Feeding Ecology of Haloniscus searlei Chilton, an Oniscoid Isopod Living in Athalassic Saline Waters

Densities of the oniscoid isopod, Haloniscus searlei Chilton, were orders of magnitude higher on solid substrata than on sediment in the athalassic saline waters of Lake Keilambete and Lake Corangamite, Victoria, Australia. The feeding ecology of H. searlei was examined in the laboratory. Three different grazing densities were employed; one was similar to the estimated density of Haloniscus in the field (c. 212 individuals per m² siderite substratum), and the other two were 3 and 5.5 times higher than field densities, respectively. It was concluded that H. searlei was a very effective grazer. After 2 weeks, treatments with the highest grazing density had 2.5 times less periphyton biomass than treatments at the lowest grazing density and over 3-fold less periphyton than ungrazed controls. Estimated consumption-index values for periphyton were 0.206, 0.124, and 0.096 for treatments ranging from low to high grazing densities. Diatom community structure remained the same in all grazing treatments after 2 weeks. The ability of Haloniscus to use Tanytarsus larvae for food was examined. Cannibalism was also noted.