This chapter looks at how marine ecosystems reacts to human pressure and the resilience of the system. Nutrient pollution is a problem in marine ecosystems because excess nutrients allow fast-growing algae to over-grow macrophytes, which play an important role in carbon storage. Over-harvesting of fisheries in the Scotian shelf off the coast of Nova Scotia and Newfoundland has meant the cod and other ground fish have been fished towards extinction. An example is given of the two alternative states between two species – the sea otter and the sea urchin – and the human influence, and the difficulty of returning to the original ecosystem state. Genetic and species diversity is important for evolutionary adaptation and the stability and productivity of the marine system.
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