Table 10. — Food of the blue crab, by crab size and by station, in the St. Johns River as percentage frequency of occurrence and 

 {in parentheses) as percentage of total volume per stomach 



[Stations and distance from mouth: 1-Clapboard Creek 15 km.. 2-Dunn Creek 30 km., 3-Trout Kiver 40 km., 4-Picolata 95 km. Number of stomachs with food 



in parentheses below designation of station] 



Food item 



Bryozoans 



Mussels 



Clams-- 



Oysters 



Snails 



Nereis pelagica 



Other annelids 



Amphipods 



Barnacles 



Ostracods 



Shrimplike forms. . 



Crabs 



Other crustaceans- 

 Insects 



Fish 



Algae 



Vascular plants 



Organic debris 



Width in mm., station number, and number of stomachs with food 



1 



(55) 



73(47) 



5(2) 

 '"2(6) 



5(3) 

 11(8) 

 ■2(0) 

 16(8) 



27(15) 

 9(1) 

 5(2) 



38(13) 



2 

 (120) 



11(0) 

 '27(13) 



11(0) 

 1 10(0) 



2(1) 



4(2) 

 12(7) 



9(4) 

 28(16) 



9(5) 

 ■2(0) 

 64(49) 



3 

 (100) 



■1(0) 

 9(3) 

 35(15) 



17(6) 

 31(9) 



16(5) 

 '2(0) 

 '1(0) 

 'l(O) 

 12(5) 

 15(8) 

 2(1) 

 27(12) 

 19(5) 

 13(2) 

 61(28) 



4 

 (31) 



13(5) 



48(30) 

 ""3(2)" 



10(4) 

 29(22) 

 6(1) 

 10(10) 

 22(4) 

 10(2) 

 45(21) 



(31) 



'6(0) 



58(31) 



6(4) 



3(1) 



16(1) 



3(1) 



6(2) 

 10(5) 

 13(0) 



48(37) 

 10(1) 

 1 10(0) 

 19(16) 



2 

 (15) 



7(3) 

 67(50) 



'7(0) 



' 13(7) 

 7(0) 



7(1) 

 20(8) 



40(25) 



20(1) 

 7(5) 



3 



(37) 



'3(0) 



30(23) 



43(28) 



11(4) 

 22(4) 

 13(0) 



4 



(56) 



61(44) 

 7(3) 



12(0) 



12(0) 

 62(28) 



8(1) 

 32(14) 



8(1) 

 ■3(0) 

 32(15) 



3(2) 

 16(2) 

 16(6) 



14(3) 



5(2) 

 '2(0) 

 20(11) 

 14(0) 



9(2) 

 16(6) 



1 



(67) 



12(5) 



43(31) 



12(7) 



'l(O) 



'3(0) 



12(2) 



52(42) 



'3(0) 



4(2) 



18(11) 



2 

 (34) 



13(0) 

 15(11) 

 59(24) 

 3(1) 



19(0) 

 ''3(6) 



13(0) 

 15(3) 



13(0) 

 62(39) 

 13(0) 

 15(2) 

 24(19) 



3 



(46) 



12(0) 

 65(45) 

 35(20) 

 12(0) 



2(1) 



2(1) 

 11(3) 



35(26) 



12(0) 

 9(3) 



4 

 (76) 



14(0) 

 79(68) 

 8(1) 



•1(0) 



29(6) 



4(1) 



13(0) 



16(3) 

 '3(0) 

 11(0) 

 17(8) 

 6(1) 

 12(4) 

 21(9) 



1 Less than 0.6 percent. 



were an important food of 5- to 10-mm. crabs. 

 Barnacles were infrequent foo(is but as many as 50 

 small Balanus ebumeus were eaten by a 124-mm. 

 crab at Picolata. Many ciiistaceans were too de- 

 comjjosed or fragmented to classify — particularly 

 microcrustacea in crabs less than 21 mm. Some of 

 the larger fragments closely resembled isopods. 



Fish was a major food, especially of larger 

 crabs. Ingested fish could not be identified, but 

 distinguishalile parts indicated that small and 

 large fish of many species were eaten. No fi.sh was 

 observed in crabs less than 11 mm. wide. 



Algae and vascular plants were frequent in the 

 stomachs of blue crabs. Algae with the exception 

 of Ulva were not identified but most often occurred 

 as many filaments. Crabs ate the leaves, stems, 

 roots, and seeds of various species of higher plants 

 (only Cerafophylhoii and YaJli'merki were identi- 

 fied). Occasionally 20 to 30 small uniform-sized 

 pieces of VaUisnerla leaves in a stomach appeared 

 to have been eaten from the plant. 



Among lesser food items, Nereis pelagica was 

 regularly consumed by all sizes of crabs at the 

 lower river stations. Other annelids were taken 

 infrequently at Trout Eiver and Picolata. Insects 

 were eaten at all stations except Clapboard Creek. 

 Each stomach always contained several individ- 

 uals. Gastric mill contents included adults of 

 Coleoptera, Diptera, Hemiptera, and Hymenop- 



tera, and young of Diptera and Odonata. Bryozoa 

 occurred only as occasional fragments. 



Blue crabs often ate the same food items during 

 each of the three seasons of sampling (table 11), 

 and they usually consumed the most available 

 foods. The largest numbers of mussels were eaten 

 in spring and summer when young mussels (less 

 than 5 mm.) were first abundant. "We found clams 

 of all sizes common in the lower river during all 

 seasons. Because small clams were uncommon at 

 Picolata the abundant mussel population probably 

 was utilized to a greater degree. Oysters and snails 

 (particularly Nasmrius ohsoletxin) were common 

 in the lower river but provided only limited 

 amounts of food. Amphipods were most abundant 

 at Picolata, where thej- were consumed most ex- 

 tensively. Young blue crabs and mud crabs were 

 common in all months of sampling, but relatively 

 few occurred in the food tracts in winter. Shrimp- 

 like forms were not eaten in proportion to the 

 large number generally present at all stations. We 

 collected many fish of all sizes the year around. 

 The percentage eaten was smaller at Picolata than 

 at the lower river stations, which served as nursery 

 areas for a greater variety of abundant species. 

 Consumption of fish was high during winter be- 

 fore recruitment of young mussels. Although 

 aquatic plants grew most profusely at Picolata, 

 they were not a j^referred food. 



30 



U.S. FISH AND WILDLIFE SERVICE 



