Exploring deep caves
Detailed international surveys of extensive limestone caves have recently documented thousands of distinct microorganisms, thereby promising important (17) ________ about the subterranean ecosystem that could (18) ________ our scientific understanding of pollution in cave systems worldwide. Many fragile organisms were found living deep in the remote (19) ________ of extensive underground limestone cave systems. Karst, the international research team, was still a (20) ________ small group to undertake a systematic mission on this scale. The expedition’s (21) ________ show considerable microbial diversity and identify organisms that support complex cave food webs. In total, thousands of microbial forms were recorded across several carefully chosen contrasting sites over three years, (22) ________ more than previously documented, and several proved unusually sensitive to water quality. Scientists warn that contamination will intensify if industrial activity around the cave network produces greater (23) ________ from nearby factories. Because these organisms react quickly to pollutants, several could eventually become locally rare and officially classified among the most (24) ________ species in the region.