How do Deep Sea Animals Find New Food Sources in the Pitch Black?

Question: How do the creatures that specialize in living at hydrothermal vents move to new or different vents? — Andrew D, Massachusetts

Answer: The short answer to your question, Andrew, is we have a general idea of how animals move from one vent to another (slowly swimming or crawling between food oases, or dispersing as larvae), but a lot of the mechanisms for this are still not fully understood! Some get lucky and when they move, and some use amazing adaptations to life in the deep sea, and some don’t move once they’re adults.

The deep sea is a fascinating and challenging place to live. It’s not just the crushing pressure, bitter cold, and total lack of light, but also the scarcity of food. Some animals eat “marine snow,” which is little bits of edible biomass (including poo) that fall from the animals living above them in the water column. Others scavenge animals that sink to the seafloor when they die, sometimes called “whale falls."

At the most famous deep sea ecosystem, the hydrothermal vent, heat and chemicals come from the vent itself. This forms the basis of the food chain grounded in chemosynthesis. (It’s far too dark for photosynthesis, after all.) These vent ecosystems can be absolutely teeming with life. But only a very small portion of the seafloor is active vents, and directly around vent is essentially a marine desert. How do deep sea animals get from one deep sea oasis to another?

Some don’t! Organisms like the iconic tube worms are sessile as adults, which means that they don’t move and are anchored in place. Think of sponges or corals in shallower water, once their larvae settle and they start to grow, they’re in one place the rest of their lives! But their planktonic larvae can move, carried by currents—which notably means they don’t have a lot of control about which direction they go, or where they end up. Deep sea organisms often have a longer planktonic phase of their life cycle than their shallow water cousins, allowing them to potentially disperse to more places, or to disperse farther away. Some larvae are lucky enough to be carried to a new hydrothermal vent—though most won’t and simply die.

Other deep sea species, like fishes, are able to move as adults when a food source disappears. When a whale fall, for example, is exhausted—bones and all— mobile animals can just swim or crawl until they find a new suitable place, stopping off at smaller sources of food along the way to a longer-term home. This is sometimes called the “stepping stone” model of colonizing a new habitat, as in crossing a river by stepping on small stones.

The long trek between oases of food means that they may go a very long time between meals. As a result, some deep sea animals like crabs are adapted to be able to eat a huge meal they can store in their stomach for weeks or longer.

Because of this, scientist had long assumed that two vents that are relatively close to each other are more likely to have similar animals living around them than two vents farther apart. New research, however, shows that this isn’t always the case.

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.