1 / 14

Rapa Whelk

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.

watson
Download Presentation

Rapa Whelk

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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: • 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

More Related