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Rapa Whelk
An Invasive Species of the
Chesapeake Bay
What is a Rapa Whelk?
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Large marine snail or gastopod
May grow as large as a softball
May live for more than 10 years
Rapana venosa (refers to distinct
horizontal black veins on some shells
• Native to oceans near Korea and Japan
How’d they get to the
Chesapeake Bay?
• Discovered in the Black Sea in the mid
1940’s--probably transferred by humans
• Since then they’ve moved to the Adriatic,
Aegean and Mediterranean Seas
• 1998: Discovered in the Chesapeake Bay
• Probably carried in ballast water from Black
Sea. Ships come to Newport News for coal
and Black Sea region is a major consumer
Why Do We Care?
• Predators-eat oysters and hard clams
• Since they are new to the Bay, they have no
enemies or predators--they may upset the
ecological balance
– Larvae: vulnerable to benthic predators (like all
whelks)
– Adults: Not vulnerable to sea turtles because of
their larger size
• Compete with native snails for food and
habitat
How to know it’s a Rapa
Rapa
Knobbed
Channeled
How to Stop the Invasion
• Since September 1998, VIMS has offered a
bounty to watermen who find and bring in
Rapas-– $5 per live Rapa; $2 per dead Rapa
• This has helped track their locations in the
Bay as well as removing some of them
• September 2009: Budget cuts forced the end
of the program
How to be a Successful Alien
Species
• Must invade the habitat and find
suitable living conditions/food
• Must be able to REPRODUCE
successfully
Stages of Whelk Life Cycle
• Egg masses
– Native whelks: laid in
shallow water on
sand or mud tidal
flats
– Rapas: laid on hard
substrates-cemented into place
Time to Maturity
• Native whelks:
– Egg strings laid in fall and develop over the winter
– Female may lay up to 3 egg strings totaling 18,000
eggs
• Rapas:
– Eggs masses laid in spring and develop one
month after being laid
– Female may lay up to 10 egg masses per year
totaling 2 million eggs
R or K selected?
• Natives: more like K selected. WHY?
• Rapas: more like r- selected. WHY?
Larval Differences
• Native Whelks: Larvae are miniature replicas
of adults--crawl on benthos.
4mm in size: don’t crawl very far
• Rapa: Swimming veliger (larvae) that lives in
water column for 4-5 weeks after hatching
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Eat plankton; stay in euphotic zone
0.3mm long when first hatched--float with currents
Easily moved throughout the entire Bay with tides
At end of this stage, sinks to bottom and
transitions into miniature adults
Why is Veliger important?
• Millions of larvae are in the water--some
of them get swept into ballast water
• Ships can travel from Norfolk to Europe
in 2 weeks
– Since swimming larvae live a month before
becoming benthic; many can survive the
trip and be introduced somewhere else!
Ecological Limits to Rapa
Success
• Planktonic veligers are vulnerable to
predators that eat plankton: sea nettles, larval
fish and adult filter feeding fish (menhaden)
• Adult benthic form: young adults face
predation by mud crabs, blue crabs (same as
all whelks)
• Large adults: no true predators because of
their large size
Environmental Limits to Rapa
Success
• Salinity: veligers don’t do well in
salinities of less than 10ppt
– Very few Rapas in upper parts of Virginia
and Maryland rivers
• Substrates: Hard substrates needed for
egg masses and for veligers when they
descend to the bottom
– Adults need soft substrate to burrow in and
need large clams to eat