20 
Charles K. Biernbaum 
sulfide. Most such areas showed a dramatic reduction in numbers of 
crustaceans, H. azteca included, while in nearby habitats that lacked 
such apparently detrimental characteristics H. azteca was frequently 
abundant. Brooding females of H. azteca were collected throughout the 
year; however, reproduction was greatly reduced in fall and winter 
(Table 7). Bousfield (1958, 1973) has previously reported that ovigerous 
females of H. azteca occur from April to October, as reflected by studies 
done in such northern locations as Ontario (Lindeman and Momot 
1983), British Columbia (Hargrave 1970, Mathias 1971); Oregon (Strong 
1972), Michigan (Cooper 1965), and New York (Embody 1912). 
However, Strong (1972) reported that H. azteca reproduces all year in a 
hot spring (12-40 °C) in Oregon. 
Crangonyx r. richmondensis, equally varied as H. azteca in the 
aquatic habitats occupied, was collected all year, but, in contrast to H. 
azteca , was common only during winter (Tables 4 and 5); it was very 
rare in summer. Mathias (1971) reported that Crangonyx is much more 
tolerant of cold than is Hyalella , and that species of Crangonyx 
frequently breed in winter and spring. No relationship was found 
between the few summer occurrences of C. r. richmondensis and specific 
habitats; it seems to become rare at all of its locations as winter passes 
into summer. Reproduction in this species occurred at the refuge from 
late fall through spring (Table 7), which is similar to Bousfield’s (1958) 
report that ovigerous females of this subspecies occurred from December 
to June in southern portions of its range. 
Hyalella azteca occurs throughout North and Central America and 
the Caribbean islands north to the tree line in Canada and Alaska in all 
permanent fresh water that reaches a monthly mean summer temperature 
of over 10 °C (Bousfield 1958). Cooper (1965) reported several sources 
referring to the high degree of association between large populations of 
this species and such aquatic plants as Chara, Elodea, and Myrio- 
phyllum. Such an association probably accounts in large part for the 
very high numbers of H. azteca frequently seen at the refuge, where 
dense growths of aquatic plants are extremely common. The presence of 
large numbers of waterfowl at the refuge provides a means of widespread 
dissemination, as reported by Daborn (1976) and Swanson (1984) for 
this species. Over Lake Marion in December 1982, J. Pinckney shot a 
female wood duck (Aix sponsa) that had 10 amphipods in the breast 
feathers. Three were retained and identified as H. azteca. 
Crangonyx richmondensis was originally described from a site in 
Berkeley County, S.C. (Ellis 1940). The subspecies C. r. richmondensis 
occurs east of the Appalachians from Georgia north to Nova Scotia and 
Newfoundland (Bousfield 1958, 1973). However, the distribution is 
disjunct, with no records of occurrence between Massachusetts and 
