486 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



may feed on oysters to a limited extent, but tlieir 

 relative importance has not been studied. 



The Gulf area is fortunate in not having to con- 

 tend with the starfish which constitutes so serious 

 a predation problem along the Atlantic seaboard. 

 The black sea drum, Pogonias, is described fre- 

 quently in the literature as a serious pest in the 

 Gulf area (Moore 1907). This writer has no 

 first-hand experience with its activities, but 

 oystermen report it as a nocturnal visitor to areas 

 containing newly bedded oysters. Large schools 

 of fish may destroy thousands of bushels of oysters 

 in a short time. Apparently this fish does not 

 attack the natural oyster reefs. 



Various species of crabs constitute a serious but 

 imperfectly defined menace to the oyster popula- 

 tion. The blue crab, Callinectes, is a common 

 inhabitant of the oyster reef, and there are many 

 observations of its activities in cracking open the 

 soft new growth on oyster shells and eating the 

 meats. In limited areas the stone crab, Menippe, 

 is an occasional marauder. Its massive claws 

 are able to crack open oyster shells with ease. 

 Mud crabs of the family Xanthidae inhabit the 

 oyster community in large numbers and undoubt- 

 edly consume many of the tiny spat. The list of 

 predators includes the oyster "leech," Stylochus 

 inimicus,^ and other polyclad flatworms of sev- 

 eral species which are common associates in the 

 oyster community. These worms may cause se- 

 rious damage, but evidence indicates that they are 

 secondary rather than primary predators (Pearse 

 and Wharton, 1938). They cause the greatest 

 harm in areas where oysters are alreatly in a 

 weakened condition because of some other factor. 

 In the healthy oyster community they are prob- 

 abl}- of little importance except in their role as 

 scavengers. 



Commensals. — Three commensal animals occur 

 in numbers sufficient to affect the biology of the 

 oyster seriously. However, their injurious effects 

 are of greater importance to the oyster industry 

 than to the continuity of the species. The bor- 

 ing sponge, Cliona, the boring clam, Afartexia, and 

 the blister worm, Polydora, dwell within the oyster 

 shell, existing at various population densities de- 

 pending upon the environment. The sponge and 

 clam are more prevalent in areas of high salinity. 

 The annelid is more commonly associated with 



^ Sti/lnclliis froittalis W'irill .ifciirtiing to L. H. Hynuin. Sec paj£c 3U1 of 

 this ttook. 



soft, muddy bottoms extending into areas having 

 lower salinity levels. All of these animals com- 

 pete with the oyster for food. Their injury to 

 the oyster is difficult to evaluate, but obviously 

 they force it to secrete excess amounts of shell in 

 order to keep the burrows of these organisms sep- 

 arated from the oyster meats. Both the sponge 

 and clam form extensive excavations opening on 

 the exterior surfaces of the shells, making the 

 shells friable and hard to handle commercially. 

 Such oysters usually have a massive eroded ap- 

 pearance, and typically, the meats are of inferior 

 quality. The annelid lives on the internal surface 

 of the valve where it is sealed off in a blister by 

 the oyster. Its injurious effect is primarily a de- 

 crease in the esthetic appeal of oysters on the half 

 shell, although in areas outside of the Gulf unusu- 

 ally large colonies of these worms have suffocated 

 oyster communities. 



The commensal crab. Pinnotheres, of frequent 

 occurrence in oysters in high salinity areas along 

 the Atlantic coast where it may be occasionally 

 injurious, is uncommon in tlie Gulf. A related 

 species, however, is often present in the bay 

 scallop in Florida waters. 



The animals and plants associated with the 

 oyster community are legion. vSome have import- 

 ance in comj)eting with the oyster for attachment 

 surface, and some in competing for food. Their 

 biological and economic importance to the oyster 

 population are mostly a matter of conjecture. 

 The relative abundance of the commensal forms 

 varies greatly from one oyster reef to another. 

 In low salinity areas these forms are relatively 

 rare, but their numbers increase to species climax 

 at different higher salinity levels. The following 

 listing of the more common members of the com- 

 niiinity does not indicate their relative numbers or 

 importance; any one of them at some time or place 

 may completely envelop the oysters, decreasing 

 the available food supply and preventing the 

 attachment of oyster spawn: 



.'Mgae, of various tyjjes. 



Sponges, l)oth eiicnistiiig and Ijoring. 



Hydroids and anoinone.s. 



I'olychaetc worni.s. 



Other niollusks, including Anomut, Cnpululn, Ostrea, 



aufl M !/liliis. 

 HariiaclcK. 



Hryozoa, hotli encrusting anil upright. 

 TuiLicatos. 



