Biodiversity patterns of epipelagic copepods in the South Pacific Ocean: Strengths and limitations of current data bases

Ecuador (~4˚S), where cool upwelled waters collide with warm tropical waters forming the Equatorial Front [81]. The South Pacific Subtropical Anticyclone or the South Pacific High, which spins counter-clockwise, is the most influential off the west coast of South America [74, 84] and acts as the dominant forcing of the subtropical gyre [85]. However, it presents seasonal variation, abiding at its northern position (26˚S, 86˚W) during the late austral fall and winter, when it is also closer to the South American continent and its intensity is weaker; whereas, during austral spring and summer the South Pacific High moves southwest (37˚S, 108˚W) and depicts its maximum intensity [85]. The latter (former) conditions generate stronger (weaker) Equatorward winds that favor (disfavor) coastal upwelling offshore central-south Chile [81]. In terms of sampling coverage for epipelagic copepods, only 4.02% of the total area of the epi- pelagic SPO has been sampled between 1993 and 2019. In fact, all the main current systems have been sampled over less than 2.5% of their area, each covering less than 1% of the total area of the SPO. An exception is the East Australian Current System with 17.28% of its area sampled and covering 2.76% of the total area of the SPO (Table 1). Environmental data selection and predictive models. The routine VSURF selected five oceanographic factors to be tested for influence on species richness (arranged in decreasing order of importance): mean temperature (Tmean), salinity (S), dissolved oxygen concentration (O2),

chlorophyll-a concentration (Chla), and the mixed layer depth (MLD). For species composition, all seven oceanographic variables were selected (arranged in decreasing order of importance): mean temperature (Tmean), chlorophyll-a concentration (Chla), dissolved oxygen concentration (O2), standard deviation of temperature (Tsd), salinity (S), temperature stability (Tstab), and mixed layer depth (MLD). The Spearman correlation matrices (S3A and S3B Fig) obtained for each sub- set of variables depicted that all were weakly correlated according to a Spearman’s rank correlation coefficient |ρ <0,7|, with exception of Tmean and O2, which showed ρ = -0.99. However, in addition to environmental variables, data on Copepoda richness within the upper 200 m of the SPO depicted that the species and assemblies were significantly associated Fig 7. Predicted spatial variation in species composition of Copepoda at the western and eastern sides of the SPO based on a principal component analysis (PCA) of the Generalized Dissimilarity Modelling (GDM)-transformed environmental predictors. Colors represent gradients in species composition. Locations with similar colors indicate more similar expected composition. Dashed line at both sides of the antemeridian (180˚ longitude) delimits the South Pacific Ocean. Map projection is WGS 84/PDC Mercator (EPSG 3832). https://doi.org/10.1371/journal.pone.0306440.g007 PLOS ONE Biodiversity of copepods in the South Pacific PLOS ONE | https://doi.org/10.1371/journal.pone.0306440 July 11, 2024 14 / 28