soft and muddy. Oyster growth is limited to the roots of the mangrove 



trees that border the shores. The inlet known as Salt River on 



St. Croix island more closely approaches estuary conditions than other 



areas. 



Besides having high temperatures, the waters of Puerto Rico and 

 the Virgin Islands are very saline, perhaps too much so for the best 

 growth and reproduction of oysters. Tjrpical of this part of the world, 

 the heat and excessive evaporation concentrates the shallow waters and 

 increases their salt content. This is true even of the surface of the 

 open ocean in this area, where salinity is greatly increased from 

 evaporation and is only reduced by mixing by storms and currents. 

 Salinities as high as 40 parts per thousand may be found even in the 

 open sea. The range of salinity observed on this short survey was 

 from 34 to 37 parts per thousand. Observations made by Mattox in 

 Puerto Rico at intervals throughout a year showed a range of from 33 

 to 40 parts per thousand in the lagoon off Boqueron Bay, Although 

 oysters will live and reproduce at high salinity, they do not do as 

 well as in more brackish waters. As a matter of fact, in the lagoon 

 areas of Puerto Rico and the Virgin Islands, the heaviest set and the 

 greatest growth of oysters takes place at locations receiving the most 

 abundant fresh water from run off of the surrovmding area. It is possible 

 that oysters may not thrive when the fresh water entering the lagoon at 

 Boqueron is diverted. Construction of dams and use of the water for 

 irrigation purposes, part of the project already underway, may have an 

 adverse influence on the lagoon at Boqueron. 



The fact that oysters are not found on the bottoms of the lagoons 

 may be the result of sever*l factors. In the first place the bottoms 

 are muddy and soft ajid there is almost nothing for the attachment of 

 oyster larvae. It may be possible that lack of suitable bottoms and 

 cultch is important in limiting their location. On the other hand, 

 the vertical aerial roots of the mangrove have oysters only in the 

 area between tide levels. They are not found below the low water 

 mark. There may be some characteristic of the movement of the larvae 

 which keeps them close to the surface at the time of their attachment. 

 Enemies of the oyster are present, including the various oyster-drilling 

 mollusks, starfish, and fishes, which may prey on oysters that are not 

 exposed at low water. Also, growth of bryoeoans is rapid and the roots 

 near the low water mark are often covered with them. Rapid fouling of 

 available surfaces may limit the attachment of oyster spat. 



Although the rate of growth of the oysters of Puerto Rico and 

 the Virgin Islands is rapid, they do not reach a large size, the 

 largest attaining a length of 2-l/2 to 3 inches, the great majority 

 being much smaller. Indications are that continued high salinity is 

 a factor in this, for the largest oysters are found in the areas of 

 lagoons receiving the most fresh water. It is probable, however, 

 that this species of oyster differs from Ostrea virgin! ca of the 

 mainland and the normal adult size is small. 



14 



