gastropod predator

Background

The Rapa whelk (Rapana venosa), a gastropod mollusk originating from the Sea of Japan, has expanded to other parts of the world, affecting the natural ecosystems of many waters. In the 1940s, Rapana venosa was introduced into the Black Sea, then extended to the Adriatic and Aegean seas. Recently, the rapa whelk has been found in the southern part of the Chesapeake Bay.

Habits and Life Cycle

• The rapa whelk is a predator that feeds upon mollusks. It attacks bivalves by rasping around the hinge region rather than boring a distinct hole.
• The rapa whelk is a gastropod, an organism characterized by its distinctive anatomy. A gastropod, literally meaning "stomach foot," moves around using the organ that contains its stomach.
• The rapa whelk reproduces by egg capsules, whose numbers vary with the female’s size, and which produce pelagic larvae.
• R. venosa can be distinguished from the three species of native whelk (channeled whelk - Busycon canaliculatus, knobbed whelk - Busycon carica, and lightning whelk - Busycon sinistru) by three distinct characteristics: small teeth along the edge of the shell, orange coloration along the inner edge of the shell and a pronounced channel.
• The color of the outer shell ranges from gray to reddish-brown, with dark brown dashes on the spiral ribs.
• The whelk can become quite large. Records exists of shells found as large as 7.2 inches in length. In the Chesapeake Bay, whelks have been found 4 to 6 inches long.
• The whelk’s expansion is considered to be one of the main causes for declining mussel populations in Bulgarian waters, the Kerch Strait and the Caucasus.

Although it is not clear how the rapa whelk was introduced to the Chesapeake Bay, resource managers are very concerned about its potential impact on native Bay species. Since it feeds on bivalve mollusks, the Bay’s clams and oysters are threatened by the spread of the rapa whelk. Studies at Virginia Institute of Marine Science are currently under way to help determine how far the rapa whelk has spread in the Chesapeake Bay, its potential environmental range and its impact on the Bay ecosystem.

Whelk photo courtesy: Virginia Institute of Marine Science

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Last modified: 12/2/04