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

Copepod resilience to climate forcing Copepod diversity may have remained stable over a long time and large space due to a strong resilience to environmental variability. In this aspect and when dissecting species composition into turnover and nestedness, we observed that the former was higher in areas where hot spots were also identified (Figs 6 and 4, respectively), coinciding with the flow of cold currents (Humboldt current, Zeehan Current in southern Australia, and southern part of the East Aus- tralian current off New Zealand into the West Wind Drift). Therefore, basin-scale ocean cur- rents seem to be an important oceanographic driver explaining the distribution of copepods in the SPO. The potential of large-scale ocean currents generating distributional patterns at vari- ous levels in the ocean has recently been studied more across different taxa [137–141], showing results that support the hypothesis and suggest that it may be a general process transcending taxa and spatial scales [141]. All these large-scale circulation patterns may allow the recoloniza- tion and mixing of copepod assemblies, thereby acting as a buffer to cope with the local impact of warming, deoxygenation, or other altered environmental conditions driven by natural per- turbations or anthropogenic origin. This buffering effect may allow planktonic organisms such as copepods to exhibit a high resilience to large-scale changes in hydrographic conditions due to global warming. Conclusion The diversity distribution of copepods in the SPO follows general patterns observed in other

organisms in the ocean, although patterns over a basin scale with presence of hot and cold spots do not replicate observed patterns reported for the North Pacific or Atlantic Ocean. The key environmental correlates for such biodiversity patterns were found to be mean tempera- ture, chlorophyll-a concentration, salinity, oxygen concentration, and residuals autocovariate. A significant role for causing and maintaining copepod diversity patterns was also attributed to large-scale circulation processes, which may act as a buffer for changes in local conditions and allow species recolonization. Therefore, we suggest that planktonic copepods may exhibit a strong resilience to climate change impact. However, caution should be taken in interpreting our findings since our modeling approaches and spatial analyses were strongly constrained by spatial and temporal gaps in sampling efforts and data availability. Future analyses are expected to improve observed pat- terns with the completion of global biodiversity data bases. Supporting information S1 Fig. Kriging interpolation analysis done for the western and eastern side of the SPO with 394 cells accounting for number of genera. Transparent squares are the 1˚ sampled cells used for Kriging interpolation, whereas the grey dotted line delimits the South Pacific Ocean. Map projection is WGS 84/PDC Mercator (EPSG 3832). (JPG) S2 Fig. Maximum height of the spline function (hence the maximum value of the trans- formed predictors), indicating the stronger predictors of the observed dissimilarities for

the Generalized Dissimilarity Modelling (GDM)-based spatial analysis. Their acronyms are: s = salinity, o2 = dissolved oxygen concentration, tmean = mean temperature, chla = chlorophyll-a concentration, mld = mixed layer depth, tstab = temperature stability, tsd = standard deviation of temperature. The spatial layers were generated and plotted with the predictors with heights over zero (i.e., s, o2, tmean and chla). (JPG) PLOS ONE Biodiversity of copepods in the South Pacific PLOS ONE | https://doi.org/10.1371/journal.pone.0306440 July 11, 2024 20 / 28