Using fibre reinforced polymer (FRP) composites together with seawater and sea sand concrete (SWSSC) in coastal areas will overcome the environmental issues of using ordinary concrete and corrosion problems of conventional steel reinforcements. The present research investigates the mechanical properties of different SWSSC filled FRP tubes after exposure to seawater. Glass, carbon, and basalt filament wound FRP tubes were filled with SWSSC and exposed to seawater for different exposure durations at different temperatures. A total number of 567 Hoop tension and compression tests were carried out after conditioning to investigate the mechanical properties degradation of the tubes. In addition, scanning electron microscopy (SEM) and micro computed tomography (micro-CT) analyses were conducted on representative samples to study the degradation mechanisms and damage progression. Finally, the long-term mechanical performance of SWSSC filled tubes under seawater was predicted based on Arrhenius theory and using the experimental data. According to the test data, generally, the samples with multiple fibres direction showed better durability compared to the tubes with fibres oriented in hoop directions. Moreover, carbon tubes experienced the smallest degradation while glass and basalt tubes showed almost the same range of degradation.