Rotifer loricas in second millennium sediment of Crawford Lake, Ontario, Canada

Abstract Crawford Lake (43° 28.1′N, 79° 56.9′W, 278 m asl) sediment is unusual because it preserves abundant loricas of Kellicotia longispina , Keratella cochlearis , K. earlinae , K. quadrata and K. hiemalis . Rotifer abundance covaries with diatoms, both of which indicate eutrophication. Dating is by varves after AD 1867 but before 1867, dating is by AMS (Accelerator Mass Spectrometry) because of irregular varve deposition. Fossil loricas become abundant about AD 1286 when Zea , Cucurbita and Helianthus pollen indicate native Iroquoian settlement and farming; a second rotifer peak begins in 1867 with Canadian settlement. Rotifers reflect nutrient-induced phytoplankton blooms as shown by Chlorella cells lodged within a lorica.