— Steven Wright
From personal hygiene to pharmaceuticals and telecommunications, it seems marine sponges have always been part of human society. The group of sponges used for centuries for bathing builds a skeleton for itself out of a material called “spongin.” Because spongin is soft and pliable, people collected these sponges, dried them and then used their skeletons to scrub themselves clean. Eventually, these sponge species became seriously overfished (many people were found to be allergic to them anyway), so synthetic sponges began to be manufactured and are predominantly used today.
Arriving on the scene around 580 million years ago, sponges are the simplest (and maybe earliest) of multicellular marine animals: no mouth and gut but pores galore that handle all the essentials of life. Sponges pass water through themselves via an organization of water canals. By pumping water though their bodies, they feed, breathe, reproduce and excrete waste. A sponge is a colonial animal, meaning that many individuals live together as one. To demonstrate that they are a mass of independence, scientists put a sponge in a blender and then placed the ground-up pieces back into an aquarium. The remaining cells re-formed themselves into another sponge. If multiple sponge species are pureed together, each species recombines with its own kind. How they do this requires understanding how cells recognize and accept or reject each other, which is somehow connected to understanding why some transplant patients reject their new organs.
One sponge species being studied has a similar system to that found in humans but of course much, much simpler. Scientists grafted together pieces of different individual sponges — simulating what happens in human transplants — and observed that a certain cell type swarmed to the graft site, suggesting that those cells are involved in recognizing alien tissue and then rejecting it. Thus, the cells isolated from the sponge may be a primitive form of our immune system’s human natural killer cells. Research continues into understanding sponge tissue rejection, which may lead to what is involved in human tissue rejection.
I see sponges all the time while scuba diving and snorkeling. From vibrant jewel tones (orange, violet, yellow, purple and red) to the bland (gray or brown), sponges off our coast mostly lack a definite form of symmetry (unlike the many vaselike or barrel-shaped tropical species) and instead grow along hard surfaces like rocks. They may measure a couple inches to several feet across. Sponges may reproduce asexually by budding off new tissue, by fragmentation in which parts grow into new sponges, and sexually (producing eggs and sperm at different times within the individual). For the sexual method, sperm are shed into the water but eggs remain in the sponge where they are fertilized.
Although mollusks (like sea slugs and chitins) and some sea stars eat sponges, they are toxic to most marine life. The toxins not only deter potential predators but also prevent animal larva and plant spores from settling on their surfaces. In this way, neighboring invertebrates can’t overgrow and smother the sponge. The potent chemicals that sponges use for protection have attracted intense interest from medical researchers and pharmaceutical companies seeking to develop new drugs. Sponges have been found to contain antibiotic substances, chemicals like steroids and anti-inflammatory, anti-viral and anti-arthritis compounds.
Optic fibers, an invention at the heart of late 20th-century telecommunications, have been occurring naturally in the frigid waters of the Antarctic for millennia, courtesy of the sponge. In a happy accident, scientists shining a laser beam onto a sponge belonging to the group whose skeletons are made up of glass spicules (silica) discovered that the sponge had light-carrying properties similar to optical fibers. Now that biologists have identified the mechanisms by which sponges synthesize this type of skeleton, work is under way to design the next, improved generation of solar energy converters, semiconductors and silicon chips — all inspired by the sponge.
Needless to say, the importance of sponges to society has changed dramatically over the centuries. How much more we can learn about sponges and their value to humans remains open for discovery and supports yet another reason to protect all facets of ocean life for our future.
— Judith Lea Garfield, naturalist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. Send comments to firstname.lastname@example.org.