It is a lot to absorb.
The breadcrumb sponge is simultaneously simple and complicated. This organism is a marine animal, albeit a very basic one, lacking nervous, digestive and respiratory systems. Which of course invites wonder at how this brainless, stomach-less and lungless beast eats, breathes and processes internal and external stimuli.
Yet somehow, it does squeeze out a successful existence.
Considered an invertebrate, the breadcrumb sponge has something of a rudimentary framework. Not a skeleton, but a silica-based structure of spine-like spicules to provide support. That framework encompasses a variety of shapes.
Breadcrumb sponge can be a bit of a chameleon. Colors range from cream to gray, green, yellow or orange, depending on its environment. Green can occur when the sponge lives in symbiosis with algae, usually in shallower water. Deeper seas favor cream and gray, and environmental factors including nutrient and oxygen concentration can also affect its hues.
This variation has caused breadcrumb sponge to be described as a new species more than 50 times. With each “discovery,” a scientist believed that they had found something no one else ever had, leading to disappointment again and again when it was realized that this “original” organism was just a different form of one already named.
I had a good look at this creature after we pulled our boat out of the water for the season. The sponge had covered a small portion of the bottom of the hull, appearing as volcano-like protrusions from an encrusting orange spreading blob. Sponges with these projections are most often found in wave-sheltered areas, while in rougher seas, the breadcrumb sponge appears as thin sheets.
The tubes are called oscula and serve to filter water through the animal’s body. That water filtering is how the sponge feeds and excretes. Sponges are in the phylum Porifera, which means “pore” or “pore bearers.” Several liters of water per day per gram of sponge provide food, oxygen and nutrients to move through its body.
Even without a brain, the organism somehow knows when conditions are bad, and can slow and even stop its filtering. Low oxygen or high nutrient conditions could shock and damage its delicate system.
Breadcrumb sponge is sessile as an adult, and attaches to a substrate. Besides boats, it could colonize seaweed, coat a rock, boulder or shells, or attach to piers or other human-built structures. A sponge can be from four to eight inches, although at their largest they may be three feet wide.
While this sponge needs a connection, it also provides one. All of their folds and valleys create habitat for others, and within this microhabitat sea stars, worms, amphibians and other marine invertebrate can find homes.
Its name describes breadcrumb sponge’s affinity to crumble when squeezed or dried. And this sponge is known to have an odor, described as reminiscent of exploded gunpower. Reproducing sexually through external fertilization, a free-floating planktonic larvae results, then sessile adults. Asexual reproduction through the breaking off and regrowth of a piece of sponge is also not only possible, but common.
Observing this sponge may soak up some time, but delving further into the hills and valleys of this simple sponge is worth the temporary absorption.
Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown, and author of Martha’s Vineyard: A Field Guide to Island Nature and The Nature of Martha’s Vineyard.