Scientific Name:

Spondylus spinosus

Κοινό όνομα:
Spiny oyster
Ταξινομική Ομάδα:
Μαλάκια

Πληροφορίες

Adults can be up to 12 cm in width. The lower valve is cemented very firmly to a hard surface and is more cup-shaped. The upper valve is rather flat and covered with fine short spines, which gradually become longer and arranged in rows close to each other. The outline of the shell is oval and irregular. The interior of the shell, where the two valves connect, has two teeth of equal size on each side. The external colour of the shells is purple, brick-red, red-brown or orange-brown, while the hinge area is white with dark spots. The interior is white, becoming darker (beige) in the hinge area.

The spiny oyster occurs on rocky bottoms at depths of 2–40 m. It can form large populations of up to 15 individuals per square metre and often can be found together with another alien bivalve, Chama pacifica.

The size at first reproduction of the spiny oyster is 30 mm shell length. In the eastern Mediterranean, gonad development began when seawater temperature was ~20°C and spawning take place at ~27°C (June-August).

This oyster resembles another Mediterranean alien species, Spondylus groschi, but the latter’s larger number of main ribs (6–16 compared with 6–7 in S. spinosus), the homogeneous shape of its spines (large and flat like a palette knife) and their colour (compared with white spines in S. spinosus) distinguish these two non-native species.

Spondylus spinosus Similar Species (0010) EL
Spondylus groschi

Native to the Indo-Pacific and Red Sea, the spiny oyster was first recorded in the Mediterranean in 1988 in Israel, subsequently spreading to the Turkish and Lebanese coasts; it is presently confined to the eastern Mediterranean Sea. It is presumed that it arrived via the Suez Canal and its further dissemination was assisted by ships.

The spiny oyster, either alone or together with the jewel box oyster, Chama pacifica, can form dense aggregations that produce solid reefs at some sites, completely replacing native oyster species.

Competition and reduced plankton availability caused by decreased water flow can also slow down the growth of other benthic organisms.

The economic impact of this invasive species is unknown. It is a valuable species for seashell collectors, with a small trading market. In Lebanon it is also harvested and sold for food in restaurants.

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 soon re-establish previous densities. These bivalves are also strongly attached to the sea bottom and their eradication implies 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 Chama pacifica.

Shabtay, A., 2011. The invasive oyster Spondylus spinosus Schreibers, 1793 in the Israeli Mediterranean coast. PhD thesis, Tel Aviv University, 97pp.

http://www.ciesm.org/atlas/Spondylusspinosus.html

Εικόνα
Spondylus spinosus Illustration

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