Abstract Despite their great importance, the sandy shores have not received the attention deserved. In Colombia they have been approached mainly from physical and geological standpoints, with few studies on the associated biodiversity, as is the case of the Johnny Cay Regional Natural Park in the Colombian Caribbean Region. To have a future frame of reference to evaluate and monitor the environmental impact on the sandy coast of Johnny Cay, the macrofaunal community of this ecosystem was characterized. Two stations were established, where three sediment samples were taken per beach zone (infralittoral, mesolittoral, and supralittoral), using a 16 cm diameter core, for a total of nine samples per station. The samples were sieved through a 500 µm mesh and processed in a laboratory. The macrofaunal community of Johnny Cay was represented by 1628 organisms, belonging to 20 families of the phyla Annelida, Nematoda, Mollusca, and Arthropoda (subphylum Crustacea). Annelids were the dominant group, representing 98% of total abundance, with two new family reports (Naididae and Enchytraeidae) for the Colombian Caribbean sandy beaches. The station EST_549 presented 67% of the macrofauna; this station is characterized by its hydro-dynamism, with a change of material due to the division in the opposite direction of the waves. Substrate samples were also taken in each beach zone for sedimentological analysis of grain size, carbonate content, organic matter content, and mineralogy; these variables were correlated with the community structure, obtaining a better correlation between the medium and coarse sands, and the width of the beach zone with the biological component. This work presents the baseline for the macrofaunal community of Johnny Cay sandy shore and sets the initial steps for its preservation and conservation. importance deserved standpoints biodiversity Region established infralittoral, infralittoral (infralittoral mesolittoral supralittoral, supralittoral , supralittoral) 1 core 50 laboratory 162 organisms 2 Annelida Nematoda Mollusca subphylum Crustacea. Crustacea . Crustacea) group 98 abundance Naididae Enchytraeidae beaches EST549 EST 549 EST_54 67 macrofauna hydrodynamism, hydrodynamism hydro dynamism, dynamism hydro-dynamism waves size content mineralogy structure sands component conservation 5 9 EST54 54 EST_5 6 EST5 EST_

Abstract The iAtlantic Project has established an international collaborative strategy to improve mapping and characterization of deep and open ocean ecosystems in understudied regions of the Atlantic and evaluate their health. In December 2022, the first iAtlantic expedition in the South Atlantic set off to map and explore seafloor ecosystems in the Santos Basin slope (200-1,000 m depths) in collaboration with the Petrobras ‘Santos Basin - Regional Characterization Project.’ The 17-day ‘iAtlantic_BR10-Petrobras’ cruise was conducted on board the research vessel NPqHOc Vital de Oliveira (Brazilian Navy) and performed (a) water column structure characterization, (b) seafloor morphology mapping, (c) description of benthic habitats and communities by seafloor imagery and biological/ geological sampling, and (d) ex-situ experiments to assess the functioning of sedimentary ecosystems and their responses to climate-related environmental changes. This study describes the rationale behind the iAtlantic_BR10-Petrobras cruise science plan, reports its sampling strategy and methods, and summarizes its collected data and preliminary results. health 2022 2001,000 2001000 200 1,000 1 000 (200-1,00 depths Project. 17day day 17 ‘iAtlantic_BR10Petrobras iAtlanticBR10Petrobras iAtlanticBRPetrobras ‘iAtlantic_BR10 BR10 BR ‘iAtlantic_BR10-Petrobras Brazilian Navy a (a b (b c (c biological d (d exsitu ex situ climaterelated climate related changes iAtlantic_BR10Petrobras iAtlantic_BR10 plan methods results 202 2001 2001,00 200100 20 1000 1,00 00 (200-1,0 BR10Petrobras iAtlanticBR iAtlanticBR10 ‘iAtlantic_BR1 BR1 iAtlantic_BR1 2001,0 20010 2 100 1,0 0 (200-1, BRPetrobras iAtlanticBR1 ‘iAtlantic_BR iAtlantic_BR 2001, 10 1, (200-1 (200- (200 (20 (2 (