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Crude oil and cadmium (Cd) are common pollutants in Ghana's coastal ecosystems,
where the cyanobacterial phytoplankton Synechococcus sp. serves as the primary
producer and forms the base of the marine food web alongside small grazers. We
hypothesized that cadmium and crude oil would disrupt microbial community
structure and function, with the strongest effects under combined exposure.
This study investigates the toxic effects of Oil (2 mL L−1), Cd (4.4 μg L−1), and their
combined impact (Cd + Oil) on functional groups within the coastal microbial community,
including Synechococcus sp., heterotrophic bacteria, nanoflagellates, eukaryotic phytoplankton,
ciliates, and dinoflagellates, as well as on copepod nauplii and copepodite development during six-day
incubations. We observed acute toxic effects on heterotrophic ciliates and dinoflagellates, with >50 %
reductions in abundance within 6 h and a marked decrease in diversity. Phytoplankton showed growth
within the first 24 h due to nutrient replenishment from the protist decay, however, their growth continued
to decline after 24 h, with Synechococcus being particularly sensitive to Cd and less affected by Oil. In contrast,
heterotrophic bacteria increased in abundance across all treatments, likely benefiting from organic matter
released during phytoplankton decay and their high adaptability. Notably, the bacterial genera Marivivens
and Rhodovulum became dominant mainly in the Oil-amended treatments. Overall, the microbial groups
exhibited diverse responses to the pollutants, with the combined Cd + Oil treatment exerting the strongest
negative effects, while crude oil alone had the least impact. These findings highlight the vulnerability of tropical
microbial food webs, typically dominated by Synechococcus and microbial grazers, to combined pollutant stress,
with potential cascading effects on higher trophic levels and coastal ecosystem productivity. This highlights the
need for comprehensive monitoring and conservation efforts in these globally significant, yet understudied, regions.
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University of Cape Coast