Investigation of ice-ice disease and the use of seagrass wrack (thallasia hemprichii) as biofertilizer in seaweed farming in the philippines

Ice-ice disease significantly threatens eucheumatoid seaweed production. This research aimed to understand ice-ice disease dynamics, evaluate a bio-fertilizer alternative, investigate microbial associations, and assess nutritional impacts. A 12-month monitoring revealed ice-ice disease prevalence was higher in the dry season and in deep-water farms. Kappaphycus striatus showed greater ice-ice spot length than K. alvarezii. No interaction between season, species, and depth was found. While most physicochemical and meteorological parameters (temperature, salinity, pH, water current velocity, wind speed, phosphate, nitrate, nitrite) showed no correlation, an inverse correlation existed between ammonium levels and ice-ice disease intensity (spot number and length). Monthly rainfall positively correlated with ice-ice disease intensity. Testing seagrass wrack (Thallasia hemprichii) extract as a bio-fertilizer for K. striatus at various concentrations (0, 9, 18, 27 mL L−1) showed no notable impact on seaweed growth, ice-ice disease prevalence or intensity, or nitrogen assimilation after 15, 30, and 45 days. Carrageenan gel strength was also unaffected. However, the highest seagrass wrack extract concentration (27 mL L−1) significantly increased carrageenan yield after 45 days. Investigations into heterotrophic marine bacteria and marine-derived fungi in relation to ice-ice disease revealed significant variations based on season, health status, and species. Heterotrophic marine bacteria abundance was higher in the dry season, in K. alvarezii, and in ice-ice disease-infected seaweeds. Marine-derived fungi abundance also showed higher levels in K. alvarezii and infected seaweeds, but no seasonal variation. Identified heterotrophic marine bacterial strains included Bacillus infantis, Pseudomonas sp., Cytobacillus firmus, C. oceanisediminis (2 strains), C. pseudoceanisediminis, Stutzerimonas nitrititolerans, Enterobacter cloacae, Staphylococcus arlettae, Bhargavaea beijinensis, and C. horneckiae. Two marine-derived fungi species, Porogramme epimiltina and Aspergillus luchuensis, were identified. These findings suggest S. arlettae and P. epimiltina play a crucial role in ice-ice disease development, potentially exacerbated during the dry season, with K. alvarezii appearing more susceptible. Analysis of K. alvarezii, K. striatus, and Eucheuma denticulatum indicated that ice-ice disease had limited impact on most macronutrients (protein, ash, total fat, fiber, carbohydrates). Moisture and salt content varied by species but were unaffected by ice-ice disease. A significant finding was increased levels of elaidic acid (a trans fatty acid) in ice-ice disease-infected seaweeds, raising potential health concerns for consumers. These studies provide critical insights for developing targeted mitigation strategies against ice-ice disease, emphasizing the need for season- and species-specific approaches, while also highlighting potential food safety considerations for affected seaweed products.