Page 456 - Environment: The Science Behind the Stories

well was capped. Eventually the oil polluted hundreds of
miles of water and shoreline along the coasts of Louisiana,
Mississippi, Alabama, and Florida and affected marshes and
many species of wildlife. Even organisms in the deep were
affected by this spill. A 2012 study found that corals living
11 km (6.8 mi) from the oil well at a depth of 1370 m (4495 ft)
were adversely affected by exposure to an underwater plume
of oil emanating from the spill site.
Such major oil spills from platforms and from the tanker
ships that transport oil make headlines and cause severe envi-
ronmental and economic problems. Yet despite the severity
of events like the Deepwater Horizon oil spill, most oil pol-
lution in the oceans accumulates from innumerable, widely
spread, small non-point sources, including leakage from small
boats and runoff from human activities on land. Moreover, the
amount of petroleum spilled into the oceans in recent years is Figure 16.18 In a harmful algal bloom, certain types of algae
equaled by the amount that seeps up from naturally occurring multiply to great densities in surface waters and produce
toxins that can harm organisms. Red tides are a type of algal
seafloor deposits (Figure 16.17b). bloom in which the algae produce pigment that turns the water red.
In response to headline-grabbing oil spills, governments
have begun to implement stricter safety standards for tankers,
such as requiring industry to pay for tugboat escorts in coastal the Chesapeake Bay (Chapter 5) and the Gulf of Mexico
waters and to develop prevention and response plans for major (pp. 428–429). The release of excess nutrients into surface
spills. The U.S. Oil Pollution Act of 1990 created a $1 bil- waters can spur unusually rapid growth of phytoplankton,
lion prevention and cleanup fund and required that by 2015 causing eutrophication (p. 126) in freshwater and saltwater
all oil tankers in U.S. waters be equipped with double hulls systems.
as a precaution against puncture. Over the past three decades, Excessive nutrient concentrations sometimes give rise to
the amount of oil spilled by tankers worldwide has decreased population explosions among some species of marine algae.
(Figure 16.17c), in part because of an increased emphasis on These dinoflagellate algae produce powerful toxins that attack
spill prevention and response. In the wake of the Deepwater the nervous systems of vertebrates. Blooms of these algae are
Horizon spill, the U.S. government is considering tighter regu- known as harmful algal blooms. Some dinoflagellates produce
lations on offshore drilling operations. reddish pigments that discolor surface waters, and blooms of
these species are nicknamed red tides (Figure 16.18). Harmful
algal blooms can cause illness and death among zooplankton,
Toxic pollutants can contaminate seafood birds, fish, marine mammals, and people as their toxins are

Aside from the harm that pollutants such as petroleum and passed up the food chain. They also cause economic loss for
plastic can do to marine life, toxic pollutants can make some communities that rely on beach tourism and fishing. Reducing
fish and shellfish unsafe for people to eat. One prime concern nutrient runoff into coastal waters can lessen the frequency
today is mercury contamination. Mercury is a toxic heavy of these outbreaks. When they occur, we can minimize their
metal (p. 388) released into the environment from coal com- health impacts by monitoring to prevent human consumption
bustion (p. 480), mine tailings, and other sources. After set- of affected organisms.
tling onto land and water, mercury bioaccumulates in animals’
tissues and biomagnifies as it makes its way up the food chain Emptying the Oceans
(p. 392). As a result, fish and shellfish at high trophic levels
can contain substantial levels of mercury. Eating seafood high As severe as the impacts of marine pollution on marine CHAPTER 16 • M AR in E A nd Co A s TA l s ys TEM s A nd R E sou R CE s
in mercury is particularly dangerous for young children and organisms can be, most scientists concur that the more wor-
for pregnant or nursing mothers, because the fetus, baby, or risome dilemma is overharvesting. Sadly, the old cliché that
child can suffer neurological damage as a result. “there are always more fish in the sea” is misleading. The
Because seafood is an important part of a healthy diet, oceans today have been overfished, and as with the ground-
nutritionists do not advocate avoiding seafood entirely. How- fish of the Northwest Atlantic, many stocks have been
ever, people in at-risk groups should avoid fish high in mercury largely depleted.
(such as swordfish, shark, and albacore tuna) while continuing The oceans and their biological resources have met human
to eat seafood low in mercury (such as catfish, salmon, and needs for thousands of years, but today we are placing unprec-
canned light tuna). We should also be careful not to eat seafood edented pressure on marine resources. Over half the world’s
from local areas where health advisories have been issued. marine fish populations are fully exploited, meaning that we
cannot harvest them more intensively without depleting them,
Excess nutrients cause algal blooms according to the U.N. Food and Agriculture Organization
(FAO). An additional 28% of marine fish populations are
Pollution from fertilizer runoff or other nutrient inputs can overexploited and already being driven toward extinction.
create dead zones in coastal ecosystems, as we saw with Only one-fifth of the world’s marine fish populations can 455

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