A floating macroalgae called Sargassum is exploding and forming huge mats of weed across the Caribbean Sea.  It washes ashore on pristine beaches prized by tourists, wreaking havoc on the environment and the economy.  Scientists believe the explosion is driven in large part by a massive nutrient influx from the Amazon River, higher water temperatures, and increased availability of dissolved CO2 in the water column.  Poor land management practices in the Amazon Basin -- land clearing, agriculture, fires, and mining -- are increasing nutrient runoff and driving this natural algae to new levels of growth.  The natural system is clearly out of balance and the Caribbean nations are paying a high price.  Meet Mariah McBride, the "Sargassum Lady," who is working with Caribbean resort operators, cities and communities to develop ways to contend with this new and disturbing phenomenon.  The trick:  figure out how to slow the Sargassum growth, keep it off the beaches, and clear and dispose of the tons of it when it coats the beach.  Not an easy task.  Hear from one of the pros in the trade. Only on ASPN.