Host-associated microbes are part of a host's extended phenotype, they can be host-specific, and influence host fitness as a trait of the host. The questions that I ask focus on the implications of variation of traits (including microbes) for organisms, populations and communities. Much of my work is focused on tropical corals and coral reefs. Corals show fantastic amounts of variation: among species, within species and in their physiology, symbionts, and response to stressors. In this seminar I will focus on coral interactions with a biotic stressor, the vermetid gastropod, Ceraesignum maximum, and coral disease and the implications of the intraspecific variation on coral populations and reef communities.