Higher Trophic Levels

Sponge Populations in Florida Bay

Florida Bay Project Profile - 58

---

Question: What is the abundance and distribution of sponge species in the hard bottom communities of southeastern Florida Bay? What were the impacts of the cyanobacterial phytoplankton blooms of the early 1990’s on sponge populations and have they recovered in recent years?

Project: The initial assessment of the sponge populations took place before the appearance of the phytoplankton blooms in the summers of 1991 and 1992 when visual sampling techniques were used at 15 sites near the middle keys. Twelve transects, which measured 100 by 2 meters, were set up at each site. The sponges living within the transects were identified through visual means, measured, and counted. Beginning in 1993, two of the 15 original sites were surveyed to assess the losses associated with the phytoplankton (cyanobacterial) blooms in the middle and upper Keys and track the recovery of the total sponge community since the widespread mortalities. A third survey site in Everglades National Park was added to the project in 1995.

Findings to Date: Highly significant decreases in sponge abundance were detected in the 1993 summer sampling period. These losses may have occurred when high densities of phytoplankton in the water column clogged the feeding (incurrent) pores of the filter-feeding sponges, but the exact mechanism of sponge mortality is unknown. Perhaps low dissolved oxygen or phytoplankton toxicity may have contributed to the mortalities. There were differences between the sites in the severity of the morality and some species were more susceptible to the blooms than others. One sponge species (Cinachyra sp.) was either particularly resistant, or able to rapidly colonize dead areas. The very large loggerhead sponges which often shelter juvenile spiny lobsters experienced widespread mortality throughout extensive areas, yet it appeared to be more resistant than other species.

There appeared to be some recovery in a few of the large and formerly abundant sponges in some areas. However, for two of the most conspicuous sponges that are most familiar to divers and snorkelers, the loggerhead sponge (Spheciospongia vesparia) and vase sponge (Ircinia campana), there has not been much regrowth. Recovery will take at least another five years and may take more than 10 years.

Status: Survey work has continued through the summer of 1998. Funding is being sought to continue the work in future years. Many years will pass before sponge populations will recover to their formerly abundant levels.

Restoration Impacts: Sponges are an important habitat for a variety of animals including the Caribbean spiny lobster. Information on sponge abundance is critical to scientists and engineers developing models which evaluate the impacts of filter feeders on water clarity, predict spiny lobster population trends and feeding relationships among bay organisms. This information is also important in understanding the importance of sponge habitat for several commercially valuable animal species.

Funding Source: Florida Department of Environmental Protection, Florida Sea Grant, and the Florida Keys National Marine Sanctuary

Status: Completed.

Related Profiles:

• FBPP - 31 • FBPP - 38

• FBPP - 88