Seasonal movements of crayfish in a fluctuating wetland: implications for restoring wading bird populations

Abstract

1. Among aquatic fauna of fluctuating wetlands, seasonal interhabitat movement is a widespread phenomenon that can strongly influence predator-prey interactions and population dynamics of vertebrate predators. For example, movements increase the availability of small fishes during seasonal drying, which is critical to the reproductive success of many wading bird (Ciconiiformes) species. However, few studies have examined movements of aquatic fauna in relation to changes in water depth, especially for those taxa that can physiologically tolerate periods of drying and whose responses to hydrology are difficult to predict (e.g. crayfish). 2. Here, we experimentally explore the movement responses of a key prey species in the Florida Everglades -the slough crayfish Procambarus fallax -to a seasonal decline in water depth. The study was conducted in four replicate wetland impoundments (wetlands) which comprise habitats characteristic of the Florida Everglades. In two wetlands, we induced a 60-cm drop in water level and examined crayfish movements between higher-elevation ridge habitats and lower-elevation slough habitats when water levels were (i) relatively deep on ridges; (ii) relatively shallow on ridges; and (iii) below ground on ridges but above ground in sloughs. In two control wetlands, we followed the identical sampling protocol but maintained the deep stage on the ridges. Crayfish movements were quantified by changes in abundance and mark-release-recapture (MRR). 3. Crayfish abundance changed little within habitats while water remained on the ridges, but it decreased on the ridges and considerably increased in the sloughs after the ridges dried. These changes were clearly due to loss of water on the ridges as abundances in control wetlands remained constant throughout sampling. Elevated slough abundances were not explained by differences in trapping efficiency or episodic releases of recently hatched crayfish, suggesting they were due largely to movements from ridges to sloughs. This was supported by the MRR data. 4. Our results show that seasonal water-level recessions can induce crayfish to move from higher to lower-elevation habitats where they become concentrated and potentially available to foraging birds. We discuss the potential implications of these movements for restoring hydrologic conditions for wading birds in large fluctuating wetlands.

Hydrological disturbance diminishes predator control in wetlands

“…Observations from a stronger uncontrolled drought in a subsequent year substantiated this observation as crayfish burrows were common in wetland sediments (N. J. Dorn, personal observation). When partially drying the same wetlands in a previous study, Cook et al (2014; M. I. Cook, personal observation) did not find crayfish disproportionately using deep alligator holes, suggesting that most crayfish stay in the wetlands and burrow rather than move to the deepest habitats where fish are concentrated. Although difficult to quantify at this scale, crayfish likely experienced some immediate stock losses to the drying caused by the stress of burrowing (Dorn and Volin 2009) and exposure to wading bird predation (Boyle et al 2014).…”

Tradeoffs between fine‐scale site measurements and coarse sensory data for long‐term monitoring of pulsed wetlands

“…However, this does not imply that crayfish do not respond to receding water. A recent study by Cook et al (2014) found the slough crayfish (Procambarus fallax) moves into sloughs as water recedes off ridges, with maximum abundance occurring at~21 cm. Once depths recede <20 cm, the slough crayfish is more likely to burrow, rather than continue to follow the drying-front.…”

Feeding on the edge: foraging White Ibis target inter‐habitat prey fluxes

“…As water depth declines during the dry season, prey densities increase in the sloughs as prey move downgradient within and between habitats (Kushlan , Cook et al. , Botson et al. ).…”

“…Aquatic prey are generally expected to move downgradient across the ridge‐slough habitat interface as water recedes in the wetlands, but movement decisions may vary among species (Cook et al. , Hoch et al. ).…”

“…Crayfish can either burrow into sediments (Dorn and Volin ) or crawl downgradient, but a study of inter‐habitat movement of slough crayfish (hereafter, crayfish) from ridges to sloughs revealed that crayfish populations moved from ridges to sloughs when water depths on ridges reached 1–11 cm (Cook et al. ). Because ridges vary little in elevation, most of the crayfish over entire ridges (40–400 m wide habitats) could be migrating into adjacent sloughs over a period of 1–2 weeks (Cook et al.…”