Antarctic invertebrates: cheaters, kidnappers and possibly lifesavers?

Antarctic seafloor species
A diverse assemblage of Antarctic invertebrates including several Synoicum adareanum tunicates (orange, center). Photo credit Bill Baker.

This past March, I had the privilege to visit the Antarctic Peninsula with One Ocean Expeditions as part of a discussion among Antarctic stakeholders on the future of Antarctica. I enjoyed seeing all the typical Antarctic animals – penguins, whales, and seals – but a real highlight was getting to meet Dr. Bill Baker at Palmer Station, which is part of the U.S. Antarctic Program. Baker studies the chemical ecology of Antarctic invertebrates and vegetation. I was already a fan of the many weird and wonderful marine invertebrates of the Southern Ocean, but since visiting Antarctica, I’ve learned more about Dr. Baker’s research into their equally weird and wonderful chemical defenses. They demonstrate that even humble species have extraordinary adaptations to give them advantages in a tough environment, and reinforce Antarctica’s incredible biodiversity.

Many invertebrate species produce chemicals to repel predators. It’s not too surprising that if you are a sponge, coral, or other relatively immobile creature, you need an effective way to defend yourself. Even more mobile zooplankton might need chemical defenses to compensate for the lack of teeth or claws. But one small Antarctic crustacean takes a shortcut. Rather than evolve its own chemical defenses, the amphipod Hyperiella dilatata kidnaps the pteropod (also called a sea butterfly) Clione antarctica and carries it around affixed to its back. The pteropod produces a substance that causes fish to spit out C. antarctica, with or without an accompanying amphipod. Without sea butterflies to protect them, amphipods get eaten. Researchers including Baker eventually discovered that C. antarctica produces a previously unknown compound called pteroenone that is unpalatable to fish. Pretty impressive for a crustacean that tops out at about 8 millimeters in length.

Antarctic sea sponge Dendrilla membranosa
Darwinolide, a substance isolated from the Antarctic sea sponge pictured here (yellow, center), could one day fight drug-resistant staph infections. Photo credit Bill Baker.

Another Antarctic member of the amphipod order, Paradexamine fissicauda, employs a similarly underhanded strategy to use another species’ chemical defenses. Instead of kidnapping, this species “cheats”. It eats Plocamium cartilagineum, a species of macroalgae that produces unpalatable chemicals, and letting those chemicals build up in its body. Voila: now P. fissicauda is itself unpalatable. The cheating aspect enters the picture because most of the time in the region where P. fissicauda and P. cartilagineum live, amphipods and chemically defended macroalgae have what scientists call a “mutualistic” relationship. The algae provide shelter from predators for the amphipods, and the amphipods eat other forms of algae that would compete with their hosts. P. fissicauda are therefore obtaining a food source and defense against the fish that would otherwise eat them without providing any services in return.

Investigations into the chemical properties of these defenses have produced equally fascinating results. The research of Baker and his colleagues has found numerous chemical defenses from Antarctic invertebrates that have shown promise in possibly treating a wide variety of human diseases. A soft coral (species currently undescribed) found near the Shag Rocks produces chemicals that were more effective at killing Leishmania donovani, a parasite that causes the awful disease leishmaniasis, than miltefosine, a drug currently used for treatment. A compound derived from an Antarctic sponge has shown antimalarial activity. A tunicate or sea squirt (Synoicum adareanum) and a sea slug (Austrodoris kerguelenensis) produce substances that can combat melanoma and a type of leukemia, respectively.

Antarctic nudibranch
Compounds derived from this Antarctic nudibranch or sea slug (Austrodoris kerguelenensis) may one day treat leukemia. Photo credit Bill Baker.

Perhaps the most exciting find is a substance called “darwinolide” isolated from an Antarctic sponge (Dendrilla membranosa) that was able to inhibit the growth of methicillin-resistant Staphlococcus aureus. While all potential new antibiotics are good news in an era of increasing antibiotic resistance, this one is particularly exciting because it was effective against the biofilm phase of S. aureus. Bacterial biofilms are a form of bacterial infection in which the cells form an extracellular matrix of DNA, proteins, and other substances. Essentially the biofilms link bacteria together, and once this happens, there are few substances that can treat the infection. Darwinolide may therefore be suitable for treating drug-resistant biofilm infections.

These results emphasize not only how much we have to learn about Antarctic species, but also how reliant we humans are on the world’s biodiversity. Even though the UN General Assembly recently issued a declaration requiring countries to come up with plans to fight antibiotic resistance, we are still likely to need multiple options for new drugs that can treat resistant infections. Nature is our most important source of those options. Furthermore, we increasingly seem to find that many challenges, from flood prevention to water purification, can be most efficiently and effectively addressed by preserving ecosystems rather than by inventing new technology. We need to enhance our ability to make use of natural solutions, and one excellent way to do so is to protect ecosystem biodiversity in as close to its undisturbed state as possible.

Antarctica is a prime location for such protection. The region has a long history of fishing and whaling, yet its habitats and species are still more untouched than those in many other parts of the world. The Commission on the Conservation of Antarctic Marine Living Resources (CCAMLR) has been discussing such protection for Antarctic marine ecosystems for several years. At CCAMLR and in other regions of the world, advocates of the creation of marine protected areas (MPAs) have been asked to justify how the benefits of conservation will outweigh the costs of restricting human activities. However, we can’t always quantify the benefits of healthy ecosystems.

If we only protect ecosystems for which current scientific research can demonstrate a value to humans, we could lose out on potential new solutions. It can be helpful to remind those skeptical of the value of biodiversity protection that we still have much to learn about the world around us, and sometimes we may learn something that could save human lives. Setting aside a portion of all our planet’s marine and terrestrial ecosystems is a kind of insurance policy, since we never know what new discoveries may be found at a later date. I hope that when CCAMLR meets this fall, its member countries will consider how to protect Antarctic invertebrates and cute penguins. Save the sponges, save us.