Revealing the contribution of seaweed farming to marine pollution in Kenya

Seaweed farming is increasingly promoted as a sustainable Blue Economy activity from its contributions to coastal livelihoods, marine productivity, and climate change mitigation. However, the sector also generates plastic waste from farming materials and infrastructure, which may contribute to marine pollution if lost or improperly disposed of. This study assessed the contribution of seaweed farming to macro- and micro-litter accumulation at three beaches in Kibuyuni, Kwale County, Kenya.

Beach litter accumulation surveys recorded an overall mean litter density of 2.11 ± 1.71 items m⁻¹ day⁻¹. Plastics were the dominant litter category (8.65 ± 4.70 items m⁻¹ day⁻¹), followed by marine and fishing gear (0.91 ± 0.41 items m⁻¹ day⁻¹) and natural gear materials (0.31 ± 0.05 items m⁻¹ day⁻¹). While non-seaweed-related litter dominated overall, seaweed-farming-related materials contributed substantially to marine debris, with a non-seaweed-related to seaweed-related litter ratio of approximately 5:1. Seaweed-farming-related litter included synthetic nylon ropes (14.3%), sacks (2.6%), and processed wood materials (0.4%).

Spatial analysis showed that the central beach recorded the highest litter accumulation rate (1.69 ± 1.47 items m⁻¹ day⁻¹), compared to the northern (0.44 ± 0.24 items m⁻¹ day⁻¹) and southern beaches (0.51 ± 0.45 items m⁻¹ day⁻¹). Synthetic ropes were the most prevalent seaweed-farming-related litter item, accumulating at a mean rate of 1.024 ± 0.55 items m⁻¹ day⁻¹. Microplastic analysis identified polypropylene and polyethylene as the dominant polymer types across the intertidal gradient, with spectral match values ranging from 67–95%.

The findings demonstrate that, despite its socio-economic and ecological benefits, seaweed farming contributes to localized marine plastic pollution through the use and loss of synthetic farming materials. Strengthening aquaculture waste management, promoting recycling initiatives, and transitioning toward biodegradable farming materials are recommended to reduce the environmental footprint of seaweed aquaculture in Kenya.