Carcinonemertes errans

Carcinonemertes errans is a ribbon worm in the family Carcinonemertidae. It lives in symbiosis with the Dungeness crab (Metacarcinus magister), consuming the crab's developing eggs. In 1980 it was implicated in the collapse of the Dungeness crab fishery in central California.

Carcinonemertes errans
Scientific classification
Kingdom:
Animalia
Phylum:
Nemertea
Class:
Enopla
Order:
Monostilifera
Family:
Carcinonemertidae
Genus:
Carcinonemertes
Species:
C. errans
Binomial name
Carcinonemertes errans
Wickham, 1978[1]

Ecology

The planktonic larva of the worm settles on a suitable crab host and encysts on the exoskeleton. Carcinonemertes errans is the first species in its genus to be found on a single host species. The worm has a permanent symbiotic relationship with its host crab but it is not a parasite as it does not feed directly on the crab but is instead an egg-predator. In male crabs, and in non-breeding female crabs, the worm may live in the axils of the limbs and encyst. After mating, the mature female crab stores the sperm for several months, before releasing a batch of fertilised eggs onto her abdomen, where she tucks them under the tail flap. At this stage, the ribbon worm migrates to the mass of eggs and feeds on the developing embryos.[2][3]

If the worm larvae happen to settle on the exoskeleton of a brooding female crab, they can move immediately to the underside of the abdominal flap and metamorphose within 48 hours into juvenile worms. When settling, the larvae are gregarious, settling preferentially on already infected crabs.[4] It has been found that the worm is adversely affected by a lowering of the water salinity. Crabs in estuaries show an estuarine gradient, with crabs nearest the ocean carrying more worms than those further upstream.[5]

Effect on the Dungeness crab industry

The Dungeness crab industry is an important fishery on the Pacific coast, with 53 million pounds (24 million kilograms) worth $170 million being harvested in 2014.[6] In 1980, the central California fishery was badly affected; Carcinonemertes errans was implicated, with 50% of the crabs' eggs produced each year being predated.[3]

References
  1. Gibson, Raymond (2005). "Carcinonemertes errans Wickham, 1978". WoRMS. World Register of Marine Species. Retrieved 25 February 2019.
  2. Light, Sol Felty (2007). The Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon. University of California Press. p. 25. ISBN 978-0-520-23939-5.
  3. Wickham, Daniel E. (1980). "Aspects of the life history of Carcinonemertes errans (Nemertea: Carcinonemertidae), an egg predator of the crab Cancer magister". Biological Bulletin. 159 (1): 247–257. doi:10.2307/1541022. JSTOR 1541022.
  4. Dunn, Paul H.; Young, Craig M. (2014). "Larval settlement of the nemertean egg predator Carcinonemertes errans on the Dungeness crab, Metacarcinus magister". Invertebrate Biology. 133 (3): 210–212. doi:10.1111/ivb.12059.
  5. Dunn, Paul H.; Young, Craig M. (2013-12-20). "Finding refuge: The estuarine distribution of the nemertean egg predator Carcinonemertes errans on the Dungeness crab, Cancer magister". Estuarine, Coastal and Shelf Science. 135: 201–208. doi:10.1016/j.ecss.2013.10.012.
  6. "Dungeness Crab Report 2014" (PDF). Pacific States Marine Fisheries Commission. Retrieved 27 February 2019.
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