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Hunter, J. 2007. 20th Annual Keck Symposium; http://keck.wooster.edu/publications - page 3 / 6





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Hunter, J. 2007. 20th Annual Keck Symposium; http://keck.wooster.edu/publications

Mosquito, 6 from Puerto Ferro, and 10 from Bahía Tapón. Depths ranged from approximately 0-4 meters. Coring tubes approximately 1 meter long were transported to the coring sites and cores were taken with a gravity-percussion coring device in polycarbonate tubes. Cores were extruded, measured, documented, and described using Munsell’s Color Charts and a USGS Grain Size chart. The six cores selected for this study were chosen based on depth, diversity of locations in the bays, species abundance, and variety of diatoms in each core after analysis with the petrographic microscope.



The prevailing diatom in all three bays was Gyrosigma Hassal. Gyrosigma was found in Puerto Mosquito cores D1, D2, 6, 8, 9, 10, and 11, in amounts ranging from 1 to 15 over the course of a ten-minute count. Displayed (Figure 2) are quantities of diatom species at similar depths in cores PM 6, PMD1, PM8,

PM9, PM10, BT9, and PFDIC.


approximately 100 micrometers in length (Figure 3), Amphipleura Kutzing, and

Stephanodiscus Ehrenberg (Figure 4) dominate

Laboratory Methods

Samples were cleaned of mud and sediment particles with a method adapted by Battarbee et al. (1984), in which 50 mL of a 10% HCl solution was added to the sample and stirred on a 115-volt Magnestir for fifteen minutes. Six mL of a 30% H2O2 solution were then added to 1 gram of sample before placing the sample into a 40°C water bath. Samples remained in the water bath for 20 minutes and then cooled. A drop of NH3 was added with a small pipette to deflocculate the leftover clay particles and the diatoms. The sample was then centrifuged for 5 minutes at 4,000 revolutions per minute in a 20°C centrifuge and decanted. Two more drops of NH3 were added before decanting the sample again, leaving primarily diatoms in the bottom of the centrifuge tube. Permanent slides were then mounted using Norland Optical Cement and a short-wavelength UV light for 30 minutes. The slides were analyzed under a petrographic microscope and examined for presence, abundance, and specific genera of diatoms. Slides were scrutinized for ten minutes each so as to remove any time duration biases from the process of their examination. The slides from similar depths with an abundance of diatoms were selected to be observed with the Scanning Electron Microscope. One drop of sample was put on a cover slip, dried, and gold-coated before being placed into the Scanning Electron

most slides from Puerto Mosquito. Although pennate diatoms dominate the observed specimens, both pennate and centric diatoms were found in the Puerto Mosquito and Bahía Tapón samples, as can be seen by the presence of both Stephanodiscus (Figure 4) and Campylodiscus Ehrenberg, both centric diatoms. The most diverse cores were PM6 (0-1) and PM6 (4-5), with genera of both centric and pennate diatoms, such as Fallacia Stickle and Mann, Stephanodiscus, Synedra Ehrenberg, and Frustulia Rabenhorst. Bahía












a dominance of Campylodiscus, Amphipleura, Gyrosigma, Fallacia, and Pleurosigma.


The presence of both centric and pennate diatoms in the samples from the three bays of Vieques, Puerto Rico, can be misleading. As cell sizes of marine diatoms can range over 4 orders of magnitude and diatoms can either be sessile or vagile, it must be assumed that both eolian as well as fluvial forces could have had an impact on the deposition of the diatoms. The small size of the diatoms can be problematic as their light weight may allow for air transport. Also, as planktonic diatoms are constructed to remain in suspension, they can


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