Human activities are changing the oceans and affecting marine life:

1. Fossil fuel burning

Increases atmospheric carbon dioxide concentrations, which will probably double over the next century.

• Substantial climatic warming over the next century is very likely.
• Sea level rise is very likely, due both to thermal expansion of seawater and to melting of glaciers, mainly those in Antarctica.

·          Sea level rise will flood low-lying coastal areas and increase coastal erosion and the damaging impact of hurricanes.

·          Some coastal ecosystems may not be able to adapt to the sea level rise, e.g., coral reefs, salt marshes, mangroves.

• Changes in precipitation and wind patterns are likely. Precipitation changes will affect land productivity; changes in winds and thermal stratification could affect ocean productivity.
• In addition to changes in total productivity, changes in community structure (the numbers and kinds of organisms present) are likely.
• For example, the 1970’s “regime shift” in Gulf of Alaska and Bering Sea waters, associated with a temperature increase of 1-2^o C, was reflected in major changes in fish and marine mammal populations.
• Large-scale changes in deep-ocean circulation are possible, with difficult-to-predict but potentially large changes in global climate. (Ocean circulation changes have been associated with past ice-age glaciations and deglaciations.)

Fossil fuel burning also introduces sulfur compounds into the atmosphere.

• This causes acid rain, which has little direct impact on the oceans because of their high acid neutralizing capacity. However, acid rain has severely damaged some lakes.
• Sulfate particles may increase clouds, decreasing warming due to carbon dioxide.

International agreements have been made to decrease rate of increase in burning of fossil fuels.

• The 1992 Global Climate Change Treaty (among 34 industrial nations) called for voluntary cutbacks in fossil fuel burning, to 1990 levels by the year 2000. This was ineffective.
• On Dec. 11, 1997 nations meeting in Kyoto, Japan agreed to mandatory cutbacks: 5-6% lower than 1990 levels by 2008-2012.
• The US has 5% of the world’s population, but burns 20% of total fossil fuel consumption. The top CO₂ producers, in millions of tons per year, are: US 1370; China 835; Russia 455; Japan 299; Germany 234. (Global total, about 7000.)
• Developing nations are exempt from controls at present.
• Industry has estimated that the treaty-mandated fossil fuel restrictions could:

·          Cost 1 million jobs in coal, oil, and chemical industries.

·          Increase gasoline prices $0.50/gallon.

·          Decrease the gross domestic product by 1.5% (relative to no-treaty 2010 level).

 

2. Eutrophication and harmful algal blooms -Red Tides

·          Eutrophication (excessive productivity of algae) is caused mainly by the use of artificial fertilizers.

• Fertilizer concentrations in major rivers have increased 3 to 10-fold over the past 40 years.
• Bottom waters of several coastal areas, including Chesapeake Bay, the continental shelf off the Mississippi River, and the Baltic Sea, have become anoxic.
• Excessive fertilizer inputs are likely also responsible, at least in part, for an increase in harmful algal blooms.
• HABs include toxic species (dinoflagellates, mainly) and species that harm fish by clogging their gills (Chaetoceros).
• In addition to fertilizer use, transport of harmful species in ballast water of ships and climate change have been cited as possible causes of the increase.
• Fish and shellfish farming probably both cause blooms and make their effects more obvious.
• There are very few records of HABs before the 1970s; however, it is not clear whether this reflects a true absence or simply a lack of record-keeping.

·          Controls on fertilizer use and sewage discharge have been very effective in developed countries (although clearly much more can be done.)

Third-world and developing nations usually cannot afford the capital costs of controlling eutrophication (although these can be cost-effective in the long run).

 

3. Overfishing

• Probably was largely responsible for the 1990s collapse of the North Atlantic fishery.
• Probably was an important contributor to the 1970s collapse of the Peruvian anchovy fishery.
• Probably was an important contributor to the 1980s collapse of the Alaskan king crab fishery.
• May be contributing to declines of marine mammals in the Bering Sea and Gulf of Alaska. (Or, the damage may already be done, e.g., 1960s-70s decline of Bering Sea herring stocks.)
• On the other hand, removal of whales from the Bering Sea may have increased production of pollock.
• Management of fisheries is very difficult.

·          Industry has fixed (and often increasing) costs due to capital investment in vessels. This results in pressure to maximize quotas.

·          Fishery managers have very limited ability to predict the productivity of a fishery in a given year.

·          Natural climatic (or other) variations can cause large (10-fold or more) fluctuations.

·          The maximum sustainable yield in one year, or decade, may not be the same as the MSY this year.

·          Managers can almost never make definite predictions about effects of fishing or overfishing. Vessel owners, on the other hand, can be absolutely sure they will be bankrupt if limits are too low.

Many fishes spend all or part of their life cycle in international waters, where restrictions (if any) are even more difficult to impose and enforce.

 

4. Toxic pollutants

• Severe local problems exist, mainly in bays and estuaries contaminated with organochlorines and metals.

o         In the US, this has resulted in the closure of fisheries (e.g., New Bedford Harbor, Boston Harbor).

o         In other countries, people are probably consuming toxic seafoods; deaths and permanent disability have resulted in the past. Worst well-documented example: Minimata, Japan methyl mercury poisoning.

o         Third-world and developing countries (and some industrial nations, e.g., Russia, former East Germany) often do not have adequate monitoring, environmental regulations, or enforcement.

• Effects of pollutants on marine organisms, and poisoning of humans, mainly occurs due to biomagnification.

o         Some organisms (mainly filter-feeding shellfish, carnivorous fishes, and marine mammals) can concentrate metals (usually organo-metallics such as methyl mercury) or organochlorines by 1,000,000 times or more relative to the water concentration.

o         This is a function of mode of feeding, trophic level, fat content, and life span.

• Toxic pollutants can be distributed far from their source through the atmosphere.

o         “Global distillation” (transfer from warm to cold climates) has led to rather high concentrations of PCBs, DDT, and other organochlorines in the Arctic and subarctic.

o         Also, marine mammals are especially large bioconcentrators, due to their high trophic level, high fat (blubber) content, and long lives.

o         Subsistence diets including whales and seals (especially blubber and oil) may expose people to undesirable levels of some toxic pollutants, although detrimental effects on health have not been demonstrated.

Most developed nations have already instituted fairly effective controls on the most toxic pollutants. Again, many under-developed and developing nations cannot afford to.

Often, the problem of controlling human impacts on the ocean

boils down to short-term, certain cost vs. long-term, less certain benefit.

Too often, short-term costs prevent effective controls

 

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