Seaweed-Eating Crabs Could Help Save Threatened Coral Reefs

Caribbean king crabs could help save coral reefs facing a steep decline for many years due to climate change, pollution, and disease.

A study published in Current Biology showed that Caribbean crabs could help combat the seaweed that devours the coral reefs to revive the habitat of many fishes.

Researchers have studied how seaweed-eating crabs behave in the Florida Keys and found that these crabs are better than other species at removing overgrown seaweeds that threatens the reefs. The Caribbean king crab could reduce seaweed cover by 50% when introduced to experimental plots on coral reefs.

The researchers believe that boosting the presence of the seaweed-eating crabs in the wild could help combat the seaweed problem that is spreading that a faster rate due to climate change and restore coral reefs in which experts project will completely disappear by the year 2100.

Reef Goats to the Rescue

The study from researchers of Florida University found that king crabs act as reef goats that eat almost any type of seaweeds and eat a lot of it.

These crabs are native to Florida and the Caribbean who eat algae, including seaweeds, as their primary food source. Their presence on the coral reefs is very much appreciated as they help restore the corals. People have been raising them for consumption, but their ecological role is mainly to help coral reefs, FIU professor Mark Butler said.

Although seaweeds are beneficial to the ocean ecosystem, too much growth can also cause harm on coral reefs. For instance, if they grow too much they can prevent the baby or new corals from settling into reefs as they block the sunlight needed for them to grow, and produce chemicals that are essential for their reproduction, immune responses, and fish attraction.

Moreover, other species also feed on seaweeds, but certain types will not graze on, like the Halimeda seaweed. The Scuba Diving website reported that the researchers conducted their experiment with nearshore waters where Halimeda seaweed is abundant. They observed that the king crabs were able to reduce the seaweed cover by around 50% to 80%.

The findings show that herbivorous crabs can be used to restore coral reefs in addition to the common approach of transplanting coral fragments onto degraded reefs, Science Daily reported. In essence, the researchers said that the crabs could improve the habitat conditions for corals and fishes.

What's Next?

To put the findings into practice, Butler said that they have already established coral nurseries to help in coral restoration and require setting up nurseries to raise large numbers of crabs. According to the researchers, they are now in a search to find the needed resources to do that.

Also, Butler said that they also need to figure out what would happen if the crabs become too many in the reefs as these animals typically stay on one reef system for the rest of their lives, so a population boom is possible.

"We're going to have to figure out what is the exact density we should keep," Butler says.

This work is supported by an NOAA-Nature Conservancy Community-Based Restoration Grant, a Garden Club of America Fellowship in Ecological Restoration, and a Paul Kirk Wetland Research Fellowship, according to Science Daily.

Check out more news and information on Coral Reefs on Science Times.