Discussion
Despite the common assumption that size is the master trait that
controls most planktonic processes, here transparency was the key trait
defining one of the main biogeochemical processes influenced by
plankton, carbon export. Higher export was found to be linked to less
transparent animals. Potential explanations for these findings could
include opacity due to full guts or the presence of pigments
particularly during the bloom period. It could also be due to the
presence of strong swimmers participating in the DVM, as those
participating require stronger muscles and thicker carapace walls (where
muscles attach), increasing the opacity of the community when they
become dominating, especially during the spring bloom. This study also
shows morphological and molecular data from the same samples can be
analysed jointly to better infer how various facets of mesozooplankton
diversity (morphological, taxonomical) vary throughout seasons and
impact biogeochemical processes. The image-based functional approach
allowed for the assignment of morphological properties to individual
plankton and added taxa that were underrepresented in the metabarcoding
data due to miss amplification. Moreover, benefiting from the “twin”
imaging and molecular datasets, we studied the quantitative property of
metabarcoding for wide taxonomic categories. Metabarcoding proved to be
a good proxy of abundance or biomass for only a few taxa (e.g. ,
Cyclopoida, Doliolida, Larvacea), but could not be related to most of
the considered taxa (e.g. , Calanoida, Euphausiacea, Salpida).