SPONGES, HYDROIDS, AND WOEMS. 149 



In addition to these principal foes, many minor " vermin " must be 

 contended with by the cultivator of our favorite bivalve. 



The oyster-catcher, and other shore-birds, steal not a few mollusks at 

 low tide. Barnacles, annelids, and masses of hydroid growth sometimes 

 form about the shells, and intercept the nutriment of the mollusk, until 

 it is nearly or quite starved ; this is particularly true in southern waters. 

 There are parasitic sponges also, which attach themselves to the oyster's 

 shell and immediately begin to penetrate its substance. One of these, 

 Cliona sulphured, is especially abundant along the middle Atlantic 

 coast, and often pushes its small burrows quite through the shell, com- 

 pelling the oyster to plug up the holes by extra layers of nacre on the 

 inside. 



Practically, however, sponges are of not much harm, while some fish- 

 ermen assert that to have the " red-beard" or branching sponge, the gray- 

 beard (Sertularia argentea), and several other hydroids and bryozoa which 

 pass under the general name of " scurf " and. " yellow moss," appear plen- 

 tifully on the beds, is a sure sign that the oysters are doing well ; should 

 an excess of these occur, however, they would both consume and tend 

 to keep from entering its mouth a part of the mollusk's food-supply, 

 and might also form eddies, acting as an impediment to catch drifting 

 matter, weeds, and the like, until the mollusks were partially buried and 

 smothered. In Narraganset Bay, a few years ago, oystermen were great- 

 ly troubled by multitudes of annelid worms (Serpulce), whose tortuous 

 cylindrical cases are formed thickly upon every shell, and serve to collect 

 a coating of cases, sand, mud, etc., which is often half an inch or more 

 thick. This is known locally as " sanding-up " or " loading," and under 

 its infliction the mollusks deteriorate greatly in quality. 



In addition to the active, animate enemies of the oyster, the beds suf- 

 fer seriously, at certain times, from the elements, as has been pointed out 

 in the preceding pages. Great storms will sweep the oysters all off the 

 beds, bury them under shifting sand or mud, or heap upon them the 

 drifting wrack torn from the shores. Beds which lie at the mouths of 

 rivers are liable to be injured by floods also, which turn the water wholly 

 fresh, or bring down enormous quantities of silt and floating matter, 

 which settles and smothers the oysters. 



To all these enemies and misfortunes cultivated oysters are more lia- 

 ble, and against them they are less defended than those growing upon 

 the natural beds, following the law that a disturbance of nature's equi- 

 librium is always to the advantage of the more powerful agencies present. 



10* 



