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The international demand for macroalgae products has increased driving the expansion of seaweed farming to many coastal rural areas worldwide. Yet it is not fully understood what the impacts of this practice are on local habitats, including seagrass meadows, one of the most productive coastal ecosystems. Additionally, high nutrient inputs to coastal systems via direct freshwater run-off or groundwater can cause algal blooms with negative consequences to seagrasses and seaweed production. This study aims to detect the short term ecological impacts of seaweed farming on seagrass meadows, as well as the influence of nutrient inputs via groundwater on seaweed productivity in the near-shore aquatic system of Rote Island, Indonesia. Seaweed farming plots were set up over seagrass meadows in two locations on the island with assumed higher and lower anthropogenic pressure in Nemberala village and Tunggaoen beach, respectively. Seaweed production rates, seagrass indices, and environmental indicators were measured within the seaweed farm and in plots directly outside of the farm over two seaweed growth cycles. Seaweed production was positively affected by environmental changes during the rainy season in the region, including lower temperatures, higher water motion and higher nutrient concentrations. On the other hand, results show 15% reduction in seagrass shoot density, as well as reduced leaf length, plant biomass, and percentage cover under the seaweed farms. Nuisance algae were found attached or entangled in the seaweed fronds, especially in Nemberala, causing further light reduction under the farms. The impacts on seagrasses also led to diminution of C org (22-23%) and nitrogen (22-29%) in surface sediment in the plots compared to unfarmed areas. δ15N of the suspended particulate matter of sampled groundwater from the beach seepages in both sites were high, 13.4‰ in Nemberala and 17.8‰ in Tunggaoen, indicating heavier sources of N either from sewage contamination or isotopic discrimination due to microbial processing of groundwater. During the rainy season, the N- and P-enriched water entering the system led to an increase in nutrient concentrations in Nemberala bay seawater, causing eutrophication. [Display omitted] • Seaweed farming negatively impacted seagrass density, percent cover and biomass. • Carbon and nitrogen sequestration capacity of seagrass habitats was reduced under seaweed farming. • Eutrophication from land-borne nutrients enhanced seaweed farming impacts on meadows. • Sustainable seaweed practices are recommended to better protect seagrass habitats. [ABSTRACT FROM AUTHOR]

Indonesia is the main tropical seaweed producer in the world with approximately 70,000 families depending on this activity. The red macroalgae Kappaphycus spp. and Eucheuma denticulatum are the most common species cultivated and used for carrageenan in the processed foods industry. Seaweed farming is an accessible form of mariculture requiring low capital investment and enabling improved living standards in different regions. Nevertheless, farmers suffer from boom and bust cycles due to seaweed price volatility and algal diseases. Limited research has been done on Rote Island, East Nusa Tenggara province, which is among one of the poorest regions in Indonesia where culturing seaweed has become popular. This study assesses seaweed farming practices and their impact on household economy by looking at the overall income generating activities of households involved in seaweed farming. The information was collected using structured interviews with questions related to socio-demographic characteristics, household income, farming practices and challenges. Findings of this study highlight farmers' dependence on seaweed farming activities in southwest Rote, where 50% of the households rely on the income through this activity as their only cash source. During the time of the study, two-thirds of the families were living under the poverty line. Seasonality played a crucial role in seaweed production with negative impacts during the dry season. Thus, families with additional livelihoods seemed to cope better during low production seasons. Seaweed farming practices show room for improvement, and farmers could benefit from activities targeting enhanced productivity of their farms. [ABSTRACT FROM AUTHOR]