Zooplankton assemblage and microplastics associated with a coastal sandspit (Tubará, Atlántico)

Zooplankton, as a foundational component of the food chain, plays an important role in the bioaccumulation and biomagnification of contaminants, including microplastics (MPs). This study focused on the structure of the marine zooplankton community and the presence of MPs in the surface waters of Tubará (Atlántico Department, Colombian Caribbean), establishing baseline data to assess the potential ingestion of MPs by zooplanktivorous organisms. Four sampling events were conducted at the Puerto Velero sandspit during the second half of 2023. The zooplankton assemblage comprised 11 phyla, with an average density of 633.18 individuals per cubic meter (indv/m³) ± 350.5 indv/m³. The community was predominantly composed of copepods (54.66 %), mollusk larvae (15.17 %), chaetognaths (10.29 %), and appendicularians (9.35 %). A total of 614 MPs were identified, corresponding to a density of 5.43 MPs/m³ ± 2.9 MPs/m³. These MPs were classified into three types and ten colors. Fibers accounted for 93.49 % of the MPs, whereas fragments and films constituted 5.86 % and 0.65 %, respectively. The most prevalent colors were red (36 %), black (33.7 %), and blue (16.9 %). Additionally, an average numerical ratio of 0.0086 MPs per zooplankton individual was recorded. This research represents the first report on the zooplankton community structure in the Atlántico Department and is also the first study in Colombia to quantify the MP-to-individual ratio. These findings are essential for guiding conservation and management strategies for marine fauna and emphasize the critical need to monitor both the plankton community and MPs in systems significantly impacted by discharges from the Magdalena River.