Ice-ice disease represents a significant challenge for seaweed cultivation worldwide, particularly affecting commercially important red algae like Kappaphycus and Eucheuma species. This condition is characterized by a visible loss of pigmentation in seaweed tissues, which then leads to their breakdown and disintegration. It is recognized as a complex biological issue arising within marine environments.
What is Ice-Ice Disease?
Ice-ice disease manifests visually as a bleaching or whitening of seaweed tissues, giving them a “melting” or “ice-like” appearance. The affected areas become soft and eventually disintegrate. This disease is considered multi-factorial, meaning it arises from a combination of biological agents and environmental stressors.
Specific bacteria, such as those from the Vibrio-Aeromonas and Cytophaga-Flavobacteria complexes, are often associated with ice-ice disease. These bacteria can lyse epidermal cells and chloroplasts, causing the seaweed tissue to turn white. Marine-derived fungi may also contribute to the disease’s induction.
Environmental factors significantly exacerbate the disease, weakening the seaweed and making it susceptible to opportunistic pathogens. Sudden changes in water temperature, particularly increases of 2-3 degrees Celsius or intense temperatures between 29.5°C and 35.5°C, can trigger outbreaks. Fluctuations in salinity, high light intensity, and deficiencies in nutrients like nitrogen and phosphorus also contribute to stress in seaweed. These stressors collectively compromise the seaweed’s health, paving the way for the disease’s progression.
Why Ice-Ice Matters to Seaweed Farms
Ice-ice disease poses substantial economic and ecological repercussions, particularly for the seaweed aquaculture industry. The disease leads directly to significant crop losses and a reduction in the quality of harvested seaweed. For instance, the Philippines experienced about 15% Kappaphycus production losses between 2011 and 2013 due to ice-ice and epiphyte infestations.
The diminished yield and quality result in financial instability for farmers, impacting local economies heavily reliant on seaweed production. In 2018, global production from Kappaphycus and Eucheuma species was approximately 11 million tonnes, highlighting the widespread impact of such diseases. When ice-ice disease lowers carrageenan quality, farmers are often advised to remove diseased portions before drying, further affecting their income.
Beyond the direct economic impact on farms, there are broader ecological implications. While primarily affecting farmed seaweed, widespread outbreaks could potentially alter marine biodiversity or the overall health of coastal ecosystems. The reduction in seaweed biomass, whether farmed or wild, can disrupt habitats and food sources for other marine organisms.
How to Manage and Prevent Ice-Ice
Managing and preventing ice-ice disease involves a combination of proactive and reactive measures. Proactive strategies focus on minimizing stress and enhancing seaweed resilience. Selecting disease-resistant seaweed strains is a primary approach.
Optimizing farm site selection is also important, considering factors like water quality, current, and depth to reduce environmental stress. Maintaining optimal water parameters, including stable temperature and salinity levels, helps prevent conditions that trigger the disease. Ensuring adequate nutrient availability, such as nitrogen and phosphorus, supports healthy seaweed growth and strengthens its natural defenses.
Implementing proper farm hygiene practices is another preventative measure. This includes regularly cleaning farming lines and promptly removing diseased seaweed thalli to prevent the spread of pathogens within the farm. Reactive measures are employed when outbreaks occur. Quarantining affected areas helps contain the disease and prevent its spread to healthy crops.
Early harvesting of diseased crops can also limit further biomass loss and reduce the inoculum for future infections. The most effective approach generally involves integrated disease management, combining these various strategies to create an effective defense against ice-ice disease.