Code and data for "Effects of phytoplankton species distribution on particulate organic carbon dynamics along a coastal gradient"

Phytoplankton communities affect carbon dynamics worldwide, strongly
influencing the quality and quantity of organic carbon in coastal
ecosystems. Yet, we still know little about the impacts of changing
phytoplankton community composition on the potential carbon pathways in
estuaries and coasts. Here, we sampled 25 sites along a coastal salinity
and nutrient gradient, collecting water for water chemistry and
phytoplankton for community composition analyses. For each site, we
determined phytoplankton taxonomic diversity and used Bayesian joint
species distribution models considering species interactions, taxonomic
relatedness, and traits to identify key environmental factors driving
phytoplankton community composition. Subsequently, we used structural
equation modelling to establish direct and indirect links between the
identified key environmental factors, taxonomic diversity (richness and
evenness), and particulate organic carbon (POC). We found that the
phytoplankton distribution along the estuarine gradient was mainly driven
by changes in salinity. Increasing salinity (ranging between 0.8 - 6.4)
benefited motile species and reduced the phytoplankton richness, which
resulted in a decrease in POC concentration. This indirect effect of
salinity on POC was stronger than a direct one, highlighting the mediating
role of phytoplankton richness. This emphasizes the importance of
diversity in regulating coastal biogeochemical processes and suggests that
future changes in salinity might shift coastal carbon dynamics due to
changes in phytoplankton community composition.