Here is a link to the article re Mullins Bay, Barbados where the construction of groins (jettys) contributed to the loss of the beach due to a halting of the natural sand migration. http://travel.yahoo.com/p-interests-35816900

About the size of the beach now. When I first set upon the Negril Beach in 1969, it was very narrow with coconut palms reaching the waters edge in places. When I was a science teacher, many moons ago, one of the experiments that we did in the Earth Science class was to observe the effect of a jetty on the migration of sand along the coast. We did the experiment in a small wave tank and the result was a loss of beach down stream from the jetty. That was a 9th grade experiment. I believe that the most important thing that can be done to protect Negril's beach is a replanting of coconut trees and related vegitation where ever possible, combined with a concerted effort to revitalize the coral reef.