Searching in the Sand

Christine Hart, Clemson University

Interim report picture

In “Exploring the Secret Garden” I discussed our studies of the benthic microalgae (BMA) that inhabit the intertidal regions of beaches. The goal of our study is to identify the mechanisms involved in the visually noticeable increase of BMA during low tide. This mechanism will be linked to changes in the type of BMA dominating the sand flat. To accomplish these goals our study will incorporate field work, molecular techniques, and DNA analysis.

During field work we will collect and manipulate sediment to distinguish between an increase in BMA by either vertical migration or growth mechanisms. The sediment will be collected on a sand flat in Grice Cove (Figure 1). Sand will be sampled using corers, which pick up a layer of sand without disturbing the vertical organization. The collected sand will be split between measurements of biomass, or BMA density, and DNA analysis. Biomass is measured by finding the concentration of chlorophyll a in the sediment. BMA synthesize chlorophyll a; therefore, the concentration of chlorophyll a is proportional to the density of BMA.

Sampling Site.png

Figure 1. Aerial view of Grice Cove sampling site with the approximate location of the 50 m sand flat transect site. Sampling sand flat is open to the Charleston Harbor. Source: “Grice Cove” 3244’58”N 7953’45”W. Google Earth. March 20, 2017. June 20, 2017.

The methods for field work are represented in Figure 2. There are two vertical migration treatments: filter and mesh. Filter treatments prevent vertical migration between cored and surrounding sediment. Mesh treatments permit vertical migration. If migration is important to the biomass increase, biomass measurements in mesh will be greater than in filter treatments. Filter and mesh treatments will also be exposed to shade and light conditions to interpret the impact of growth on biomass. Sunlight provides the energy necessary for BMA growth. Without sunlight growth will be limited. If growth is the mechanism of biomass increase, the shaded samples will have a lower biomass than the light exposed samples.

Field Work Diagram.png

Figure 2. Field work methods visualization. Locations of replicates along the 50 m transect are chosen using a random number generator and marked with flags. Random coordinates and a quadrat of 50 cm by 50 cm are used to determine where sediment will be sampled and treatments will be placed. Three controls (T0, TM, and TF) are taken at time intervals 1.5 hours apart after sand exposure. During TM and TF time points, samples are taken from the 4 treatments shown above: filter, mesh, filter + shade, and mesh + shade. Filter treatments prevent vertical migration, while mesh treatments permit vertical migration. Shaded and non-shaded filter and mesh treatments will be important in determining the role of sun exposure in biomass increase.

To link the mechanism of biomass increase to the BMA composition, we will use molecular techniques and analyze the DNA found in the sediment. DNA will be extracted from the sediment and amplified using a polymerase chain reaction (PCR). The DNA will be sequenced using High Throughput Ion Torrent technology. The results from sequencing will identify the BMA present at each time point and within each treatment. This information will link the mechanism of biomass increase to the changes in BMA composition. Our understanding of BMA dynamics will establish a basis for the BMA ecology in the Charleston Harbor. In the future, BMA dynamics could be compared to our study to assess changes caused by human influences in Charleston estuaries.


Thank you to my mentor, Dr. Craig Plante, and my co-advisor, Kristina Hill-Spanik, for their support and guidance. This project is funded through the National Science Foundation and supported by College of Charleston’s Grice Marine Laboratory.


Literature Cited:

Lobo, E. A., Heinrich, C. G., Schuch, M., Wetzel, C. E., & Ector, L. (n.d.). Diatoms as Bioindicators in Rivers. In River Algae (pp. 245-271). Springer International Publishing. doi:10.1007/978-3-319-31984-.

MacIntyre, H.L., R.J. Geider, and D.C. Miller. 1996. Microphytobenthos: the ecological role of
 the “Secret Garden” of unvegetated, shallow-water marine habitats. I. Distribution, abundance and primary production. Estuaries 19: 186-201.


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