Do Different Species of Marine Animals Ever Help Each Other?

Question: “Do different species of marine animals ever help each other?” – an 8-year-old member of the Hughes family in Washington, DC

Answer: Yes, this is actually pretty common in the animal kingdom. I’d like to bring your attention to two general types of interspecies interactions in the ocean: mutualism and commensalism. In mutualism, both species benefit. With commensalism, one species benefits while the other isn’t helped or harmed. (I’m sure you can think of lots of cases of the opposite, where two species interact, one benefits and one is harmed, including parasitism and predation, but that’s not what your question was about.)

Two classic examples of mutualism, where both species benefit, take place underwater. One is the relationship between coral and zooxanthellae, a microscopic photosynthetic organism that lives inside the coral animal. Both species here benefit: the coral gets food from the zooxanthellae and the zooxanthellae gets protection from organisms that might eat it. There’s a similar kind of interaction between bacteria and hydrothermal vent organisms. The deep sea is so deep that sunlight never reaches, so the symbiotic bacteria aren’t photosynthetic, meaning they make their food from the sun. Instead, they are chemosynthetic, making food for their host from chemicals entering the water through deep sea hydrothermal vents! These habitats are so deep that you’ll never encounter them scuba diving, but it’s cool to know what’s down there.

Another is the relationship between cleaner fish (or cleaner shrimp) and the animals they clean. Cleaner fish eat parasites off of other marine animals, including inside the mouths of predators like sharks and barracuda. The sharks and barracuda don’t eat the cleaner fish, much to the shock of the first humans to observe this interaction! Both species benefit here—cleaners get food and don’t get eaten by predators, while the other animals get healthier as a result of having parasites removed.

There’s also interspecies cooperative hunting, which has been observed between groupers and moray eels. These animals are both predators that feed on similar prey, and by working together they’re able to access prey that might otherwise be out of reach, like small fish hiding in reef crevices that narrow-bodied eels can access but groupers cannot.

What about commensalism, where one animal benefits and the other isn’t really helped or hurt? One example of this are worms that make a burrow in the sand to make their home. Sometimes small fish or crabs will hide from predators in that habitat, occasionally living there long term. The worm has helped the small fish or crab by giving them a place to live, and the presence of the small fish or crab doesn’t really affect the worm one way or the other.

The many examples of animals from different species working together, helping each other, really is one of the most fascinating things about the study of marine ecology!

Ask a Marine Biologist is a monthly column where Dr. David Shiffman answers your questions about the underwater world. Topics are chosen from reader-submitted queries as well as data from common internet searches. If you have a question you’d like answered in a future Ask a Marine Biologist column, or if you have a question about the answer given in this column, email Shiffman at WhySharksMatter@gmail.com with subject line “Ask a marine biologist.”

Dr. David Shiffman is a marine conservation biologist specializing in the ecology and conservation of sharks. An award-winning public science educator, David has spoken to thousands of people around the world about marine biology and conservation and has bylines with the Washington Post, Scientific American, New Scientist, Gizmodo and more. Follow him on Twitter, Facebook and Instagram, where he’s always happy to answer any questions about sharks.

The views expressed in this article are those of David Shiffman, and not necessarily the views of Sport Diver or Scuba Diving magazines.