Colossal Corals Open a Window to the Past:
Exploring National Marine Sanctuaries
By Matt Malinowski
April 2023
Thousands of miles west of the U.S. coastline and south of the Equator, resilient
reefs thrive and super-sized corals grow within and around the protected waters of
National Marine Sanctuary of American
Samoa. This living marine laboratory provides
a better understanding of coral biology and may unlock secrets to how corals cope
with changing ocean conditions.
A Remote Journey
As the first golden light emerges above the horizon of Tutuila Island, a small team of NOAA
scientists and coral specialists make final checks over technical equipment and dive gear.
Their small boat undergoes a safety inspection and is fueled for an open-water voyage. The
motor purrs to life, breaking the silence of the morning, and the crew leaves the flat water
of Tutuila behind.
Researchers aboard a vessel prepare to dive off Ta’u to check the health of a
massive coral. The Manu'a islands can be seen off in the distance on this clear day. Photo:
Matt McIntosh/NOAA
The vessel darts across the expansive sea for more than four hours before reaching the
targeted coordinates. The island of Ta’u lies over fifty miles to the east of the main
island of Tutuila. The water within this unit of National Marine Sanctuary of American Samoa
is glassy and crystalline blue. The team cuts the engine and readies their scuba
gear before
slipping into the still water.
Visiting a Giant
It isn’t long before the divers spot a large mound rising from the ocean floor. This giant
lifeform, shaped like an oversized mushroom cap, has rested beneath the waves for hundreds
of
years. Once considered to be the largest coral in the world, Big Momma is one of several
massive
Porites corals living within the boundaries of National Marine Sanctuary of American
Samoa
and the National Park of American Samoa. This area has a high density of large Porites
colonies, and
has
been nicknamed the “Valley of the Giants.”
Giant Porites corals tower over the rest of the reef within the Valley
of the Giants. Photo: Matt McIntosh/NOAA
Big Momma’s vast dome casts a shadow that swallows the sunlight as the divers descend towards
the seabed to make their approach. Communications and outreach coordinator for the
sanctuary,
Nerelle Que Moffitt, says that being in the presence of the gargantuan coral “makes you drop
your jaw and say, ‘I can’t believe this is real’.” Like doctors evaluating a patient, the
team
spends the next hour making several close passes looking for any signs of distress or
ailment.
The divers look
miniaturized as they hover over the textured coral that is as tall as a
two-story house and the width of a tennis court. The team makes direct observations and
collects
video and photographic evidence for further evaluation back on dry land. They take note of a
few
growth anomalies, and notice areas where coral tissue is missing due to bites from hungry
pufferfish. Thankfully, there are no signs of major physical damage and no visible
indicators of
other coral diseases. Big Momma is in good shape—despite a bleaching event due to warmer
water
temperatures that affected other corals within the area in 2020.
In order to see these layers, scientists drill cores out of large coral heads,
like this Orbicella faveolata in Flower Garden Banks National Marine Sanctuary.
Extracting a core allows them to look at many years-worth of layers in one compact unit.
The larger the coral colony, the more years of data they can extract. Photo: NOAA
Learning from the Layers
Another group of scientists carefully removed a
core
sample from Big Momma in 2011 that helped
to uncover some of the coral’s secrets. They evaluated growth patterns similar to tree rings
to
determine the coral was roughly 500
years old. “This is a very old coral and it opens a
window
into historic conditions in Ta’u,” said Val Brown, research coordinator for National Marine
Sanctuary of American Samoa.
Oxygen is one of the best ways to learn about past climates. Oxygen comes in heavy or light
varieties (or isotopes) and these molecules get left behind in layers of the coral core. The
ratio of oxygen isotopes changes with temperature and could be used like a historical
thermometer to peer into the water chemistry of the past. The data led researchers to
conclude that where Big Momma sits may be a naturally protected zone. Weather patterns that
alter sea
surface temperature and other chemistries appear to have less of an effect near Ta’u. The
Valley of the Giants lies within an El
Niño Southern Oscillation (ENSO) null zone and its natural
shielding from temperature fluctuations may be why corals here can become so massive and
long-lived.
A Culture of Conservation
The Samoan culture is one of the oldest in Polynesia extending back thousands of years.
Throughout this time, Samoans have found ways to thrive with limited resources and developed
a vibrant society that values tradition and family. They understand the importance of living
in connection with nature and their reliance on the surrounding ecosystem for food and
livelihood. The awareness of the Valley of the Giants is relatively new in the scientific
community, but
Samoans have known about these spectacular corals for generations. Through their balanced
and communal lifestyle, called Fa’a Samoa, they have played an integral part in safeguarding
the
local marine ecosystem.
A Living Laboratory
Much like the Samoan people that inhabit this special place, ecosystems
here are strong and
resilient. Reefs across the entire territory of American Samoa have been found to be
more tolerant of higher temperatures that have caused coral reefs in other parts of the
world to
go through severe bleaching events and die offs. These rich waters serve as a living
laboratory,
where NOAA scientists can study and monitor the health of a diversity of reef life. They
remotely evaluate water
chemistry and carbon dioxide levels, and search for understanding of why corals here
are so hardy.
While corals within and around National Marine Sanctuary of American Samoa
are
resilient and healthy overall—especially those near Ta’u and in the Valley of
Giants—they are still susceptible to impacts from climate change. Thickets of
branching
corals shown here bleached during a warm period in 2015. Photo: XL Catlin Seaview
Survey.
A monitoring
buoy in Fagatele Bay collects data on carbon dioxide from
surface
seawater and the atmosphere as well as data on water temperature, salinity, pH,
oxygen,
and chlorophyll. Photo: Nerelle Que Moffitt/NOAA
Though they are nearly 5,000 miles west of the U.S. mainland, the scientists are also aware
that
these rich, thriving reefs with colossal corals are not immune to the impacts of human
action
and a changing ocean climate. A recent condition
report
from National Marine
Sanctuary of
American Samoa outlines that while the area is healthier than many other ocean ecosystems,
it
still faces challenges. Rising water temperatures due to climate change have caused coral
bleaching events and the abundance of some marine species is diminishing due to
human impacts.
NOAA scientists hope to annually monitor corals like Big Momma. They are looking into using
technologies like 3D mapping to
study changes in volume over time and underwater sound recorders
to monitor fish, marine mammal, and vessel sounds. Continued conservation and understanding of
these
unique habitats will be key to their future resilience.
A Coral Community
Brown has seen a spectacular diversity of life around the Porites coral on her
scientific
dives.
“It definitely takes my breath away every time I drop into the site,” says Brown. According
to
Brown, spiny lobsters and schools of fish like snappers and sweepers hide under Big Momma’s
ledges. Sea turtles glide by the boulder-sized coral while large parrotfish and dazzling
sweetlips forage nearby. Even in areas where Big Momma has suffered tissue damage, branching
Pocillopora and Acropora corals have settled, providing protection for clouds
of damselfish
to
hide from predators.
The real estate market is highly competitive on a coral reef. Hard and soft
corals, sponges, hydroids, algae, and more, all compete for a prime location. When
parts of large corals like Big Momma die, sometimes another coral finds an
open spot to build its home. Photo: Wendy Cover/NOAA
Big Momma took hundreds of years to grow to its current size, but the managed conservation of
the Valley of the Giants and National Marine Sanctuary of American Samoa has grown
exponentially
in just a small amount of time. Though it started as the smallest, the sanctuary was
expanded
and is currently the largest in the U.S. National Marine Sanctuary System covering more than
13,500 square miles of sparkling ocean.
Continued protection and long-term monitoring of this remote marine ecosystem will help
scientists better understand how corals respond to the stresses of a changing ocean climate
and
may unlock solutions to conservation and preservation techniques to mitigate human impacts
on
these environments. This information is especially important as practitioners
race against the
clock to respond to multiple issues, like coral bleaching and coral diseases, in places like Florida
Keys National Marine Sanctuary and throughout the Caribbean.
Matt Malinowski is a former communications intern with NOAA’s Office of National Marine
Sanctuaries