Rising population densities and associated coastal development as well as increased fishing, agricultural, and industrial activities are the major causes of pressures on Caribbean coral reefs. These sources have changed little in recent decades, but they have intensified dramatically.  Over millennia, reef communities have adapted to many natural pressures, such as hurricanes, where damage was followed by recovery, but now, a great range of direct and indirect human pressures have been added. Acting alone or in combination, these pressures can lead to acute or chronic ecosystem stress, which results in the breakdown and loss of coral communities, or to more subtle changes in ecosystem structure, such as the flourishing growth of algae on reefs. Changes to reefs can be gradual or rapid, but ultimately these changes diminish the value of goods and services derived from reefs by, for example, reducing coral reef habitat available for fisheries or reducing the shoreline protection afforded by reefs.
Coral reefs vary considerably in their ability to withstand pressures and to recover from damage or disturbances. This may be partly driven by ecological factors, including the species composition of the reef itself and its connectivity to other reefs. In addition, the physical setting of a reef (distance from land, reef depth, and the rate of water flow in the area) influences its vulnerability. Characterizing the pressures acting on any reef is complex, as there are multiple sources of stress operating over several spatial and temporal scales. 
This chapter examines the four region-wide threats included in the Reefs at Risk Caribbean model: coastal development, sedimentation and pollution from inland sources, marine-based threats, and overfishing. In addition, the issues of climate change (including coral bleaching) and coral diseases are discussed. Remedies applicable across the Caribbean region are suggested to address each of these threats. The chapter concludes with the integration of these four threats into the Reefs at Risk Threat Index, which attempts to represent the cumulative threat to coral reefs from these four key categories. In the following chapter, Chapter 4, these region-wide projections of threat are linked with observed changes in coral reefs and management responses in nine Caribbean sub-regions.