Determining Bioindicators for Coastal Tidal Marsh Health Using the Food Web of Larvae of the Greenhead Horse Fly (Tabanus nigrovittatus)
Semester of Graduation
Master of Science (MS)
The greenhead horse fly Tabanus nigrovittatus Macquart is native to coastal marshlands from Texas to Nova Scotia. The larvae are apex invertebrate predators and their development is dependent on the food web in the soil. Surveillance of T. nigrovittatus after the 2010 Deepwater Horizon oil spill in the Gulf of Mexico showed population crashes of adults in the coastal marshes of East Louisiana near places where oil made landfall, but not in West Louisiana where the oil did not reach. Sediment collection in 2011 from West and East Louisiana revealed larval population crashes in the Eastern coastal region. We hypothesized that due to the oil contamination a critical component of the food web of the larvae was destroyed and/or direct toxicity of the oil led to tabanid larval population crashes. With the aim of deciphering the tabanid larval food web in the Louisiana marshes, we used 18SrRNA metagenomics to identify the components of the food web in larval guts (n=16) and the surrounding sediment (n=25) from East and West Louisiana. An approximately 400 bp region at the 5’ end of the 18SrRNAgene was sequenced using the Illumina MiSeq sequencing platform. Downstream analysis was conducted in QIIME (v1.9). Effect of oil, sediment biochemistry and sediment toxicity on larvae and their food web was determined to explain larval decline in East Louisiana. We found insects and fungi to dominate the tabanid larval guts. Insects identified belonged to the families Drosophilidae, Culicidae and Tabanidae. Bioindicators of minimally oiled sediments are Hymenostomatia (Tetrahymena), Bivalvia (mollusks), Maxillopoda (Crustacea) and Peronosporomycetes (fungus like eukaryotes). “Phylum” Opisthokonta dominance in sediments is an indicator of larval presence in West Louisiana but not the East. Oil contamination, sediment biochemistry and toxicity could not explain larval population crashes in the East. Decline in the adult population led to fewer breeders and subsequently fewer larvae.
Bhalerao, Devika Rajeev, "Determining Bioindicators for Coastal Tidal Marsh Health Using the Food Web of Larvae of the Greenhead Horse Fly (Tabanus nigrovittatus)" (2018). LSU Master's Theses. 4377.
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