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How were graptolite extinction events related to changes in Silurian sea level?

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Silurian paleogeography — Silurian Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the middle part of the Silurian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

During the Silurian Period, the evolution of graptolites—small, colonial, planktonic animals—was marked by ten distinct extinction events, during which 52 to 79 percent of these organisms disappeared. These extinction events appear to be linked to global fluctuations in sea level, with most of these occurrences corresponding specifically to drops in sea level.1

These planktonic animals, which were often preserved in deep-water shales, may have been particularly sensitive to environmental shifts, including changes in water temperature associated with minor episodes of glaciation. While these sea level fluctuations were a recurring feature of the Silurian, they were distinct from the more severe, glacially induced drawdown that characterized the end of the preceding Ordovician Period.1234