Structure and Functioning of the "Egg Bank" of a Fairy Shrimp in a Temporary Pool: Chirocephalus ruffoi from Pollino National Park (Southern Italy) as a Case Study

Abstract

To investigate their distribution and total numbers, resting eggs of the anostracan Chirocephalus ruffoi were collected from the bed of a temporary pool in southern Italy. Samples were taken at 0.5 m intervals along six transects oriented at 30° from each other, by means of a cylindrical core sampler. The horizontal distribution of intact resting eggs was extremely patchy, with cyst number per core ranging from 191 to 1,400 (CV = 32.7%), corresponding to a mean of between 0.8 and 4.3 cysts cm-3. Differences observed were related to core position and transect orientation, total cyst numbers being markedly higher in the leeward area of the pool compared to the windward area. Marked variation was also evident in vertical distribution, a significant, though weak correlation was recorded between egg density and sediment depth. Cyst-bank size (±95% confidence limits) of the pool bed, estimated from the mean cyst number cm-3 obtained for the 6 transects, ranged between 1.0 x 108 and 1.3 x 108 cysts. Hatching in the laboratory was very erratic. Despite significant differences in hatching, the observed variation was unrelated to most of the variables considered (position within sections, cores and transects, pre-incubation treatment) and was explained only by initial sediment conditions (moist/dry). In none of the experimental conditions tested was synchronous hatching obtained. Possible causal factors (mixing of the bottom sediments by cattle, egg age, storage conditions, differential exposure to environmental cues as well as variability in hatching response even at clutch level) are discussed.