Scientific Name:

Chama pacifica

Common Name:

Jewel box oyster

Taxonomic Group:

Molluscs

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Information

Key Identifying Features

A large ovoid-shaped oyster that can grow to about 8–10 cm in length. The shell is usually thick and irregularly rounded. The valves are different sizes, the lower one usually being larger and deeper than the upper, which is usually flat.

The external valve surface bears short spines that curve out from the surface and are larger and more prominent on the larger valve near the shell margin. The internal margin of the shells is encircled by a rim of close, fine ridges that look like a zip fastener. The external colour is highly variable, from white to pinkish-red with pale-rose blotches around the shell margin; the spines are often white.

Identification and Habitat

Chama pacifica occurs on rocky shores and hard substrates, usually on exposed sites from the intertidal zone down to a few metres’ depth, occasionally to 40 m. It is able to thrive in harbour environments and is usually found together with other oysters (Spondylus sp.) on bare rocks where it attaches tightly to the substrate with one valve. Fouling organisms often attach to the shells. It has a low tolerance to salinity changes, particularly low salinity.

Reproduction

Sexes are separate and fertilization is external. The jewel box oyster has a single, annual, temperature-dependent spawning season, usually occurring during spring and summer when the water temperature is higher than 21 °C. This prolonged spawning period partly contributes to the success of the species in new environments. Eggs hatch as free-swimming planktonic larvae.

Similar Species Description

The native oyster Chama gryphoides can be distinguished by its smaller size (up to 2.5 cm), irregular radial ‘ribs’ arranged in concentric rows and the white colour of its shell.

Chama pacifica Similar Species (0010) EN — **Chama gryphoides**

Chama pacifica Similar Species (0020) EN — **Chama gryphoides**

Chama pacifica Similar Species (0030) EN — **Spondylus spinosus**

History and Route of Introduction

Widespread in the Indo-West Pacific, C. pacifica was recorded for the first time in the Mediterranean Sea from Alexandria (Egypt) in 1905. From here, it colonized many areas of the south-eastern basin: Israel, Lebanon, Cyprus, Turkey, Syria and Greece. Its presence in the Mediterranean is due to the opening of the Suez Canal, while it has probably been spread further by ships and recreational boats as part of the hull fouling assemblage.

Ecological Impacts

Chama pacifica has become an important component of the eastern Mediterranean shallow benthos, and is occasionally found in association with Erythrean spiny oyster, Spondylus spinosus, another alien oyster. Both species singly or together can form dense aggregations, producing solid reefs at some sites and completely replacing native species such as the European thorny oyster, Spondylus gaederopus, or the smaller oyster, Chama gryphoides. Competition and reduced plankton availability caused by decreased water flow can also slow down the growth of other benthic organisms.

Economic Impacts

It is a valuable species for seashell collectors, with a small trading market. The impact of this invasive species is unknown.

Management Options

A suggested prevention action is to conduct public awareness campaigns combined with monitoring.

Control actions are feasible only in specific circumstances, such as when individuals are localized in a very confined area. Fouling communities on recreational boats and ships can be removed but larvae can re-establish previous densities. These bivalves are also strongly attached to the sea bottom and their eradication involves the removal of part of the local benthic communities and their substratum. This procedure clearly has a considerable impact and must be shown to be justifiable by means of an environmental impact assessment, as in the case of the other alien bivalve Spondylus spinosus.