By James Dyer, PhD candidate, School of Environmental Sciences, Charles Sturt University
Researchers have long wished to understand what governs the distribution of organisms. For riverine animals and plants, hydrology (flow) almost always seems to have a strong influence (Schlosser 1985). At small spatial scales, these organisms tend to be distributed along gradients of current velocity and depth (Aadland 1993), and at large scales, they tend to be distributed along upstream-downstream gradients (Evans & Noble 1979). Populations also typically change at small (daily) and large (annually) temporal scales in response to low- and high-flow events (Fausch & Bramblet 1991). And riverine organisms have evolved morphological, physiological, life history and behavioural traits to enable them to survive, grow and reproduce within the context of spatial and temporal variations in flow (Gatz 1979; Vogel 1994; Leavy & Bonner 2009).
Like most animals and plants, shrimp need access to a variety of habitat types for feeding, reproduction and refuge throughout their lives (Richardson & Cook 2006; Price & Humphries 2010). Depending where habitats are in the landscape (or riverscape), shrimp may need to – and often do – move considerable distances to find scarce or vital resources to survive and complete their life cycles. Therefore, movement may be important in explaining the distribution of stream shrimps (Covich et al. 1996; Richardson et al. 2004).
Although we know something about some of the habitat associations of shrimp, we know little about the riverscape and flow variables that might be important in influencing the distribution of shrimp in rivers. We also have a poor understanding of changes in shrimp abundance and distribution over time, especially seasonally, or how movement is related to age or life stage. Finally, we know very little about how well our species of shrimp swim or are able to maintain position in the river currents; two traits which are obviously important when moving around.
Three species of shrimp commonly occur in the Murray-Darling Basin: Paratya australiensis, Caridina mccullochi and Macrobrachium australiense. All three species are widespread and often dominate macroinvertebrate assemblages. Recent studies have shown that there are obvious trends in abundance, which seem to be related to hydrology and associated habitat variables (Price 2010; Richardson et al. 2004). They are good models for ecological investigation, because they are abundant, ubiquitous, and the three species grow to different sizes and have different life histories (Richardson and Humphries, 2010).
My PhD aims to investigate the role of movement in explaining the distribution of riverine shrimp. More specifically, it aims to describe the distribution of shrimp in the southern Murray-Darling Basin and relate this to riverscape (gradient, geomorphic zones, the location of dams, tributaries etc) and hydrological variables; describe the temporal and spatial patterns of shrimp distribution and abundance in a small river system and relate this to hydrology and habitat; look more closely at shrimp movement seasonally and at different life history stages; and lastly to see how well shrimp swim and can maintain position, in a series of laboratory experiments.
With luck and a lot of hard work, I hope that I can use shrimp in the Murray-Darling Basin to gain some understanding of the role of movement and movement capability of riverine organisms in influencing where they live. This information will not only provide knowledge of the ecology of these little-studied animals, but also help in the better conservation and management of our rivers generally.
Aadland, L. P. (1993). Stream Habitat Types: Their Fish Assemblages and Relationship to Flow. North American Journal of Fisheries Management, 13(4), 790-806. Covich, A. P., Crowl, T. A., Johnson, S. L., & Pyron, M. (1996). Distribution and Abundance of Tropical Freshwater Shrimp Along a Stream Corridor: Response to Disturbance. Biotropica, 28(4), 484-492. Fausch, K. D., & Bramblett, R. G. (1991). Disturbance and Fish Communities in Intermittent Tributaries of a Western Great Plains River. Copeia, 1991(3), 659-674. Gatz, A. J. (1979). Ecological morphology of freshwater stream fishes. Tulane Studies in Zoology and Botany, 21: 91–124. Leavy, Tracy R., & Bonner, Timothy H. (2009). Relationships among Swimming Ability, Current Velocity Association, and Morphology for Freshwater Lotic Fishes. North American Journal of Fisheries Management, 29(1), 72-83. Vogel, S. (1994). Life in moving fluids, Princeton, New Jersey: Princeton University Press. Price, A. E. (2010 ). Integrated Monitoring of Environmental Flows: Freshwater Shrimp in Regulated Rivers. Final Report prepared for the NSW Department of Water and Energy by The Murray-Darling Freshwater Research Centre 46pp. Price, A. E., & Humphries, P. (2010). The role of dispersal and retention in the early life stages of shrimp in a lowland river. Canadian Journal of Fisheries and Aquatic Sciences, 67(4), 720-729. Richardson, A. J., & Cook, R. A. (2006). Habitat use by caridean shrimps in lowland rivers. Marine and Freshwater Research, 57(7), 695-701. Richardson, A. J., Growns, J. E., & Cook, R. A. (2004). Distribution and life history of caridean shrimps in regulated lowland rivers in southern Australia. Marine and Freshwater Research, 55(3), 295-308. Richardson, A., & Humphries, P. (2010). Reproductive traits of riverine shrimps may explain the impact of altered flow conditions. Freshwater Biology, 55(10), 2011-2022. Schlosser, I. J. (1985). Flow Regime, Juvenile Abundance, and the Assemblage Structure of Stream Fishes. Ecology, 66(5), 1484-1490.