55 



growth upon the valves of oysters produces a buoyancy 

 entailing much loss to parkers at Arcachon. The 

 specific gravity of these algae is scarcely more than 

 that of sea water and so when their tufts fall flaccid 

 upon themselves on the recession of the tide, many of 

 the gas bubbles disengaged by their cells during the 

 process of assimilation are imprisoned among the fila- 

 ments ; on the return of the tide the accumulation of 

 these bubbes is often sufficient to render the tuft so buoyant 

 that the oysters whereon they grow are floated up and 

 carried towards the boundary of the park. There the 

 palisade of pine branches may arrest their further course, 

 but wherever a gap occurs they are carried through either 

 to float into an adjacent park or to be lost in the no-man's 

 land of the channels. It is noteworthy that " bouquet" 

 is a trouble of recent origin. In 1878 it was not known 

 or at least was so unimportant as not to be noted as an 

 oyster culture danger by MM. de Montauge, practical 

 culturists, who published in that year an exhaustive 

 summary of the then known oyster enemies and maladies 

 of the Arcachon basin. Both the alga? included under the 

 term '' bouquet" are species properly belonging to the 

 Mediterranean and subtropical Atlantic and while the 

 range of Chondria tenuis sima extends to England, Hypnea 

 musciformis is not known to thrive north of Arcachon. 

 Another alga, the " balloon weed ", Colpomenia st'nuosa, 

 is another very active species in floating away oysters, but 

 so far it has not established itself in the Arcachon district. 

 Considerable loss from this cause can be avoided only 

 by constantly cleaning the oyster shells, rubbing them 

 against one another, a process which necessitates the 

 expenditure of much labour. High level parks suffer 

 least as a hot sun or heavy showers of rain occurring at 

 low water during spring tides kill off the bulk of the 

 harmful tufts of "bouquet". Sauvageau # suggests 

 the utilization of the herbivorous periwinkle, Littorina 



*" A piopos du Colpomenia sinuosa." [Travaux des labcialoires du Station 

 biologique d'Arcachon, 1906.] 



