The Biology and Fishery of Florida's Commercial Sponges
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The Biology and Fishery of Florida's Commercial Sponges

   

The Biology and Fishery of Florida's Commercial Sponges1

John Stevely and Don Sweat2

Sponge History

Until the mid 19th century, the world's sponge supply came from the Mediterranean Sea. However, suitable sponges were found at that time in Florida and the Caribbean. Important sponge fisheries were quickly developed with Florida, Cuba, and the Bahamas becoming the primary producers. Until the 1890s all of Florida's sponges were harvested from the Florida Keys, but the discovery of commercial sponges in the northern Gulf of Mexico, along with the introduction of Mediterranean deep diving techniques, led to the rapid growth of the industry in Tarpon Springs, Florida. During the early part of this century the sponge fishery was very important. However, a mysterious disease in the late 1930s, red tides, over-fishing, and introduction of synthetic sponges during the 1950s, reduced the fishery to a small fraction of its former importance.

Worldwide over 9,000 species of sponges have been described, but only a few species are of economic importance. Only those species that have a skeleton made of spongin fiber (a protein-like substance somewhat similar to hair) and arranged in a particular pattern, are durable, soft, and able to absorb water. In general, these species are not found in coral reef areas and research has shown that they represent a very small part (2.4 percent) of the sponge community in habitats where they are harvested (Figure 1).
Figure 1. Sponge community biomass - Florida Keys sponge grounds.

Five species in Florida are harvested commercially. Three of these, sheepswool sponge, yellow sponge, and the grass sponge are the primary marketed sponges. Sheepswool is the most important species because it is the softest and most durable (Figure 2 ). Two other species, the glove sponge and finger sponge easily fall apart when used and only very small numbers are harvested for ornamental purposes.
Figure 2. Sheepswool sponge.

Sponge Biology

Sponges obtain their food by filtering microscopic food particles from the water. They are somewhat unique from other filter feeding organisms (clams, barnacles, sea squirts, etc.) in that they can filter even smaller food particles down to the size of bacteria. Water is pumped through small openings on the side (ostia), filtered through a maze of canals and chambers, and then expelled through larger openings on the top of the sponge (Figure 3).

Figure 3.

Water is driven through the sponge by special cells equipped with a twirling whip-like filament (flagellum). In many habitats, sponges are an important consumer of microscopic food particles in the water.

The canals and chambers of sponges provide habitat for a myriad of small shrimp-like and worm-like organisms. In a way, they can be thought of as apartment buildings for these organisms. These sponge inhabitants do not appear to have any deleterious effects on the sponge.

Sponge Production Methods

The living sponge is much different in appearance than the cured commercial sponge. A living sponge is covered with a black skin (Figure 4 inset). Commercial spongers are very adapt at differentiating the commercial varieties from other sponge species.

Prior to World War II, Florida annually produced approximately 600,000 pounds of sponges. On average there are approximately 13 sponges to the pound. In recent years, Florida production has been 60,000 - 70,000 pounds of sponges annually, a fraction of the quantity harvested at the peak of the fishery.

In the Florida Keys sponges are harvested by hooking. When the water is clear and the wind is calm, fishermen working from small boats (sometimes associated with a larger "mother" ship) scan the bottom until they have spotted a sponge. They use a long pole with a hook (Figure 4) to tear the sponge free from the bottom. The hook is 5 inches across and is used to measure the sponge to insure it is legal size.
Figure 4.

In the northern Gulf, sponges are found in deeper water and diving gear is allowed to harvest sponges. In the past divers used a hook to tear the sponge free, but now many divers use a knife to cut the sponge free, thereby increasing the chances the sponge will regenerate. Research results have shown that if sufficient sponge tissue is left attached to the substrate, the sponge can survive and regenerate.3 Because diving for sponges is prohibited in the Keys, cutting sponges is not practical in this area. However, even when a hook is used, sponges still grow back about one-third of the time. Because diving for sponges is prohibited in the Keys, cutting sponges is not practical in this area. However, even when a hook is used, sponges still grow back about one-third of the time.

To clean the sponges, they are removed from the water to allow the living tissue to die. Sponges are then kept under wet burlap or returned to the water to allow a rotting process to continue for several days. This helps in the removal of the outer "skin" and other non-skeletal tissue. The final step is to squeeze, or paddle, the sponges so the remaining skin and tissue is eliminated and only the sponge skeleton remains.

The remarkable regenerative ability of sponges led to attempts to "farm" sponges. A sponge could be cut into pieces, attached to a concrete disk, and the sponge would grow to a commercially valuable product. However, slow growth rates, poaching, and most importantly, periodic episodes of sponge disease, killed the densely "planted" sponges.

Sustaining the Sponge Resource

In addition to leaving enough sponge tissue intact to encourage regeneration, there are several fisheries management measures intended to protect the sponge fishery.

Future Miracles from the Sea?

This fact sheet has focused on commercial sponges. However, some non-commercial sponges may contain the secrets for future important pharmaceutical breakthroughs. Many of the biologically active compounds isolated from sea dwelling creatures, and that are the subject of medical research, come from sponges. It is thought that because sponges are sessile creatures (cannot move) they have evolved chemical defenses to deter predation and enable them to compete with other organisms for living space. Sea Grant researchers are currently working on identifying and manufacturing new drugs from sponges.

Interesting Sponge Facts

Footnotes

1. This fact sheet is SGEF-119 published by the Florida Sea Grant College Program with support from the National Oceanic and Atmospheric Administration, Office of Sea Grant, U.S. Department of Commerce. Published March 2000.

2. This fact sheet was produced by John Stevely, the Florida Sea Grant Marine Agent for Manatee, Sarasota, Hillsborough and Collier Counties, and Don Sweat, the Florida Sea Grant Marine Agent for Levy, Citrus, Hernando, Pasco, and Pinellas Counties. For more information contact Florida Sea Grant, PO Box 110400, Gainesville, FL 32611-0400, 352-392-5870.

3. Florida Sea Grant publication, TP-38; Published 1985; Title: Survival and growth of cut vs hooked commercial sponges in the Florida Keys; Authors: John Stevely and Don Sweat ; Go to: http://nsgl.gso.uri.edu/cgi-bin/zgate for full version; NSGL#: FLSGP-T-85-007

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.


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