Red swamp crayfish Procambarus clarkii in the Atchafalaya River Basin: biotic and abiotic effects on population dynamics and physiological biomarkers of hypoxic stress

Abstract

Crayfish harvested from the Atchafalaya River Basin (ARB) represent the majority of Louisiana wild crayfish landings. However, excluding water level influences, it is difficult to elucidate inter-annual harvest differences and intra-annual population variability among habitats. This research investigated ecological influences on population characteristics of red swamp crayfish Procambarus clarkii in the southeastern ARB as well as physiological biomarkers of hypoxic stress in P. clarkii. Biotic and abiotic effects on P. clarkii populations were examined throughout the 2008 and 2009 commercial crayfish seasons. P. clarkii catch per unit effort (CPUE) at sampling locations increased nearly 600% between sample years despite similar hydrologic and physicochemical conditions. The passage of Hurricane Gustav between sample years caused near anoxic conditions for several weeks throughout the lower ARB. Increased allochthonous inputs and reduced fish predation associated with Gustav likely contributed to the increased P. clarkii CPUE observed during 2009. During 2008, P. clarkii CPUE was highest at sample locations characterized by high dissolved oxygen (DO) concentrations and lowest at locations with relatively low DO levels. In addition, chronically hypoxic sampling locations yielded lower mean CPUE and carapace length during 2008. An increase in P. clarkii mean CPUE and a concomitant decrease in mean carapace length during the 2009 crayfish season indicated density-dependent growth. While abiotic factors undoubtedly influenced crayfish population characteristics, relative density appeared to have the largest effect on P. clarkii carapace length and may have depressed any physicochemical influences. Lactate, glucose, and protein concentrations in P. clarkii hemolymph were examined in individuals from chronically hypoxic ARB habitats and laboratory simulated hypoxia experiments. P. clarkii from normoxic and hypoxic natural habitats did not display significantly different hemolymph lactate or glucose concentrations, however, mean hemolymph protein concentration was significantly lower in crayfish from hypoxic areas. P. clarkii exposed to severe hypoxia in laboratory experiments had significantly higher hemolymph lactate and glucose concentrations, whereas large differences in protein concentrations were not observed. A hand-held lactate meter and refractometer proved to be reliable methods for determination of P. clarkii hemolymph lactate and protein concentrations, respectively.