During the 1920s, dredging of the area that connected the Alafia River to the Tampa Bay's main shipping channel created two man-made islands from spoil material: Bird Island and Sunken Island.
The two islands became collectively known as the Alafia Bank Bird Sanctuary after they began serving as a habitat for a wide variety of bird species.
"Essentially, we've been protecting birds that nest there for more than 70 years," said Ann Paul, regional coordinator for Audubon of Florida. "Even though it's an artificial habitat created by dredging, it's extremely important."
The latest effort to preserve that habitat is a 425-foot-long reef. The reef is comprised of 212 concrete balls, each of which is four foot wide, three-and-a-half foot tall and weighs about 1,300 pounds.
In addition to helping prevent further erosion of the Bird Island cove, the reef will also serve as an oyster habitat.
"The reef balls are specially designed to allow planktonic oysters to grow there," Paul said. "We chose to install it now because this is the time of year oysters are spawning." The oysters on the reef will also help clean the water near Bird Island cove. Bird Island is located about two miles west of the Williams Park Boat Ramp in Riverview.
The Sarasota-based Reef Innovations began installing the reef on April 18 and the job was completed eight days later. The project was funded mostly by a $75,000 grant from the Environmental Protection Commission of Hillsborough County. The Tampa Bay Estuary program donated an additional $9,500 in mini-grants.
The Alafia Bank Bird Sanctuary is home to about 10,000 pairs of colonial waterbirds per year.
"It's one of the most diverse colonies in the continental United States," Paul said. "It's a huge white ibis colony."
The white ibis is one of 17 different species on the two islands, according to Paul. The American oystercatcher, roseate spoonbills and tri-colored heron are among the other birds that also make their home at the Alafia Bank Bird Sanctuary.
"The freedom from terrestrial predators is a big reason why they choose these islands," said Mark Rachal, field biologist for Audubon of Florida.
Bird Island covers about 30 acres, while Sunken Island spans almost 70 acres.
Paul and Rachal said their organization's next project is to create an even stronger wave catcher for Sunken Island. They hope to get started this summer.
"Our concept for helping grow these birds is, if we let them do their jobs and raise their own birds, then we're doing our jobs," Paul said.