2013 REU Research Projects

Riley Brady (Univ. of South Carolina)

Mercenaria mercenaria impacts on estuarine shallow water primary production

Abstract:  Mercenaria mercenaria is a filter-feeding consumer that alters nutrient composition by producing nutrient-rich biodeposits. There has been evidence that these biodeposits can have a positive effect on seagrass productivity. However, little is known about their effect on the water column in comparison to the benthos. Furthermore, studies have been done on the response of seagrasses, but not other primary producers in the system. In a mesocosm experiment, the effects of high-density Mercenaria mercenaria on total primary productivity in an oligotrophic, shallow-water estuarine model system were examined. The effects of clam excretion and induced water circulation on the water column were separated from the effects of biodeposition on the benthos. Experimental treatments with clams consistently enhanced phytoplankton concentration (p = 0.002) and inhibited seagrass growth (p = 0.038). When the benthos was exposed to clam-circulated water, there was a significant increase in the concentration of benthic microalgae (p = 0.008). Although the presence of clams yielded higher epiphyte coverage, it was not significant (p > 0.05). The data illustrate a strong benthic-pelagic coupling between benthic microalgae and the water column. They also indicate that the physical presence of clams has a negative impact on seagrass primary productivity, likely due to increased turbidity and epiphyte coverage. These findings suggest that the presence of clams in a low flow, warm environment can enhance overall primary productivity, but is detrimental to the health of seagrasses.

Erica Wenzel (Muhlenberg College)

Evaluating the effectiveness of cercarial shedding methodologies in determining larval trematode infections in Littoraria irrorata

Abstract:  Parasites can cause behavioral changes in their host that influence the structure of the ecological community. Because L. irrorata is a keystone species, the effects parasites have on the snails could indirectly have large influences on the rest of the marsh ecosystem. To perform behavioral studies on how the parasites impact the snails, it is important to be able to distinguish between infected and uninfected snails. This study evaluates a methodology for determining if a snail is infected. Snails were collected from Hoop Pole Creek marsh and incubated in warm water for either 3 or 24 hours. After incubation, the water was examined microscopically to determine if there were cercariae (the free-swimming stage of a trematode parasite that moves from one intermediate host to another host) present.  The snails were dissected to determine if they were infected and to what intensity. The presence of shed cercariae proved to be an effective and accurate method to determine if a snail was infected. The 3-hour and 24-hour trials correctly identified the infection status of the snail. There were no significant differences between their ability to identify the infection status of the snail. Thus, this method can be used to identify infected snails for use in subsequent behavioral and ecological experiments that require treatments comparing infected and uninfected snails.

Taylor Bennett (Mount Holyoke College)

Overwash, aeolian transport and the absence of a paleo-hurricane record at a coastal pond, Onslow Beach, NC

Abstract:  Understanding past storm cycles is essential in forecasting future storm activity.  Anecdotal storm records only extend over the past 200 years, thus, geological methods are necessary to extend storm records.  The beaches and barrier islands of the North Carolina coast are, and have been, vulnerable to tropical and extra-tropical storms; however, no paleo-hurricane record exists there.  The objective of this study was to construct a paleo-hurricane record from washover sand layers preserved in a back-barrier pond on Onslow Beach, NC, a rapidly transgressing barrier island.  A transect of five vibracores was collected across the island from a vegetated washover fan (seaward) through a Phragmites marsh and into the pond (landward), which is ~100 m landward from the ocean shoreline.  The vibracore collected at the pond was analyzed for a storm record at 2-cm intervals using sediment grain size (using a CILAS particle size analyzer), percent organic material and sand (using the loss on ignition method) as proxies for storms.  Two stacked washover fans were identified as ~ 1 m thick sand beds, capped by paleosols in cores collected from the seaward part of the transect.  Those washover fans thin landward and pinch-out seaward of the pond.  The pond core sampled an upper 50-cm thick marsh unit composed of varying amounts of sand and organic sediment.  The sand component is well sorted, fine-grained, contains frosted and well-rounded grains, and is interpreted as being aeolian.  Sandy intervals, defined as percent sand >1SD from the mean, were identified at 5 cm and 31 cm and are interpreted as periods of high flux of wind-blown sand.  The two sandy intervals in the pond core likely correspond to the two adjacent washover fans.  When the washover fans formed, they buried previously existing vegetation and increased the connectivity between the primary dune and the back-barrier pond.  Based on the stratigraphic position of the two fans, they are likely less than 200 years, therefore, the storm record in this pond core does not extend past the anecdotal record.

Katelyn Chellemi (University of North Florida)

Bioerosion rates of Cliona celata and impacts on eastern oyster recruitment

Abstract:  Bioerosion rates of the boring sponge, Cliona celata, on Crassostrea virginica shells was measured for an 18-month period in Morehead City, North Carolina. A mean bioerosion rate was estimated by the decrease in shell density over time. There were three treatments observed. The first was a clean cultch shell paired with another clean cultch shell, which showed no infestation of boring sponge. The second treatment consisted of one clean cultch shell paired with a currently infested shell collected off a North River cultch site. This treatment saw a significant difference in density change, and the erosion rate was determined from this treatment. The third treatment was a single, currently infested shell also collected from the North River cultch site.  It showed no significant difference in change of density. Recruiting oyster juveniles were counted and measured after the experimental period.  I found a strong association with heavily infested oyster shell and oyster recruitment. All three treatments were significantly different from one another for number of recruits per 100 mL of shell volume. The cultch shell paired with cultch shell treatment had the most recruits per 100 mL of shell volume, and the sponge-only shell had the least.

Marissa Boyer (St. Lawrence University)

The effects of photochemical aging on the bioavailability of dissolved organic nitrogen to estuarine microbial communities

Abstract:  Many aquatic coastal waters receive high amounts of nutrients from human activities in the watershed.  Frequently, predicting the effects of the nutrient additions is hampered by an inadequate understanding of the fate of these chemical compounds in the natural system.  In this study we determined whether photochemical aging of river concentrate and/or the addition of a labile carbon source would increase the bioavailability of high molecular weight riverine dissolved organic nitrogen (DON) to an estuarine microbial community.  I manipulated light levels, the concentrations of nitrate and phosphate, and the age of water from up-estuary and down-estuary sources within cubitainer mesocosms and measured the resultant primary production.  My results indicated that the estuary was nitrogen limited, there were no measureable effects of short-term (several days) photochemical aging, and no effect, over the same time interval, of priming the water with labile carbon.

Tommy Franklin (Appalachian State University)

Are shorebirds and rove beetles exploiting resource pulses on a barrier island washover fan?

A common landscape feature of barrier islands are washover fans, extensive blankets of sand placed over the barrier island by the overwash of water associated with large storms.  When these washover fans are created they destroy existing habitats while simultaneously producing conditions that support different flora and fauna.  This study examined whether shorebirds foraging on a washover fan benefit from the early-stage, successional species of diatoms and insects that exploit the washover habitat.  I documented the occurrence of diatoms and high abundances of beetles throughout the entire area of the washover fan.  However, diatom (potential food for the rove beetles) distribution did not predict the distribution rove beetle abundances.  Birds exploited the rove beetle prey unpredictably.  Other factors than those measured in this study influence beetle and shorebird exploitation of resources in the washover fan.

Elizabeth Paul (University of Rhode Island)

Analyzing data from a direct numerical simulation to improve turbulent measurements in the coastal ocean

Abstract: A good understanding of turbulent mixing in coastal and estuarine systems is required to explain and predict distributions of water-borne materials such as contaminants, nutrients, phytoplankton, and sediment. However, measuring turbulence in shallow systems is complicated because waves advect turbulence past sensors in an unsteady way. In this study, I used data from direct numerical simulations (DNS) of a turbulent boundary layer to investigate the effect of waves on turbulence measurements, and to test methods commonly used to estimate turbulence properties from field data containing waves.  A prior experimental study provided a correction factor for the dissipation rate and the results of this study concurred with that model.

Mary Weiss (Georgetown University)

The evaluation of cultural methods for the direct isolation, differentiation, and enumeration of Vibrio vulnificus from shellfish matrices

Abstract:  Some biotypes of Vibrio vulnificus, a bacterium found in coastal waters, can cause human illness or infections when they are consumed in undercooked shellfish or from wounds arising from handling shellfish.  Accurate and rapid means of identifying the presence of the pathogenic biotypes in shellfish matrices is an important public health issue and several alternative media and techniques are used to test for Vibrio.  PCR analysis is most accurate but is costly and requires equipment not readily available.  Traditional plating techniques cost less and are more widely available.  In this study I compared different media (triple plating, VVX, CPC+, and Chrom) for their ability to detect Vibrio and distinguish the pathogenic biotypes.  VVX proved to be very accurate (81%) at relatively low cost, but the procedure is complicated to perform correctly.  Chrom has high accuracy as well (74%) and is very easy to perform correctly but it is expensive.  Neither triple plating nor CPC+ were effective.

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