BOTTON and HASKIN: DISTRIBUTION AND FEEDING OF HORSESHOE CRAB 



took place early in the summer, thus enabling a 

 comparison of the southern and northern parts of 

 the coast without a confounding effect of time. 

 Both area (ANOVA, P < 0.01) and time (P < 0.01) 

 effects were significant, and percent occurrence 

 and abundance were low from Beach Haven Inlet 

 northward, where horseshoe crabs were particu- 

 larly scarce offshore of 1.8 km (Table 5). The inner 

 0.9 km from Barnegat Inlet to Shark River Inlet 

 had significantly more L. polyphemus on 24 June 

 (x = 5.48, n = 12) than 17 August (x = 0.07, n = 

 10) (F = 11.913, P < 0.005). From 3.7 to 5.5 km 

 offshore between Townsends Inlet and Absecon 

 Inlet, the density in late July (3c = 3.24, n = 8) was 

 significantly higher than the density found on 17 

 May or 26 June (x = 0.88, n = 6 and x = 1.4, n = 3, 

 respectively) (F = 6.646, P < 0.005). Stations on 28 

 August and 16 November, also contained fewer 

 crabs (x = 0.19, n = 4 and 3c = 0.44, n = 2, respec- 

 tively). 



Stomach Contents 



Stone Harbor individuals were collected on 24 

 July 1978, from a station, 13.4 m depth and 3.7 km 

 offshore, which contained 150 L. polyphemus. 

 Their digestive tracts were packed (3c = 383.2, 

 range 88-791 individuals/crab) with blue mussels, 

 Mytilus edulis\ there were only traces of other food 



(three other bivalves, four brachyuran crabs, two 

 foraminifera, and polychaete setae). The mean 

 length of 38 whole valves was 6.3 mm, with a 

 range from 4.2 to 9.0 mm. Virtually all remaining 

 umbones were estimated to be from mussels in 

 that range. 



Crabs in the Atlantic City series ate a variety of 

 food, primarily bivalves, annelids, and arthropods 

 (Table 6). The surf clam, Spisula solidissima, was 

 an important prey item, ranking first in frequency 

 of occurrence and third in total abundance. Valves 

 <1 mm in length were found, as were portions of a 

 35-40 mm shell length individual; about 62^ of 

 the valves were >4 mm. Other important bivalves 

 were Tellina sp. and Siliqua costata. Twelve 

 polychaete taxa were identified, of which Nereis 

 sp. was the most frequently occurring, while the 

 most abundant were unidentified Spionidae. Fif- 

 teen digestive tracts contained one or more speci- 

 mens of brachyuran crabs, which in several cases 

 were identified as young rock crabs, Cancer ir- 

 roratus. 



Stomachs of the seven horseshoe crabs from the 

 Point Pleasant series contained little food. Only 

 four bivalves (one S. solidissima and three M. 

 edulis), a gastropod (Nassarius trivittatus), and a 

 brachyuran were identified. Polychaete setae were 



TABLE 5. — 1979 Limulus polyphemus survey results. Area 

 means are expressed as the number of crabs per standard tow, 

 as defined in the text. CV = coefficient of variation. Data were 

 log transformed prior to Analysis of Variance. Area locations 

 are shown in Table 1. 



TABLE 6. — Ranking of food items by total abundance and 

 frequency of occurrence, from 24 Limulus polyphemus collected 

 in the Atlantic City series, summer 1978. 



Item 



Foraminifera 



Unidentified bivalve 



Spisula 



Tellina 



Brachyura 



Siliqua 



Spionidae 



Nematoda 



Cancer 



Fecal pellets 



Plant material 



Gemma 



Glycera 



Polychaete setae 



Ensis 



Polynoidae 



Mytilus 



Nereis 



Cirnpedia 



Spiophanes 



Ampharetidae 



Anomia 



Capitellidae 



Isopoda 



Mulmia 



Nemertea 



Ostracoda 



Turbellana 



Unidentified gastropod 



Unidentified oligochaete 



(Tie- 17 items) 



Number of 

 specimens 



Rank 



Number of 

 occurrences 



Rank 



387 



