Hunter, J. 2007. 20th Annual Keck Symposium; http://keck.wooster.edu/publications
evolutionary growth stage (Tappan, 1980). Most diatom taxonomy is based on the opaline skeleton or frustule of the diatom (Stevenson and Pan, 1999). The diatom cell wall is composed of approximately 95% opaline silica (Armstrong and Brasier, 2005). Because both forms of diatoms are autotrophic, they are typically limited to the photic zone of the ocean (<200 m) during the duration of their lives. The photosynthetic pigments in marine diatoms include chlorophyll a and c as well as accessory carotenes and xanthophylls. Light availability can have a strong impact on both the growth and seasonal fluxes of the diatoms. Diatoms bloom primarily in the spring and late summer (Armstrong and Brasier, 2005), when light availability, temperature (and therefore salinity) increase.
available amount of phosphorus does not exceed 6x10-14 grams/cell for certain genera.
Most marine diatoms tolerate a wide range of temperatures (Tappan, 1980), typically ranging from 1.9º C to 30.5º C. The temperatures of the Vieques bays in June, when data were collected, ranged from 29º C to 32º C. Accommodations for changes in temperature can be reflected in alterations of frustule ornamentation, such as thinner walls and elongated spines (Tappan, 1980). Marine diatoms range from marine to brackish water, and the greatest diversity of marine diatoms exists at a neutral pH. The form of silica in the diatoms (orthosilicic acid (Si(OH)4)), is more soluble in alkaline conditions. The nutrients available in the marine environment also greatly affect the concentration and diversity of diatoms present. Whereas some diatoms prefer high nitrogen concentrations, others prefer low nitrogen-to-phosphorus ratios (Tappan, 1980). Diatoms fail to reproduce or divide if the
In areas where nutrients are in part derived from the land, diatom assemblage composition tends to change most rapidly. Some environments are more apt to sustain high levels and varieties of diatoms due to their high silica, phosphate, nitrate, and iron content (Burckle, 1971). The tropical climate of Vieques provides a great range of diversity as well as land-derived nutrients to support a rich diversity of diatoms (Figure 1).
Field Methods Coring sites were chosen based on depth, location in the bays, and facility of access. Eleven cores were extruded from Puerto