Tracking the Invasive Veined Rapa Whelk

River Watch

Summary
Determine the risk of a successful rapa whelk (Rapana venosa) invasion for four hypothetical estuaries.

Introduction
Veined rapa whelks (Rapana venosa) are predatory marine snails that have been introduced into the Chesapeake Bay, USA. These large snails eat ecologically and commercially valuable shellfish including oysters (Crassostrea virginica) and hard clams (Mercenaria mercenaria). There are few predators in Chesapeake Bay that can successfully attack and eat large rapa whelks. Since rapa whelks are long lived (possibly more than 15 years) and reproductively active at 2-3 years old, once introduced, rapa whelks are very likely to become established if the habitat environmental conditions are suitable.

Rapa whelks are native to Asian waters near Japan and Korea. They were introduced to the Black Sea in the 1940s and have since spread into the Aegean, Adriatic, and Mediterranean Seas as well as Chesapeake Bay (USA), the Rio del Plata (Uruguay and Argentina), Brittany coast of France, and the North Sea near the Netherlands. Recent introductions are most likely the result of ballast water transport of swimming larval rapa whelks from occupied habitats into new environments.

The Chesapeake Bay is home to several of the largest ports on the US Atlantic coast, notably Hampton Roads-Norfolk. Most of the rapa whelks caught in the Chesapeake Bay have been from the Hampton Roads-Norfolk region. Aquatic scientists, resource managers, and commercial shellfish growers up and down the US Atlantic coast are very concerned that vessel traffic from Chesapeake Bay may introduce rapa whelks into other habitats. The million dollar question for everyone is: If rapa whelks are introduced to this habitat, will they survive and establish a self-sustaining population?

The answer to this question is a complicated one and will vary from place to place. The secret to finding an answer lies in understanding the biology and physiology of the rapa whelk. Larval period duration, or the length of time that a baby rapa whelk stays planktonic (swimming), and the length of time the larva is in ballast water affect whether or not a transported larva will be able to survive and be pumped out with ballast water into a new habitat. Salinity and temperature tolerances of the larval whelk will determine if the larvae survive if added to a new place via ballast water. The proper substrate and food availability will determine if the whelks survive to maturity and can reproduce, creating a self-sustaining population.

Data Activity
In this activity, we will determine the risk of a successful rapa whelk (Rapana venosa) invasion for four hypothetical estuaries. In order for an introduction of rapa whelks to a habitat to be considered a successful "invasion," the whelks must survive to reproduce in the new habitat and establish self-sustaining resident populations.

Download the teacher's copy of the Rapa River Watch booklet and distribute the background pages (1-3) and activity pages (4-7, 11-26) to the students. Divide students into small groups or research teams. Have each research team complete the Rapa River Watch Habitat Evaluation Worksheet (p. 7) for the four hypothetical estuaries.

Discussion Questions

1. Why are the environmental tolerances of an invading species so critical in the establishment of the animal in a new habitat?
2. Are all alien species harmful?
3. Suggest strategies that scientists, resource managers, and policy makers should adopt to reduce the number of harmful invasive species in the United States.