Gracilaria chilensis aquaculture faces increasing epiphytic pest pressures, threatening its sustainability. We developed spatially explicit models predicting host and epiphyte (Chaetomorpha , Rhizoclonium ) distributions across Chile (35.5°-47.5°S) for 2050 (RCP 8.5). Maximum Entropy models achieved exceptional performance (AUC = 0.994-0.995). Results showed carbonate/nutrient chemistry dominated habitat suitability (46.6-52.3% contribution) over coastal proximity. G. chilensis showed greater offshore tolerance (36.8% coastal dependency) than epiphytes (44.4-53.4%). Climate change dramatically increased host-epiphyte spatial correlations (0.78-0.835 to 0.89-0.92) and total habitat overlap (+83%). Rhizoclonium risk zones expanded 42% while Chaetomorpha pressure declined. High-risk areas were identified where epiphyte suitability exceeds host suitability, enabling targeted interventions for climate-informed aquaculture zoning.