Fungal Zombieland

From the introduction:

Zorus Island is occupied by a small outpost and watchtower and is tasked with keeping an eye on the Zorus Strait. Coastal transports periodically stop to re-provision the small garrison at a pair of docks, but the most recent supply run returned to port with an aghast crew, claiming that they encountered grotesque zombies as they began unloading. They fled without investigating or searching for survivors. A subsequent message relayed by carrier pigeon warned that the island outpost was under zombie assault. The message was partly illegible, but closed with, ‘beware the black dust.’