Branchiopod and Malacostracan Crustaceans 
25 
crayfish present. In addition, in June there are population pulses of 
several cladoceran species, including Simocephalus serrulatus , Eurycer- 
cus vernalis, Ceriodaphnia reticulata , Scapholeberis kingi, and Sida 
crystallina. The occurrence of one or two population pulses during a 
year is characteristic of many cladoceran species (Pennak 1978). 
In summer, the cladoceran fauna, with the exception of a few 
species, is again generally reduced in numbers. Peracarids that are 
commonly encountered include Hyalella azteca, Caecidotea laticaudata, 
and reduced numbers of Caecidotea forbesi. Dryness eliminates many 
shallow-water habitats for Caecidotea forbesi and, in late summer, this 
aridity, as well as the growth and decomposition of large quantities of 
vegetation in certain locations, leads to reductions in numbers of 
Hyalella azteca and other crustaceans at several sites. Populations of 
Palaemonetes paludosus consist of large numbers of postlarvae and 
juveniles in summer. 
Late autumn is characterized by increasing numbers of Caecidotea 
forbesi , Lirceus lineatus, and Crangonyx r. richmondensis , and 
decreasing numbers of Caecidotea laticaudata and, to a moderate 
extent, Hyalella azteca. Large numbers of Palaemonetes paludosus 
mature during this period. 
Two habitats on the refuge are quite distinctive and warrant further 
investigation. Dingle Pond is unique in the refuge in that all seven 
peracarid species occur there. The pond itself is in the latter stages of 
hydrarch succession, characterized by a mixture of connected open 
pools and swamps, with scattered tree- and bush-covered hummocks. 
The second habitat is in Cuddo unit; it consists of a small, forest- 
surrounded borrow pit encircled by a series of small, swampy pools. In 
it I found Procambarus blandingii, Fallicambarus uhleri , Caecidotea 
forbesi , Crangonyx r. richmondensis , Simocephalus exspinosus, and, 
occasionally in summer, Streptocephalus seali and Eulimnadia ven- 
tricosa. Streptocephalus seali and Eulimnadia ventricosa were restricted 
to shallow pools bordering the borrow pit during low water when fishes 
were abundant but limited to the borrow pit. That these two crustacean 
species disappeared when the water rose, making the pools and borrow 
pit confluent, suggests that predation by fishes may eliminate them. The 
usual absence of non-cladoceran branchiopods from bodies of water 
containing fishes is well known and has been thought to be the result of 
predation on these large, easily seen, and almost totally defenseless 
species (Pennak 1978). 
ACKNOWLEDGEMENTS. — I thank the Managers (Paul Ferguson 
and Glen Bond) and staff of the Santee National Wildlife Refuge for 
permission to do the study and for their assistance. I also thank J. R. 
