10 
Charles K. Biernbaum 
34 °C, but it is certain that temperatures occasionally exceed this in 
small exposed pools or ditches on hot days. During the winter some 
locations may rarely have a thin sheet of ice on the surface. Mid-June 
pH measurements along the margin of Lake Marion ranged from 6.9 to 
7.3, depending on location. Other aquatic habitats had pH values from 
5.4 to 6.3. 
Most aquatic habitats of the refuge, with the exception of swamps, 
are characterized by having dense growths of a variety of aquatic plants. 
Most such locations have large populations of floating plants, including 
water lilies ( Nymphaea odorata ), American lotus ( Nelumbo luted), and 
frequently water shield ( Brasenia schreberi ) and duck weed ( Lemna 
spp.). Submergent plants that are very abundant include bladderwort 
( Utricularia sp.), hornwort ( Ceratophyllum demersum), Brazilian water- 
weed ( Elodea densa), water milfoil ( Myriophyllum sp.), Chara sp., and 
a variety of filamentous green algae. Along the bordering shallows such 
emergent plants as arrowhead ( Sagittaria latifolia ), water pennywort 
( Hydrocotyle sp.), alligator weed ( Alternanthera philoxeroides ), smart- 
weed ( Polygonum spp.), pickerel weed ( Pontederia cordata), and an 
introduced false loosestrife ( Ludwigia uruquayensis) are usually abun- 
dant. At the water’s edge a variety of sedges ( Cyperus spp.), rushes 
(Juneus effusus , Scirpus spp.), and cattails ( Typha sp.) are frequently 
found in dense stands. Many impoundments additionally have but- 
tonbushes ( Cephalanthus occidentalis ) scattered throughout. Bald 
cypress ( Taxodium distichum), water tupelo (Nyssa aquatica ), willows 
( Salix spp.), and redbay ( Persea borbonia) are commonly found. Trees 
usually dominating swamps include those listed above plus sweet gum 
(Liquidambar styraciflua ), oaks ( Quercus spp.), and, in those swamps 
and flooded woods not bordering the lake, some pines ( Pinus spp.). 
METHODS 
Sampling was done approximately every 4 to 8 weeks from January 
1982 to November 1983. Occasional samples were taken during 1984. 
Aquatic sampling was done primarily by use of a dipnet (0.9-mm mesh), 
although some supplemental collections were made by plankton net 
(100-^m mesh) at selected locations. Sampling was reduced in certain 
areas during the cooler months to avoid disturbing overwintering 
waterfowl. Specimens were collected at 105 refuge locations, over 75% 
of which were sampled during at least two different months. Sixty-three 
stations were sampled during at least two different seasons, 34 stations 
during at least three seasons, and 16 for all four seasons. 
Specimens were preserved in the field and returned to the laboratory 
for identification and enumeration. Owing to the difficulty in identifying 
females of Caecidotea to the species level, occurrences of species of this 
