Agents of change act on communities across multiple temporal and spatial scales. Consider a coral reef community in the indian ocean. If you look back at it over the last few decades, you would observe slow and subtle changes, as well as catastrophic ones. Coral reef communities in the indian ocean have experienced significant changes over the last few decades. The agents of change have been subtle and catastrophic, natural and human-caused. Species interactions, such as competition, predation, and disease, can case the gradual replacement of species over time. Changes in abiotic conditions, such as sea level and water temperature, can cause physiological stress, coral bleaching, and eventually mortality. Catastrophic disturbances, such as tsunamis, can cause massive injury and death in coral reefs. In the 1980s, an unusual alga (caulerpa taxifolia) was found in the mediterranean sea. It was a native of warm caribbean waters (18 20 degrees).