ENVIRONMENT OF THE OYSTER 91 



physical conditions are also favourable to the presence and muliplica- 

 tion of numerous diatoms and other minute food-supplying organisms, 



A tidal rise of 3 or 4 feet, especially when flowing among islands or over 

 sand-bars or extensive flats, does not bring such a deep and sudden change 

 of cold water as to dangerously lower the temperature beyond the power 

 of accommodation of the oysters. In many cases the water brought up 

 by the tide is to a large extent the same as was carried out by the pre- 

 vious tide, and has consequently not been cooled by extensive mixing with 

 ocean water. It is warmed by the sun and by contact with the air and 

 with the extensive sand-beaches of the shore and of islands, sand-bars and 

 sand-flats. The oscillation of the tides back and forward mixes colder and 

 warmer water and saltier and fresher water, and preserves a greater uni- 

 formity, effects aeration, distributes food organisms, and carries eggs and 

 larvae to new areas. 



The depth of water in which the great masses of our oysters are found 

 varies from from one to three fathoms. At places, there are considerable 

 numbers exposed between the tide-marks, while at other places there are 

 oysters so deep as to be unattainable by the tongs. Oyster beds, banks, 

 or reefs that come to within 2 or 3 fathoms of the surface may be sur- 

 rounded by much deeper water, as is the case with the Curtain Island beds, 

 from which the depth falls off rapidly to 4 or 5 fathoms. 



A river, or in case of extensive areas several streams of fresh water 

 may discharge over or in proximity to the oyster beds. 



The salinity may vary to a great extent without endangering the life 

 of the oyster. At Bay du Vin it is as low as 1-012, and at Shediac as high 

 as 1 • 020. At Caraquet it varies from 1 • 016 to 1 • 019, according to whether 

 taken at low or high tide, for in the former case there is a greater pro- 

 portion of river-water and in the latter of sea-water. The low salinity of 

 Bay du Vin is due to the large amount of fresh-water brought down by 

 the Miramichi river. At the mouth of Miramichi bay the salinity is 

 1'019 — the same as at Malpeque, Cascumpeque, Summerside, Cocagne, 

 and most other places bordering on the Gulf or the Strait. 



Lime {calcium carbonate) is required by the oyster for the construction 

 of its shell, which forms the greater part of the weight of the oyster. The 

 amount of this existing in oyster (not to speak of other) shells is enormous, 

 all of which, or the constituents of which, must be contained in the water. 

 It comes from the disintegration of old shells, from rocks in the ocean and 

 along the shores, but especially from the river-water that has drained 

 through the land and over the rocks of river-basins. It constitutes a small 

 portion of the 12 to 20 parts in 1,000 of sea-water that we call salt, the 

 greater portion of which consists of common salt (sodium chloride). The 

 small amount of calcium carbonate is of great consequence to the 

 oyster, and may be the chief factor in limiting the size to which oysters 

 attain. 



