The threats facing the oceans are many and include unsustainable and destructive fishing practices, illegal and unreported fishing, pollution from both land-based and ship-based sources, habitat destruction, the introduction of invasive species, ocean noise, ship strikes (collisions between cetaceans and vessels), the mining of minerals, and the extraction of oil and gas. The adverse impacts resulting from these activities act cumulatively with the effects of ocean acidification, ocean warming, shifting currents, reduced mixing and decreasing oxygen levels. While marine ecosystems and species might be able to withstand one type or intensity of impact, they are much more severely affected by a combination of effects.