Final answer:
Both "The Reef" and "Metamorphoses" share the theme of Transformation and change, where characters or environments undergo significant alterations.
Step-by-step explanation:
The common theme in both "The Reef" and the excerpt from "Metamorphoses" is Transformation and change. This theme encompasses the idea of natural or supernatural changes that impact the characters or environment within a story. Given the context from "Metamorphoses", which revolves around mythological transformations, and the implications of change in "The Reef", such as in marine life, thematic elements of change are central to both works.