Evaluating vegetative cultivation strategies for Gracilariopsis lemaneiformis in Peru using a tree-line system

Gracilariopsis lemaneiformis is a commercially valuable red seaweed traditionally cultivated for agar extraction and increasingly recognized for its environmental benefits in integrated aquaculture systems. In Peru, despite being native, its cultivation has remained limited since early trials in the 1990s. In this study, we applied for the first time a tree-line system to evaluate the vegetative cultivation of G. lemaneiformis under field conditions on the southern coast of Peru. Three experiments were conducted to test the effects of substrate type, initial inoculum density, and cultivation mode (suspended vs. bottom) on daily growth rate (DGR) and final wet biomass (WB). Results demonstrated that polypropylene ropes significantly outperformed mesh bags, achieving higher DGR (4.23 ± 0.13 % day⁻¹) and WB, due to improved water flow and reduced fouling. Lower inoculum density (25 g/CU) resulted in superior growth (5.47 ± 0.33 % day⁻¹), highlighting the importance of reducing intra-thallus competition. Additionally, bottom cultivation showed slightly higher productivity than suspended culture, attributed to lower epiphytism and better operational stability. These findings suggest that bottom cultivation using low-density inoculation and polypropylene substrates is a technically feasible and scalable method for restoring and commercializing G. lemaneiformis aquaculture in Peru. The results provide a foundation for future efforts in sustainable seaweed farming, particularly in multi-trophic systems where this species can contribute to nutrient removal and ecosystem restoration.