Under heat stress, levels of PUFA decreased, and SFA increased significantly.
Cymodocea nodosa showed a higher fatty acid plasticity than Posidonia oceanica.
Warming may induce a decrease in PUFA/SFA ratio affecting seagrass nutritional value.
The key role of EFA in seagrass consumers could be affected by future warming.
% of PUFA and PUFA/SFA ratio were correlated with latitude and in situ SST.