Heyward Mathews has been scuba diving and spearfishing the Gulf of Mexico for more than 40 years. An oceanographer by trade, Mathews is trained to observe and record changes in the undersea world.But Mathews will be the first to tell you it doesn't take a marine biologist to figure out something's wrong with Florida's offshore reefs."Lionfish," Mathews said in a recent telephone interview. "Head out to the Middle Grounds and they are everywhere."The exotic creature, a native of the Pacific Ocean, was introduced into the Atlantic Ocean in the late 1980s. It's a mystery how or exactly when the first lionfish found its way into the wild, but many scientists suspect the invasive species probably got a foothold somewhere in South Florida and worked its way into the Gulf of Mexico.In less 30 years, lionfish have worked all the way up the East Coast to the Carolinas and as far south as Brazil. The lionfish has no natural predators in this part of the world, so the venomous species has spread virtually unchecked."There is really no way to get rid of them except to go down there and spear them," said Mathews. These fish might look pretty in an aquarium, Mathews said, but in the gulf, lionfish upset the natural balance on the reefs and compete for food with local species such as grouper and snapper.Divers do not have to kill every lionfish on a reef to make a difference. Removing just 25 percent of these invasive predators from an area can make a difference."Lionfish can eat more than 20 small snapper, sea bass or other reef fish in a single day," Mathews said. "On some coral reefs in the Caribbean, the lionfish have eaten so many of the parrot fish, the corals have become covered in algae."For several years, divers in the Florida Keys have put together "lionfish roundups," which have proved effective in reducing the number of these fish on local reefs. One hunt removed more than 500 fish in a day.Lionfish seldom take bait on a hook, so the only way to really combat this piscatorial plague is to enlist the support of spearfish anglers.Meanwhile, the Florida Fish and Wildlife Conservation Commission has taken steps to keep the problem from getting worse. New regulations under consideration include a prohibition on the importation of live lionfish and the development of a lionfish aquaculture industry.The commission also wants to loosen some regulations so lionfish hunts can be held in areas that do not allow spearfishing. This would be done through a special permitting system.In Tampa Bay, Mathews and his colleagues at Reef Monitoring Inc., a small nonprofit group of marine scientists from St. Petersburg College and the University of South Florida, is organizing a lionfish roundup.Saturday, Reef Monitoring hosts the first in a series of local lionfish hunts. Prizes include $500 to the team that collects the most lionfish, and $300 for the largest and the smallest lionfish. The weigh-in is at the Clearwater Harbor MarinaWhy a prize for the smallest lionfish? Mathews and his fellow researchers plan to measure each fish, look at the stomach contents and remove the otoliths, or ear bones, from each head. Marine biologists use these bones to age the fish, much like foresters count the rings in a tree trunk.Several local dive shops have special dive packages that include a two-tank dive, rental of a pole spear and a collection bag.General registration is $20. Go to reefmonitoring.org to learn more.