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Climate Change
The gradual warming of the Earth may have devastating consequences for marine life. A 2010 study published in the journal, "Nature," links increases in temperature to a 40 percent decrease in phytoplankton, the tiny surface water plants that form the foundation of the ocean's intricate food chain. A significant loss of plankton triggers a loss of every other species. Scientists believe increases in water temperature will also change the natural distribution of marine life. Warm-water species will expand into new areas that were previously too cold, while cold-water animals will be driven into deeper and more northern parts of the ocean. As marine animals shift their habitats, they will encounter new predators and other challenges to their survival.
Ocean Acidification
Scientists estimate that oceans absorb about 30 percent of the carbon dioxide in the atmosphere. As amounts of carbon dioxide increase, oceans grow more acidic, a chemical change that endangers marine life in several ways. Ocean acidity reduces the amount of calcium carbonate, the compound needed for marine animals to grow protective shells and skeletons. Less calcium carbonate would also stunt the growth and impact the health of coral reefs. A decline in shellfish populations would throw off the marine food web and the effects would reach throughout the entire ecosystem. A loss of coral means a loss of essential habitat for many marine species.
Pollution
Pollution poses significant threats to marine life. Farms, forests and lawns drain fertilizers into waterways that carry the nutrients to the ocean where they trigger an overgrowth of algae. As the excess algae dies and decomposes, it consumes all available oxygen in the water leaving a dead zone where no other marine life can survive. Human and animal waste dumped into the water causes the same chain reaction and also carries bacteria that could spread disease among sea life. Industrial waste water fed into oceans from factories sometimes contains heavy metals and other toxins that accumulate in marine animals and diminish their ability to reproduce. Plastics that wash into the water from coastal communities and boats entangle, choke and kill large fish and marine mammals.
Ocean Industrialization
The increased use of ocean areas for different types of industry creates another set of risks for marine life. Drilling for oil and natural gas and underwater mining for metal and minerals churns up sediment and releases earlier generations of pollutants buried under the sea floor. The activity also creates underwater clouds of particles that choke the gills of fish and block sunlight needed for plant growth and photosynthesis.
The marine transportation industry generates continual streams of pollution along shipping lanes and also poses physical hazards to some animals. The highly endangered right whale is prone to ship strikes. Like all types of marine industry, shipping makes noise that can cause disorientation in some marine animals and leave them vulnerable to injury and predators.
Aquaculture
Aquaculture, or fish farming, is touted as a solution to overfishing and the depletion of fish populations. However, large, underwater pens of fish create new threats that endanger marine life. Fish farms pollute the surrounding marine environment with excess food and fish waste. Crowded and cramped aquaculture pens leave fish vulnerable to diseases that could affect the entire ecosystem. Aquaculture stocks are often treated with preventative antibiotics that spread to animals in the natural environment and the long-term effects of that treatment on marine life are unknown. Some farm-raised fish inevitably escape and scientists warn that interbreeding could change the genetic makeup of wild populations of fish.