An investigation of effects of dissolved oxygen level, sediment type, stocking density and predation on the growth rate, survivorship, and burrowing behavior of juvenile brown and white shrimp

Brown shrimp (Farfantepenaeus aztecus) and white shrimp (Litopenaeus setiferus) are important components of estuarine food webs and support valuable aquaculture and commercial fishing enterprises. Both species exhibit clumped distributions correlated with sediment type. Escalating cultural eutrophication in estuaries over recent decades has increased the frequency, spatial scale and duration of concurrent hypoxia (dissolved oxygen, DO, ≤2.0 ppm), which is often associated with specific regions of estuarine bottom, where shrimp may have higher risks of exposure with negative impacts. Shrimp densities may increase in unimpacted habitats due to avoidance of hypoxia, where aggregative responses, density-dependent mortality and growth attrition may result. I used laboratory and field experiments to investigate effects of DO level, sediment type, density and predation on the growth rate, survivorship, burrowing behavior and sediment preference of juvenile brown and white shrimp.; Results indicate that there may be different consequences of sublethal low DO, even at levels that are not considered hypoxic, for the growth rates of these two closely related species, with white shrimp being more vulnerable. Hypoxia increases the vulnerability of shrimp to predators by increasing exposure time, but predation threat can dampen the emergence response, emphasizing behavioral considerations when examining the net effect of biotic and abiotic factors. Both species preferred sand substrate, suggesting that observed field distributions may be based less on foraging considerations than on other factors (substrate penetrability, ease of respiration when burrowed, habitat recognition, predator-avoidance tradeoffs, and on proficiency at locating preferred substrate). Substrate type did not affect shrimp growth rate, whereas shrimp density appears to be critical. Outside hypoxic zones, density-mediated growth attrition and predation mortality may be important factors affecting shrimp populations. This highlights the necessity for further research using larger-scale studies to more precisely characterize and quantify the extent of such impacts.