The answers to this quiz appear in blue below each question.
1. Three of these four statements about the geomorphology of the
coral reefs are true. Which one is false?
(A) Their modern shape has been influenced by sea level changes
over geologic timescales.
(B) The reefs have grown over millions of years atop ancient volcanic
(C) Unless there is too much sediment present in the water, some of
the reefs can grow at depths of up to 170 meters.
(D) The reefs tend to grow in density and thickness where the water
flow is greatest due to prevailing ocean currents.
Answer: C is false
Todayís coral reefs were formed over the last 500 million years and are
influenced by climactic and geologic processes. Coral reefs can typically
only accumulate at a rate of several millimeters per year. If the Earthís
crust is subsiding or sea level rising slowly enough, reefs are able to
construct their protective calcium carbonate encasements at a rate fast
enough to keep abreast of the diminishing coastline. Volcanoes that form
near mid ocean spreading centers gradually subside as the crust on which
they stand cools and moves away, and the coral reefs that fringe their
edges grow upward as the volcanic rock sinks, leaving behind coral atolls
such as those pictured here. Reef-building corals benefit from a symbiotic
relationship with photosynthetic algae, and since the algae rely on sunlight,
reefs do not grow at depths greater than 70 meters below the oceanís
surface. Coral reefs are also restricted to the relatively nutrient-poor tropical
oceans, where their growth is affected by prevailing ocean currents. The
currents agitate the water and provide the coral and their algal partners
(zooxanthellae) with more calcium, nutrients, and food particles. This
stimulates faster coral growth on one side of the outer reef, so that the
reefs become wider and denser over time near the locations where the
water flow is the greatest.
2. Three of the following four statements accurately describe coral
atoll ecosystems. Which one does not?
(A) Other living organisms besides coral help to build the atolls through
calcium carbonate production.
(B) Symbiotic zooxanthellae provide reef corals with the calcium and
nutrients they need to grow.
(C) Atolls can be very open, entirely closed, or have a number of entry
points by which a lagoon area is open to the ocean.
(D) The diversity and abundance of corals is greater along the protected
inner atoll and lagoon areas than along the outer reef slopes.
Answer: D is false
Various types of corraline algae help to produce calcium carbonate,
including zooxanthellae which live in the tissues of modern reef-building
corals. Zooxanthellae are intimately related to the rate of reef building in
that they help these coral to produce calcium carbonate encasements
faster during the day when photosynthesis occurs. Hard corals obtain
calcium from the seawater and carbon dioxide from cell respiration, and
bring these products into the internal tissues of the coral polyp. The
zooxanthellae provide nutrients for the coral community via photosynthesis
and assist in calcium carbonate formation by exchanging the products of
photosynthesis and cell respiration. Atoll shapes are extremely varied, and
range from the classic closed ring and inner lagoon, to a completely open
reef rim. The diversity and abundance of corals is greater along the outer
atoll edges, where the flow of relatively nutrient-rich water is greater.
3. Three of these four statements about the atolls of the left-hand image
are true. Which one is false?
(A) The many small saucer-shaped reef structures within the lagoonal
areas make this reef system different from all others.
(B) The word "atoll" is a term that comes from a language native to this
region, and has been expanded for use worldwide.
(C) The two largest cities in these atolls are home to about 8000 people
(D) At one atoll, construction of an artificial reef began in November 2001.
Answer: C is false
AThe many small saucer-shaped closed oceanic atolls that occur within
the larger lagoonal areas are called "faros" and are part of the nation of
the Maldives. These atolls grew upon a submerged mountain range
named the Laccadives Chagos Ridge, which runs north-south along
2000 kilometers of the Indian Ocean. While "faro" is simply the Maldives
name for a reef with a central enclosed lagoon or depression, the
processes that created faros in the Maldives are different to the processes
that created atolls worldwide. The native language of the region is Dhivehi
and the word "atoll" comes from their word, atholhu. The capital city, Male,
only covers about 2 square kilometers, but is home to about 70,000 people.
The maximum elevation of the atolls is only 5 meters above sea level, and
the very existence of these atolls and their inhabitants depends on healthy
coral reefs. In the last few decades the reefs have been damaged by higher
than average sea-surface temperatures and unsustainable resource
management practices. One method used to restore damaged reef structures
is to construct artificial reefs and artificially stimulate the coral growth (e.g.,
the Vabbinfaru Lotus Structure on North Male Atoll).
4. Three of these four statements about the atolls of the right-hand image
are true. Which one is false?
(A) In this region the prevailing ocean current, or swell, comes from the south.
(B) The chemical character of the inner lagoons is not significantly influenced
by the size of the openings in the reef rims.
(C) Within the image area there is a designated biosphere reserve and
breeding grounds for at least 3 species of sea turtle.
(D) The most extensive freshwater is found at the small, round, green
atoll that appears along the left-hand image edge.
Answer: either A or B accepted as false
The right-hand image includes (in whole or part) 11 of the 77 atolls that make
up the Archipelago of Tuamotu in French Polynesia. The Tuamotus are located
within the ocean current known as the South Pacific Gyre, and the surface
hydrological characteristics here are particularly stable, warm, clear and salty.
Although the dominant wind and ocean currents are from the east, the dominant
wave direction (swell) is from the south. Since wave direction (or swell) and ocean
current (or circulation) are different attributes, statement (A) is accepted as false.
Statement (B) is also false since the openings of the atoll rims enable, to a greater
or lesser degree, water exchange between the lagoon and the open sea, and
thereby influence the chemical character of the lagoon waters. Taiaro Atoll (the
small circular atoll at the right-hand image edge) was designated as a biosphere
reserve in 1977. There are three turtle species (green, hawksbill and leatherback)
at Taiaro. The most extensive fresh-to-brackish-water marshes in the Tuamotus are
thought to be at Niau, the small green atoll at the left-hand image edge.
MISR was built and is managed by NASA's Jet Propulsion Laboratory,
Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The
Terra satellite is managed by NASA's Goddard Space Flight Center,
Greenbelt, MD. JPL is a division of the California Institute of