|John Cheeseman, Mat Wooller, Marilyn Twin Cayes
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.
My first collecting expedition included Matthew Wooller, postdoctoral fellow at Geophysical Laboratory. Wooller joined my lab group after completing his Ph.D. 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 Ph.D. from Great Britain, was a novice in the field.
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 Univ. 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 quantity 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 heals 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 of 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.