Seaweed Farming Could Reshape Vietnam’s Mekong Delta, but the Evidence Is Thinner Than the Hype

The Mekong River Delta is one of the most productive and most vulnerable aquaculture regions on Earth. Saltwater is creeping farther inland each dry season, shrimp ponds dominate the coastal landscape, and policymakers in Hanoi have pinned hopes on a “blue economy” that turns the delta’s brackish waters into sustainable livelihoods. Into that policy moment comes a sobering synthesis from Vietnamese researchers, who have now systematically combed the scientific literature to answer a deceptively simple question: how much socioeconomic promise does seaweed aquaculture actually hold for the delta, and how solid is the evidence behind that promise?

The study, published in the journal Ambio by a team at An Giang University and Vietnam National University Ho Chi Minh City, is an integrative review conducted under PRISMA-informed screening procedures, the same reporting discipline typically applied to medical evidence. The authors began with 460 records after removing duplicates and retained 85 evidence sources for detailed synthesis. Rather than simply cataloguing seaweed species, they compared species suitability, farming systems, value chains, economic evidence, and governance constraints. The verdict is nuanced: for one specific pathway, seaweed integrated into shrimp ponds, the evidence is genuinely encouraging. For a mature, delta-wide seaweed industry, the paper argues, the quantitative foundation simply does not yet exist.

The standout organism is Gracilaria tenuistipitata, a red seaweed that thrives in the brackish conditions typical of the delta’s improved-extensive shrimp ponds. Vietnamese field studies surveyed standing biomass of the alga at between 2.13 and 11.78 tonnes of fresh weight per hectare in ponds in Bac Lieu and Ca Mau provinces, and reported associations with higher shrimp yields and profits. This is not incidental. Gracilaria performs an ecological service inside the pond: it absorbs dissolved nitrogen and phosphorus, nutrients that intensive shrimp farming releases in effluent and that would otherwise degrade water quality. Co-culture experiments showed that whiteleg shrimp raised alongside the red seaweed under partially reduced feeding rates maintained water quality, growth, and feed efficiency, while black tiger shrimp polycultures displayed improved post-larval performance and greater resistance against the pathogenic bacterium Vibrio parahaemolyticus, the agent responsible for devastating early mortality syndrome.

The technical logic of this integrated multi-trophic aquaculture, or IMTA, is central to the review’s conclusions. In a shrimp-seaweed system, the seaweed acts as a living biofilter, harvesting waste nutrients and converting them into saleable biomass. Research from the delta demonstrated that Gracilaria tenuistipitata could remove nitrogen and phosphorus from effluent of intensive black tiger shrimp farming at different stocking densities and aeration regimes, and studies elsewhere in Asia have confirmed the bioremediation capacity of the species when co-cultured with Pacific white shrimp. Because the seaweed tolerates the fluctuating salinity that characterizes delta ponds, particularly during the increasingly severe saline intrusion events that have hammered the region in recent years, the shrimp-seaweed IMTA model is better aligned with the delta’s hydrological reality than near-shore carrageenophyte farming, which demands stable, full-strength seawater.

That tolerance matters because climate change is actively reshaping the delta’s salinity regime. The 2020 saline intrusion was described in earlier work as the worst such disaster of the past century, pushing salt far up the Hau and Co Chien rivers, and modelling studies project continued intrusion driven by reduced upstream discharge and sea level rise. A seaweed species that not only tolerates variable salinity but monetizes it gives coastal farmers an adaptation option rather than a liability. The delta’s own policy framework, Government Resolution 120 on sustainable and climate-resilient development of the Mekong River Delta and the 2021 national scheme for marine aquaculture to 2030, explicitly encourages such diversification, providing an institutional tailwind for pond-integrated seaweed cultivation.

Yet the review is emphatic that enthusiasm must stop at the pond’s edge for most other candidate species. Kappaphycus and Eucheuma, the tropical carrageenophytes that anchor seaweed economies in Indonesia and the Philippines, and the green algae Ulva and Caulerpa all received only site- or market-specific validation, with no demonstrated readiness for broad deployment in the delta. Carrageenophyte farming elsewhere carries well-documented risks, including ice-ice disease, an environmentally and microbiologically driven syndrome that devastates cultivated Kappaphycus across Southeast Asia, along with epiphyte outbreaks and food-safety concerns over metal contamination in coastal pond systems. Vietnam does have experience with Kappaphycus striatus in Cam Ranh Bay, where researchers have tracked seasonal changes in growth rate and carrageenan yield, and Caulerpa lentillifera, the so-called sea grape, has been trialled in Van Phong Bay with post-harvest quality assessments. But transferring these systems to the delta’s turbid, salinity-fluctuating waters remains unproven.

The economic picture is where the review delivers its sharpest criticism of the existing literature. The authors found reported net present value and internal rate of return figures across the source studies, but these values were too heterogeneous to pool validly, and no standardized, delta-specific economic estimates were available. In practical terms, this means that claims about seaweed profitability in the Mekong Delta rest on fragmented, methodologically inconsistent fragments rather than on comparable cost-benefit analyses. For a region weighing major public investment under its blue economy strategy, that gap is not academic. It means the sector cannot yet be described as mature or quantitatively documented, and it leaves open the risk that policy incentives might be calibrated against numbers that were never measured under delta conditions.

Beyond the farm gate, the value chain presents a familiar bottleneck seen across the global South. Seaweed is predominantly exported as dried raw material, with hydrocolloid processing, the extraction of carrageenan and agar used in foods, pharmaceuticals, and cosmetics, concentrated in a handful of countries. Global assessments from the FAO, the World Bank, and UNCTAD have highlighted both the explosive growth of seaweed markets and the gender and development dimensions of the sector, since seaweed farming in countries such as Tanzania and the Philippines is often performed by women and smallholders exposed to volatile farm-gate prices. Vietnam’s own position on the world seaweed map remains modest relative to Asian leaders, and the review suggests that without post-harvest processing capacity, quality standardization, and organized supply chains, the delta’s farmers would capture only the thinnest slice of value from any expansion.

The governance and financing landscape adds further caveats. Payments for ecosystem services, a mechanism successfully piloted for mangrove carbon in provinces such as Ca Mau, are increasingly discussed for seaweed because cultivated macroalgae can sequester carbon and strip excess nutrients from coastal waters, and certification methodologies for seaweed-based carbon removal have begun to appear. But the review’s evidence base shows that integrated recirculating aquaculture systems combining seaweed with intensive shrimp culture, so-called IMTA-RAS designs, remain at pilot scale and capital-intensive, putting them out of reach of most smallholder households in the delta without targeted support. The authors, writing with funding from Vietnam National University Ho Chi Minh City, frame their synthesis as a decision-support tool: it identifies where the evidence is strong enough to act and where it is not.

The bottom line is a rare example of restraint in a hype-filled field. Seaweed aquaculture is frequently presented as a climate solution, a food-security engine, and a rural jobs program all at once, and for the Mekong Delta the review confirms one concrete, evidence-backed entry point: integrating Gracilaria tenuistipitata into existing brackish shrimp ponds, where it can improve water quality, support shrimp health, add harvestable biomass, and hedge against salinity-driven losses. Everything beyond that, offshore carrageenophyte lines, high-tech recirculation systems, carbon credit markets, and delta-wide industry projections, awaits standardized local data on yields, costs, and returns. In a delta where adaptation decisions carry existential weight for millions of people, knowing precisely what the evidence supports, and what it does not, may be the most valuable finding of all.

Subject of Research: Socioeconomic potential of seaweed aquaculture and shrimp-pond integration in Vietnam's Mekong River Delta

Article Title: Socioeconomic potential of seaweed aquaculture in the Mekong River Delta, Vietnam: An integrative review

Article References: Socioeconomic potential of seaweed aquaculture in the Mekong River Delta, Vietnam: An integrative review. (n.d.). https://doi.org/10.1007/s13280-026-02489-6

Image Credits: AI Generated

DOI: 10.1007/s13280-026-02489-6

Keywords: seaweed aquaculture, Mekong River Delta, Gracilaria tenuistipitata, integrated multi-trophic aquaculture, shrimp farming, blue economy, saline intrusion, value chains, economic valuation, Vietnam, biofiltration, climate adaptation