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Marine pollution is defined as any
substance that humans add to the ocean and that results in harm to living organisms that live in
the ocean or that use the ocean’s resources. It’s an important definition, because some toxins and
destructive substances in the ocean are naturally produced and released, such as natural oil seeps,
neurotoxins emitted by harmful algal blooms, and, well, if you’re a salmon, you might consider
a shark harmful to your well being. None of these are considered pollution. So what ARE
some examples of harmful substances that we humans put into the ocean? For starters, anything that is
left on the sidewalk near a storm drain will enter the ocean through rain runoff. That can include
oil drippings from your engine, antifreeze, detergent, fertilizers from your garden,
pesticides, plastics, and styrofoam. Sometimes we are more deliberate in our dumping. Some countries
dump their garbage directly into the ocean. New York City did so until very recently. This map
shows 4 different dumping sites along the East Coast near New Jersey. The first site chosen,
on the continental shelf, caused a lot of problems when longshore currents produced by waves arriving
from storms to the North caused the garbage to get spread southward along the New Jersey
beaches. It was a common sight at that time to find garbage, including hypodermic syringes,
along these beaches. The uproar over these sights caused the dumping to be pushed further offshore,
eventually onto the bottom of the continental slope. Garbage has been dumped directly into the
ocean by human civilizations for millennia. Unfortunately with human population now at
7 billion and rising, it is becoming increasingly difficult to pretend this dumping isn’t a problem.
Finding areas of the ocean without pollution is harder and harder. The worst problems are with
materials that are difficult to break down. One of the worst is plastic, which takes hundreds to
thousands of years to break down. It breaks into smaller and smaller pieces as it’s exposed to
sunlight – we call that photodegrading. Plastic is a highly useful material that was designed
specifically NOT to break down easily. It has many important uses in our society. However, BECAUSE
it doesn’t degrade, it’s important that we find a way to properly dispose of it or recycle it.
Otherwise it will simply collect in greater and greater amounts in the ocean. Refer to the video
tutorial on ocean currents to learn more about where and how plastics collect in the ocean.
Other types of marine pollution include discarded fishing nets, many, unfortunately,
trapping and killing animals as they float across the world’s oceans, oil,
and radioactive waste. There have been a few nations that have discarded their radioactive
waste in barrels in the oceans. It was a practice performed by the US Navy right after World War 2,
and there are thousands of these barrels right now around the Farallon Islands off the coast of
San Francisco sitting in the sediment. Mapping projects have located a number of these dump
sites, but they are in waters around 200 to 1000 meters deep, and are thought, at this point,
to be better left alone than disturbed. Oil is an emotionally impactful pollutant for humans,
because of its immediate and disastrous impact on bird and mammals that live in the area. However,
oil breaks down quite quickly relative to many other pollutants – and the oil that floats atop
the ocean surface will break down with the aid of sunlight and bacteria and be gone in
a few weeks. Some of that floating oil can even be collected immediately after a spill, if contained,
using skimmers. However, denser oils can sink to the bottom or collect on beaches will take
longer to degrade, but they will eventually do so naturally, within a few decades at most.
Oil pollution is a short-term catastrophe, but not a long-term issue, like radioactive waste
and plastics, the former of which can last for millions of years, the latter for thousands.
Other pollutants include heavy metals like copper, mercury, and lead and long-chain molecules like
DDT, a pesticide. These tend to collect in sediments along the shorelines and become
highly concentrated in the organisms that live in these areas through bioaccumulation. Basically the
material is ingested faster than the body can eliminate it, so it accumulates in greater and
greater amounts each day. Although DDT has mostly been eliminated in usage in the United States, it
is still in use in other parts of the world. And its legacy lives on in the sediment in which it
collected. A similar legacy was left behind after the Gold Rush of 1849 in California. Mercury was
used to remove gold from the river sediments, and it collected in large amounts in the Sacramento
River and its sediments, eventually making its way into the San Francisco Bay. Today’s bay sediments
are continually moved around by tidal currents moving in and out under the Golden Gate Bridge,
and these moving sediments can mean the uncovering of old deposits of mercury-rich material. That’s
especially a problem in areas where we dredge to maintain the shipping channels. It is for this
reason that people are warned not to eat, with frequency, fish caught within San Francisco Bay.
Other pollutants to the ocean include heat and carbon dioxide. This image of coral bleaching
shows what happens to corals when the water becomes too warm. This happens as the ocean’s
temperature increase due to global warming or near where power plants dump hot waters that
have cooled their structures. Healthy coral have a garden of brightly colored microscopic
dinoflagellates (algae) living within them. The corals harvest these gardens as their primary
food source. These dinoflagellates cannot survive water that is too hot. When they die, the corals
lose their colored gardens and become just white calcium-carbonate apartment buildings, within
which live tiny coral polyps that have lost their primary food source. If the temperatures stay
warm, and no dinoflagellates return, the corals will starve and die. As for increased carbon
dioxide, as discussed in detail in the carbonated oceans video tutorial, increased carbon dioxide
can lead to a drop in pH and more acidic seawater, which will dissolve the calcium carbonate shells
of organisms that live in these waters. Another way humans pollute the ocean is
through fertilizers and detergents picked up and carried to the oceans by rivers. Fertilizers and
detergents are nutrients, which accumulate in high amounts at the river deltas and lead
to dead zones. Why? High nutrients cause a bloom in algae. Algae populations have quick turnover,
so as one population dies and the next takes over, there can be a glut of decomposing material in the
water. Decomposition requires oxygen, and with so much oxygen going into decomposition, the water
can end up with extremely low oxygen levels, otherwise known as hypoxic. Heterotrophs can’t
survive and will have to migrate away or die en masse. This image shows some of the locations in
the world where dead zones have been identified. You’ll notice they concentrate around major river
deltas and cities. One of the key indicators that a dead zone has developed is when there’s
a big die off of fish in the area, as this beach in Narragansett Bay, Rhode Island demonstrates.
In the San Francisco Bay area, humans have wrought many changes on the marine environment,
including the loss of 95% of the original wetlands that lined the edges of the Bay.
Wetlands are necessary nurseries for young fish and invertebrates. Without the wetlands,
populations of these organisms will be lower. Wetlands are also areas where toxins can be pulled
out of the water and settle into the sediment eventually broken down by plants and transformed
into nontoxic byproducts. Fewer wetlands means less of a natural cleaning system for the bay.
Since human populations have migrated along coastlines, we have actively introduced new
species into the ecosystems of coastal bays. These species are ones that traveled along, unbeknownst
to humans, attached to boats, fishing gear, and bait. Sometimes they were purposely brought in
to create new fisheries, like Striped Bass and East Coast Oyster species. These little Asian
Clams came in from ports in China as microscopic larvae carried in the ballast water of ships. The
result? A complete transformation of the local ecosystem as new, more competitive species take
over and the native species are squeezed out. The repercussions of these introduced species
can be felt all the way up the food chain. For example, the Asian Clam has completely taken
over the bottom sediment in many parts of the Bay. Their filter-feeding has removed large amounts of
plankton from the water column and caused fish that depend on that food source to migrate to
other areas. Meanwhile, other fish, like sturgeon, that bottom feed on mollusks have a new food
source and have grown in their populations. Fish is a major food source for a significant
portion of the world’s population. To satisfy these food needs, fishing industries all over
the world’s oceans have removed as much as 90% of the populations of many of the world’s major
fisheries, including Atlantic Cod and BlueFin Tuna. Though there are some sustainably managed
fisheries, these are dependent on decisions made by individual countries and only for
waters in which they have management. In addition to overfishing, we have also managed to destroy a
large amount of the ocean’s fish population through bycatch and ecosystem destruction.
Indonesia, for example, has removed entire swaths of mangrove forest to support shrimp farming. And
the fishing technique of trawling, which drags a net behind a boat along the bottom of the
seafloor, will remove and destroy everything in its path. The amount of wasted marine life
is immense. Bycatch is a problem in all types of fishing, especially with trawling and nets.
So what can we do about all these problems? Education – understanding the problems yourself
and then spreading the word to others. We can develop technology that limits bycatch
like the turtle exclusion device. And another thing that helps is international cooperation.
In the 1980s many nations of the world got together to create a few “rules of the sea”
around national borders and waters. One of the things that was developed was a definition of
the Exclusive Economic Zone or EEZ. This is an area over which a nation has control of fishing,
mining, and pollution regulations. In comparison, a nation’s territorial waters, over which it has
all jurisdiction and can prevent other nations from entering, extends only 12 nautical miles
off its shoreline or about 22 kilometers. But its EEZ extends 370 km or 200 nautical miles. And its
seabed rights extend up to 648 km. Here’s what the U.S.’s EEZ looks like across the Pacific and
Atlantic Oceans. What have we done with these areas? In some cases we’ve created National
Marine Monuments and Sanctuaries to protect the local sea life. In all of them we try to control
pollution and regulate fishing industries, both in numbers of catch and in types of fishing that are
allowed. And to help us determine, among other things, the mineral potential of these zones,
right after the EEZ was developed, the U.S. government commissioned the development of
side-scan sonar images of the continental shelves and slopes within the EEZ. That work allows us
to see far more detail of the continental slope including all of its detailed submarine canyons.
What can you do to limit the negative impact of humans on the oceans? Recycle. Reuse. Dispose
of garbage responsibly. Support legislation to produce more marine sanctuaries. And participate
in local beach cleanup days. When you see garbage on the ground, pick it up, so it doesn’t end up
in the ocean. Clean up oil spills on our streets. And spread the word. Stewardship of our oceans is
a role the entire world must play.
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