Ecotoxicological Effect of Kappaphycus alvarezii Extract on Zea mays and Ceriodaphnia silvestrii

Marine algae are recognized as promising sources of natural biostimulants in agriculture, with potential applications in seed physiological conditioning. However, the environmental implications of their production, management, and disposal remain insufficiently addressed. This study evaluated the ecotoxicological effects of a commercial Kappaphycus alvarezii extract on Zea mays and Ceriodaphnia silvestrii. Conditioning assays with maize seeds were performed at extract concentrations of 0, 25, 50, 75, and 100%, assessing germination, vigor, and early seedling growth. Acute toxicity tests with C. silvestrii exposed individuals to 0.1–4% concentrations, and immobility was recorded to determine the median effective concentration (EC50). Concentrations up to 50% did not impair germination, with 25% promoting significant vegetative growth, while higher concentrations reduced germination due to phytotoxicity. In C. silvestrii, 2.06% caused 50% mortality. These results demonstrate the dual role of algal extracts, highlighting agronomic potential alongside ecotoxicological risks, and reinforce the need for safe production, management, and environmentally responsible disposal practices to ensure sustainability.