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Grant Agreement “CERES” No. 678193 and from the Spanish Ministry of Economy and Competitiveness (CTM2010-18874 and CTM2015-68543-R). Eduardo Ramirez-Romero received funding from “Govern de les Illes Balears—Conselleria d’Innovació, Recerca i Turisme, Programa Vicenç Mut.”, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)