Can we detect oceanic biodiversity hotspots from space?

Abstract

Understanding the variability of marine biodiversity is a central issue in microbiology. Current observational programs are based on in situ studies, but their implementation at the global scale is particularly challenging, owing to the ocean extent, its temporal variability and the heterogeneity of the data sources on which compilations are built. Here, we explore the possibility of identifying phytoplanktonic biodiversity hotspots from satellite. We define a Shannon entropy index based on patchiness in ocean color bio-optical anomalies. This index provides a high resolution (1 degree) global coverage. It shows a relation to temperature and mid-latitude maxima in accordance with those previously evidenced in microbiological biodiversity model and observational studies. Regional maxima are in remarkable agreement with several known biodiversity hotspots for plankton organisms and even for higher levels of the marine trophic chain, as well as with some in situ planktonic biodiversity estimates (from Atlantic Meridional Transect cruise). These results encourage to explore marine biodiversity with a coordinated effort of the molecular, ecological and remote sensing communities.

Figure 1

(a) Index τ for the global ocean: average of daily maps of τ computed over 7-day composites of PHYSAT data for the period 2003–2010. The hotspots emerging from this analysis characterize regions with a standing representation of several nearby communities, as identified by their dominant phytoplankton types (PHYSAT algorithm applied to SeaWiFS radiances). (b) Average of daily chlorophyll-a maps (SeaWiFS, 2003–2010).

Figure 2

Time-averaged index τ versus average sea surface temperature at the same location (AMSR-E, 2003–2010). The cyan lines are the best quadratic fit to the data (R²=0.26, P<10⁻⁴) and one s.d. of the residuals. The red points are the Shannon index for nano- and microplankton, from measures of the AMT-2 cruise and rescaled so that the two data sets have the same mean and s.d. (see Supplementary Information for further details).