1. An Invasive Species of the Chesapeake Bay
Rapa Whelk
An Invasive Species of the Chesapeake Bay

2. What is a Rapa Whelk? 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

3. 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

4. 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

5. How to know it’s a Rapa
Rapa
Knobbed
Channeled

6. 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

7. How to be a Successful Alien Species
Must invade the habitat and find suitable living conditions/food
Must be able to REPRODUCE successfully

8. 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

9. Time to Maturity Native whelks: Rapas:
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

10. R or K selected? Natives: more like K selected. WHY?
Rapas: more like r- selected. WHY?

11. 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
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

12. 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!

13. 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

14. 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