Seven restoration sites along the bay side of Grassy Key. This area, known colloquially as the Burnt Point area, was the site of a rich sponge community prior to the passage of Hurricane Irma. Yellow squares represent the four sites assigned to receive 3,800 sponges/0.25 ha. White squares represent the three sites assigned as controls.
Map showing locations of sponge surveys conducted during December 2016 to assess the extent of sponge moratality near the Sandfly Key sponge nursery. Summarized are the percentages of Ircinia campana, I. variabilis, Spongia barbara, S graminea, and Hippospongia lachne sponges that were dead or exhibited some degree of necrotic tissue during the surveys.
Several shots of one of the in situ sponge nurseries. Clockwise from top left: newly propagated glove sponges; glove sponges approximately oneyear after propagation; vase sponges approximately one year after propagation; researcher holding a newly propagated fragment of a vase sponge and a vase sponge several years after propagation.
FWRI researcher holding a newly propagated fragment of a vase sponge and a vase sponge approximately three years after propagation.
Spiny lobsters sheltering under a loggerhead sponge in Florida Bay.
Marine sponges are perhaps best known for the use of their dried skeletons in the kitchen and bath, but they are also vitally important components of south Florida’s marine ecosystem. A typical sponge filters a volume of water equal to many times their own body volume each day. By so doing, they influence the physical and chemical structure of the water column, especially in the shallow waters of Florida Bay. They filter microbes and capture dissolved and particulate carbon. Some even add dissolved oxygen to the water using photosynthesis through symbiotic cyanobacteria; they also alter water column nitrogen biogeochemistry. Large sponges provide shelter for an array of fish and invertebrates, including commercially important spiny lobster and stone crab, plus many fish utilize sponge rich hardbottom communities in Florida Bay. Within the sponges’ internal canals lives a community of animals that includes sound-producing snapping shrimp that contribute substantially to the marine soundscape. This soundscape facilitates the recruitment of organisms to hard-bottom habitat and can influence the recovery of degraded sponge communities.
Unfortunately, Florida Bay has undergone extensive anthropogenically (caused by humans) related ecological alterations over recent decades that have resulted in the widespread mortality of the bay’s sponge community. The hard-bottom sponge community in large areas of Florida Bay has become severely degraded due to an array of stressors, chief among these being periodic blooms of algae that have occurred since the early 1990s. These blooms have resulted in the loss of sponges over an estimated 500 square kilometer area of Florida Bay, including the large, structure-forming species, especially loggerhead sponges. Given the important role of sponges in hard-bottom communities, their loss over such a large area of Florida Bay has undoubtably had substantial ecological consequences, reducing habitat structure and weakening the bay’s role as a nursery for many species.
In response to the loss of sponges, researchers with FWRI’s Restoration Ecology Program is testing the efficacy of sponge community restoration using sponges propagated from non-bloom-impacted sponge communities. Propagating sponges is a simple process. Much like the “coral gardening” method commonly used in coral restoration efforts, sponges can easily be cloned from “donor” individuals. These sponges can be left to grow in nurseries and provide biomass from which to create additional sponges. Previous studies aimed at transplanting propagated sponges to bloom-impacted areas showed this technique to be a viable means of restoring some aspects of Florida Bay’s sponge community and warranted further study. In 2015, FWRI garnered support from the Environmental Protection Agency, The Nature Conservancy, Bonefish and Tarpon Trust, and Florida Keys Environmental Fund to refine sponge propagation techniques using in situ sponge nurseries and to conduct the largest-scale sponge restoration effort attempted to date.
FWC researchers have established a network of sponge nurseries along the periphery of Florida Bay and within these created approximately 15,000 sponges of six species. These sponges are being transplanted to degraded areas in Florida Bay where they will support research to better understand how sponge restoration influences the broader hard-bottom community. Researchers anticipate that continued monitoring of these restored areas will yield information on spiny lobster and stone crab recruitment useful for fisheries related research conducted by both FWRI programs and outside researchers. Along the way, researchers have conducted several manipulative experiments to further understand how the sponge propagation process affects the ecological function of the sponges produced. In fact, they discovered that the snapping shrimp returned to normal numbers in the internal canals a few months after the sponges were outplanted and the soundscape was restored.
All members of FWC’s Restoration Ecology Program are involved in this project; present staff are William Sharp, John Hart, Kristene Parsons, Kristine Fisher, Brian Reckenbeil, Kerry Maxwell, and Kylie Smith. Other staff headquartered at the South Florida Regional Laboratory have assisted as needed. Chief among these is Jack Butler of the Spiny Lobster Program.
This project has shown that sponge nurseries, when placed in appropriate areas along the periphery of Florida Bay, are an effective means to create and maintain sponge biomass to support restoration. Results of this project also indicate that these propagation methods result in ecologically functional sponges, though maintaining sponges in high densities may result in resource competition that reduces their growth rates. Building on this first large-scale project, our researchers continue to develop sponge community restoration techniques that are efficient, environmentally sound, and produce ecologically functional and self-sustaining sponge communities. The results of this project have substantial utility in restoration of the broader south Florida marine ecosystem and will assist researchers around the globe in developing additional methods of sponge propagation to support restoration.