Diatoms in Indian Geothermal Hot Springs: Current Evidence, Environmental Drivers, and Research Priorities

Indian geothermal hot springs contain diverse thermal and hydrochemical habitats, yet their diatom communities remain poorly characterized. This structured narrative review synthesizes historical and recent records of Indian geothermal diatoms, supported by selected international geothermal observations and experimental studies. We identified the literature through Google Scholar, locality-specific searches, and reference screening, and we evaluated records for sampling context, temperature measurements, identification method, and evidence of thermal association. Indian studies document diatoms in spring tanks, outflows, microbial mats, and deposits, but differences in sampling effort, taxonomic resolution, and environmental reporting preclude reliable nationwide comparisons. Observations from selected Indian sites, consistent with international studies, suggest frequent occurrence in moderately heated waters and cooler spring margins; however, this is not a quantitatively established Indian pattern. Crucially, microscopy records, molecular detections, and preserved valves do not independently demonstrate active growth, thermotolerance, or thermophily. Temperature, pH, hydrochemistry, and silica plausibly influence these assemblages, but their independent effects on Indian assemblages remain unresolved. Experimental work involving geothermal and non-geothermal diatoms identifies potential heat-response mechanisms that require testing in Indian taxa. We propose an evidence-classification scheme and priorities for spatially matched sampling, integrative taxonomy, controlled growth experiments, and long-term monitoring to support future bioassessment, contingent on Indian calibration and independent validation.