‘Multi-trophic aquaculture key to sustainable seaweed farming’

Zanzibar. The adoption of Integrated Multi-Trophic Aquaculture (IMTA) has been proposed as a sustainable solution to improve seaweed farming in Tanzania.

This approach integrates seaweed cultivation with other aquaculture species, such as sea cucumbers and milkfish, to enhance productivity and resilience.

Speaking to journalists in Zanzibar, a researcher at the Zanzibar Seaweed Cluster Initiative, Flower Msuya, said seaweed farmers also face challenges of theft and high mortality rates of aquaculture species during heavy rains.

“The growing problem of land shortages and the theft of sea cucumbers further strain the seaweed farming community.

These combined challenges have made it clear that supporting farmers with better technologies, infrastructure, and access to markets is crucial for the future of seaweed farming in Tanzania,” she said. Seaweed farming has become a vital source of income for thousands of farmers, particularly in coastal areas.

The sector employs more than 30,000 farmers, over 80 per cent of whom are women.

Tanzania currently produces over 30,000 tonnes of dried seaweed annually, with projections for growth in 2024.

Despite its economic significance, the industry is grappling with numerous challenges, many of which are linked to climate change.

One of the most pressing concerns is the rising seawater temperature, which has surged to between 31 and 38°C in recent years, putting immense pressure on the seaweed ecosystem.

“This temperature spike has led to the prevalence of diseases and pests, such as ice-ice disease and epiphytes, which damage seaweed crops,” Msuya said.

Consequently, many farmers are experiencing declining production levels, particularly with the high-value red seaweed species, Cottonii, which struggles to thrive in warmer conditions.

Some farmers have even been forced to abandon cultivation altogether. Additionally, the prolonged hot season, lasting up to three months, disrupts farming activities, leading to seasonal production halts.

A major constraint is the shortage of seed supply, which worsens after poor seasons, leaving many farmers without the necessary seedlings to restart cultivation.

To address this issue, experts have suggested the development of nurseries and tissue culture techniques to ensure a stable and reliable supply of seaweed seedlings.

Traditional off-bottom farming methods are becoming less effective, prompting a shift towards deeper farming techniques, where seaweed is cultivated at depths of 2–6 metres during low tides.