ZANZIBAR, July 11 -- ALONG the sun-drenched shores of Tanzanias coast, beneath the shimmering waves of Zanzibar, Lindi, Tanga, and Coast Region, something remarkable is happening.

The sea, once simply a source of fish or other sources of seafood, is being reimagined.

Its becoming a living field, a floating farm, and for many, a lifeline.

Seaweed, quiet and unassuming, is transforming lives in ways that few would have imagined a decade ago.

Where fishing nets once cast for sardines, ropes now stretch across the shallow ocean floor, anchored by wooden stakes and gently cradling strands of seaweed. Before the morning tide rises, women, many of them mothers, grandmothers, and daughters, wade into the cool, waist-deep water, crouching over...