Key Concepts:
Adverse Effects of Human Activity
- Pollution is the addition of substances to or the alteration of the
ocean ecosystem in a manner that is deleterious (harmful) to the ocean
ecosystem or its resources.
- Pollution includes discharge of harmful waste, activities such as
overfishing,
construction of structures, and other harmful human activities that
adversely affect ocean ecosystems by changing currents, distribution
of dissolved substances or heat, or sediment transport patterns.
- Contaminants with large quantities of suspended particles (turbidity)
can block the light needed for
photosynthesis.
- Eutrophication occurs when excessive nutrients are present as a result
of sewage discharge.
- Alterations of marine habitats by dams, bulkheads, levees, etc., can
alter current patterns, affect sedimentation and prevent some sea life
from migrating. Marine diversity is usually limited as a result.
Climate Oscilllations
- Most of the open ocean has low productivity, the exception being certain
high latitude regions and the equatorial upwelling band across the eastern
Pacific.
- High productivity in subtropical and tropical oceans is limited to
areas of upwelling.
- Year to year and several-year oscillations of climate that are related
to ocean-atmosphere interactions also have an impact on fisheries. These
oscillations involve temperature changes in ocean water that in turn
has an effect on upwelling. Two such examples have been studied in the
Pacific Ocean.
- One is related to the vast North Pacific Ocean where surface waters
become slightly warmer or cooler than normal for a period of years.
- The other is called El Nino, which originates in the tropical Pacific
Ocean and is associated with climate changes over much of the globe.
- With the onset of El Nino, water temperatures offshore Peru rise noticeably,
nutrient levels drop, phytoplankton populations plummet, and anchoveta
(anchovies) become scarce. Some of the larger fish
migrate to cooler
water. Many birds and mammals suffer from lack of food resources and
die of starvation.
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