FAO, the International Oceanographic Commission of UNESCO (IOC-UNESCO) and the International Atomic Energy Agency (IAEA) have published new joint guidance on the monitoring of algal toxin in bivalve molluscs, including the surveillance of harmful algal blooms and the management of harvesting and production areas.
The document is designed to support competent authorities, laboratories and food safety institutions in developing or improving monitoring programmes adapted to the risk profile of each production area.
The guidance comes at a time of strong growth in the global bivalve sector. According to the document, world production of bivalve molluscs increased by 49% between 2011 and 2023, while international trade grew by approximately 41% over the same period. This expansion is especially relevant for the Mediterranean, where mussels, clams, oysters and other bivalves form part of both local production systems and cross-border seafood supply chain.
The document highlights that harmful algal blooms are natural phenomena, but their frequency, intensity or distribution may be influenced by factors such as ocean warming, eutrophication and local oceanographic conditions.
In Mediterranean coastal and lagoon systems, where shellfish farming often takes place in semi-enclosed or environmentally sensitive areas, these factors can directly affect harvesting continuity, market access and consumer confidence.
One of the key operational messages for producers is that the presence of toxic microalgae does not always provide a clear early warning. In some areas, bivalves may exceed legal toxin limits even when cell concentrations are low or when toxic events develop rapidly.
For this reason, the guidance stresses the need to combine water-based microalgae monitoring with toxin analysis in bivalve flesh, rather than relying on a single indicator.
The guidance recommends representative and fixed sampling points, early warning systems, local risk profiling, clear procedures for closing and reopening production areas, and the use of validated analytical methods.
Where an area is closed due to toxin levels above regulatory limits, reopening should be based on consecutive analytical results below the established limit, separated by at least 48 hours.
Key elements of a monitoring system for algal toxins in bivalves
| Element | What the guidance recommends | Why it matters for producers |
|---|---|---|
| Area risk profile | Assess toxic species, bloom history, currents, temperature, nutrients and sources of contamination. | Helps anticipate risks before starting or expanding production activity. |
| Microalgae monitoring | Carry out periodic monitoring, at least weekly during the harvesting season, adapted to local risk. | Acts as an early warning tool for potential toxin accumulation. |
| Bivalve flesh analysis | Keep toxin analysis in tissue as the central element of sanitary control. | It is the critical test for deciding whether the product can be placed on the market. |
| Area closure and reopening | Close areas when limits are exceeded and reopen only after consecutive negative results. | Reduces sanitary risk and protects the commercial continuity of the area. |
| Traceability and communication | Define protocols to inform operators, authorities and the public when a risk exists. | Enables rapid withdrawals, prevents unsafe harvesting and strengthens market confidence. |
For Mediterranean producers, the importance of the document lies less in the publication of a new technical guide and more in the shift toward adaptive risk management.
Monitoring programmes should reflect the characteristics of each area, including historical bloom data, dominant currents, water temperature, nutrient dynamics, species farmed and the presence of toxin-producing microalgae.
The guidance also reinforces the responsibility of food business operators for the safety of products placed on the market. This makes own-check controls, batch traceability, rapid communication with authorities and the use of fit-for-purpose testing tools increasingly important, particularly when bivalves are intended for international markets with specific compliance or equivalence requirements.
In a Mediterranean context marked by climate pressure, coastal competition and growing scrutiny of seafood safety, algal toxin monitoring is becoming not only a public health requirement but also a factor of commercial resilience.
The ability to anticipate risk, document controls and response quickly to harmful algal events will be central to maintaining trust in bivalve production and trade.
Source: FAO, IOC-UNESCO and IAEA. 2026. Joint FAO/IOC-UNESCO/IAEA guidance on monitoring of algal toxins in bivalve molluscs – Including monitoring of harmful algae and management of harvesting and production areas. Food Safety and Quality Series, No. 34. Rome. https://doi.org/10.4060/cd8990en
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