Female Crabs Only Eat Their Own Young When They’re Hungry

Hemigrapsus on Orcas Island 06 For many ocean invertebrates, the first stage of life occurs as tiny larvae in the plankton.  The toughness of the planktonic larval life has caused many scientists to wax poetically, as we tend to do on subjects of invertebrates. As noted by Emery in 1973, these larvae face a “wall of mouths” ready to consume them. More recently Miller and Morgan (2014) state the larvae navigate a “gauntlet of planktonic predators.”  A host of adaptations by both the larvae and adults try to change the rules of this predation game. Some larvae have chemicals that make them unpalatable. Others possess spines that ward off predators. Some larvae are able to sink or flee in the presence of a hungry mouth.  Adults do their part by synchronizing larval release during times of less predation or by moving to new areas with fewer predators to release larvae.

Zoea larva identified by DNA barcoding. Off Newport Aquatic Center, Newport Beach, Orange County, CA. 12/05/12. © Peter J. Bryant.

Please mom don’t eat me!  Zoea larva of a Yellow Shore Crab. Photo courtesy of © Peter J. Bryant.

But sometimes the hungry mouths that larvae need to avoid are their own parents and relatives.

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Sometimes even recent crab mothers get hungry. ~25% of recent mothers cannibalized larvae. But in 2007 recent mothers were a little more hungry about 2x as hungry.

Many marine invertebrates suspension feed, basically straining plankton snacks out of the ocean.  But what is a good parent to do when their own young gets mixed into the food bowl?  Yellow shore crabs and European green crabs reduced their eating when they recently released young.  Note I say reduced and not just stop.  A hungry parent still needs to eat.  Female crabs that recently carried eggs, i.e. ovigerous, ate only 25-30% of their own larvae.  Non-ovigerous…well they got their ‘eat on’ consuming about 90% of larvae.  However, a year later in 2007 there was little difference between ovigerous and non-ovigerous females in cannibalism of their own larvae.  The authors hypothesized and then tested the idea that hungrier females would consume more of their own larvae.  Twenty-two days of starvation increased the cannibalism of larvae by 30%!

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How many larvae will a female crab eat of her own species (conspecific) versus other species (interspecific)? Depends on how hungry she is!

So to sum up, larvae are fine just along as the parents aren’t too hungry. Miller, S., & Morgan, S. (2014). Temporal variation in cannibalistic infanticide by the shore crab: implications for reproductive success Marine Ecology DOI: 10.1111/maec.12172

Emery A.R. (1973) Comparative ecology and functional osteology of fourteen species of damselfish (Pisces: Pomacentridae) at Alligator Reef, Florida Keys. Bulletin of Marine Science, 23, 649–770.

Dr. M (1629 Posts)

Craig McClain is the Assistant Director of Science for the National Evolutionary Synthesis Center, created to facilitate research to address fundamental questions in evolutionary science. He has conducted deep-sea research for 11 years and published over 40 papers in the area. He has participated in dozens of expeditions taking him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses mainly on marine systems and particularly the biology of body size, biodiversity, and energy flow. He focuses often on deep-sea systems as a natural test of the consequences of energy limitation on biological systems. He is the author and chief editor of Deep-Sea News, a popular deep-sea themed blog, rated the number one ocean blog on the web and winner of numerous awards. Craig’s popular writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web.





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