How Do Sponges Eat?
Although sponges lack the power of motion possessed by most animals, being nearly always attached, in one position or another, to some object, the study of their habits in captivity brings out many of their animal characteristics in a striking manner. Small specimens taken from the sea and placed in dishes of salt water may be kept alive for several hours if well cared for; and by using finely powdered coloring matter, such as carmine or indigo, the manner of their feeding may be readily observed. Sponges are more active in fresh sea water than in stale; they cannot be kept alive out of water and soon die if exposed to the air. Being unable to go in search of food, as a natural result, they can grow only in places where there is always an abundance of food suited to their wants. The great sponging grounds of the world are wholly confined within waters having a relatively high temperature during the entire year. The Old World sponges grow principally in the Mediterranean and the Red seas; the New World sponges are found about the Bahamas, southern and western Florida, and parts of the West Indies. The finest sponges come from the East, but one of the American species, the so-called “sheep’s wool,” stands high in favor.
The commercial sponges are separated into six species, three of which are European and three American. They are all referred to a single genus called spongia, and though having much in common as regards structure, their texture varies to such an extent as to make them of very unequal value for domestic purposes.
The Old World species may be arranged as follows, in order of their grade of excellence, beginning with the best quality: The Turkey cup sponge, Levant toilet sponge, the horse, honey comb, or bath sponge, and the Zimoca sponge. The American species include the sheep’s wool sponge, the yellow glove, violet, and grass, sponges. A very close relationship exists between the species of the two continents.
All known regions in which useful specimens abound contribute to the world’s supply. The trade is extensive. The demands upon the fisheries are great. In the Mediterranean, the fishing is carried on in some places at a depth of forty fathoms. Divers, naked, or in armor, go down to the bottom and tear off the sponges from their places of growth. In some places drag dredges are employed.