Download Answers to STUDY BREAK Questions Essentials 5th Chapter 14

Answers to STUDY BREAK Questions
Essentials 5th
Chapter 14
BENTHIC COMMUNITIES
1. Where would you expect to find a benthic organism?
Benthic organisms live on or in the ocean bottom. Some benthic creatures spend their
lives buried in sediment, others rarely touch the solid seabed; most attach to, crawl over,
swim next to, or otherwise interact with the ocean bottom continuously throughout their
lives.
2. What is implied in a random distribution of objects?
A random distribution implies that the position of one organism in a bottom
community in no way influences the position of other organisms in the same community. A
truly random distribution indicates that conditions are precisely the same throughout the
habitat, an extremely unlikely situation except possibly in the unvarying benthic communities
of abyssal plains.
3. What is the rarest natural pattern of organisms?
Uniform distribution with equal space between individuals, such as the arrangement
of trees we see in orchards, is the rarest natural pattern of all.
4. How can seaweeds (multicellular algae) survive without vessels to transport fluid and
nutrients?
Algae is a collective term for autotrophs possessing chlorophyll and capable of
photosynthesis but – unlike plants – lacking vessels to conduct sap. All parts of a seaweed
are productive, so material is cycled (used) where it is made and needed. Land plants, by
contrast, must conduct water and nutrients from roots to leaves, and then pay the roots for
their efforts by transferring carbohydrates back down to the roots.
5. How are seaweeds classified?
Seaweeds are classified by the presence of accessory pigments, colored compounds in
their tissues. These accessory pigments (or masking pigments) are light absorbing
compounds closely associated with chlorophyll molecules. Accessory pigments may be
brown, tan, olive green, or red; they are what give most marine autotrophs, especially
seaweeds, their characteristic color. Multicellular marine algae are segregated into three
divisions based on their observable color. The green algae, with their unmasked chlorophyll,
are the Chlorophyta, the brown algae Phaeophyta, and the red algae Rhodophyta.
Phaeophytes are most familiar to beachcombers, and rhodophytes the most numerous.
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6. How can seaweeds photosynthesize below the depth to which red light penetrates?
Rhodophytes can live in surprisingly deep water. They excel in dim light because
their sophisticated accessory pigments absorb and transfer enough light energy to power
photosynthetic activity at depths where human eyes cannot see light. The record depth for a
photosynthesizer is held by a small rhodophyte discovered in 1984 at a depth of 268 meters
(879 feet) on a previously undiscovered seamount in the clear tropical Caribbean.
7. Give some examples of marine vascular plants. How are they different from seaweeds?
Similar?
Seaweeds may look like plants, but they are actually a form of multicellular algae.
The single-celled diatoms and dinoflagellates discussed in the last chapter are unicellular
algae. As we have seen, algae lack the vessels and other structural and chemical features of
true plants. Nearly all large land plants are vascular plants. A few species of vascular plants
have recolonized the ocean. All have descended from land ancestors, and all live in shallow
coastal water. The most conspicuous marine vascular plants are the sea grasses and the
mangroves.
Perhaps the most beautiful sea grass is the vivid, emerald-green surf grass, genus
Phyllospadix, with its seasonal flowers and fuzzy fruit. These hardy plants survive in the
turbulent, wave-swept intertidal and subtidal zones of temperate East Asia and western North
America (Figure 14.5).
8. What makes estuaries so productive and high in biomass?
Primary productivity in estuaries is often extraordinarily high because of the
availability of nutrients, the great variety of organisms present, strong sunlight, and the large
number of niches. The mass of living matter per unit area in a typical estuary is among the
highest per unit of surface area of any marine community.
9. Few habitats are as rigorous as rocky shores, yet a great many organisms have become
adapted to these places. What advantages do rocky shores provide?
One reason for the great diversity and success of organisms in the rocky intertidal
zone is the large quantity of food available. The junction between land and ocean is a natural
sink for living and once-living material. The crashing of surf and strong tidal currents keep
nutrients stirred and ensure a high concentration of dissolved gases to support a rich
population of autotrophs. Minerals dissolved in water running off the land serve as nutrients
for the inhabitants of the intertidal zone as well as for plankton in the area. Many of the
larval forms and adult organisms of the intertidal community depend on plankton as their
primary food source.
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10. What specific defenses do organisms deploy to succeed in the rocky intertidal
environment?
For intertidal areas exposed to the open sea, wave shock is a challenging physical
factor. Motile animals, like crabs, move to protective overhangs and crevices where they
cower during intense wave activity. Attached, or sessile, animals hang on tightly, often
gaining assistance from rounded or very low profile shells, which deflect the violent forces of
rushing water around their bodies. Some sessile animals have a flexible foot that wedges into
small cracks to provide a good hold; others, like mussels, form shock-absorbing cables that
attach to something solid.
11. What problems confront dwellers on sand beaches? What adaptations have evolved to
allow success?
A beach is a forbidding place. Sand itself is the key problem. Many sand grains have
sharp pointed edges, so rushing water turns the beach surface into a blizzard of abrasive
particles. Jagged grit works its way into soft tissues and wears away protective shells. A
small organism's only real protection is to burrow below the surface, but burrowing is
difficult without a firm footing. When the grain size of the beach is small, capillary forces
can pin down small animals and prevent them from moving at all. If these organisms are
trapped near the sand surface, they may be exposed to predation, to overheating or freezing,
to osmotic shock from rain, or to crushing as heavy animals walk or slide on the beach.
12. Are sand or cobble beaches generally highly populated habitats?
No. Only a few specialized species can live in these places. Occasionally, when
conditions are good, a population explosion of one of these species will occur, but such
events are few and far between.
13. I have written (in Chapter 6 and 13) that the tropics are generally devoid of nutrients and
support very little life. Why do tropical coral reefs support such huge numbers of life forms?
The key to the difference between the open tropical ocean and the tropical reefs lies
in the productivity of the reefs themselves, wave-resistant structures dominated by strong and
rigid masses of living (or once-living) organisms. Not all reefs are built of coral -- other reef
builders include red and green algae, cyanobacteria, worms, even oysters -- but we think first
of coral reefs when the words reef and tropics are mentioned together.
14. How is hermatypic coral different from ahermatypic coral?
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Tropical reef-building corals are hermatypic, a term derived from the Greek word for
mound-builder. Their bodies contain masses of tiny symbiotic dinoflagellates. Coral's
success in the nutrient-poor water of the tropics depends upon its intimate biological
partnership with specialized dinoflagellates. The microscopic dinoflagellates carry on
photosynthesis, absorb waste products, grow, and divide within their coral host. The coral
animals provide a safe and stable environment and a source of carbon dioxide and nutrients;
the dinoflagellates reciprocate by providing oxygen, carbohydrates, and the alkaline pH
necessary to enhance the rate of calcium carbonate deposition. The coral occasionally
absorbs a cell, "harvesting" the organic compounds for its own use. The dinoflagellates are
captive within the coral, so none of their nutrients are lost as they would be if the
dinoflagellates were planktonic organisms that could drift away from the reef. Instead
nutrients are used directly by the coral for its own needs. The cycling of materials is short,
direct, quick, and very efficient.
Deepwater corals, know as ahermatypic corals, build smooth banks on the cold, dark,
outer edges of temperate continental shelves from Norway to the Cape Verde Islands, and off
New Zealand and Japan.
15. What is coral bleaching? What is thought to cause coral bleaching?
Marine biologists have been baffled by recent incidents of coral bleaching—corals
expelling their symbiotic dinoflagellates (zooxanthellae)—in the Caribbean and tropical
Pacific. As noted above, hermatypic corals depend on these dinoflagellates for a portion of
their carbohydrate and oxygen requirements. For reasons that are not well understood, when
water temperature exceeds a normal summer high by 1°C (1.8°F) or more for a few weeks,
coral polyps eject their dinoflagellates, turn pale, and begin to starve. If the water
temperature returns to normal in few weeks the coral can regain their algae populations and
survive the bleaching event. If not, filamentous algae or other decomposers overtake the
polyps. A coral reef’s ability to survive bleaching depends on the level of stress that it
endures before and during such events. The warm El Niño year of 1998 saw the death of
about 16% of living corals worldwide. As the ocean warms, bleaching events will probably
be more widespread.
16. How are coral reefs classified?
As their name implies, fringing reefs cling to the margin of land. As can be seen in
Figure 14.14a, a fringing reef connects to shore near the water surface. Fringing reefs form
in areas of low rainfall runoff primarily on the lee (downwind side) of tropical islands. The
greatest concentration of living material will be at the reef's seaward edge where plankton
and clear water of normal salinity are dependably available. Most new islands anywhere in
the tropics have fringing reefs as their first reef form. Permanent fringing reefs are common
in the Hawaiian Islands and in similar areas near the boundaries of the tropics.
Barrier reefs are separated from land by a lagoon (Figure 14.14b). They tend to occur
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at lower latitudes than fringing reefs, and can form around islands or in lines parallel to
continental shores. The outer edge -- the barrier -- is raised because the seaward part of the
reef is supplied with more food and is able to grow more rapidly than the shore side. The
lagoon may be from a few meters to 60 meters (200 feet) deep, and may separate the barrier
from shore by only tens of meters, or by 300 kilometers (190 miles) in the case of
northeastern Australia's Great Barrier Reef. Coral grows slowly within the lagoon because
fewer nutrients are available and because sediments and fresh water run off from shore. As
you would expect, conditions and species within the lagoon are much different from those of
the wave-swept barrier. The calm lagoon is often littered with eroded coral debris moved
from the barrier by storms. The Australian Barrier Reef is the largest biological
construction on the planet.
An atoll (Figure 14.14c) is a ring-shaped island of coral reefs and coral debris
enclosing, or almost enclosing, a shallow lagoon from which no land protrudes. Coral debris
may be driven onto the reef by waves and wind to form an emergent arc on which coconut
palms and other land plants can take root. These plants stabilize the sand and lead to
colonization by birds and other species. Here is the tropical island of the travel posters.
17. How are atolls thought to have been formed?
A quick review of Figure 14.14 will remind you that coral grows upward as an
island’s fringing reef sinks. In this case, the island does not sink at a rate faster than coral
organisms can build upward.
18. What is the most striking feature of the deep-sea floor?
The relative richness of species diversity, in my opinion (see next answer). Also, the
adaptations to this habitat (which include gigantism, chemosynthesis, and extremely long
lifespans, to name a few).
19. Which generally contains more organisms per unit area – an intertidal sandy beach or a
typical sedimentary deep bottom habitat?
Most of the deep-ocean floor is an area of endless sameness. It is eternally dark,
almost always very cold, slightly hypersaline (to 36‰), and highly pressurized. Scientists
once thought that such rigors would limit the extent of communities there. Not so. In the
1980s researchers investigating bottoms at depths between 1,500 and 2,500 meters (5,000 to
8,000 feet) found an average of nearly 4,500 organisms per square meter. There were 798
species recorded in 21 1m2 samples, 46 of which were new to science!
20. Why do deep vent communities depend on chemosynthesis to produce carbohydrates?
Isn’t photosynthesis more efficient?
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Photosynthesis is very efficient if light is available. Other less-efficient energybinding pathways evolved in its absence.
21. Could deep vent organisms colonize ocean surface environments – tidal pools, for
example?
Very unlikely. The slow growing pogonophorans and other vent invertebrates would
be subject to rapid predation, their enzymes would be unsuited to surface conditions, and
they’d roast in the sun. Their symbiotic bacteria would be especially displeased, one should
think.
22. How do you suppose organisms sense the presence of a whale fall?
As sulfide produced by these bacteria diffuses out of the bone, planktonic larvae of
vent organisms might sense its presence—perhaps by smell or another chemical signal -settle, grow, and reproduce. With luck, their offspring might drift to another whale fall and
repeat the process.
23. Why would “stepping stones” be needed between vent communities? How could a whale
fall act as a “stepping stone?”
Even though humans have greatly diminished the numbers of living whales,
researchers estimate that whale carcasses may be spaced at roughly 25 kilometer (16 mile)
intervals across areas like the North Pacific. If a vent community were to “go quiet” (that is,
if the vents ceased to be geologically active), the larvae of the residents might be capable of
drifting toward a (relatively) nearby whale fall, but not all the way to a new and distant vent.
Repeat the process a few times, and a new vent system could be colonized.
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