Unraveling the Mystery of the Rare Rocky Shoals Spider Lily

Katie Baucom, Andy Grunwald, Althea Hagan

Abstract

Hymenocallis coronaria, also known as the rocky shoals spider lily , is a rare species that is restricted to Alabama, Georgia, and South Carolina. The purpose of this research is to determine what factors are needed for optimal growth of the rocky shoals spider lily in order to inform future restoration on Stevens Creek in McCormick, South Carolina. Two sites along Stevens Creek have been monitored and compared to determine why one site is doing better than the other. Spider lilies were grown in a greenhouse to determine what factors affect seed germination and will later be outplanted. A kayak survey was done through Stevens Creek to find any new populations. Data was collected using game cameras and South Carolina Adopt-A-Stream protocols for water quality and macroinvertebrate surveys. Water quality and macroinvertebrate results were similar at both sites and there was no evidence captured of deer herbivory. For growing the spider lilies, timing of seed collection and the amount of aeration did not have an effect on germination. In the future, more research will focus on identifying the most important habitat  characteristics to inform successful restoration and management of the rocky shoals spider lily.

Introduction

Hymenocallis coronaria, also referred to as the rocky shoals spider lily is an emergent, aquatic macrophyte that can only grow in fast flowing, rocky shoals of rivers and streams. It is listed as threatened in the state of South Carolina. The lily sheds its green, photosynthetic seeds which sink and become lodged in rock crevices where they germinate, forming a bulblet, leaves, and roots with the seed still attached (Gordon and Wear 2011). They have fragrant, white flowers and peak blooming occurs from May to June. The Rocky Shoals Spider Lily has been found to be pollinated by many species (Campbell et al. 2014). Populations are in decline and many studies have been implemented to understand the cause of this. Flow rate and deer herbivory may have a significant role in the decline of Rocky Shoals Spider Lilies (Gordon and Wear 2011). The lack of optimal habitat and the disturbance caused by building dams is also a likely cause of decline (Markwith and Parker 2007).  In this study, two sites along Stevens Creek in McCormick, South Carolina were monitored and compared to determine what environmental factors are affecting the populations. Seeds were collected and grown in a greenhouse to be later outplanted as seedlings and seeds were also distributed at the deteriorating sites to see if these places can be restored with new populations.

Materials and Methods

To determine water quality, dissolved oxygen, pH, temperature, conductivity, phosphate, nitrate, and e-coli levels were measured using Adopt-a-Stream reagents and calibrated meters (Figure 1). A macroinvertebrate survey was conducted using a kick net and species caught were identified and counted. Game cameras were set up and pictures were assessed for animals and potential herbivory (Figure 2). A kayak survey was conducted through Stevens Creek and populations of spider lilies were mapped. Seeds were collected in June and placed in 4 pools with differing amounts of aeration (Figure 3). Air stones and pumps were used to provide oxygen to the seeds in the pools. Later, in July, more seeds were collected and placed in a separate 5th pool. The % germination in each pool was monitored and recorded. Germinated seeds with well developed roots and shoot (Figure 4) were potted, 25 in each pool. Germinated and un-germinated seeds were distributed out to both sites.

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Figure 1: Dissolved oxygen and pH levels were measured using Adopt-A-Stream kit reagents.


Figure 2: Game camera photo with a great blue heron.


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Figure 3: 6 pools with spider lily seeds in greenhouse experiment.


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Figure 4: germinated seed of rocky shoals spider lily with root and shoot coming out.

Results

stevens creek map

Figure 5: Map of Stevens Creek

Figure 6: Comparison of dissolved oxygen levels at each site


Figure 7: Parameters for water quality according to SC Adopt-a-Stream protocols: Poor: <11, Fair: 11-16, Good: 17-22, Excellent: >22

Figure 8: Wildlife that was seen near the rocky shoals spider lily populations during peak blooming in May-June 2019 and May-June 2020

Table 1. Greenhouse Experiment with % Germination of seeds
Pool #Seed status when harvestedAeration method % Germination
Pool 1attached to plant (n=146)air stone82.2%
Pool 2attached to plant (n=146)aquarium pump and air stone81.5%
Pool 3attached to plant (n=146)aquarium pump91.1%
Pool 4detached from plant (n= 22)aquarium pump and air stone68.2%

Conclusion

We kayaked through Stevens Creek to map out and survey all populations of rocky shoals spider lilies. The three main sites indicated on the map had the most significant number of spider lilies. Site 1 is the largest and healthiest population while the populations at the other two sites are smaller and less dense. Site 1 and site 2 were monitored for water quality and deer herbivory. There was no discernible difference in water quality between the two sites. Dissolved oxygen levels were similar at both sites. The invertebrate surveys also showed not much difference for water quality, with similarities in number of species at both sites. Analysis of game camera photos determined that herbivory was not an observable factor affecting the decline in populations. The greenhouse experiment showed no differences in % germination between the used methods of collection and aeration. After the experiment ended, all seeds eventually germinated. In the future, more research will focus on the quantity of water and geophysical characteristics of the sites to further define the habitat requirements of the rocky shoals spider lily. Future research will also look to assess success of various spider lily restoration methods.

References

Campbell, J., Starring, A., & Smith, G. L. (2014). Flower Visitors ofHymenocallis coronaria(Rocky Shoals Spider-lily) of Landsford Canal State Park — South Carolina, USA. Natural Areas Journal, 34(3), 332-337. doi:10.3375/043.034.0316

Gordon, J. E., & Wear, D. J. (2011). Parameters Affecting the Success of Protected Shoals Spider Lily,Hymenocallis Coronaria, in the Savannah River Basin, Georgia. Natural Areas Journal, 31(1), 34-42. doi:10.3375/043.031.0105

Markwith, S. H., & Parker, K. C. (2006). Conservation of Hymenocallis coronaria genetic diversity in the presence of disturbance and a disjunct distribution. Conservation Genetics, 8(4), 949-963. doi:10.1007/s10592-006-9249-z