Tropical species fare little better. Nile tilapia, the world’s most widely farmed finfish, shows optimal growth at 28-30°C. Above 32°C, feed conversion ratios plummet; at 36°C, mortality approaches 50%. With equatorial regions projected to experience an additional 2-3°C warming by 2050, tilapia farming in countries like Bangladesh, Egypt, and Indonesia will become thermally marginal or impossible. If warming is the acute fever, acidification is the slow, systemic disease. The oceans have absorbed approximately 30% of anthropogenic CO2 since the Industrial Revolution, triggering a 30% increase in hydrogen ion concentration—a pH drop from 8.2 to 8.1, with a projected decline to 7.8 by 2100. For shellfish, this is existential.
In Bangladesh, the world’s fifth-largest aquaculture producer, sea-level rise threatens 50% of the coastal shrimp and prawn farms. Saltwater intrusion also contaminates freshwater aquifers used for hatcheries and processing. Farmers face a cruel irony: shrimp farming requires brackish water, but the precise salinity tolerance of black tiger shrimp (15-25 ppt) is narrow; too much freshwater from upstream dams, or too much salt from sea intrusion, both cause mortality. Climate change intensifies the hydrologic cycle, producing more frequent and severe cyclones, floods, and droughts. For aquaculture, which requires stable water quality and physical infrastructure, extreme weather is an immediate, destructive hammer. aquaculture climate change
Integrated multi-trophic aquaculture (IMTA) mimics natural ecosystems by farming fed species (fish or shrimp) alongside extractive species (seaweeds and bivalves) that absorb waste nutrients. Seaweeds, in particular, buffer pH locally through photosynthesis (which consumes CO2) and provide shelter from thermal stress. A Canadian IMTA farm producing salmon, blue mussels, and sugar kelp reported 15% higher salmon survival during a 2021 heatwave compared to monoculture neighbors, alongside a 40% reduction in waste nitrogen discharge. Beyond adaptation, the industry faces mounting pressure to reduce its own emissions. The most promising mitigation pathways transform aquaculture from a carbon source to a carbon sink. Seaweed Farming: The Blue Carbon Breakthrough Macroalgae aquaculture—farming kelp, nori, and other seaweeds—requires no feed, fertilizer, or freshwater. Seaweeds absorb CO2 directly from seawater through photosynthesis, and a portion of this carbon is sequestered when senescent biomass sinks to the deep ocean or is buried in sediments. Global seaweed farming currently covers 2 million hectares, producing 30 million wet tons annually. If expanded to 70 million hectares (0.5% of the ocean surface), seaweed farms could sequester 1 billion tons of CO2 per year—equivalent to Germany’s annual emissions. Tropical species fare little better