StoryImage( ‘/Images/Story//Auto-img-113338532713275.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘Bath sponges are offered for sale at the dock in Tarpon Springs, Fla.’);
Sponges are the lowest evolutionary form of animal life on Earth. Most zoologists these days do not believe they are true animals because they lack many features of bona fide members of the Animal Kingdom. For example, sponges lack a mouth, with the main opening to the body being outgoing instead of incoming, they have no gut cavity, and they are immobile. In addition, the cells of sponges are not organized into tissues. In modern textbooks, they are placed in a subkingdom of the Animalia: The Parazoa (alongside the animals).
On the evolutionary tree of life, the sponges are regarded as a side branch near the bottom that ended in a blind alley. Yet, there are similarities to full-fledged animals, one of which is that the carbohydrate digesting enzyme in digestive cells of sponges is Amylase, the exact same carbo digesting enzyme found in humans. Sponges have been around a long time as evidenced by the fossil record dating back hundreds of millions of years. They have done pretty well as more than 5,000 species are known worldwide. Most are found in the marine environment, with three small groups having adapted to fresh water. I once observed a freshwater species, Spongila, in the Franklin Creek Natural Area in Lee County.
The body plan of a sponge can be quite simple as in the freshwater forms or quite complex as in the commercial bath sponge with which most of us are more familiar. The main body of the bath sponge is made of a flexible protein called spongin that is supported internally by numerous calcareous rods known as spicules. Sponges reproduce by both sexual and asexual means. In the sexual mode, certain cells act as both sperm and egg and, after fertilization, a larva is formed. In the asexual mode, even the smallest fragment broken off will develop into a new sponge.
Many years ago, a zoologist at the University of Texas performed an interesting experiment that demonstrated how prolific asexual reproduction is in sponges. He squeezed a piece of living sponge through a fine-meshed silk stocking, thus separating the individual cells. He placed the individual cells in separate dishes, and, lo and behold, each cell grew into a new sponge. Today, we would term this an experiment in cloning. The Texas professors sponge work was, however, long before we knew that every cell of the body contained the necessary DNA to create a completely new individual.
The commercial sponge capital of the world is on the Greek island of Kalymnos in the Aegean Sea. For 200 years, in the crystal-clear sea, the main occupation of that island was sponge diving. It was and is a dangerous occupation, and its techniques were handed down from father to son for generations. Usually, several men would go out in a small boat, and an observer would peer at the bottom through a metal tube with a glass bottom. When sponges were spotted, a diver would go overboard with a net and a rake and harvest the creatures. Some dives would be in 100 feet or more of water, and the diver would carry a large stone over the side to hasten his descent to the sea bed.
In the early days, there were no such things as diving suits or SCUBA gear, so the diver simply had to hold his breath while underwater. Many divers suffered from the bends (Caisson Disease) resulting from gas bubbles in the tissues due to a rapid decrease in pressure. Sponge diving then was a dangerous occupation, and only the most daring practiced it.
In the 1890s, many Greek immigrants to America settled in Tarpon Springs, Fla. and found the Gulf of Mexico an ideal place to continue the time-honored occupation of sponge diving. Of course, the invention of the classical diving suit in the late 1800s and SCUBA in recent times has dramatically reduced the dangers of diving. Tarpon Springs is still the sponge diving capital of the United States. But today, diving for sponges is mainly a tourist attraction, and thousands of visitors each year are attracted to the sponge docks in Tarpon Springs with its many fine Greek restaurants.
The advent of man-made sponges of synthetic materials spelled the end to commercial sponging in the United States.
When was the last time you saw a natural bath sponge in your home or in the garage to be used in washing the car?
Dr. Robert Hedeen is a former resident of Marylands eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.
From the Nov. 30-Dec. 6, 2005, issue