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Sight in the sea: Exploring light and color in coral reef
ecosystems
falseLipkin, Richard. Science News148.12 (Sep 16, 1995): 184-
186. Full textAbstract/Details
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Eight teams of scientists per year can study sea life in the
shallow Atlantic Ocean for up to two weeks in the National
Oceanic and Atmospheric Administration's undersea laboratory
Aquarius. Research activities being conducted at Aquarius to
study light and color in coral reef ecosystems are discussed.
Eight teams of scientists per year can study sea life in the
shallow Atlantic Ocean for up to two weeks in the National
Oceanic and Atmospheric Administration's undersea laboratory
Aquarius. Research activities being conducted at Aquarius to
study light and color in coral reef ecosystems are discussed.
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Tinting the surf's sapphire ripples with tangerine light, dawn
over Florida's coral reefs summons sea creatures from within
calcareous crags and cauliflowerlike mounds.
Cautiously, some of these creatures eye the seascape for
predators and prey. A silvery 7-foot tarpon, a prized game fish,
tears along, hunting for its morning meal, while an angelfish
preens its yellow and black fins. Finger-long mantis shrimp
tussle in a claw-snapping fight. And swarms of peach-colored
fish, like dollops of sherbet, glitter in the light against a
backdrop of swaying sea sponges.
The reef comprises a neighborhood little different in spirit from
a rain forest ravine, where animals feed, play, and mate--
tangling over dominion of food, shelter, and territory. But
unlike a rain forest, this scene explodes with color. Why has
nature painted such iridescent prairies in these shallow seas?
With animals in nearly every other kingdom struggling to
vanish into their surroundings, to camouflage themselves from
predators, what makes tropical sea life so splendorous?
"They don't see the world as we do," says Thomas W. Cronin, a
marine biologist at the University of Maryland at Baltimore.
"Their visual systems have adapted to enable them to survive in
a completely different world." Unlike humans--whose vision has
been tuned for survival in rain forests--many ocean creatures
view the world in ultraviolet (UV) and polarized light,
perceiving aspects of light that humans cannot.
"Marine animals have evolved visual systems to distinguish
predators and prey at long distances, in murky water, and in dim
light, all of which are critical to their survival," Cronin
explains. "It's another world for the."
"Our task is to understand better what it is that they see."
Since 1993, the National Oceanic and Atmospheric
Administration (NOAA) has maintained an undersea laboratory
4 miles off the Florida coast, near Key Largo. The lab's
mission: to address scientific questions pertaining to ocean
environments and marine life. Planted 67 feet below the surface,
bolted to a 200-ton platform on the seafloor, the 43-foot-long

Aquarius habitat houses the world's only permanent underwater
research station.
After Congress passed the National Marine Sanctuary Act in
1990, with the aim of protecting coral reefs and offshore U.S.
resources, NOAA moved the habitat from the Virgin Islands to
Key Largo. Now, eight teams of scientists per year can study
sea life in the shallow Atlantic Ocean for up to 2 weeks.
"This program emerged out of a recognition that coral reefs in
the Florida Keys are an important national resource," says
Aquarius science director Steven L. Miller, a marine biologist
with the University of North Carolina at Wilmington, which
operates Aquarius. "Very little has been known until recently
about the health or status of these reefs."
Researchers visiting Aquarius study, for example, black band
disease, which kills coral and threatens sea life. Coral
bleaching, another phenomenon seen worldwide during the past
decade (SN: 12/8/90, p.364), has led habitat researchers to
examine the impact of ozone depletion and the resulting
increase in UV light passing through the atmosphere. Upsetting
the belief that UV light does not penetrate deep into seawater
researchers measured enough UV exposure underwater to bleach
corals at depths of 80 feet.
Fast spray, an azure sky, and a buzzing outboard engine herald
the mid-June journey of Strike Force, a research vessel ferrying
five marine biologists to Conch Reef, a sea shelf 9 miles
northeast of Key Largo. Here, the researchers will spend 10
days studying underwater light and marine animals in their
native habitat.
With Strike Force thwacking the waves, a shadowy speck grows
on the horizon, revealing a great barge at anchor. The boat
slows and the five scientists hop onto the barge's bobbing deck.
Cronin and his four fellow aquanauts prepare for "saturation"--
their 10-day residence in the laboratory 20 meters below.
Leaping into the turquoise waters, the biologists spiral slowly
down to the giant steel capsule. They stop momentarily at the
"gazebo"--a small, air-filled enclosure in which they can

communicate with the surface support staff on the barge--then
move on.
Throughout their mission, the scientists maintain two-way
communication via microphones and video cameras with the
support crew, who offer assistance or, in an emergency, help.
"In many ways this is like a space mission," says Craig Cooper,
Aquarius' operations manager. "We need to keep a close eye on
them to make sure everything's okay. Anything they need, we
get it to 'em."
In the habitat, the aquanauts bubble up from underneath the
massive steel housing, doff their air tanks, fins, and weight
belts, and rinse off. Onboard technician Glenn Taylor hands
each aquanaut a towel. "Salt attracts moisture," Taylor says.
"And we've got a lot of corrosive electrical equipment in here.
So it's critical that everyone is totally dry and saltfree." Diving
gear stowed, the scientists enter the habitat's main chamber,
stepping through an airlocked door.
Aquarius's interior resembles a cross between a laboratory, a
submarine, and a well-stocked Winnebago. At one end,
computers, cameras, and sundry paraphernalia lie on lab
benches. At the far end stand two tiers of bunks that sleep six
scientists. In the midsection, life-support equipment hums
behind a panel of switches, pressure gauges, radios, and
monitors. Alongside a stunningly blue porthole a galley
complete with stovetop and booth awaits. On the counter stand a
box of cornflakes and a bottle of ketchup.
Roy L. Caldwell of the University of California, Berkeley, peers
out the porthole. For him, a marine animal behaviorist, living
underwater on a reef for 10 days is like a 12-year-old camping
in Disneyland. As Caldwell meditates on sea animals, Cronin
and Nadav Shashar, a researcher from Israel, assemble a
finicky, handcrafted camera specially outfitted to measure and
record the spectral distribution and polarization of ambient light
on the reef.
"We have a decent understanding of marine animal vision,"
Cronin says. "But we know very little about the world in which

these animals use their vision. What are they looking at? What
do they perceive? Do they use UV and polarized light to
enhance their vision--and if so, how?
"The basic properties of light underwater are poorly
understood," he adds. "We believe that various parts of the
spectrum help animals see details at different distances. But
which wavelengths most enhance the visibility of objects
underwater? How do animals use visual cues to communicate
with each other, particularly with colored marks on their
bodies?"
At another bench in the undersea laboratory, Canadian biologist
Daryl C. Parkyn of the University of Victoria in British
Columbia prepares to capture fish using a dilute anesthetic. An
astute observer of marine animals in their native habitats, he has
honed an unusual method of collecting specimens. With a soft
jug of anesthetic under his arm, he gently stalks a fish, then
doses it. "We call this the bagpipe method," he says. Parkyn
says that this method proved superior to a previous technique
involving a Super Soaker, a toy water pistol that, owing to its
forceful thrust, "blew the fish away--literally."
Meanwhile, neuroscientist N. Justin Marshall of England's
University of Sussex tinkers with his computerized camera for
measuring the spectral reflectance of fish. The system, sealed in
an airtight housing, can be carried onto the reef to peer at
marine animals. Marshall believes it will help decode fish color
signals.
"We humans don't usually think about communicating with
color," Marshall says. "By communication, I mean showing
aggression, attracting attention, conveying a state of sexual
readiness, or vanishing into the background." Though an
angelfish appears colorful to our eyes, he notes, its markings
succeed as camouflage underwater because of differences in
animal vision.
To signal each other, marine animals flash concealed areas of
their bodies, spreading fins or inverting claws to display
markings that reflect UV light. "They can see W and polarized

light, which are invisible to us," Marshall says. "But by using a
camera sensitive to ultraviolet rays, we can look at a fish's
otherwise invisible reflections."
The evolution of color vision in animals depends not only on
the animals' needs, but also on the light in their habitat,
Marshall says. The visual systems of all organisms in an area
evolve together, influencing one another. "For us, the colors of
a coral reef are mind-blowing in their beauty," says Marshall.
"To the creatures that live there, color signals help them
manage life and death." The markings and visual systems of
these animals, he explains, serve three primitive needs: eating,
avoiding predators, and mating.
"We have no idea what an angelfish or mantis shrimp sees when
it looks at an angelfish," Marshall says. "The only way to get
some sense of what they might see is to use a nonsubjective
method, like a camera that records UV reflections."
Back on the surface, the operations crew watches the aquanauts
on video monitors, then prepares a delivery pot--an airtight
container of gear and snacks lowered overboard and ferried by
divers to Aquarius.
A few hundred yards away, bobbing in 4-foot swells, Captain
Catherine Liipfert anchors Wild Card, the transport boat now
carrying Cronin's own surface support team. Donning their gear,
Erik Herzog, Nerina Holden, and Pamela Jutte, all visiting
marine researchers, prepare to dive 110 feet to collect
specimens.
To extend their underwater time, each diver carries two tanks of
specially blended gas, an oxygen-enriched version of
compressed air that enables them to remain underwater longer
than they could under ordinary scuba conditions. Working at
great depth for long periods of time, divers must monitor
nitrogen accumulations in their blood and body tissues. Under
several atmospheres of pressure--one for each 33 feet of water--
divers absorb more nitrogen than they expel. If they ascend too
rapidly, the dissolved nitrogen can bubble up in their blood.
This condition, known as decompression sickness, or the bends,

can cause great pain, even death.
Descending along the boat's anchor line, Herzog and the support
team vanish into a cloud of blue bubbles. During the day, they
make three dives, delivering equipment to the aquanauts and
chasing grunts with squirt guns. Grunts, colorful fish prevalent
in the region, earned their name the sound they make when
squeezing their water bladders.
"We want to know if fish have circadian rhythms--that is,
whether external light cues or an internal clock governs their
behavior," says Herzog. By observing the fish at various times
of day and night and running a controlled experiment in the lab,
Herzog can identify changes in the fishes' behavior.
"If they grunt or move around more at night than they do during
the day," he says, "then that will tell us something about their
circadian rhythm. Are the fish's behavioral patterns driven by
daylight or an internal clock? We don't know the answer."
At night, dark blue fades to black. Caldwell, intrigued by what
he sees, decides to venture into the inky abyss. Toting a
flashlight, bedazzled intermittently by luminescent sea
creatures, he's on the lookout for the larvae of mantis shrimp--
an obsession of his.
"They're very curious creatures, to the point of being stupid,"
Caldwell observes. "I often wonder why they come out to look
at me, knowing that I present a threat. Of course, the answer is
clear--they can't help it. They need the sensory information
merely to make a decision."
Predatory crustaceans feeding mainly on shellfish, mantis
shrimp--or stomatopods--dwell in seafloor burrows throughout
the tropics. Though shy, often peering from behind coral, the 4-
inch shrimp that Caldwell studies behave aggressively in
capturing prey and defending territory. Wielding two large
raptorial claws, they spear and smash their prey's outer shells,
justifying their nickname of "thumb busters."
Indeed, with the striking force of a bullet, stomatopod claws can
break the glass of aquarium walls. As evolutionary holdovers
from the Jurassic era more than 135 million years ago,

stomatopods have spawned more than 350 modern species,
ranging in length from half an inch to more than 1 foot.
Among their distinguishing features are colorfully marked
appendages and extraordinary eyes. "They have one of the most
unusual visual systems in the animal kingdom," Caldwell says.
"Whereas we humans have four visual pigments in our eyes,
they have 16. They also make fine distinctions in the spectrum,
including the ability to see ultraviolet and polarized light. So
we think they can tell us a lot about underwater vision."
Cronin, Marshall, and Caldwell have all come to the conclusion
that many secrets of undersea sight may reside in stomatopod
eye. "They have receptors for detecting long wavelengths of
light," Cronin says. "They can see far-red and infrared
wavelengths, light that many land animals can't see. And yet
they're not supposed to have those receptors, because there's
little long-wavelength light underwater--the water absorbs most
of it.
"Clearly, they have these receptors for a reason. So we're
presuming that long wavelengths of light convey relevant
information, though we don't know what that information is."
Unlike the human eye--which presents a complete image to the
brain by focusing light on the retina--the stomatopod's eye
scans images somewhat like a television or fax machine, one
line at a time, says Marshall. With visual receptors lined up in
rows, the mantis shrimp bob their eyes up and down, scanning
the scene before them. "It's an economical system, minimizing
receptor duplication," Marshall says.
"Nature often solves problems with clever engineering."
Why go to all this trouble to study thumb-busting shrimp? Who
cares if fish signal each other with colorful signs or see in light
so dim that to human eyes all appears dark?
"There are, of course, implications for human beings," Marshall
retorts. "Much of what we know about our own brains and
vision systems comes from studying more primitive forms of
life, such as snails and squids." Studying the stomatopods' eyes
may deepen our understanding of color vision chemistry.

The mantis shrimp have evolved a way to enhance images with
polarized light, Marshall observes. Not surprisingly, military
agencies find this research intriguing, particularly with regard
to "seeing in the dark and not being seen by others," says
Marshall. The ability to see details at greater distances, in low
light, or underwater tantalizes agencies aiming to improve
tactical defense.
The only way to understand how animals master environments
that leave humans struggling is to enter their world, see what
they do, and learn their peculiar ways, says Marshall.
"We have evolved, essentially, from nocturnal mammals in rain
forests, so we have relatively poor color vision compared to
many other animals. With stomatopods, their color vision has
evolved over 100 million years. It's like an arms race Animals
evolve vision that's good at spotting camouflage. Then other
animals respond by evolving colors that can't be seen. There's
always a give-and-take, evolution and counterevolution.
"In a coral reef, the evolution of color has gone to an extreme."
Word count:
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Copyright Science Service, Incorporated Sep 16, 1995
Climate change, human impacts, and the resilience of coral
reefs
falseHughes, T P
; Baird, A H
; Bellwood, D R
; Card, M; et al. Science301.5635 (Aug 15, 2003): 929-33.
Full textFull text - PDFAbstract/Details
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The diversity, frequency, and scale of human impacts on coral
reefs are increasing to the extent that reefs are threatened
globally. Projected increases in carbon dioxide and temperature
over the next 50 years exceed the conditions under which coral
reefs have flourished over the past half-million years. However,
reefs will change rather than disappear entirely, with some
species already showing far greater tolerance to climate change
and coral bleaching than others. International integration of
management strategies that support reef resilience need to be
vigorously implemented, and complemented by strong policy
decisions to reduce the rate of global warming. [PUBLICATION
ABSTRACT]

decisions to reduce the rate of global warming. [PUBLICATION
ABSTRACT]
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decisions to reduce the rate of global warming.
Coral reefs are critically important for the ecosystem goods and
services they provide to maritime tropical and subtropical
nations (1). Yet reefs are in serious decline; an estimated 30%
are already severely damaged, and close to 60% may be lost by
2030 (2). There are no pristine reefs left (3-4). Local successes
at protecting coral reefs over the past 30 years have failed to
reverse regional-scale declines, and global management of reefs
must undergo a radical change in emphasis and implementation

if it is to make a real difference. Here, we review current
knowledge of the status of coral reefs, the human threats to
them now and in the near future, and new directions for
research in support of management of these vital natural
resources.
Until recently, the direct and indirect effects of overfishing and
pollution from agriculture and land development have been the
major drivers of massive and accelerating decreases in
abundance of coral reef species, causing widespread changes in
reef ecosystems over the past two centuries (3-5). With
increased human populations and improved storage and
transport systems, the scale of human impacts on reefs has
grown exponentially. For example, markets for fishes and other
natural resources have become global, supplying demand for
reef resources far removed from their tropical sources (6) (Fig.
1). On many reefs, reduced stocks of herbivorous fishes and
added nutrients from land-based activities have caused
ecological shifts, from the original dominance by corals to a
preponderance of fleshy seaweed (5, 7). Importantly, these
changes to reefs, which can often be managed successfully at a
local scale, are compounded by the more recent, superimposed
impacts of global climate change.
The link between increased greenhouse gases, climate change,
and regional-scale bleaching of corals, considered dubious by
many reef researchers only 10 to 20 years ago (8), is now
incontrovertible (9, 10). Moreover, future changes in ocean
chemistry due to higher atmospheric carbon dioxide may cause
weakening of coral skeletons and reduce the accretion of reefs,
especially at higher latitudes (11). The frequency and intensity
of hurricanes (tropical cyclones, typhoons) may also increase in
some regions, leading to a shorter time for recovery between
recurrences (10). The most pressing impact of climate change,
however, is episodes of coral bleaching and disease that have
already increased greatly in frequency and magnitude over the
past 30 years (9-14).

Bleaching, Acclimation, and Adaptation
Regional-scale coral bleaching is strongly associated with
elevated temperatures, particularly during recurrent ENSO (El
Nino-Southern Oscillation) events (8). Stressed, overheated
corals expel most of their pigmented microalgal endosymbionts,
called zooxanthellae, and become pale or white. If thermal
stress is severe and prolonged, most of the corals on a reef may
bleach, and many may die. A popular model (9) shows an
invariant bleaching "threshold" at ~1[degrees]C above mean
summer maximum temperatures. This threshold will be
chronically exceeded as temperatures rise over the next 50
years, leading to predictions of massive losses of all corals (Fig.
2A). This model is based on two simplifying assumptions: that
all corals respond identically to thermal stress, and that corals
and their symbionts have inadequate phenotypic or genetic
capabilities for adapting rapidly to changes in temperature.
Below, we challenge the conventional understanding of these
key issues.
Bleaching is conspicuously patchy (15-17), providing clear
empirical evidence of the absence of a single bleaching
threshold for all locations, times, or species (contrary to the
conventional model depicted in Fig. 2A). Consequently,
bleached and unbleached corals are often encountered side by
side (Figs. 3A and 4B). The sources of this variation are poorly
understood and have been variously attributed to extrinsic
environmental patchiness (e.g. temperature, light, turbulence),
as well as intrinsic differences (phenotypic and genetic) among
corals and their microalgal symbionts (15-19). Whatever the
mechanisms, bleaching thresholds are more realistically
visualized as a broad spectrum of responses (Fig. 2B).
Furthermore, bleaching susceptibilities may also change over
time as a result of phenotypic and genetic responses (Fig. 2C).
In particular, substantial geographic variation in bleaching
thresholds within coral species provides circumstantial evidence
for ongoing evolution of temperature tolerance.
Average summer water temperatures differ enormously within

the geographic boundaries of a typical coral species' range.
Based on our current knowledge of taxonomy, the median
latitudinal extent of coral species in the Indo-Pacific is
56[degrees] (20), with many species' ranges straddling the
equator and extending to or beyond the limits of reef growth (at
~30[degrees]N and ~30[degrees]S) where water temperatures
are much cooler (Fig. 3B). Similarly, the geographic extent of
35% of coral species in the Arabian Gulf (where the mean
summer maximum is 36[degrees]C) (21) also includes Lord
Howe Island (24[degrees]C), the southernmost coral reef in the
Pacific Ocean (Fig. 3C). Importantly, corals in the Arabian Gulf
do not bleach until they experience temperatures that are
extreme for that location, well over 10[degrees]C higher than
summer maxima in cooler regions elsewhere in the same
species' ranges, providing circumstantial evidence of local
adaptation. Furthermore, the lower bleaching threshold in cooler
locations implies that there is strong selection for corals and
their zooxanthellae to evolve thresholds that are near, but not
too far beyond, the expected upper temperature at that location.
This pattern points to a potential trade-off between the risk of
mortality from extreme temperatures versus a high cost of
thermal protective mechanisms (e.g., antioxidant enzymes, heat
shock, or photoprotective proteins and pigments).
An emerging area of research points to the importance of
genetic variation as a determinant of bleaching responses in
both corals and zooxanthellae. Corals exhibit high levels of
genetic diversity, as expected for species with large population
sizes and prodigious sexual reproduction (22). Similarly,
zooxanthellae (Symbiodinium spp.) cluster into a number of
groups (based on cladistic analysis of DNA sequences), with
seven clades being recognized so far, comprising many species
(19). This recent finding raises the issue of current and future
patterns in the distribution and relative abundance of
zooxanthellae clades. A hypothesis that bleaching is "adaptive,"
increasing coral fitness by facilitating expulsion of susceptible

zooxanthellae species and uptake of more resistant ones (23),
has not been supported by observations on the fate of bleached
corals. Bleaching is more accurately described as a stress
response, which is often followed by high mortality, reduced
growth rates, and lower fecundity (16, 24). Although adult
corals may acquire a previously undetected clade under
experimental conditions (25, 26), a change in the relative
proportions of zooxanthellae as a result of bleaching, like
similar rearrangements of coral assemblages (Fig, 3B), does not
necessarily indicate that any evolutionary response has
occurred.
A major concern is that the accelerating rate of environmental
change could exceed the evolutionary capacity of coral and
zooxanthellae species to adapt. A common view is that corals
are too long-lived to evolve quickly, and that geographic
differences in temperature tolerances have evolved over much
longer time frames than the decadal scale of current changes in
climate. Although some corals are indeed very long-lived,
sexual maturity is reached within 3 to 5 years and most species
at all depths rarely live longer than 20 years (27). Nonetheless,
highly skewed fecundity distributions (where a few very large,
old individuals swamp the gene pool), strongly overlapping
generations, and high levels of asexual reproduction are
common traits that are likely to retard rapid evolution in many
coral species. Although mortality rates from bleaching events
are often very high, we know virtually nothing about how much
selection this exerts or the heritability of physiological traits in
corals. Furthermore, adaptive evolution could be limited if traits
under selection are negatively genetically correlated (28) or if
gene flow is high enough to preclude local adaptation. On the
other hand, high gene flow or connectivity will promote
resilience and recovery from recurrent bleaching. The available
evidence indicates that rates of gene flow in corals vary
substantially among species (22, 29), which implies that their
differential ability to migrate in response to climate change and
to adapt will result in further changes to community structure

beyond the immediate effect of selective mortality caused by
severe bleaching. In contrast, subpopulations on isolated islands
or archipelagoes (e.g., Hawaii and Bermuda) may represent
genetic outposts for virtually all coral reef species, with little
input from other, distant localities. If isolated reefs bleach,
recovery is likely to be far slower than in more central,
interconnected populations.
Lessons from the Past: The Geological Record
The geological record provides the only source of data on long-
term effects of climate change on coral reef species and
assemblages (30, 31). Many extant species of corals extend
backwards in time to the Pliocene [1.8 to 5.3 million years ago
(Ma)], and most scleractinian genera originated in the Eocene to
Miocene (55.0 to 5.3 Ma) (32). Extant species have dominated
modem reefs for the past half-million years, providing an
invaluable baseline long before human impacts began (3, 4).
New assessment of past climates has revealed unexpectedly
rapid shifts over decades or less, especially at high latitudes,
with ice-age transitions being linked to abrupt changes in the
North Atlantic circulation (33). Further rapid climatic changes
may have also occurred at lower latitudes in warmer periods
since the last glacial maximum (34). Consequently, there is now
some uncertainty about the speed of expected climate change
relative to the past, although we can be certain nonetheless that
the projected increases in carbon dioxide and temperature over
the next 50 years will substantially and very rapidly exceed the
conditions under which coral reefs have flourished over the past
half-million years (10).
During the Pleistocene and Holocene, many extant species of
tropical and subtropical organisms underwent dramatic shifts in
geographic range in response to periods of warming and cooling
(35, 36). Some species migrated faster than others, producing
rapid shifts in species composition, especially near faunal
boundaries (35). For corals, range boundaries of extant coral
species in the warm Late Pleistocene extended up to 500 km
further south along the western Australia coastline (to

33[degrees]S) than they do today (37). Closer to the center of
their geographic range, however, coral diversity and species
presence or absence in eastern Papua New Guinea changed
remarkably little during nine reef-building intervals from 125 to
30 ka (31). On a regional scale, these same species underwent
dramatic changes in distribution and abundance as Quaternary
glacial-interglacial cycles caused sea level to repeatedly flood
and drain from continental shelves and oceanic islands (38).
Many marine species exhibit a genetic legacy of these range
shifts, local extinctions and expansions, and the marked
population fluctuations caused by past climatic variation (29,
39, 40). Based on this past history, we can expect regional and
global-scale disruption to coral reefs due to climate change to
accelerate markedly in coming decades. Already, relative
abundances of corals and of other organisms are changing
rapidly in response to the filtering effect of differential
mortality (from bleaching and other, more local human impacts)
and differences in rates of recovery of species from recurrent
mortality events (16, 17, 41, 42).
There are two major differences, however, between current
climate-driven changes and the recent past. First, because the
oceans today are already at a high sea-level stand, the projected
rise [0.1 to 0.9 m in the next 100 years (10)] will be very small
compared with sea-level changes during the Pleistocene.
Second, unlike the past, the response of reef-dwelling species to
projected climatic trends will be profoundly influenced by
people. As outlined below, human impacts and the increased
fragmentation of coral reef habitat have preconditioned reefs,
undermining reef resilience and making them much more
susceptible to future climate change.
Managing Coral Reef Resilience
Clearly, the capacity of coral reef ecosystems to continue to
generate the valuable goods and services (on which human
welfare depends) has to be better understood and more actively
managed. Sustaining this capacity requires improved protection
of coral reef resilience (43). Marine protected areas (MPAs) are

currently the best management tool for conserving coral reefs
and many other marine systems (44, 45). MPAs range from
ineffective "paper parks," to multiple-use areas with varying
degrees of protection, to marine reserves, or no-take areas
(NTAs). NTAs provide the most effective protection for
extractive activities such as fishing, affording a spatial refuge
for a portion of the stock from which larvae and adults can
disperse to adjoining exploited areas (44, 45).
NTAs, when properly supported and policed, are effective in
preserving fish stocks because they change human behavior.
They do not, however, prevent or hold back warm water, or stop
bleaching. For example, in 1998, the biggest and most
destructive bleaching event to date killed an estimated 16% of
the world's corals, including reefs in the western Pacific,
Australia, and Indian Ocean that are widely regarded as the best
managed and most "pristine" in the world (2). If NTAs do not
provide a refuge from bleaching, then how can they help protect
coral reefs from climate change? Overfishing, particularly of
herbivorous parrotfish and surgeonfish, affects more than just
the size of harvestable stocks-it alters the entire dynamics of a
reef (3-5, 46). Reduced herbivory from overfishing, increased
levels of disease, and excess nutrients can impair the resilience
of corals and prevent their recovery following acute-disturbance
events like cyclones or bleaching, leading instead to a phase
shift to algal-dominated reefs (Fig. 4, D to F). Resilience is also
eroded by chronic human impacts that cause persistently
elevated rates of mortality and reduced recruitment of larvae (7,
12, 41, 43).
Although climate change is by definition a global issue, local
conservation efforts can greatly help in maintaining and
enhancing resilience and in limiting the longer-term damage
from bleaching and related human impacts. Managing coral reef
resilience through a network of NTAs, integrated with
management of surrounding areas, is clearly essential to any
workable solution. This requires a strong focus on reducing

pollution, protecting food webs, and managing key functional
groups (such as reef constructors, herbivores, and bioeroders) as
insurance for sustainability (7, 46).
NTAs also act to spread risk, whereby areas that escape damage
can act as sources of larvae to aid recovery of nearby affected
areas (47). This highly desirable property of NTAs raises the
issue of how close they need to be to promote connectivity-the
migration of larvae and/or adults-between them (44, 45).
Critically, coral reef organisms, including different species of
corals, vary greatly in their larval biology and potential for
dispersal (22, 29). The clear implication is that NTAs must be
substantially more numerous and closer together than they are
currently to protect species with limited dispersal capabilities.
Furthermore, isolated reefs that are largely self-seeding are
unlikely to be protected by distant NTAs, and therefore will be
much less resilient to climate change.
Research and Management Challenges
Coral reefs are highly productive hotspots of biodiversity that
support social and economic development. Their protection,
therefore, is a socioeconomic imperative, as well as an
environmental one. Global warming, coupled with preexisting
human impacts, is a grave threat that has already caused
substantial damage. However, the available evidence indicates
that, at a global scale, reefs will undergo major changes in
response to climate change rather than disappear entirely.
There is, nonetheless, great uncertainty whether the present
economic and social capacity of coral reefs can be maintained.
To limit the damage, emerging management strategies based on
greatly expanded networks of NTAs, coupled with stronger
protection of adjacent habitats, need to be vigorously
implemented. NTAs are unlikely to prevent mortality of corals
from bleaching, but they will facilitate a partial recovery of
reefs that are reconfigured and populated by a subset of
resistant species and genotypes. NTAs are not a panacea; their
implementation needs to be complemented by heightened

protection of adjacent areas and by strong international policy
decisions to reduce the rate of global warming.
Research in support of reef management urgently needs to
increase the scale of experiments, sampling, and modeling to
match the scale of impacts and key biological processes (e.g.,
dispersal, bleaching, and overfishing) and go beyond the current
emphasis on routine monitoring and mapping. Indeed, most
coral reef research is parochial and short-term, and provides
little insight into global or longer-term changes. For example,
current knowledge of biogeographic-scale patterns on reefs is
based on species presence or absence at local sites and pays
scant attention to temporal, regional, or global patterns of
relative abundance or functional attributes of species (48) that
could be exploited for management of resilience. Similarly,
studies of intergenerational (genetic) responses to climate
change (28) are urgently needed for reef organisms, particularly
corals and zooxanthellae. Another crucial area for future work
is genetic dissection of population structure and modeling of
connectivity, which could incorporate many of the unusual life-
history traits of clonal organisms, selection coefficients based
on mortality from bleaching, and experimental measurements of
heritabilities. Emerging research on marine reserves and how
they work to protect harvested stocks and spread risk (44, 45)
also needs to be expanded and applied specifically to the
tropics. These approaches must be integrated with
socioeconomic aspects of coral reef resilience, incorporating
adaptive management systems that operate locally, regionally,
and globally.
International integration and scaling-up of reef management is
an urgent priority (2). Ecological modeling studies indicate that,
depending on the level of exploitation outside NTAs, at least
30% of the world's coral reefs should be NTAs to ensure long-
term protection and maximum sustainable yield of exploited
stocks (49, 50). Yet, even in affluent countries, such as the
United States and Australia, less than 5% of reefs today are
NTAs. Wealthy countries have an obligation to take the lead in

increasing the proportion of reefs that are NTAs, while
simultaneously controlling greenhouse-gas emissions.
References and Notes
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7. T. McClanahan, N. Polunin, T. Done, in Resilience and
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38. D. C. Potts, Paleobiology 10, 48 (1984)
39. M. E. Hellberg, D. P. Balch, K. Roy, Science 292, 1707
(2001).
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955 (2001).
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(1999).
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413 (2000).
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Appl. 13, S3 (2003).
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47. J. Bascompte, H. Possingham, J. Roughgarden, Am. Nat.
159, 128 (2002).
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49. A. Hastings, L W. Botsford, Ecol. Appl. 13 (suppl.), S65
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50. J. Roughgarden, P. R. Armsworth, in Ecology: Achievement
and Challenge, M. C. Press, N. J. Huntly, S. Levin, Eds.
(Blackwell Science, Oxford, 2001), pp. 337-356 .
51. We thank James Cook University and The Queensland
Government for funding a meeting of the authors, and A. Green,
N. Knowlton, and B. Willis for providing comments on a draft.
This is contribution No. 078 of the Centre for Coral Reef
Biodiversity at James Cook University.
T. P. Hughes,1* A. H. Baird.1 D. R. Bellwood,1 M. Card,2 S.
R. Connolly,1 C. Folke,3 R. Grosberg,4 O. Hoegh-Guldberg,5 J.
B. C. Jackson,6,7 J. Kleypas,8 J. M. Lough,9 P. Marshall,10 M.
Nystrom,3 S. R. Palumbi,11 J. M. Pandolfi,12 B. Rosen,13 J.
Roughgarden14
1Centre for Coral Reef Biodiversity, James Cook University,
Townsville, Qld 4811, Australia. Environmental Protection
Agency, Old Quarantine Station, Cape Pallarenda, Townsville,
QLD 4810, Australia. 3Department of Systems Ecology,
Stockholm University, SE-106 91 Stockholm, Sweden. 4Center
for Population Biology, Division of Biological Sciences,
Section of Evolution and Ecology, 1 Shields Avenue, University
of California, Davis, CA 95616, USA. 5Centre for Marine
Studies, University of Queensland, St Lucia, QLD 4070,
Australia. 6Scripps Institution of Oceanography, University of
California San Diego, La Jolla, CA 92093, USA. 7Smithsonian
Tropical Research Institute, Box 2070, Balboa, Republic of
Panama. 8National Center for Atmospheric Research, Post
Office Box 3000, Boulder, CO 80307, USA. Australian Institute
of Marine Sciences, PMB #3, Townsville, QLD 4810, Australia.
10Great Barrier Reef Marine Park Authority, Post Office Box

1379, Townsville QLD 4810, Australia. 11Department of
Biological Sciences, Stanford University, Hopkins Marine
Station, Pacific Grove, CA 93950, USA. 12Department of
Paleobiology, Smithsonian Institution, Post Office Box 37012,
National Museum of Natural History, Washington, DC 20013,
USA. 13Department of Zoology, The Natural History Museum,
Cromwell Road, London SW7 5BD, UK. 14Department of
Biological Sciences, Stanford University, Stanford, CA 94305,
USA.
*To whom correspondence should be addressed. E-mail: [email
protected]
Copyright American Association for the Advancement of
Science Aug 15, 2003

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Marine Biology 1
Running head: Marine Biology
Marine Biology
Student Name
Allied American University
Author Note
This paper was prepared for Marine Biology, Module 7
Homework taught by Instructure name.
Directions:
the impact global warming and human impact have on the coral
reef communities, globally. Focus on primary production and
the different effects it has on the marine environment. Also,
incorporate how you could help lessen the degree of
degradation.

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