Global mesozooplankton communities show lower connectivity in deep oceanic layers

Abstract

Mesozooplankton is a key component of the ocean, regulating global processes such as the carbon pump, and ensuring energy transfer from lower to higher trophic levels. Yet, despite the importance of understanding mesozooplankton diversity, distribution and connectivity at global scale to predict the impact of climate change in marine ecosystems, there is still fragmented knowledge. To fill this gap, we applied DNA metabarcoding to mesozooplankton samples collected during the Malaspina-2010 circumnavigation expedition across temperate and tropical oceans from the surface to bathypelagic depths. By conducting a hidden diversity analysis, we highlight the still scarce knowledge on global mesozooplankton diversity and identify the Indian Ocean and the deep sea as the most understudied areas. By analysing mesozooplankton community spatial distribution, we confirm global biogeographical patterns across the temperate to tropical oceans both in the vertical and horizontal gradients. Additionally, we reveal a consistent increase in mesozooplankton beta-diversity with depth, indicating reduced connectivity at deeper layers, and identify a water mass type-mediated structuring of bathypelagic communities, instead of an oceanic basin-mediated as observed at upper layers. This suggests limited dispersal at deep ocean layers, most likely due to weaker currents and lower mixing of water mass types. Overall, our work supports the neutral theory of biodiversity and thus the importance of oceanic currents and barriers in dispersal in shaping global plankton communities, and provides key knowledge for predicting the impact of climate change in the deep-sea.

Divergent patterns of zooplankton connectivity in the epipelagic and mesopelagic zones of the eastern North Pacific

“…Together with taxon‐specific environmental ranges that mirror the primary environmental variability found within each depth zone, greater community similarity and decreased rates of endemism suggest that midwater zooplankton community composition is more strongly influenced by environmental selection than by physical dispersal due to ocean mixing. Our results contrast with recent observations of decreased community similarity at depth and stronger effects of physical distance than of environmental distance on community similarity (Canals et al., 2023 ). However, our sampling locations comprise a strong latitudinal gradient in productivity, while the Pacific Ocean locations sampled by the Malaspina expedition were restricted to primarily equatorial and subtropical environments.…”

“…Our results contrast with recent observations of decreased community similarity at depth and stronger effects of physical distance than of environmental distance on community similarity (Canals et al, 2023). However, our sampling locations comprise a strong latitudinal gradient in productivity, while the Pacific Ocean locations sampled by the Malaspina expedition were restricted to primarily equatorial and subtropical environments.…”