Sea sponge shield

Article by Karen B. Roberts August 23, 2016

Animation by Jeffrey Chase

Encrusting sea sponges use chemical cues as shield to deter predators, expand territory

Sea sponges are benthic organisms that reside on the sea floor, fixed in one place. Known for their presence on coral reefs, these animals also can be found from the shallow to the deep waters of the ocean.

In a new paper out in Scientific Reports, a Nature journal, University of Delaware postdoctoral researcher Eva Ternon and colleagues at several international universities report new evidence that the Mediterranean encrusting sponge Crambe crambe (C. crambe) emits chemical cues from its tissues to generate a chemical shield, most likely for defense and communication purposes.

Since the 1950s, marine sponges have been widely studied for pharmaceutical use as they produce a large array of original and complex compounds, known as specialized metabolites. Ternon explained that, through chemical extraction, compounds can be isolated and separated from the sponge tissue and tested against various cancers or other human diseases.

When a compound is found to be active against a particular type of cell, natural product scientists often explore the compound’s usefulness for drug development. According to Ternon, to date three such marine compounds have been approved by the FDA and commercialized for use in the treatment of breast cancer, leukemia and lymphoma, and herpes simplex virus.

Similarly, chemical ecologists use complex techniques and scientific instruments to detect in the seawater chemical compounds that are likely to act as cues to better understand how organisms interact with their environment. Though C. crambe chemical cues are present at very low concentrations in water, and though chemistry is a challenge in the marine environment, Ternon believes “chemical ecology is a key masterpiece” to improving human understanding of the ocean.

The extinction of C. crambe and other sea sponges could impact the nutrients cycles and subsequently the overall functioning of the ocean ecosystem
- EVA TERNON Postdoctoral Researcher

As a postdoctoral student working with Olivier P. Thomas, currently a professor at the University of Road in Galway, Ireland, and principal investigator on the project, Ternon conducted the first study of and developed a sustainable protocol to retrieve specialized metabolites from the sponge tissue known to have a valuable pharmaceutical purpose.

In the study, the researchers observed that the sponge species, C. crambe releases its compounds expelling them through their exhaling canals. The team theorized that the sponge could be using the toxic compounds as chemical cues.

To confirm this, the research team collected sponge samples, as well as water samples from the water column surrounding the sponge, during fieldwork in the Mediterranean Sea on the French Riviera.

Ternon used a special polymer filter to extract and measure the dissolved and particulate concentrations of two specific families of specialized metabolites (Crambescins and crambescidins) from seawater samples.

The research team then demonstrated that the sponges constantly produced and released toxic compounds into the surrounding water by expelling small cells, called spherules, each containing up to 136,000 molecules.

The team concluded that the toxins are stored in sponge cells and are most likely biosynthesized by them, although “bacterial input could still be possible.” These small toxic balls diffused and settled around the sponge, leading to a shield of toxic compounds around to deter predators and to prevent occupation of the sea floor by other benthic species.

The researchers then exposed sea squirt embryos to the toxic compounds just prior to the larval stage. Sea squirts are another benthic species that inhabits the sea floor and prefers to stick to a substrate, making it a competitor of the sea sponge. The researchers discovered that the C. crambe sea sponge compounds were toxic to and caused developmental problems for sea squirt embryos.

While this finding may not be true for all species of sea sponges, Ternon believes the findings could be important as scientists continue to explore and piece together the scientific puzzle known as the ocean.

“As filter feeders, sea sponges quickly recycle nutrients in the water column while also extracting dissolved nutrients and organic matter, as well as particles like bacteria and tiny phytoplankton as food. Yet they are often forgotten when researchers study the water column despite their sensitivity to environmental changes, such as increases in temperature,” she said.

“The extinction of C. crambe and other sea sponges could impact the nutrients cycles and subsequently the overall functioning of the ocean ecosystem. To avoid this worst-case, we need to better understand sponge ecology. This involves fully comprehending their release of chemical cues and their subsequent implication at the ecosystem level,” she continued.

The paper, titled “Spherulization as a Process for the Exudation of Chemical Cues by the Encrusting Sponge C. crambe” first appeared in Scientific Reports on July 6. Co-authors on the paper include the project’s principal investigator, Olivier P. Thomas, Lina Zarate, Sandrine Chenesseau, Julie Croue, Remi Dummollard and Marcelino T. Suzuki.

The work was funded under a framework of the European project called BAMMBO - Biologically Active Molecules of Marine Based. The project is led by Ireland's Limerick Institute of Technology.

About the researcher

Eva Ternon joined the University of Delaware as a postdoctoral researcher in 2015. Working with Kathy Coyne, associate professor in the School of Marine Science and Policy in the College of Earth, Ocean, and Environment, Ternon’s current research involves characterizing the chemistry of the compounds found in a promising new antitoxin synthesized by a marine bacteria discovered in Coyne’s lab to prevent or mitigate harmful algal blooms of dinoflagellates algae.

Ternon previously was a postdoctoral fellow at the University of Nice, where she focused on the chemical ecology of sponges and harmful algal blooms. Prior to this, she was an engineer with IAEA (Monaco), where she studied marine hydrocarbon pollution and with Safege Company, where she worked on marine water quality.

She earned her doctoral degree in marine biogeochemistry from the University of Paris 6 in 2010.