Supporting data for the paper "Three major mesoplanktonic communities resolved by in situ imaging in the upper 500 m of the global ocean"

Aim
The distribution of mesoplankton communities have been poorly studied at global scale, especially from in situ instruments. This study aims  to (1) describe the global distribution of mesoplankton communities in relation with their environment and (2) assess the ability of various environmental-based ocean regionalisations to explain the distribution of these communities.

Location
Global ocean, 0 - 500 m depth.

Time period
2008 - 2019

Major taxa studied
28 groups of large mesoplanktonic and macroplanktonic organisms, covering Metazoa, Rhizaria and Cyanobacteria.

Methods
From a global data set of 2500 vertical profiles making use of the Underwater Vision Profiler 5 (UVP5), an in situ imaging instrument, we studied the global distribution of large (> 600 µm) mesoplanktonic organisms. Among the 6.8 million imaged objects, 330,000 were large zooplanktonic organisms and phytoplankton colonies, the rest consisting of marine snow particles. Multivariate ordination (PCA) and clustering were used to describe patterns in community composition, while comparison with existing regionalisations was performed with regression methods (RDA).

Results
Within the observed size range, epipelagic plankton communities were Trichodesmium-enriched in the intertropical Atlantic, Copepoda-enriched at high latitudes and in upwelling areas, and Rhizaria-enriched in oligotrophic areas. In the mesopelagic layer, Copepoda-enriched communities were also found at high latitudes and in the Atlantic Ocean, while Rhizaria-enriched communities prevailed in the Peruvian upwelling system and a few mixed communities were found elsewhere. The comparison between the distribution of these communities and a set of existing regionalisations of the ocean suggested that the structure of plankton communities described above is mostly driven by basin-level environmental conditions.

Main conclusions
In both layers, three types of plankton communities emerged and seemed to be mostly driven by regional environmental conditions. This work sheds light on the role not only of metazoans, but also of unexpected large protists and cyanobacteria in structuring large mesoplankton communities.