Sponge Defenses
Sponges possess diverse defense mechanisms to deter predation. These defenses fall into two categories: structural and chemical, making them less appealing or even harmful to potential consumers.
Microscopic, needle-like elements called spicules are a primary structural defense. These spicules, composed of either calcium carbonate or silica, are embedded throughout the sponge’s soft tissues. Their sharp, intricate shapes make the sponge physically abrasive and unpalatable, potentially causing internal damage to predators.
Many sponge species also produce an array of chemical compounds. These secondary metabolites can be toxic, distasteful, or irritating. These chemical defenses are often unique to specific sponge species and serve as effective deterrents against marine herbivores.
Animals That Eat Sponges
Despite their defenses, certain animals have evolved specialized adaptations to consume sponges. These spongivores play a role in the marine food web by overcoming the physical and chemical barriers sponges present.
Hawksbill sea turtles (Eretmochelys imbricata) are prominent spongivores, especially in coral reef ecosystems. Their narrow, pointed beaks are well-suited for prying sponges off reef surfaces and crushing their spicule-laden tissues. These turtles possess specialized digestive systems capable of processing abrasive spicules and neutralizing or tolerating chemical compounds found in sponges.
Certain nudibranchs, often called sea slugs, are highly specialized sponge predators. These mollusks exhibit an ability to sequester or incorporate defensive chemicals and spicules from the sponges they consume. They neutralize the sponge’s defenses and utilize these compounds for their own protection, becoming toxic or unpalatable to their own predators.
Some fish species, such as angelfish and parrotfish, also include sponges in their diets. These fish have developed strong jaws and specialized teeth or scraping mouthparts that allow them to graze on sponge tissues. Their digestive systems are adapted to handle the challenging composition of sponges, including spicules and chemical compounds.
Some sea star species are also known to prey on sponges. These invertebrates often employ a unique feeding strategy where they evert their stomachs over the sponge. Digestive enzymes are then released externally to break down the sponge tissues before the partially digested material is absorbed, bypassing the need to directly ingest the entire sponge structure. Other invertebrates, such as certain crabs and mollusks, may also occasionally consume sponges.