(0.6-59.6 per 1 m.^), 12 contained Sesarma (0.6- 

 19.8 per 1 m.^), 10 contained Neo-panope (0.5-9.7 

 per 1 m.^), and 9 contained Panopcus (0.5-2.3 per 

 1 ni.^). ^Megalops of IJca and Sesarma were more 

 abundant than CalUnectes. As for CalUnectes, 96 

 percent of the megalops of the other genera were 

 from bottom collections. 



Plankton collections were made also at buoy 63, 

 40 km. from the mouth of the river, during May 

 and October 1961 and August 1961 and 1962 (ta- 

 ble 6). CalJinectes zoeae occurred in three May 

 samples (1.2-4.7 per 1 m.^) and 10 August samples 

 (0.9-6.1 per 1 m.^) ; 10 of these 13 samples were 

 taken near the bottom. One bottom sample in May 

 contained second-stage zoeae (2.4 jaer 1 m.^), and 

 two bottom collections in August had megalops 

 (both 1.2 per 1 m.^). Rithropanopeus^ Sesarma, 

 and Vca were the most abundant genera in the 

 collections. Megalops collected in May were, in de- 

 creasing order of abundance, Sesarma, Uca^ Rlth- 

 ropanopeus, and Panopeus. August samples con- 

 tained megalops of only Vca and CalUnectes. 



Most of the lai-val CalUnectes collected in the St. 

 Johns Eiver occurred at stilinities and tempera- 

 tures favorable to larvae reared in the laboratory. 

 Laboratory-reared larvae of G. sapidus had a uni- 

 fonn rate of growth in salinities between 20.1 and 

 31.1 p.p.t. at 25° C. (Costlow and Bookhout, 1959). 

 Even though almost all CalUnectes larvae captured 

 near the mouth of the St. Johns River (buoys 11- 

 38) both at the surface and near the bottom were 

 in favorable salinities, some of those captured up- 



river (buoy 63) were in salinities which probably 

 would be too low to sustain them over extended 

 periods. Salinity near the mouth (surface and bot- 

 tom) was between 25 and 35 p.p.t. from April to 

 July and between 12 and 36 p.p.t. from August to 

 October. Bottom salinity was nearly always greater 

 than that at the surface, particularly during ebb 

 tide. At buoy 63, larval CalUnectes were captured 

 in salinities from 9 to 27 p.p.t. Water temperature 

 (April to October) in the lower 40 km. of river 

 ranged from lows of 20° C. in April and October 

 to a high of 31° C. in August. Temperature at the 

 surface and bottom usually differed less than 1° C. 



Plankton was collected between buoys 2 and 3 in 

 south Jacksonville (48 km. above mouth of river) 

 during August and October 1961. No CalliTiectes 

 larvae were obtained. Zoeae and megalops of 

 Rithropanopeus were predominant and present in 

 almost all of the collections (zoeae: 0.7-61.7 per 

 1 m.^). Zoeae of Vca and Sesarma. many of them 

 dead, were the only other larvae collected. Surface 

 salinities in these months ranged from to 10 p.p.t. 

 and bottom salinities from 5 to 11 p.p.t. 



Plankton collections made in the South Atlantic 

 by the Theodore N. Gill in 1953-54 have been 

 analyzed for the occurrence of CaJUnectes larvae 

 (Nichols and Keney, 1963). Six stations were 

 sampled off the mouth of the St. Johns River — one 

 at the mouth, and five others, 32 km. apart, extend- 

 ing due east. Stages of zoeae found at the inshore 

 station were the same as in the river — primarily 



Table 5. — Estimated average number of crab zoeae per cubic meter of water, bettoeen buoys 11 and 38 {3-11 km. above mouth 



of St. Johns River) in January-November, 1962 



[Number of samples each month in parentheses) 



Species Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Total Rank in 



— ._, — — — — — — „„. ,„,„» abundance 



CalUnectes sp 



Dissodactylus sp 



Eurypanopeus sp 



Hepatus sp 



Leucosiiftae 



Menippe sp.. 



Neopanope sp 



Ptichygrapsus sp 



Panopeus sp 



Pilumnus sp 



Piiiniin sp 



Pinnotheres maculalus 

 Pinnotheres ostreum... 



Polyonyx sp 



PoTtunus gibbesii 



Portunus sayi 



Rithropanopeus sp 



Sesarma sp 



Uca sp 



Unknown A 



Unknown D 



17 

 5 

 9 

 12 

 11 

 6 

 19 

 4 

 19 

 7 

 14 

 8 

 13 

 15 

 10 

 16 

 3 

 1 



18 

 19 



1 Less than 0.06. 

 BIOLOGY OF BLUE CRAB IN ST. JOHNS RIVER, FLORIDA 



25 



