Marine scientists who studied crustaceans from three Pacific Ocean trenches, including the Mariana Trench, have discovered the depth of the influence of human activity on ocean ecosystems. Shrimp-like amphipods feeding at the bottom of the trenches were found to have elevated levels of carbon-14, which researchers attributed to nuclear bomb testing decades ago. Other studies have shown elevated levels of industrial pollutants, including PCB and flame retardant, in these bottom dwellers.