What Is a Cliona Sponge and What Does It Do?
Learn about the Cliona sponge, an organism that shapes marine environments by breaking down shells and coral to recycle nutrients and create new microhabitats.
The Cliona genus represents a group of marine organisms known as boring sponges, defined by their ability to excavate hard, calcareous surfaces like shells and coral skeletons. This behavior makes them a significant agent of change in marine ecosystems. Their role is complex, as their boring activity can be both destructive and beneficial to their environment. Understanding this organism begins with recognizing its physical forms and distribution.
Identifying Cliona Sponges
Identifying a Cliona sponge is complicated by its varied appearance, which changes throughout its life. The sponge has three growth forms, the alpha, beta, and gamma stages, which can look like different species. Colors are also variable, with common species like Cliona celata appearing as yellow or orange, while others can be green or red.
The initial alpha stage is almost entirely hidden within the substrate it excavates, appearing as small, colored dots on the surface of a shell or coral. These visible portions are the papillae, or openings, that allow water to flow through the main body of the sponge as it creates a network of tunnels inside. For many species, this excavating form is the only one they achieve.
As the sponge grows, it may enter the beta stage, where the individual papillae merge to form a thin crust over the substrate. This encrusting layer can cover large areas, with the underlying structure of the shell or coral often still visible beneath the sponge tissue.
A few species progress to the gamma stage, where the sponge has completely overgrown and destroyed its original substrate. It becomes a large, free-living, massive sponge, sometimes forming thick, wall-like structures that bear little resemblance to its earlier forms.
The Boring Mechanism
Cliona sponges excavate calcium carbonate using a two-part system of chemical and mechanical action. The sponge does not eat the material for nutrients but bores into it to create a protected shelter. Specialized cells work together to break down and remove the hard substrate, carving out galleries and chambers.
The initial step is chemical, performed by etching cells. These cells attach to the calcium carbonate surface and secrete agents, likely an acid or enzyme, at the point of contact. This secretion dissolves a small portion of the substrate, isolating a tiny, scalloped chip of material.
Once a chip is chemically detached, the mechanical phase begins. The loosened fragment, between 40 and 60 micrometers in diameter, is physically removed from the excavation site. The sponge’s internal water canal system then transports these chips through its body and expels them into the surrounding water.
Habitat and Distribution
Cliona sponges are found globally in all oceans except the Antarctic, from shallow coastal waters to deep-sea environments. While individual species may have limited ranges, the genus as a whole is cosmopolitan.
These sponges colonize a wide variety of hard, calcareous substrates, including the shells of mollusks like oysters and clams, limestone coastlines, and the skeletons of living and dead corals. As adults, they are sessile, meaning they remain fixed in one place. The availability of this material drives their habitat choice, making substrate selection during the larval stage important for survival.
Ecological Impact
The ecological role of Cliona sponges is complex, with both destructive and constructive impacts. Their boring activity is a source of bioerosion, the breakdown of hard substrates by living organisms. This process has consequences for coral reefs and commercial shellfish operations.
In coral reef ecosystems, Cliona sponges can be destructive. They are capable of invading live coral, especially corals already stressed by warming water, pollution, or physical damage. The sponge undermines the coral’s structure from within, causing the living tissue to recede as the sponge takes over the skeleton. This activity weakens the reef framework, making it more susceptible to storm damage.
Conversely, this bioerosion is part of natural recycling in marine environments. By breaking down old coral skeletons and mollusk shells, Cliona sponges help to recycle calcium carbonate. The network of tunnels and chambers they create also provides microhabitats, offering shelter to a variety of small fish, worms, and crustaceans, which increases local biodiversity.