Do Red Tides Affect Crabs?

By Jeremy Cato
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A red tide is a dangerous and ecologically disruptive natural phenomenon. It can cause marine fish to die in massive numbers and can even harm the lives of land animals and humans. Land crabs and marine crabs can be affected by red tides.

Red Tide Information

A red tide is a form of massive algal bloom -- particularly of the microscopic algae species, Karenia brevis -- although other microscopic algae can form red tides. A red tide appears as a reddish-brown mass floating on the surface of a large body of water. Red tides can be incredibly large; some can even be seen from space. They are not always red. Some can appear brown, green, purple or may even be clear, causing no water discoloration. The exact cause of red tides is unknown.

Crab Information

Crabs are crustaceans -- marine, freshwater and land animals that have thick exoskeletons, claws and 10 legs. There are more than 3,000 existing species. They reproduce sexually, and the females lay eggs as opposed to giving live birth. They are also largely omnivorous animals that eat mostly algae, though they consume shellfish, fungi, bacteria, other crustaceans and even dead animal and plant matter. Many crabs species are edible; hence the lucrative industry of crab fishing.

Crabs and Red Tides

Unlike other animals, crabs aren't directly affected by red tides. This is because they aren't filter feeders. Red tides produce algae that can build up massive amounts of toxins in the water. Filter feeding animals, such as oysters, clams, mussels and some fish, filter tons of water and develop concentrations of these toxins. However, because red tides can kill the animals that crabs eat, they may suffer starvation. Also, red tides remove many nutrients and oxygen from water that can also affect crabs.

Other Information

Because crabs don't filter feed and can't build up high concentrations of toxins, they're usually safe for humans to eat -- even when there is a red tide. Crab fisheries can still experience a slowdown in sales because of the negative stigma attached to red tides. Red tides can harm humans, because the toxins that shellfish can absorb can cause deadly paralysis in humans. Take every precaution when consuming seafood when a red tide has been discovered.

About the Author

Jeremy Cato is a writer from Atlanta who graduated with Phi Beta Kappa honors and an English degree from Morehouse College. An avid artist and hobbyist, he began professionally writing in 2011, specializing in crafts-related articles for various websites.