Award: OCE-2136377

The project studied distributions of the small organisms living in the sediments of Mexican flooded cave systems over approximately 2 years. Little is known about these organisms because it is so difficult to access these caves. The project sought to better understand the diversity of these communities, how they are distributed, and what environmental factors contribute to their distribution. The research provides important baseline information for ecosystems vulnerable to climate change, sea-level rise, and coastal development. 

The research team completed multiple field expeditions to collect sediment and water samples from cave systems in the Yucatan Peninsula and Cozumel Island, Mexico. Additionally, environmental conditions such as dissolved oxygen, salinity, temperature, and water level were monitored during and between sampling campaigns. Genetic results show that for all three main groups of eukaryotic organisms (metazoans, fungi, protists), approximately half of the sequences could not be matched to known species. The communities of these main types all vary depending on environmental conditions; these communities are unique so coastal development should consider impacts to these ecosystems. Comparisons of environmental and geochemical parameters with community composition showed that drivers of community structure in the aerated island sites are primarily physical parameters (e.g., salinity, temperature) whereas environmental drivers in further inland and low-oxygen caves are primarily energy-related (e.g., nutrients, carbon availability). 

Genetic results of foraminifera, small single-celled eukaryotes, showed similar results with nearly half of the sequences belonging to species that have not previously been sequenced. Foraminifera were individually picked and counted using a microscope and separated based on whether the individual was living, recently living, or dead at the time of collection. Comparisons in abundance and diversity were made between a cave with little to no oxygen, and a cave with abundant oxygen. Foraminiferal assemblages in the low-oxygen cave had lower diversity and abundance, primarily composed of agglutinated species that build their shells out of sediment particles. In comparison, the high-oxygen cave had high diversity and was composed of species that secrete their shells out of calcium carbonate. To further assess how foraminifera survive in these caves, cell structure was examined. Results verified that foraminifera are actively living in cave systems with little to no oxygen, with adaptations previously associated with low-oxygen environments. 

This project produced valuable research resources that will benefit the broader scientific community. In addition to data archiving, the project provided funds to train a graduate student (PhD level) who gained extensive experience in field research and planning, molecular biology, microscopy, geochemistry, data management, and regional and international scientific collaboration. Several other early-career scientists and postdoctoral investigators were supported through this project. Informal talks about caves and the organisms living in them were given to K-12 students.  Project results have broader societal importance because healthy groundwater systems are essential for coastal environments. By documenting the unique biodiversity and ecological processes within these cave systems, the project provides information that can support conservation efforts and inform resource management decisions. The new knowledge generated by this project will help inform future efforts to preserve these unique and ecologically important habitats. 

Last Modified: 07/29/2026
Modified by: Joan M Bernhard