The most dramatic deterioration has been caused by biological factors. It used to be thought that the depths of the ocean were a lifeless desert, but research carried out since the mid-1980s has found that the ocean floor is teeming with life and may rival the tropical rainforests for biodiversity.[104] During the 1991 IMAX expedition, scientists were surprised by the variety of organisms that they found in and around Titanic. A total of 28 species were observed, including sea anemones, crabs, shrimp, starfish, and rattail fish up to a yard (1 m) long.[85] Much larger creatures have been glimpsed by explorers.[105]