I spent last week in St. John, US Virgin Islands, on
what my friend Lauren called a “
Mama Science Vacation.” That was a great term
for it – a vacation from our overwhelming house renovations, and from Southern
California traffic, and spending 90% of my brain capacity calculating when
Ryder might next need to eat or sleep or use the toilet, and feeling guilty I
didn’t have enough enriching activities planned for him.
This week gave me a chance to reconnect with my adult self, think
deeply about science, and see wild coral reefs again in person for the first
time in more than a year. It’s amazing how enriching it is to be physically
immersed in the environment I’ve been studying mostly remotely for the past
decade. Today I saw the most extensive stand of Acropora cervicornis, the
endangered “Staghorn coral,” that I have ever witnessed. These corals used to
dominate shallow Caribbean reefs, along with their relatives Acropora
palmata, or “Elkhorn coral.” But both
species of Acropora all but
totally died off decades ago from a disease that swept through the Caribbean.
Today, we saw not only thriving large colonies of adult Acroporids but also lots of juveniles – and interestingly these
were often growing on dead colonies of the same species. This recalled a study I read (which of course I can't find, now) that found
coral larvae of particular species preferentially settle on dead colonies of
their own kind – perhaps because of some lingering chemical cues those
skeletons exude?
This doesn’t have any particular bearing that I can think of
right now towards my own work, but I find it really fascinating.
So, what have we been doing here in St. John? The short of
it is that I’m starting a new project in collaboration with colleagues at the
University of San Diego, where I’m aiming to tie records of past water quality
based on coral skeletal chemistry to data they have been collecting using
sediment traps and other instruments. You might remember that corals build
their skeletons from chemicals in seawater, and slowly grow larger over
time—thus, their skeletons record changes in water quality. Annual changes in
skeletal density also provide a lovely chronometer for these chemical records.
If we can tie these recent records together, I can extend records of runoff
farther into the past (perhaps a century or more) using core samples from large
old corals. To see if this idea will work, the first step is to collect short
cores from living corals to tie to the sedimentology datasets. Hence, this
trip.
Coral cores are collected using an underwater drill by
divers using SCUBA equipment. Scientists either use a hydraulic drill driven by
a hydraulic engine in a boat at the surface, and long hoses that deliver the
hydraulic fluid down to the drill. These rigs tend to be giant, heavy, and
awkward. I helped collect cores from fossil corals on land using a hydraulic
drilling system at Tabuaeran Atoll way back in the dark ages of 2005, and
quickly learned that unless I was going to bring along a bevy of much stronger
people as field assistants, this wasn’t something little me could handle. I
opted for a pneumatic drill, driven by compressed air – these drills are much
smaller though less powerful (so it takes longer to collect an equivalent core
length).
The cool thing about pneumatic drills is that they can be
driven by an on-ship, gasoline-powered air compressor (ideally), but if this is
unfeasible, they can also be driven by SCUBA tanks. Theoretically this
shouldn’t be a big problem—if you have gotten to a place set up for SCUBA, there
should also be a supply of tanks available to use to drive the drill. Shipping
around 200-lb air compressors is, on the other hand, rather difficult and
expensive. So for this trip, I opted for the SCUBA tank option.
The trip was thrown together somewhat last-minute, though it
had been in the wings of planning for more than a year. Suddenly, various
logistical issues came together and made it necessary to jump and get the trip
organized. I was able to gather two worthy field assistants – my friend Lauren
Freeman who I knew at Scripps, and a grad student at USD named Whitney who had
spent at least part of the past 7 years at the Virgin Islands Environmental
Resource Station (VIERS), where we were headed.
We converged in St. Thomas, where we rented much-too-large
of a car and drove across the island, stopped to stock up on groceries and then
get WD40 at Home Depot (how civilized), took the car ferry to St. John, and
again drove across that island to VIERS. There, we settled into a 2-bedroom
ensuite cabin with open, screened sides, a small kitchen, and an open air
shower out back. Multiple cabins sat in the jungle encircling a large open area
with picnic tables and a fire pit, all connected by elevated boardwalks ready
for the rainy season. We slept to the sounds of tree frogs and insects, and the
intermittent heart-stopping crash of
mangos falling on the corrugated metal roof.
The first day consisted of getting the ladies oriented to
the coral drilling gear, getting ourselves oriented to the workings of VIERS,
and identifying sites to target via snorkel. We were able to swim around most
of Great and also Little Lameshur bays, looking for the right sized colonies of
the right coral species at the right depth. After discussions with the folks
who oversee permitting for the Virgin Islands National Park, and following
preliminary scouting Whitney had completed last year, I had decided to target a
coral called Siderastrea siderea, or
“Massive Starlet coral,” partly because it is more abundant than the coral I’ve
worked with previously, Orbicella (previously
Montastraea) faveolata, and partly because it seems a bit hardier than Orbicella. Coral reefs are in bad shape around the world these
days, but particularly in the Caribbean. I believe that some collection is Ok for
scientific purposes that are justified – but I still would rather minimize my
small collection footprint. I aimed to do this by taking samples from corals
that have shown evidence they may persist into the future amongst the onslaught
of human impacts (sediment and nutrient runoff, overfishing, and climate change
are the biggest culprits).
The next day, we got to work. It was—how shall I put
this—basically complete underwater chaos. The tanks were lighter underwater
than we anticipated and kept trying to escape off into the blue, the 50 foot
air hose turned into a bird’s nest and got tangled with the tanks (which we’d
daisy-chained together with a rope), nobody had enough dive weights on for this
kind of work and couldn’t easily stay put at the target coral, the surge didn’t
help things, and we hadn’t yet worked out how to communicate efficiently
underwater. Thus we wasted huge chunks of time writing long epics on our dive
slates and getting confused by one another. The worst part was that the drill
ate up much more air than we anticipated – each tank was only lasting about 6
minutes. Using 6 SCUBA tanks to drive the drill, we collected a measly 2.5cm
diameter, 4cm long core over the course of 2 dives, which took in total about
4.5 hours (including loading and unloading the boat at the dock, motoring to
the site, mooring, getting geared up, etc.). It was not looking good for my
goal of collecting ten 10cm-long cores in the 3 remaining diving days we had
that week.
That evening my friend Rich—who had done some
dive-tank-driven coral coring the previous year with my gear—gave some
suggestions over email for improvement. The major idea was to float the tanks
at the surface: because the air metered out of the tanks wouldn’t be under
additional pressure from the water, the same volume of air would be delivered
at a slower pace, and each tank should drive the drill for a longer time. We
also decided to make a bridle with dive weights to hang over the drill; we were
using a smaller, lighter core barrel than I had previously used, and we thought
that the weights might help the coring move along at a more reasonable pace.
The skeleton of Siderastrea was much
more dense than Orbicella, so I
had expected things to go slowly – but not ten times more slowly, as they had
our first day.
Floating the tanks at the surface using a lift bag
worked—but it was also chaotic. One person had to corral the tanks together
(they were daisy-chained with rope but the currents and waves made them each
constantly try to escape) and change the regulator from one tank to the next as
they emptied. This turned out to be rather exhausting and caused much
skull-banging and seasickness for the tank exchanger, but we were ecstatic to
see that each tank now lasted about 12 minutes. With the lead-weight bridle and
the tank flotilla, we were able to collect 2 whole cores in the time we’d taken
the previous day to collect half a core. Things were looking up.
Each dive, we improved. We next commandeered a small kayak
to hold all of the drilling tanks, which made things much easier (except when
it capsized close to the rocks). Importantly, our underwater communication
improved, and Lauren and Whitney quickly figured out what tasks needed to be
done and developed their own drilling techniques to combat the surge while
avoiding damage to other parts of the reef.
We finished collecting all ten cores with a day to spare, so
were able to go out with a local retiree who knows practically every inch of
Coral Bay – the adjacent developed watershed in which I plan to collect future
cores to contrast with the runoff history in the undeveloped watersheds of the
National Park. He took us snorkeling to identify future collection sites for
another trip, plus to see the secret spot where we were staggered by prolific thickets
of Acropora corals.
This fall comes the next fun part: geochemical analysis of
these precious and hard-won samples at my new lab at UMass Boston. I can’t
wait.
