There are a handful of theories about what might cause ships and planes to vanish, including underwater alien bases, tidal waves, magnetic anomalies, sea monsters, and exploding bubbles of methane gas. But before examining the validity of the theories it's important to ask a basic question: Is there anything unusual that needs explaining?
There are a few things to note about the area and the claims surrounding it. Let's examine this statement: "Since the mid-90s, there have been at least 15 reported incidents in which small aircraft have either crashed, disappeared or declared emergencies while traveling through the area." The first thing to point out is that it does not mention 15 mysterious disappearances, just 15 incidents - which include crashes (whose causes are known) and aircraft that had some unspecified emergency on board (which could include anything from a passenger having a heart attack to some mechanical problem).
Second, fifteen "incidents" since the mid-1990s comes to a startling average of about one incident per year, out of the hundreds of flights per day over those waters (including from Simón Bolívar International Airport outside of Caracas, which carries about 10 million passengers each year). The Caribbean Sea north of Caracas has lots of boat and plane traffic; there are more resort islands clustered in that area than anywhere else in the world, including Aruba, Curacao, Grenada, St. Lucia, Antigua, Barbados, and of course Puerto Rico. The only way to get to and from those islands is by boat or plane, and - like cars, boats, or anything else - more traffic than average means more accidents and mishaps than average. If anything, it's surprising there aren't more crashes.