Rapa Whelk

An Invasive Species of the Chesapeake Bay

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

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

ChanneledKnobbed

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– 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