This is "rerun" of earlier blogs, but is presented in chapter format rather than short pieces.
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| Carrie Bow Cayes dual outhouses, 2011 |
If you’ve ever spent time in southern
Florida out in the Everglades, it’s likely you’ve seen mangrove trees---trees
that are at home with their “feet” in seawater. Often characterized by aerial
roots that form impenetrable thickets, the red mangrove (Rhizophora mangle)
is the iconic species occurring from Florida all the way south to Panama.
Mangroves, in general, encompass a wide variety of tree species, all of which
are salt tolerant and grow in coastal zones in the tropics and sub-tropics
worldwide. The mangrove ecosystem hosts a diverse community of organisms in the
trees’ canopies, underlying soils, and adjacent waters. They are some of the
most productive ecosystems on the planet fixing carbon at fairly high rates and
providing fuel for important fisheries. Because they grow at the land-water
interface, mangrove ecosystems protect inland communities from flooding,
hurricanes, tsunamis, and sea level rise. Unfortunately, because they are on
coasts, these forests are often targeted for destruction to make way for
development. Understanding how they function in their natural state, and in
proximity to humans, is key to learning how they tolerate and adapt to changing
global conditions.
By far some of the most engaging
research in my career started in the late 1990s when I joined an
interdisciplinary group of ecologists led by Candy Feller, Smithsonian
Environmental Research Center (SERC). Feller is a plant and insect ecologist,
who teamed up with Myrna Jacobson, a geochemist, then at Georgia Tech. Candy
and Myrna attended a workshop where the concept of studying ecosystems using biocomplexity
theory was introduced. Biocomplexity is defined as “properties emerging
from the interplay of behavioral, biological, chemical, physical, and social
interactions that affect, sustain, or are modified by living organisms,
including humans.” (Michener et al., 2001). Feller and Jacobson swapped
research interests and a collaboration was born. Candy Feller along with
Catherine Lovelock, plant physiologist, and Karen McKee, USGS ecologist, were
already studying the effects of nutrient pollution on the growth and health of
mangroves. Our research team included scientists from six institutions and was,
at that time (1999), one of the larger projects I had ever worked on.
I started this research with a lot of
excitement and enthusiasm. Joining a new collaborative research study with biocomplexity
as the central theme was a challenge for me. Over the next 12 years, I learned
a lot about mangrove ecosystems and interdisciplinary collaborations. Along the
way, I mentored several bright postdocs and students--Matthew Wooller, Barbara
Smallwood, Quinn Roberts, Isabel Romero, David Baker, and Derek
Smith--providing them with awesome scientific experiences that they will
remember for a lifetime. What began as a straightforward study morphed quickly
into a project that demanded creative thinking to figure out how the mangrove
trees we were studying managed to survive, and thrive, in nutrient-poor
conditions. We discovered that the mangroves depended on the interaction of
microorganisms living in surrounding sediments for their growth and success.
How we came to this discovery called on innovative sampling in the field, new
techniques in the laboratory, and the development of theoretical ecological
models.
Getting there:
I made a dozen or so trips to Belize
over the next twelve years, working on three different projects. Going from Washington
DC we boarded a plane at National Airport to Miami, where we joined a group of
mostly tourists heading south to Belize City. After passing through Belizian
customs with large, plastic containers of our supplies and gear, we made our
way south to Dangriga. Sometimes, we
hired an old station wagon to take us from the airport to Dangriga, that more
frequently than not broke down for a period of time along the way. If we
managed to jump on a small plane, often our luggage was too big and was delayed
in Belize City until a truck could be found.
Dangriga is a mid-size coastal town
with an airstrip located next to the Pelican Beach Resort Hotel. If we arrived
by plane, we were met at the airfield by two men who worked at the hotel. They
loaded our luggage and gear onto two wooden hand carts, then we walked on a
dirt path through a field to the dock area where a small boat awaited us for
transportation to the offshore Cayes. With our gear wrapped in plastic trash
bags, we were taken across 20 kilometers of choppy, coastal waters to
Smithsonian’s research station at Carrie Bow Caye, a small, 50 meter sand atoll
on the edge of a coral reef.
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| Wooller and Marilyn, circa 2001 |
Carrie Bow Field Station
Arriving at Carrie Bow was always
exciting and special. From a distance, we could see the small island emerge
with its few palm trees defining the landscape. We were greeted by our cook and
the station managers on the dock, where we hauled up our personal gear and
boxes of scientific equipment.
Scientists share communal living and
lab space, and meals prepared by a Belizian cook who always made healthy,
delicious local foods. Electricity is generated by solar power. Food and fresh
water are brought in once a week by boat. The laboratory consisted of a wet lab
complete with running seawater, and a dry lab where we set up small equipment
for nutrient and pigments analyses. During hurricanes the Carrie Bow Caye is
often covered with water. Once it was almost completely leveled by fire, with
the exception of one or two older cabins.
One
of the more unusual features of the station was the location and positioning of
the outhouse. At the end of a 40 meters small catwalk positioned over a
“pristine” coral atoll, the outhouse looked out over the Caribbean Sea with
small gentle waves lapping over the corals at low tide. The hole in the
outhouse led directly into the ocean where bodily fluids and solids, along with
toilet paper, flushed out with the tide. Usually, you walked quickly away and
avoided searching for your “business” among the invertebrates lining the
shallow waters. After a week or so on the island, particularly at night, it was
not uncommon for someone to be intentionally locked inside of the outhouse.
A major joy of working at this field
station was the food cooked and served by local cooks who served on Carrie Bow
for many years. They negotiated with local fishermen to obtain reef fish and
haggled with folks from Pelican Beach Resort to bring out fresh papayas,
mangoes, bananas, coconuts, watermelon and a variety of fresh vegetables as
well. Breakfasts were special treats with Johnny cakes, pancakes, fruit, and
eggs that fueled our morning field excursions. Usually one of the first to
arise in the morning, I made fresh coffee. Lunches in the field were basic: the
cook would assemble simple sandwiches and fruit. Those stuck on the island were
treated to a fully cooked lunch.
Armed with hot coffee, I spent the
early cool part of the morning before breakfast out on a Belizian wooden chair
overlooking the water. It was the time for quiet reflection, for refining the
exciting fieldwork for the day, and thinking about what I’d learned the day
before. I was often joined a little later by Wooller, Jacobson, or Dave Baker
(coral biogeochemist) who also took advantage of the peaceful time of day.
While some people feel troubled by jumping off the grid or being in a remote
environment, I found it completely invigorating.
Before dinner and after showering off
the day’s mangrove muck, we cracked open Belican beers and headed out to the
end of the dock wearing Hawaiian shirts and dresses, excited to discuss the
day’s adventures. On rainy days, sometimes we remained inside the labs, but
usually the rain cleared by sunset. Dinners were spectacular culinary delights.
In 2011, on a trip with postdoc David Baker, Chris Freeman, and student Derek Smith,
Martha learned how to prepare lion fish that Dave and Chris had speared earlier
in the day. My favorites were beans and coconut rice with fried plantains along
with fresh fish. We ate our meal on the back porch of the field station as the
sun set and darkness set in. Drinks that were offered to us, other than the
beers we had to chip in for, were syrupy fruit concoctions--passion fruit,
orange, lime flavored mixed with bottled water hauled over from the main land.
After breakfast each day, we hopped
into a 3-4 meter boat with an outboard motor and headed to Twin Cayes, a pair
of islands several kilometers to the west of Carrie Bow. The boats were always
a source of both pleasure and pain. They were moored about 30 meters offshore
of Carrie Bow. In the morning, someone had to don their dive booties and walk
into the cold water to manually drag the boat closer to shore so all could
board. No one looked forward to the task. Being older, senior women, Myrna
Jacobson and I asked Mat, Babs, or any of the other students to wade out. One
morning while dutifully bringing in the boat, Mat Wooller was stung by one of
the stingrays that lived on the bottom of the calcareous sediments. He spent
the day with his foot in boiling water, then sprinkled with Adolf’s meat
tenderizer. I’ve rarely seen grown men cry in the field. He didn’t, but it was
a close call.
Each day when we left the station, we
were handed a waterproof Pelican case with a marine radio to communicate back
to Carrie Bow if we encountered any problems or were delayed for any reason. We
dutifully carried the radio box with us. One afternoon, we called in to alert
the station managers that we were delayed, so they wouldn’t worry. Turns out
that they were annoyed we used the radio even when it was an actual emergency.
Mat always answered, “Terribly sorry. Shan’t happen again.” Several times there
we ran out of gas, had engines not start, couldn’t reach Twin Cayes due to
strong winds, and lost numerous things off the side of the boat. Once, Candy
Feller was returning from a solo trip to Twin Cayes, hit rough water, and was
thrown from the boat. She did not have the kill switch on her wrist, so the
boat kept going until it ran out of gas. Fortunately, she was rescued.
Mangrove Research
Twin Cayes were originally preserved
for scientific research, but with time, local fishermen built small enclaves
with shacks, outhouses, and rickety docks on several areas. In general, our
field sites were kept safe from interference by others, including tourists, but
we were required to find remote areas of the islands to set up more permanent
experimental plots.
Feller and her colleagues had three
areas that they established in 1995 at The Dock, Boa Flats, and The Lair. At
each of these sites, a transect between mangrove trees growing at the fringe of
the island through a transition zone at higher tide level and ending in an
interior region was established. Trees at each zone (i.e, fringe, transition,
and interior) were marked with plastic flagging. The experimental design
included three treatments: control where nothing was done, nitrogen fertilization, and phosphorus
fertilization. Twice per year, Feller and colleagues traveled to Twin Cayes to
fertilize the trees, collected leaf samples for isotope analysis, and measured
the trees’ productivity and other biological parameters.
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| View from Carrie Bow Caye at sunrise |
My first collecting expedition included
Matthew Wooller, postdoctoral fellow at Geophysical Laboratory. Wooller joined
my lab group after completing his PhD at the University of Swansea in Wales.
Mat, a British citizen, has a devilish sense of humor. His language is peppered
with British slang and off-color phrases. We were joined by Myrna Jacobson and
her postdoc Barbara Smallwood. Myrna, now at the University of Southern
California, was a fountain of ideas, sometimes coming out in torrents of words
with a slightly quirky bent to them. Accustomed to field work, her expertise in
geochemistry provided a foil to our biogeochemistry. Babs Smallwood, also a
recent PhD from Great Britain, was a novice in the field.
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| Marilyn in the muck, circa 2003 |
My task in this project was to collect
the leaves, stems, and roots from different species of mangroves, decaying
mangrove biomass (detritus), surface mud (sediment), seagrasses, particulate
organic matter (small bits of decaying leaves, some bacteria, and
phytoplankton), and any animals we could catch. In the lab in Washington, we
were to measure the stable isotope composition of carbon and nitrogen of each
of these organic matter groups, as well as the amount of carbon and nitrogen in
each type of sample. The data was to be used in a theoretical model crafted by
Bob Ulanowicz and Ursula Scharler of the University of Maryland. The model was
designed using our data in order to connect the branches of possible food webs
and for determining nutrient flows in the fringe, transition, and dwarf
mangrove ecosystem zones. The model would also quantify how fertilization
affected the mangrove ecosytem. This seemed like a very straight-forward task.
Mangroves are trees using a type of carbon fixation in photosynthesis similar
to terrestrial trees. We expected them to show similar patterns in carbon
cycling as terrestrial plants. Twin Cayes were small islands. We figured there
would be very small variations in nitrogen cycling as well.
Wooller and
I planned to collect the above samples across the Cayes at locations laid out
on a grid--every 100 meters. We came armed with GPS coordinates, a couple older
GPS units, and a lot of sample bags and tubes. Jacobson, on the other hand,
shipped a portable gas chromatograph for measuring gases evolving from
sediments. The instrument was held up in customs so the USC team had to cool
their heels for several days. Also, the instrument required a clean source of
helium to operate; there was no helium of suitable purity in the entire country--they
were stuck. Because they lacked the right equipment for their work, Jacobson
and Smallwood joined our efforts. We became a team.
Adventures awaited us at nearly every
“station” that we occupied. The locations of Feller’s experimental transects
were readily accessible, once you climbed over some serious mangrove roots and
waded maybe 10 meters onshore. Our grid stations provided greater challenges.
GPS units in 1999 were not as accurate as they are today. Under the mangrove
canopies, we often lost signals and had to approximate our location. Climbing
over mangrove roots is a learned skill. Wearing rubber dive booties and loaded
down with sampling gear, we balanced carefully on flat sections of roots, while
keeping our eyes out for tree crabs and boa constrictors.
Dangers of fieldwork
We
encountered sharks, crocodiles, boa constrictors hanging from low branches,
stinging jellyfish, and deep holes in the mangrove peat that swallowed up our legs
and banged our shins. In a day, we could sample about 6-7 stations and returned
at night to Carrie Bow, filthy, sunburned, covered with mangrove muck and the
microbial soup that flourished in the interior ponds. After a shower, a couple
of beers, and dinner, we were refreshed and headed up to the lab to prepare
samples, write up our field notes, and analyze nutrients.
Most memorable were the encounters with
“dangerous” animals. Our first season of collecting samples at unknown grid
stations took us to an area of the eastern Twin Caye. To get to this site
required extensive bushwhacking over 1-meter high red mangrove prop roots
(i.e., portions of red mangrove roots grow above ground) for several hundred
meters. We ended up in a clearing with a shallow pond right around dusk.
Wooller typically led the group with PVC poles in hand and GPS extended in his
hand towards the pre-determined site.
When we hit the clearing, there was a
sudden thrashing in the water about 15 meters away followed by this sound,
“Urnk, Urrnnk, Arrrnnnk!” Mat yelled, “Crocs!” We all plowed our way back
across the pond as fast as anyone could with our feet in deep muck and hurled
ourselves back into the protection of prop roots. We listened carefully and
there it was again: the sound of a crocodile, probably protecting its young.
Needless to say, we did not return to this station.
Barbara (Babs) Smallwood was
particularly sensitive to the ubiquitous jellyfish that inhabited the open
interior ponds. One particular voyage into the very center of Hidden Lake, a
several hundred meter wide shallow (<2 meters) interior pond was especially
disconcerting for Babs. No boats could reach Hidden Lake. We tied up our boat
to mangrove roots at the entrance of a narrow, 2-meter wide channel, then leapt
into the water and climbed into small kayaks or onto large inflatable inner
tubes. Then we paddled about 200 meters with low hanging mangrove vegetation
above us towards the Lake. Once, a boa constrictor was seen draped over a
branch. Twice, I went to Hidden Lake towed via a rope tied around the waist of
a helpful colleague, Quinn Roberts (2002) and Dave Baker (2011) so that I could
collect sponges and mangrove leaves along the way. Laughter rang out in the
air. We were a noisy bunch.
Cassiopia is the species of
jellyfish that almost exclusively inhabits these waters. On sunny days they
float with their tentacles sticking up to allow the symbiotic algae in their
tissues to catch sunlight to fix carbon in photosynthesis. During rainy or
cloudy weather, they turned bell side up and rested on the sediment surface.
The afternoon we came with Babs into Hidden Lake was sunny and beautiful.
Unfortunately the jellyfish were floating in force. It did not take long for
Babs to notice that what was a mild sting for the rest of us caused a painful
rash for her. She had to jump from mangrove root to mangrove stump to avoid the
stings, screaming all along the way.
Nitrogen isotope “signals” in mangrove tissues
When we analyzed our first set of
samples from the grids stations, we were surprised at the variations we found
in the types and concentrations of nitrogen isotopes (we’ll call these
“signals”) in the mangrove leaves. Fringing mangroves, primarily the red
mangrove had nitrogen signals nearly similar to the nitrogen in air (Fogel et
al., 2008). Transition red mangrove leaves had slightly different signals.
Dwarf mangroves, gnarled decade old trees, had very unusual signals, in fact
never measured before in any plants that we knew of. If only I had a portable
isotope ratio mass spectrometer (the instrument we use to make stable isotope
measurements in our labs) in Belize, we would have analyzed every mangrove tree
on Twin Cayes. About one-third of
our samples were from tall, fringing
trees, another third from medium height mangroves in transition zones, and the
remaining third were dwarfed trees, no higher than about 1-1.5 meters tall,
growing in the island’s interior.
Because
this was a biocomplexity project, we thought about this data in a slightly
different way than we normally do when analyzing the isotope signals in plants.
In biocomplexity theory, an “emergent property” is an observation that is
nonlinear, that may explain organizational properties of a system. The nitrogen
isotope signal of mangrove leaves was our emergent property. As far as we could
tell, these were some of the most unusual nitrogen isotope signals measured in
naturally-growing plants. At this point,
there was no easy explanation for why we discovered the variation from a single
species on two very small islands. The hunt for an explanation ensued and
consumed Wooller, Jacobson, John Cheeseman (University of Illinois), and me
with respect to this study for the next four years of the project. Fringing
mangroves grow at the edges of the ecosystem, whereas the dwarf mangroves with
their sculpted morphology were excellent examples of self organization.
Feller, Lovelock, and McKee had
been collecting mangrove leaf samples from their prior fertilization areas.
When we saw their results, the nitrogen isotope signals of dwarf trees were
strongly influenced by phosphorus fertilization and the control and nitrogen
fertilized trees looked like the dwarf trees we’d analyzed from other areas. We
started collecting leaves from all of the experimental trees so that we could
compare recent data with samples collected several years prior. Our results for
the nitrogen-fertilized trees were slightly different than McKee et al. (2002),
but the trends were identical. Fertilizing a mangrove tree with phosphorus
changed the way the tree metabolized nitrogen.
We did not know why.
Hints from Phosphorus
To figure out the relationship between
phosphorus and nitrogen, we started a phosphorus fertilization experiment with
dwarf trees that we guessed had unusual nitrogen signals we’d measured in
similar trees, then collected newly grown leaves periodically over the next two
years. Within 2-3 months, we recorded changes in leaf nitrogen signals
documenting the timing in which the plant used phosphorus to change nitrogen
metabolism. We found interior mangrove trees distributed around the islands
that had been fertilized with phosphorus almost a decade ago, without
subsequent phosphorus additions. These plants was similar in terms of their
isotope signals to recently fertilized trees in the experimental plots. Our
conclusion was that once a tree was provided a slug of phosphorus, a limiting
nutrient on these islands, it held onto it for a very long period of time.
Phosphorus is important for many things
in a plant, in particular for making ATP, an organism’s energy storage
compounds. The enzyme (i.e., a protein that catalyzes biochemical reactions)
that transports nitrogen into a plant’s roots requires several molecules of
ATP, and therefore phosphorus, for each nitrate molecule transported. We
concluded that the phosphorus effect related to more efficient uptake of
nitrogen. We expanded our analytical tools and collected and measured the
ammonium in surface sediments, water, and air. In sediments and water samples,
the nitrogen isotope “signals” were not remarkable. In microbial mats, thick
strata of photosynthetic bacteria in shallow ponds, the nitrogen signals showed
us that the microbes were actively assimilating atmospheric nitrogen.
Ammonia in the air--the smoking gun?
How and why we found unusual patterns
in dwarf mangrove tissues continued to challenge us. Later we read a
publication by scientists studying the effects of a bird rookery on a frigid
island in the South Atlantic Ocean (Erskine et al. 1998). They found similar
unusual nitrogen isotope signals in plants collected downwind of the bird
rookery and postulated that the isotope signals in ammonia volatilized
from bird guano were incorporated into plant tissues. Wooller and I found a
nifty way to measure ammonia concentrations in the air. We purchased disposable
“badges” that could be tied to tree branches to absorb ammonia.
After a couple of hours, a
color-sensitive dye embedded in the badges turned dark purple and eventually
black if ammonia concentrations were high enough. Our first deployment of these
detectors took place over a 50 centimeter thick microbial mat, where in midday,
oxygen bubbled vigorously from the surface. After one to two hours, we were
able to see substantial ammonia emissions! We did a little dance in the pond
and whooped like Texans. After this first deployment, we measured ammonia
emissions in several locations on the islands. Emission rates were highest over
microbial mats and nitrogen fertilized experimental areas. Our next test was to
capture the ammonia, and return the sample to the laboratory where we could
measure its nitrogen isotope signal.
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| Blonde Pond where we documented ammonia signals |
As we worked through the puzzle of
interpreting the complex isotope signal data, our group settled in on a
strategy of nightly meetings in the Carrie Bow library. Armed with large pieces
of fresh paper, sharpies, and a bottle of One Barrel rum, we argued and laughed
our way through a myriad of ideas and hypotheses as to why we found such a
range in the nitrogen isotopes of mangrove leaves. Wooller and I were the ringleaders.
Myrna Jacobson, Babs Smallwood, Quinn Roberts, John Cheeseman, and Isabel Romero
joined in. I saved one of these pieces of paper from a particularly fruitful
conversation. Our original mission was to collect specimens of the major
plants, microbes, and animals of Twin Cayes and measure their isotopic and
elemental compositions. We had yet to sample the lichens. Wooller dramatically
penned in “Lichens--Not important” on the corner of the page. As you will see,
the lichens provided the smoking gun to understanding nitrogen patterns in
leaves.
There are large differences in the nitrogen
isotope signals between the two chemical phases of ammonia (the gas you smell
near animal feed lots) and the dissolved ammonium (the solid chemical in
fertilizer). The nitrogen isotope signals of ammonia in the air in Twin Cayes
was very similar to what we measured in the dwarf mangrove leaves. Our final
experiments showed that mangrove leaves can, indeed, take up gaseous ammonia
when their leaves take up carbon dioxide for photosynthesis. Last, we found the
unusual nitrogen isotope “signals” in lichens growing on the bark of mangroves
throughout the islands. Lichens, microbial symbioses with no roots, take up any
available nitrogen from the air. The nitrogen isotope signals of lichens had
the same signals as the mangrove leaves collected in the different zones.
Studying food webs
How
did the nitrogen cycle influence the food webs? Capturing mangrove tree crabs
can be a very real active sport. These small (4-10 centimeter) crabs perch on
mangrove branches, scuttering up and down as they feed. We tried shaking the
trees and dislodging them. If they did fall, they quickly disappeared in the
complex root system of the tree. A combination of netting, shaking, and quick
footwork was needed to get an adequate sample. Snails were another story: you
could easily pluck them off the mud or the trees, but snail hunting was not
nearly as fun as crab hunting. As Wooller remarked, “It’s not exactly rhino
hunting.” After collecting a full complement of animals on the islands, we
found that the animals living amidst the dwarf mangroves had unusual nitrogen
isotope “signals,” showing the importance of mangroves to food webs in this
ecosystem.
One of our “fishing” trips at an
interior pond led to a combination of serious sampling and tremendous fun.
Although we could catch small fish with our nets, the large mangrove snappers
were able to evade them when they saw us coming. Mat, Quinn Roberts and I
desperately wanted to sample some of the larger fish because it was important
to learn whether they depended at all on mangrove biomass for their diet. One
afternoon, we set up our net at the end of the pond where a school of large
snappers were seen daily. Then, smeared with mangrove peat and armed with
smaller nets, we hooped and hollered our way tumbling across the swamp forcing
the fish into our nets. Two people were stationed at either end of the net
ready to close it once our prey was inside. As we dragged the net onshore, we
looked. “Hardly enough for dinner,” I said disappointed. Perhaps not a sampling
success, but a hell of a good time.
Extreme Dining
Contrary to the image of the
stereotypical scientist, most of us like to have just as much fun as anyone. On
Carrie Bow we started a tradition called "Extreme Dining.” Mat Wooller was
a leader in many ways on these Belize trips: boat tender, sample organizer,
out-of-the-box thinker, and prankster. Out of many memorable escapades was his
instigation of the Extreme Dining Society. He’d organized one or two of these
up in Alaska. Diners were required to don formal attire (e.g., tuxedos for the men and evening gowns for the
women). In Alaska, the diners rafted down a chilly Arctic river while consuming
a four-course meal.
In Belize, we scouted out an appropriate
location--a small 5 meter coral island barely above sea level. Wooller brought
china, cutlery, wine glasses, and an ancient gramophone down from Alaska with
him. On the evening of the formal dinner, Martha loaded up coolers with hot
foods and cold foods. We assembled a potted plant, boards to construct a table,
chairs, table clothes, and the Belizian flag into two boats. The menfolk waded
ashore first and set up the dining area. The womenfolk remained in the boats
and put on their dresses, while the men turned their heads to the other
direction. Finally when all was ready, we women were carried ashore so as not
to sully our formal clothes.
As the gramophone played old timey
music, we lifted our glasses to a toast. Having way more fun than a scientist
is supposed to have, our research cares slipped away and we discussed other
topics. At the end of the meal, dancing began with slow waltzes and some jitter
bugging, getting our feet wet as we danced. A couple of other boats saw us,
came closer to see if we were in distress then veered away wondering what the
heck was going on. Before sunset we packed everything up, leaving no trace, and
returned to Carrie Bow.
Examining the Past Belize’s mangrove islands
One of my goals as a biogeochemist is
to learn about present ecosystems so that I can understand how these ecosystems
functioned in the past. In particular, scientists are interested in knowing how
the environment at any location might have changed over geologic time. We refer
to this line of work as paleoenvironmental reconstruction--figuring out
what climate and biological parameters were important. In order to accomplish
this work, we needed to collect cores of the sediments meters in length that
had been laid down on the mangrove islands over the past 10,000 years.
Sediments on these islands are composed of about 20% mineral sediment--usually
carbonate from weathered corals--and 80% peat--organic remains of mangrove
tissues and microbial muck.
Starting with a trip to Florida’s
mangrove swamps near the Smithsonian’s Pierce Laboratory, Wooller began his
quest to sample mangrove peat. He sharpened the edges of PVC pipes or found
old, rusted iron pipes at the back of the station, with which he tried mostly
unsuccessfully to get decent cores. At the end of every attempt he always
noted, “What we need is a Russian peat corer!” His attempts extended to Twin
Cayes, and again were stymied by the lack of a Russian peat corer. Even the
station managers, hearing him over dinner, knew about the Russian peat corer. Finally,
in 2003, I purchased one and we brought it down to Belize. A full Russian peat
corer kit comes with a series of 0.5 meter extension rods, one “business end,”
a handle, and an attachment to engage and disengage the rods.
The business end had a dense 10 centimeter
pointed metal tip that sliced smoothly through the peat. The barrel was a half
cylinder that was covered by a sharp blade running its entire length. When the
corer was pushed into the peat, the handle turned the corer 180°allowing the
blade to cut through the peat. We were able to sample 10-meter cores in this
manner, lifting 0.5 sections up each time. Although the work was physically
demanding, the results from coring were first rate. Usually samples were
shipped back to Alaska for sampling leaf fragments and pollen. We determined
that small leaf fragments buried in surface sediments had nitrogen isotope
signals similar to the isotope signals of the type of trees growing just above.
Fragments with unusual nitrogen signals corresponded to dwarf trees, whereas
leaf bits with more typical nitrogen signals denoted fringe trees.
Using the isotope signals of leaf
fragments plucked from peat cores, we were able to determine whether mangroves
came from dwarf (shallow water), transition (higher land), or fringing
(coastal) mangroves. Coupled with accurate dates from the leaf fragments and
pollen records, Wooller and team assembled a climate and environmental record
of the Holocene in tropical Belize. They could tell when sea level rose quickly
versus when it slowed.
Coming off the Island
Returning to the States after a couple
of weeks on the cayes required a lot of planning. On one of our trips returning
from Dangriga, we took a short flight on Tropic Air airlines back to Belize
City. The pilots were on the young side, and it was unclear whether these small
planes were flying by sight or guided by navigational instruments. Midway,
while going in and out of clouds, the plane swerved suddenly to the right. We
looked out our window to see another similar aircraft about 50 meters away from
us making a similar evasive move.
After that “adventure” we decided to go
by car or truck. Local Dangriga guys had a larger truck to transport tourists’
gear to Belize City. Once, they took Mat Wooller early in the morning up to the
Belize airport, while the rest of flew. Apparently, as soon as they were
underway, a bottle of local moonshine was cracked open and passed around. Mat,
not wanting to appear snobbish, took a sip or two, later reporting that this
was the foulest drink he’d ever consumed. Part of the highway had been washed
out during a storm. While driving on this rough section of road, the truck--now
traveling at a high rate of speed--hit a bump, and half our gear and samples
flew out of the truck onto the road. By this time, the driver was too impaired
to make sure everything was loaded back in. Mat saw that everything made it
back in the truck, fortunately. He never wanted to get stuck with that chore
again.
When we arrived at Miami International
Airport, we reported to Customs officials and the USDA to declare our
specimens. Fortunately, because they were all marine plants and sediments--not
crop plants or soils--the US Dept. of Agriculture was not concerned. Only once
did Customs officials question us seriously. We had to convince them that our
computers, small instruments, and chemicals were purchased in the United
States, rather than Belize. Being an older woman, I used my persuasive skills
to get Customs folks to back off and let us into the country.
Coral Capers
In 2009, after accepting a position at
the National Science Foundation, I wrangled a Carnegie postdoctoral fellowship
for David Baker. Baker, a grad student from Cornell University, visited the
Geophysical Lab a couple of times asking for a postdoc so he could continue his
work on isotopes in corals. Finally, I recognized that here was a determined,
smart young man who had a vision of how he wanted his career to unfold. He
managed to get a matching fellowship at the Smithsonian, which opened up the
possibility of going to Twin and Carrie Bow Cayes again. At the same time,
Derek Smith, a former student from James Scott’s lab at Dartmouth, was working
on his PhD on purple sulfur bacteria. We developed close ties with each other,
including afternoon trips to the Lab’s attic where a small gym allowed us to
benchpress weights and have some laughs.
In 2011, we planned our trip to Carrie
Bow to include mainly working on coral biogeochemistry, but also some time for
me to show them my mangrove field area and to introduce Derek to the real world
of microbial muck. Our trip down was smooth. Dave and Chris were certified
scientific divers working on examining corals and their symbionts to determine
when bleaching events occurred. Their research determines the quantitative role
that the symbiotic dinoflagellate Symbiodinium has on whether corals
exist as autotrophs or heterotrophs.
Every few days, we would go offshore or
near another coral island, so they could collect samples for later experiments
and isotope measurements. Derek and I were responsible for staying in the boat
and figuring out when and where the divers would surface. One particularly
choppy day just off shore Carrie Bow, we waited anxiously for the dive
“balloon” to surface so that we knew where they were. That particular day,
Chris was to hold on to the balloon, but he forgot to attach it to his wrist. I
was concerned that our propellers would hit them as they surfaced. Derek was
concerned that as we drifted, we’d end up on the reef. We drifted about 100 meters from the divers,
but learned some important boat safety and gained some confidence. Baker and
Freeman were pretty surprised when they surfaced and saw the boat quite a
distance from them.
Baker was interested in studying the effects
of nutrient additions to coral’s symbionts. His field areas included
Australia’s Great Barrier Reef, Panama, Florida, Mexico, and now Belize. Chris
Freeman, a grad student at the University of Alabama, studied the microbial
aspects of coral symbiosis. With their coral collections, Dave and Chris set up
a series of experiments with small 5 centimeter pieces of a couple of coral
species that were incubated in temperature controlled pools on Carrie Bow. Each
morning and evening they measured dissolved oxygen levels in their experimental
bottles to determine respiration and photosynthetic rates.
At night we also extracted chlorophyll
from corals and measured nutrients. At the end of a long day, outside under the
stars, we had a glass of One Barrel rum. One evening I introduced the gang to
Panty Rippers, a favorite of Mat Wooller: two parts coconut rum and one part
fruit juice of your choice. Shake with ice and serve. Although this drink was much
more palatable to me, the others were rather foggy the next day. Henceforth,
they stuck to plain rum.
Baker and Freeman also targeted rouge
lionfish, an invasive species that escaped from aquaria over the past 25 years.
Lionfish are native to the Indo-China region where they are top carnivores. In
the Caribbean, they are decimating native fish populations, altering the
trophic structure of coral reefs. As Dave and Chris collected their coral
samples, they speared lionfish if they could, collecting over 100 fish.
Lionfish have very poisonous spines, which need to be carefully removed before
preparing them to eat. The daily chore of Baker and Freeman was to prune the
spines before handing them to chef Martha.
I was treated to the thrill of seeing
“my” mangrove trees again. I took the group to all of the major sites I’d
published on. With Derek, we waded through an interior pond with 1.5 meters of
microbial soup, a thick gelatinous mass of anaerobic microorganisms, many of
which were purple sulfur bacteria. One day we traveled to one of the other
coral islands so they could dive to deeper waters looking for corals with
unusual types of Symbiodinium. The boat was anchored near a steep
dropoff going from a shallow 2-3 meters to about 25 meters depth. Dave and
Chris donned their scuba gear, dropped off the side of the boat, checked the
anchor then descended.
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| Microbial mats mixed with mangroves |
Derek Smith and I were instructed to
turn the engine on and rev it a few times if we wanted them to return.
Meanwhile, Derek and I donned snorkeling gear and took off to see the shallow
underwater sights. As an experienced tropical researcher, I was 150 meters or
so from the boat and surfaced periodically to check to see where I was in
relation to the boat. I saw Derek back on board and wondered why he’d returned
so quickly. The boat seemed about 200 meters away, so I started to head back.
It took me longer than I thought to return, because unbeknownst to me the boat
was adrift. The anchor had come off the bottom and was now dangling in deep
water. We were headed straight to Honduras! After I boarded the boat, we started
the engine, revved it up, and waited. We tried for 30 minutes to alert our
divers to no avail. We continued to drift, then circled around far from our
original mooring. Derek saved the day by realizing the boat was adrift and
returning to it while it was still within reach. Without his quick thinking,
the four of us might have been stuck there with no way home.
Thorny Collaborations
This research started innocently and optimistically, but soon moved into a
complex realm that challenged in the field, in interpretation, and in the
laboratory. While I developed a collaborative team with many people for the
Biocomplexity project, I also had one of the more contentious collaborations
with Feller, McKee, and Lovelock. Early on in the project, when we told Feller
and Lovelock our surprising results about the isotope values from grid samples,
they were not impressed. In fact, Candy remarked, “That’s nothing. We’ve seen
that before.” Postdocs Wooller and Smallwood felt deflated. And I was
surprised at the reception they’d received. I was under the impression that
we’d found something exciting. This was the start of a period of distrust on
both sides.
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| Myrna Jacobsen Myers, a brilliant biogeochemist, circa 2001 |
As we grew more experienced with mangrove ecosystems, our group grew
concerned that the fertilization experiments were contaminating the rest of
Twin Cayes. With time and careful sampling, we learned that the fertilization
experiments affected a much greater portion of Twin Cayes than just a few
trees---probably at least 100 meters from the experimental plots depending on
the location. With time, we learned that the fertilization experiments were not
causing the unusual nitrogen signals we measured in remote places. I never
recovered good communication or collaboration with half the biocomplexity team
after the initial negative encounter that Mat and Barbara had. When the project
officially ended, the collaboration was over---one of the most difficult in my
career.
Conversely, the work I did with Wooller, Quinn Roberts, and Val Brenneis (a
high school teacher who worked part time in the lab) from Carnegie, with Myrna
Jacobson, Barbara Smallwood, and Isabel Romero from USC, and John Cheeseman
from Illinois, was some of my most fun and productive research. When Mat moved
to Alaska, he brought down some of his students. We had uproarious times in the
field.
I loved starting a new line of research into a field I knew very little about
before diving in with limited knowledge. Invariably, the quest for knowledge
became a fascinating scientific journey, made much more fun and interesting by working
with early career scientists and new collaborators. Together we could see
what effects very small additions of nutrients from fertilizers can have on
mangrove ecosystems, which had the potential to change food webs and perhaps
how these ecosystems will adapt to higher sea levels and climate changes.
Working with like-minded people who foster creativity and curiosity is
essential for sustaining a long scientific career. The study of mangrove
ecology and paleoecology turned into a 10-year course of study. I still have
volumes of unpublished data that need to be turned into scientific manuscripts,
a chore that I hope to tackle once I’m officially retired.
