Eswarakumar: Effects of invasive plants on the tidal marsh

Effects of the Invasive Plant, Phragmites australis, on Tidal Marsh Insect Communities and its Dietary Repercussions for Saltmarsh Birds. 

Saltmarsh sparrow and seaside sparrow diet in salt marshes in coastal Connecticut.

Carlin Eswarakumar  and Chris Elphick

University of Connecticut

I intended to study the relationships between the invasive saltmarsh grass, Phragmites australis, and various communities in CT saltmarsh ecosystems. I focused my study on insects and insectivorous birds of the saltmarsh. My study aims to answer two main research questions: How does the invasive plant, Phragmites australis, affect the insect community when it replaces the native saltmarsh plant community of Spartina grasses? And how do these resulting changes in the insect community impact endangered saltmarsh sparrows and other insectivorous birds living in the tidal marsh ecosystem? I hypothesized that the introduction of Phragmites australis will displace native insect populations to areas of the marsh where Spartina grasses remain or reduce overall insect abundance. Native insects likely have not yet evolved to obtain their critical shelter or food resources from the significantly different Phragmites plant. I additionally hypothesized that if Hypothesis 1 is correct, Phragmites australis will indirectly affect saltmarsh birds because they will have less prey. Thus, the future status of endangered saltmarsh birds will depend on how much native Spartina grasses remain.

To study this, I compared the insect communities found on the invasive P. australis to three species of native vegetation found in the salt marsh, short form Spartina alterniflora, tall form S. alterniflora, and S. Patens.  I sampled insects at 108 plots of near-isolated patches of each type of vegetation: 36 plots per vegetation type, throughout three different saltmarsh sites, at Sluice Creek in Guilford, Hammonasset in Madison, and Great Meadows Marsh in Stratford. I used two different sampling methods, vacuuming and sweep-netting. The vacuum samples will be sent for DNA identification, known as metabarcoding, while the sweep-net samples will be manually identified with microscopy up to morphospecies within an order. Metabarcoding is a DNA analysis process that identifies unique taxa sequences within a pool of DNA. During the same sampling period, I additionally worked with other lab members to mist-net Saltmarsh Sparrows and Seaside Sparrows and collected fecal samples at the same three saltmarsh sites. These fecal samples will also go through metabarcoding to identify the families of insects the birds are consuming and will show any relationship between insectivorous birds and how their prey selection is affected by the invasive P. australis. The goal at the end of this study is to see if an invasive plant significantly changes the communities of the saltmarsh.

I am still in the progress of completing these goals. I am currently working on insect identification and am awaiting results from the DNA analysis. But I believe this research is important not only because it will give us an idea of how invasive plants affect the at-risk saltmarsh habitat and insight into potential ramifications for marsh restoration, but also provides us with data of insects that are vastly understudied in CT saltmarshes.