Abstract:
Microplastics can be ingested by marine organisms and may lead to negative impacts at the base of marine food
chains. This study investigated the occurrence and composition of microplastics in the sea-surface water and sought
evidence of ingestion by zooplankton. Surface seawater was collected using a stainless-steel bucket and sieved
directly through a stainless-steel sieve (250-μm mesh), while a 500-μm mesh net was towed horizontally to collect
zooplankton, at 11 georeferenced stations off the Kenyan coast in February 2017, on board the national research
vessel RV Mtafiti. Microplastic particles were sorted and characterised using an Optika dissecting microscope.
Polymer types were identified using an ALPHA Platinum attenuated total reflection—Fourier-transform infrared
(ATR-FTIR) spectrometer. A total of 149 microplastic particles, with an average abundance of 110 particles m –3 ,
were found in the surface seawater. A total of 129 particles were found ingested by zooplankton groups, where
Chaetognatha, Copepoda, Amphipoda and fish larvae ingested 0.46, 0.33, 0.22 and 0.16 particles ind.–1
, respectively.
Filaments dominated both the surface-water microplastics and the ingested microplastics, contributing 76% and 97%
to those compositions, respectively. White particles were prevalent in the water (51%), whereas black was the colour
found most commonly (42%) across the zooplankton groups. The sizes of particles that were in the water were in
the range of 0.25–2.4 mm, and those ingested ranged between 0.01 and 1.6 mm. Polypropylene was predominant in
the surface water, whereas low-density polyethylene was the most-ingested polymer type. The results provide the
first documented evidence of the occurrence, composition and ingestion of microplastics by zooplankton in Kenya’s
marine environment, indicating that microplastics have the potential to enter pelagic food webs and cause pollution in
the study area.
