Stehlik et al.: Distribution patterns of various crab species in the Hudson-Rantan Estuary 



. 703 



Table 3 



Twelve mutually exclusive prey categories that contributed 80^ of the prey volume of all crabs examined. Codes are used in 

 Figures 7 and 9. "Other" means uncommon identified taxa. 



CODE 



Category 



Identifiable species 



Nassarius trivittatus, N. obsoletus 



Crepidula fornicata, C. convexa, C. plana 



Ensis directus 



Mytilus edulis 



Mulinia lateralis 



all 



all 



Crangon septemspinosa, unid., other 



Libinia sp.. Cancer irroratus. Ovalipes ocellatus, Callinectes sapidus, crab unid. 

 and others excluding Paguridae or Xanthidae 



Pagurus acadianus, P. longicarpus, unid., other 



Xanthidae: Dyspanopeus sayi, unid., other 



all 



outer strata (4, 5, and 7) that consumed large quanti- 

 ties of M. edulis. Clumps of recently settled and larger 

 mussels were frequently collected in trawl nets in these 

 strata. Group B contained crabs from Gravesend Bay, 

 (stratum 6 ) that ate primarily M. edulis and M. lateralis. 

 Group C contained crabs caught in the siltier southern 

 strata and nearby channel (strata 1, 2, and 9) that con- 

 sumed mainly M. lateralis, M. edulis, and CRABS. Group 

 D consisted of rock crabs collected at inner strata (2, 

 3, and 8) that fed primarily upon E. directus and Xan- 

 thidae. Ensis directus was most common in diets in the 

 northern sandier strata (strata 3, 5, 6, and 7). Groups 

 E and F consisted of lady and rock crabs that consumed 



mainly M. lateralis. Four species-stratum combinations 

 did not cluster with any groups. 



Temporal, spatial, and trophic niche breadth and overlap 



Niche breadth and overlap were calculated for both sexes 

 of the three crab species (Table 4). Lady crabs of both 

 sexes had the narrowest temporal niches (3.896 and 

 4.592), reflecting their presence in the estuary strictly 

 in warm months. The temporal niche breadth of female 

 blue crabs (8.187) was greatest, reflecting their year-long 

 presence in the study area, even in the cold months when 

 many males remain in rivers. The temporal overlaps of 



