American oyster, continued 



Individuals of this species in high salinity areas are 

 more susceptible to disease infection by the patho- 

 genic protozoan, dermo (Perkinsusmarinus) (Hofstetter 

 1 977, Soniat et al. 1 989, Berrigan et al. 1 991 , Killam et 

 al. 1 992). Dermo interferes with growth and reproduc- 

 tion, and is associated with, and primarily responsible 

 for, annual losses of 1 0% to 50% of the market oysters. 

 Water temperature is an important factor in controlling 

 the occurrence and effects of this organism. Repro- 

 duction of dermo is drastically lowered in water tem- 

 peratures below 20°C, and warm water temperatures 

 during the summer months may promote it. The 

 ectoparasitic gastropod, Boonea impressa, which in- 

 fests the American oyster, is also capable of transmit- 

 ting dermo from one oyster to another (White et al. 

 1987). Troublesome boring organisms reduce the 

 market value, as well as consume energy in shell 

 growth and repair. The most common of these are 

 Cliona, the boring sponge, and Diplothyra smithii, the 

 boring clam. Oysters infested with burrowing clams 

 and sponges have been indicated to be much more 

 susceptible to predation by black drum and possibly 

 other predators because of weakened shells (Cave 

 1978). Intertidal oysters, because of their slower 

 growth, thicker shells, and less relative time underwa- 

 ter, seem to be less susceptible to this predation than 

 subtidal oysters. Blooms of red tide are another source 

 of natural mortality. High concentrations (500 cells/ml) 

 of this diatom, Colchlodinium heterolobatum, can kill 

 oyster larvae (Killam et al. 1992). The oyster crab 

 (Pinnotheressp.) sometimes lives in the mantle cavity 

 of the oyster where it may cause damage to the gills 

 (Stanley and Sellers 1986). 



The American oyster also competes for space and food 

 with other organisms. Competitors include bryozoans 

 (Conopeum commensale), barnacles (Balanus sp.), 

 slipper shells (Crepidula sp.), hooked mussel 

 (Ischadium recurvum), jingle shells (Anomia sp.), 

 anemones, serpulid worms (Eupomatus dianthus), 

 tunicates, and algae (Marshall 1954, Schlesselman 

 1955, MacKenzie 1970, Berrigan et al. 1991). The 

 impact of competition for settlement space in the Gulf 

 of Mexico has not been fully determined (Berrigan et al. 

 1991), but heavy sets of barnacles can seriously re- 

 duce the area of hard surface available to settling 

 oysters (Ingle 1951). Young oysters can also be 

 smothered by the excreta from polychaete worms 

 (Polydora sp.) (Stanley and Sellers 1986). In some 

 cases, these organisms have a purely commensal 

 relationship with oysters, or do not seriously compete 

 with them (Stanley and Sellers 1986, Berrigan et al. 

 1991). 



Personal communications 



Van Hoose, Mark S. Alabama Division of Marine 

 Resources, Dauphin Island, AL. 



References 



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Alvarez, M.R., F.E. Friedl, and CM. Hudson. 1991. 

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