There is no better place, for a shell collector, than a high discard pile full of good stuff that was dredged offshore. This one was located in the backyard of an oyster farm, asleep in the summer, in the very bottom of the Gulf of Morbihan, southern Brittany, France.

This boat is used to collect oysters. Click in the pic to load a panoramic view (515Ko).

The last Sea Valorisation Scheme for the Gulf of Morbihan (feb. 2006) maintains the surfaces allowed to conchyliculture at their previous level of 4075 acres (1650ha). Farmers extract annually around 5000 tons of oysters (C. gigas and O. edulis), mostly in the western part, while the east is more dedicated to Cardiidae and Veneridae. Each farm manages oyster-banks situated near at hand, on lower intertidal to hight subtidal grounds, 50 to 700m offshore.

Great qualities in these species. Buccinum undatum reached here adult sizes (73 to 83mm), a fact that is not such common than expected; most of specimens found on markets live in colonies that are, unfortunately, overfished; their lengths rarely exceed 50mm. On local oyster banks, the whelks live in a perfect tranquility. They are not "commercially interesting" (means too rare).
Aequipecten opercularis. This is the Gulf form, a variant thas was discussed in a previous article (see here for shells from NE. Quiberon bay, at the mouth of the Gulf). This form is characterized by the dominant colour "red-algae", with pale marblings in addition.

Hopefully for shell collectors, it seems that there is no competition for food between the native muricid O. erinaceus (Linnaeus, 1758) and the invasive Japanese Drill P. inornata (Récluz, 1851): if both species love oysters, inornata can live in shallower waters than erinaceus.
Of course, oyster farmers have an other opinion, and must adapt their methods to the behaviour of their ennemies. The "on-bottom" culture, where young oysters were scattered on the ground and regularly moved, tends to be abandoned on behalf of a more secure practice, "off-bottom", where oysters are displayed on large tables, in net-bags. In order to avoid drills, these tables have their feet protected by a kind of boots that crawling molluscs cannot easily clear: often, necks of bottles. Of course, if this tip works well against Ocenebrinae, it remains ineffective with some fishes like Sparus auratus Linnaeus, 1758 Sparidae (die Goldbrasse, the Sea Bream, la Dorada), a species that has a jaw able to crunch Oysters.

Most of invasive molluscs were introduced, accidentally or not, by aquaculure. Successes of Pteropurpura inornata & Crepidula fornicata are two obvious examples: farmers are responsible of their introductions, and their concessions, which are found on all the coasts of Atlantic, strengthen the expansive power of these species by giving them excellent shelters and first quality seafood.

Delicate sculpture for these O. erinaceus dredged in the channel of Irus island.

P. inornata appears in 1995 in Oleron area. The population shows stronger similitudes with american stocks than with the original japanese specimens. It seems that french shells came from British Columbia in 1970, as "hitchhikers" during oysters transfers. The Pteropurpura is found today in the Gulf of Morbihan and in Mount St-Michael's bay: both are places of intense shell-farming. As there is no pelagic larval stage in the species, the only way to increase its distribution range remains the oyster sharing between different localities. "People of Charentes are the only responsible of this dispersion on our brittanic coasts" says a farmer who sells his production on Rennes fishmarket.

Inornata and erinaceus can destroy huge quantities of young oysters (up to 90% in Marennes-Oléron, around 60% in the Gulf). All this story began when people decided to cultivate only one species, Ostrea edulis, and not an assortment. When the flat oyster disappeared from many spots (diseases caused by Bonamia ostreae, Marteilia refringens & Herpesviridae), it was replaced by Crassostrea angulata, the Portuguese Oyster, which began to be overfarmed, and to fall ill (1970's). Again, obviously, a link was established between the monospecific character of oyster farming and the extension of this last illness caused by the well named Thanatostrea polymorpha...
Quickly, japanese oysters Crassostrea gigas were imported from eastern Pacific and took the place previously hold by these poor portuguese oysters; hidden among the shells, arrived Crepidula fornicata and Pteropurpura inornata.

Large and top-quality Flat oysters O. edulis from Cancale, Mount St-Michael Bay, N. Brittany. Farmers of the northern coast begin to undergo the pressure of inornata, but at lower levels than in the south. Click in the pic to see a heavy specimen of 12cm long. The labelled price is 2 euro each.

Ocenebra erinaceus and Pteropurpura inornata love oysters, but, also, mussels. "They can eat up to 90% of my shells" deplores an other farmer of the Gulf. "Even the bouchots are not safe from these damned beasts!". The word "Bouchot" refers to a technic of mussel farming: the cluster is fixed to a wooden pillar, and the mussels clutch the ones with the others, and with the post, by their byssal filaments. Too often, farmers discover Ocenebrinae quietly hidden inside the clusters. The arrival of inornata is perceived like a new subject of concern; and, so far, nobody discovered how to protect mussels banks from these predators, the European and the Japanese Drills.

Above and below: little (56mm) Pecten maximus from the Irus channel. This shell was attacked by two types of diseases: something close to the Brown Ring, of infectious origin, and, as a sequel, the Valves Thickening: malformations of the margins, anarchic growth.

"... il n'est pas déraisonnable de penser que le brunissement pathologique puisse engendrer des déficiences des structures minéralisées. Celles-ci créent alors un environnement favorable au développement de parasites, ou de micro-organismes, provoquant d'autres altérations coquillières."

Source in french: univ.brest.fr.Pecten Maximus: anomalies coquillières...

"... it is not unreasonable to suppose that pathological tanning can generate deficiencies in mineral-bearing structures. Those then create an environment favorable to the development of parasites, or micro-organisms, causing other shelly deteriorations."