Rapa Whelk An Invasive Species of the Chesapeake

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 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. 4 mm 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. 3 mm 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 10 ppt – 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