Despite thousands of studies about the processes controlling the recruitment of fish larvae in nursery areas, its variability is not fully understood, especially during larval migrations between spawning and nursery habitats (“lost” phase). It is known that fish larvae use sensorial and swimming capabilities to detect and ingress into nursery habitats and to control their distribution in coastal areas. However, studies on in situ swimming and sensorial acuity of larval phases are few and more restricted to tropical reef fish species. Small changes in oceanography have been demonstrated that have huge consequences on fish survival and distribution and forecasted climate change will impact recruitment processes. These aspects will provide a deep understanding of recruitment variability and connectivity of marine populations since they are vital tools for the management of MPAs and coastal ecosystems with direct impact on Sustainable Development Goals (SGD14.4-5), for their restoration to achieve healthy and productive oceans (14.2), including by strengthening their resilience to climate change (13.1). Thus, the innovative idea to be tested is that temperate and tropical fish larvae are sensing and behavioral responding to environmental variability according to their sensorial capabilities, conditioning their survival and distribution. This proposal will contribute to the knowledge development within the Atlantic Ocean together with Miami University collaboration, where in situ chambers to study fish larvae behavior have been developed and will be innovated. It will focus on fish species with socio-economic importance in East – Portugal (PT) and São Tomé and Príncipe (STP; Small Island Developing State- SIDS), and West Atlantic – Dominica (DOMN; SIDS), comprising four hypotheses: H1) early phases of fishes have good capabilities to control their transport into coastal areas, and to detect and follow sensorial cues to reach nursery habitats; H2) ocean warming and acidification will affect swimming and sensory capabilities of fish larvae, and their recruitment; H3) early changes in the development of fish species are accompanied by molecular modifications (gene expression) that could be influenced by environmental changes (phenotypic plasticity); H4) healthy transitional ecosystems will provide adequate cues and good physiological condition for recruitment success in nursery habitats. Thus, this proposal is structured in five tasks: T1) characterize swimming and sensorial capabilities of fish larvae, their behavioral responses and how they use them to follow nursery cues (H1,H4); T2) evaluate the effects of climate change on larval behavior and swimming capabilities (H2); T3) understand the regulatory factors that influence fish larvae development and phenotypic plasticity (H3), and condition (H4); T4) estimate patterns of fish larvae dispersal and consequences for the connectivity of marine populations (H1,H4); T5) modelling and quantifying the dispersion and ingress of fish early phases into nursery habitats (H1-H4). This approach will be useful as a tool to refine the management of important fisheries and will contribute to increasing the scientific knowledge in East and West Atlantic margins as well as to a better understanding of local communities concerning the protection of coastal ecosystems. The present proposal will deliver impactful outputs, with far-reaching implications for marine ecology/conservation and fisheries sustainability.