The hidden beauty of sponges.

Story & Photos By Melissa Heres, Waterfront Assistant, The School for Field Studies

Sponges, in my humble opinion, are likely the most underrated of all marine organisms. Often underappreciated and tossed aside as a bathing accessory or the feature of children’s TV shows, sponges don’t necessarily come to mind when one thinks of extraordinary marine life. That, however, should change. Sponges—although classified as the simplest animal forms (and yes, they are animals!)—have extraordinary characteristics, features and life stages that are truly awe-inspiring.

Sponges come in all shapes and sizes but are characterized by their pore-like structures.

Let’s start with a quick crash course in sponge biology. Sponges are considered to be some of the simplest animals due to their structure—they lack true tissue, organs or even a brain, and instead rely on specialized cells. These cells work together to filter water through the sponge, allowing the organism to absorb oxygen and gain nutrients. This filtering occurs when cilia, or hair-like projections, move in order to create an area of negative pressure inside the atrium of the sponge, driving water into the sponge’s cavities via pores, or ostia, and out through the main opening, or osculum, located near the top of the sponge. Sponges also contain spicules, which act as support to the structure, as well as spongin, which is a type of collagen which give sponges their “spongy” structure.

One of the ways to capture a sponge’s beauty is to put it under a microscope. Spicules—those support structures mentioned earlier—can come in a variety of different shapes, all of which are unique to different sponges. By figuring out whether the spicules within a certain sponge are composed of calcium or silica, as well as by determining the shape of the spicules, scientists can identify sponge species.

Sponges can reproduce in three ways: By spawning, fragmentation and budding. Spawning occurs when sponges release their sperm into the water column in hopes that it will reach another sponge. If it does, the cells of the sponge can capture the sperm and transport it to the eggs for fertilization and brooding of larvae. Later, the sponge will release the brooded larvae. This is the only time in the sponge’s life when they’re not immobile, as the sperm, and later the larvae that form, can move with ocean currents until they find a spot to settle on the sea floor. Interestingly, most sponges are actually hermaphroditic, and produce both egg and sperm.

Fragmentation occurs when a part of a sponge breaks off, for example, and then is perhaps moved by currents or wave action to settle in a nook elsewhere. Finally, budding occurs when part of a sponge actually begins growing a clone of itself, which can eventually break off to settle elsewhere, or remain attached to begin a colony of sponges.

Freshwater sponges have a unique adaptation that allows them to survive dormant in unfavorable conditions, such as cold water, droughts or anoxic (low oxygen) environments. These sponges can create gemmules, which have an outer protective layer and can remain dormant for long stretches of time. When conditions become favorable again, these gemmules can release cells that create new sponges, and some gemmules have even been stored for up to 25 years!

This giant barrel sponge stands tall at a dive site off the coast of South Caicos.

Sponges and corals are often confused for one another and I’ve even heard someone refer to a sponge as a “coral-sponge.” Sponges and corals are, however, two different types of organisms. Sponges can be identified by their telltale ostia and osculum. Sponges will have what look like pores all over their structure, which are the ostia, as well as a main large opening, usually near the top of the sponge, which is the osculum. Corals don’t have these pores or the osculum. If observed closely, corals do have polyps—structures with tentacles used to capture food—and will lack any opening or osculum.

Sponges are fascinating and bizarre creatures that have incredible abilities. The following are some ways that scientists have researched sponges in order to learn more about these unique organisms. With a quick search online, interesting videos can be found of this research, but please keep sponges safe and don’t try this on any sponges you see in the water!

One interesting way to check out a sponge’s flow of water is to fill a syringe with water and food dye and release this concoction around the base of a sponge. You will soon see the colored water being released out of the osculum at the top of the sponge, which shows how sponges can filter water very quickly in order to get proper nutrients and oxygen!

Sponges are widely considered the most basic animal form, yet they actually have incredible abilities to regenerate. Scientists have studied this characteristic by separating sponge cells by squeezing them through a silk cloth. Sponges are then actually able to re-form their cells into a sponge. Even more interestingly, if two sponges are separated in this method, they can recognize their own cells and re-form as two sponges!

Although there are several types and body plans of sponges, one in particular stands out as an awe-inspiring and incredible animal. The Venus flower basket (Euplectella aspergillum) is a type of glass sponge. These sponges live in the deep sea, and have an intricate shape created by layers of silica made in a precise pattern to keep them structurally sound. The most interesting part of this sponge, however, are its inhabitants. These sponges are almost always seen with two shrimp living inside of them, one male and one female. It is thought that these shrimp swim into the small pores of the sponge as larvae and are soon too large to escape.

This sponge is being colonized by sponge zoanthids.

A bit closer to home in the Turks & Caicos Islands, there are several other types of sponges that you might encounter. From the giant barrel sponge (Xestospongia muta) that can grow as large as six feet across, to the red boring sponge (Cliona delitrix)—so named for its ability to bore into rock and other substrates and only growing about a foot long—sponges throughout the Caribbean can come in a variety of shapes and sizes. Sponges can also be a habitat for many smaller creatures that live among the reef. Brittle stars—closely related to sea stars—and shrimp call some species of sponge home. So the next time you’re snorkeling or diving on one of the TCI’s beautiful reefs or walls, keep an eye open for these incredible eyeless creatures.

For additional information about The School for Field Studies, visit www.fieldstudies.org or contact us on South Caicos at hhertler@fieldstudies.org.