Sedimentation - can cause death by burial or due to the expenditure of extra energy to clear away sediments. However, since the Belize barrier reef is so widespread, a large part of it is far enough from shore that it isn't effected by sedimentation. Contamination - as with all living things, if harmful chemicals are taken in or they are exposed to them, it can be deadly. Corals live in very clean water so only small amounts of a chemical can have a very widespread detrimental effect on them. Increased nutrients - this can cause coral death in a number of ways.
Bacteria CAN kill coral tissue.
Increased water column productivity may benefit filter feeders that compete with corals like sponges, bryozoans, AND tunicates. 1979 Field guidebook to the reefs of Belize.