British Tanks of WW2 (1)

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They coexisted with calcareous algae, large calcareous sponges, and other organisms. Also important during Late Jurassic time were deeper-water reef mounds, dominated primarily by siliceous sponges and calcified microbes. Warming climate and flooding of extensive shallow-shelf areas enhanced reef development in the Jurassic. 8. Cretaceous Reefs and the Rise of the Rudists The expansion of reef ecosystems within the warm-water tropical Tethys continued into Early Cretaceous time with a full complement of reef guilds.

3. 1. How Do Reef Ecosystems Evolve and Are There Any Common Patterns? From the perspective of geology and the history of life, one cannot help but be impressed by the profound and global nature of the changes that have affected the reef ecosystem during its more than one billion-year tenure on Earth. As discussed below, these changes were closely tied to a number of mass extinctions. Mass extinctions punctuate Earth history and serve as high-level mechanisms of change. The disruption of life sometimes results in complete collapse of a long-lived reef ecosystem and consequently opens up possibility for wholesale restructuring of new ecosystems.

Sometimes these eclipses lasted 2-10 million years or more (Fig. 9). An average eclipse interval of 1-2 million years, characterizes many nonreef ecosystems that include level-bottom communities and temperate or cooler water ecosystems. Relative to nonreef ecosystems, reefs appear to be the first ecosystem to collapse and the last to recover. This poses a central question: Because reefs are such complex ecosystems, do they merely require an inordinatly lengthy time to "reevolve" their ecological complexity or are other factors involved?

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