Everything is not everywhere: can marine compartments shape phytoplankton assemblages?

Area of Science:

• Marine ecology
• Biogeography
• Microbial oceanography

Background:

• The concept of 'everything is everywhere, but the environment selects' is a cornerstone of microbial biogeography.
• Marine phytoplankton are often cited as a model group for ubiquity, with distinct assemblages forming due to environmental selection.
• While coastal phytoplankton assemblages vary, the interplay between regional sea compartmentalization and local environmental factors remains under-examined.

Purpose of the Study:

• To investigate the relative importance of spatial structure versus local environmental conditions in shaping marine phytoplankton assemblage composition.
• To partition the effects of spatial structures, environmental conditions, and their overlap on phytoplankton community variation.
• To test the 'everything is everywhere' hypothesis for marine phytoplankton in coastal embayments.

Main Methods:

• Data collection from coastal embayments within two distinct water compartments of a regional sea.
• Application of principal coordinates of neighbour matrices (PCNM) and asymmetric eigenvector maps (AEM) for spatial analysis.
• Partitioning of variation in assemblage composition attributed to spatial structure, environmental conditions, and their interaction.

Main Results:

• Models explained a substantial portion of phytoplankton assemblage variation (59-65%).
• Spatial structure, reflecting marine compartmentalization, was a more significant driver of assemblage composition than local environmental conditions.
• Limited dispersal via surface currents between compartments did not overcome the influence of compartmentalization.

Conclusions:

• Contrary to the 'everything is everywhere' paradigm, marine phytoplankton distribution is significantly structured by spatial factors, even in coastal areas.
• Marine compartmentalization plays a crucial role in shaping phytoplankton assemblages, overriding local environmental selection in some cases.
• Dispersal limitations can maintain distinct phytoplankton communities despite connectivity, challenging assumptions of ubiquity for even cosmopolitan species.