ECOLOGICALLY ASSOCIATED ORGANISMS 



Plankton Study 



Our efforts during the year have been devoted 

 to completing food studies, describing the 

 benthic fauna off Galveston, Tex., and assisting 

 in starting a plankton study of the Gulf of 

 Mexico which will be continued in the future by 

 the Gulf Oceanography Program. 



Food Studies 



Samples for studies of the food of brown 

 shrimp were collected from January 1966 to 

 January 1967. Subsamples of brown shrimp 

 were drawn from catches made at night in 

 12.7 to 63.6 m. (7 to 35 fathoms) of water off 

 Galveston and Freeport, Tex. 



The average amount of food, by percentage of 

 stomach capacity, was similar in males and 

 females (fig. 5). Throughout the year, identifi- 

 able contents were predominantly the remains 

 of squid and crustaceans. Occasionally, star- 

 fish (echinoderms), nematodes, and fish parts 

 also were observed. 



The food of four species of fish inhabiting 

 the brown shrimp grounds off Galveston Island 

 were studied through the sunnmer of 1966. In 

 the spring and summer, crustaceans were 

 dominant food items of the Atlantic croaker, 

 Micropogon undulatus ; silver seatrout, Cynos- 

 cion no thus ; and shoal flounder, Syacium 

 gunteri . MoUusks and polychaete worms dom- 

 inated the food items identified in the longspine 

 porgy, Stenotonnus caprinus . 



Bottom Fauna Survey 



Our survey of bottom fauna off Galveston 

 Island was the most intensive ever made in 

 this area. Samples were taken at stations in 

 depths from 5.4 to 36.3 m. (3-20 fathoms). All 

 specimens taken have been sorted to the major 

 taxonomic groups. On the basis of preliminary 

 identification of the moUusks, the sannples 

 included about 16 species that have not been 

 previously reported from this area. Re- 

 searchers at Texas A&M University, the U.S. 

 National Museum, and the Canadian National 

 Museum are studying many of the moUusks 

 and amphipods from these collections. 



JAN PE8 M4R flPH MAY JUN JUL AUG SEP OCT 



NOV DEC JAN 



Figure 5. — Relative abundance of stomach contents in 

 male and female brown shrimp, 1966-67. 



During February and March, we made a 

 plankton survey to compare the productivity 

 of the waters in various parts of the Gulf 

 of Mexico. Plankton samples were collected 

 at 87 locations throughout the Gulf. These 

 samples were taken from the upper 100 m. 

 (55 fathoms) of water with a vertically towed 

 cone-shaped (Hensen) net with a 3/4-m. (2.5- 

 foot) diameter opening. 



Plankton volunnes, measured in cubic centi- 

 meters per 100 m.^ (3,534 cubic feet) of 

 water filtered, are shown in figure 6 to delineate 

 areas of high and low concentrations. Greatest 

 volumes were collected in the western Gulf, 

 over and just beyond the Continental Shelf 

 south of the Texas coast. Volumes were 

 generally greater in the northwestern Gulf than 

 in the southwestern Gulf. In the eastern Gulf, 

 plankton was sparse over the relatively deep 

 waters in the Yucatan Channel and the Florida 

 Straits. 



Donald Moore, Project Leader 



FLORIDA BAY ECOLOGY STUDIES 



The shallow waters of Florida Bay and the 

 Florida Keys are important nursery grounds 

 for pink shrimp of the Tortugas grounds. 

 Since 1965, we have made biological observa- 

 tions on postlarval and early juvenile pink 

 shrimp in these extensive estuaries. 



Postlarvae are sampled quantitatively once 

 each nnonth on incoming night tides at Whale 

 Harbor Bridge near Islamorada (upper Florida 

 Keys). As part of a cooperative plan similar 

 observations are taken at three additional sites 

 in the lower Keys by biologists of the Florida 

 State Board of Conservation. This work has 

 established that large numbers of postlarval 

 shrimp enter Florida Bay from the Atlantic 

 Ocean and that recruitment continues through- 

 out the year. Most postlarvae pass through the 

 Keys into Florida Bay in late spring, summer, 

 and early fall (fig. 7). 



We expanded the sampling of juvenile shrimp 

 in 1967. Quantitative sannples have been taken 

 monthly with a modified marsh net (fig. 8) at 

 ZZ widely distributed shallow-water sites. 

 Earlier samples were taken with the unit-area 

 suction sampler designed by personnel at this 

 station. Examination of samples from Florida 

 Bay revealed that early juveniles increase in 

 abundance during the summer and become 

 most numerous during the fall. This concurs 

 with the observation that postlarvae enter 

 Florida Bay before and during these seasons. 



The data we have collected on incon-iing 

 postlarvae and early juveniles indicate that 

 the distribution of early juvenile pink shrimp 

 in Florida Bay depends primarily on the degree 

 of postlarval penetration. Maximum concentra- 

 tions of early juveniles occur in the western 



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