Download 16_3eEOC

16
Marine and Coastal
Systems: Resources,
Impacts, and Conservation
Answers to End-of-Chapter Questions
Testing Your Comprehension
1. Approximately 71% of Earth’s surface is covered by ocean waters
containing, on average, about 3.5% salt. Water temperature declines with
depth, and density increases slightly at lower temperatures and higher
salinities. Therefore, deep water tends to be colder, saltier, and denser than
the surface water.
2. Ocean currents are driven by the prevailing wind currents at the surface, by
gradients in water temperature, by gravity, and by the Coriolis effect. Surface
currents move horizontally in large circulation patterns. Vertical currents
(upwellings and downwellings) slowly mix the deep waters with the surface
waters, affecting the distribution of nutrients and primary productivity.
3. Biologically productive areas are concentrated in areas of upwelling, in the
shallower waters along continental margins, and at hydrothermal vents of the
deep mid-ocean ridges.
4. Along the coasts there are kelp forests that shelter invertebrates, smaller
fishes, seals, and top carnivores such as great white sharks. Coral reef
communities, which include zooxanthellae, anemones, sponges, hydroids,
tubeworms, molluscs, flatworms, starfish, urchins, and thousands of fish
species, are among the most diverse and productive ecosystems on Earth.
Intertidal ecosystems include rocky and sandy beaches, salt marshes,
estuaries, and mangrove forests, which serve to buffer the land from the
effects of storm surges and act as nursery areas for many marine organisms
of economic importance, such as shrimp.
5. Coral reefs absorb wave energy and protect shorelines from damage, as well
as providing essential habitat for many species. Increased water temperatures
from global climate change, turbidity, nutrient influx (as from agricultural
fertilizers in runoff), and toxic pollutants can all damage coral reef
communities. Salt marshes and mangrove forests are often drained and
converted to residential, commercial, recreational, or agricultural uses.
6. Examples include government policy regulating the shipping industry to cut
down on oil spills; volunteer beach cleanups to pick up plastic trash and other
7.
8.
9.
10.
non-biodegradable debris that can choke or injure organisms that ingest or
become entangled in it; and policy and approaches to reduce overuse and
runoff of excess nutrients that cause eutrophication, as with the Gulf of
Mexico’s dead zone (Chapter 7).
Overfishing can remove the larger and fully mature fish faster than they are
replaced by the population, thereby resulting in a decline in catch size and
quality, and a decrease in the fish population because the death and export of
individuals exceeds birth and import. Some fishing techniques (bottom
trawling, for instance) physically damage or destroy certain marine
ecosystems. The collapse of North Atlantic cod fisheries is a prime example
of overexploitation through trawling damage and direct fishing pressure.
Myers and Worm concluded that the oceans today contain only one-tenth of
the large-bodied animals they once did, and that the loss (from industrialized
fishing) happened so quickly in most places that scientists never knew the
original abundance of these animals.
Commercial driftnetting catches and kills (by drowning) marine mammals
and turtles, as well as many non-target fish species that die from exposure to
air on ships’ decks. Similar by-catch problems exist with longline fishing,
which hooks unwanted species as well as those desired, and even catches and
kills marine birds. Bottom-trawling disturbs the seafloor and reefs,
destroying habitat inhabited by many species.
Nearly all marine protected areas allow fishing or other extractive activities,
whereas marine reserves do not permit such activities. Such marine reserves
can serve as production areas for fish larvae that then disperse outside the
reserve and stock other parts of the ocean.
Interpreting Graphs and Data
1. Before the management plan, swordfish biomass was declining fairly rapidly.
Beginning immediately after the plan, biomass rebounded. The opposite
trends are apparent for fishing mortality: it rose before the plan and
decreased after the plan. Overall, there is an inverse correlation between
fishing mortality and biomass of the stock.
2. If trends continue, the swordfish stock should continue to increase.
3. The establishment of marine reserves (i.e., protected habitat) is vital for
many species, although this is not always the case with large open-ocean fish
such as swordfish unless the reserve is very large. For a species hunted for its
meat like the swordfish, consumer seafood preferences may make at least as
much difference; if people show concern for the species’ decline and reduce
their consumption of swordfish, these purchasing choices will drive down the
price of the fish and fishers will have less economic incentive to fish for
them.
Calculating Ecological Footprints
Consumer group
You
Your Class
Your State
The United States
The World
Annual consumption
North America
China
(21.6 kg per
(27.7 kg per
capita)
capita)
21.6 kg
27.7 kg
Answers will vary Answers will vary
Answers will vary Answers will vary
6.48 × 109 kg
8.31 × 109 kg
1.38 × 1011 kg
1.77 × 1011 kg
World
(16.2 kg per
capita)
16.2 kg
Answers will vary
Answers will vary
4.86 × 109 kg
1.04 × 1011 kg
1. North American versus world fish consumption: 21.6 kg/16.2 kg = 1.33.
North American vs. world ecological footprints: 3-nation average of 6.6
hectares/2.2 hectares = 3.00. With regards to fish consumption, North
America is not as far above the world average as compared to our ecological
footprint as a whole. This may be because of a greater popularity of seafood
in many other cuisines around the world. We are, however, still 33% above
the world average.
2. China’s large population already has an ecological footprint that exceeds the
land area of its country. In order to feed that population, they must either
import food from other countries, or harvest food from a common area that is
part of no country (i.e., Earth’s oceans).
3. Answers will vary, but globally, fisheries are already suffering from
overexploitation. The total human impact on those fisheries is the product of
our population size and our per capita consumption rates, so if both are
increasing, their product will increase even more quickly. The ecological
consequences of such overexploitation may not be reversible, and numerous
marine species could be driven to extinction.