Biology and Ecology of Juvenile Procambarus alleni
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| Biology and Ecology of Juvenile Procambarus alleni and Procambarus fallax from the Everglades, Laboratory Studies
Peggy VanArman Palm Beach Atlantic University, West Palm Beach, FL and Nova SE University Oceanographic Center, Dania, FL Crayfish, fish, and mussels are important members of food webs in most freshwater aquatic ecosystems in North America, where crayfish often serve as keystone species, and may dominate energy and nutrient flow. Despite the wide-spread influences that crayfish have on all trophic levels, they are almost completely overlooked in conservation efforts. The roles of crayfish as herbivores and detritivores are well documented, but their importance as carnivorous predators has received little attention until recently. A growing list of crayfish prey includes leeches, tadpoles, newts, fish eggs and fry, and molluscs. As intermediates in food webs, crayfish form part of the diet of more than 36 species of vertebrates that inhabit the Everglades, including the keystone American alligator and wading birds. Crayfish burrows provide refugia for other organisms during times of drought and support an entire burrow ecosystem. Two species of epigean crayfish, Procambarus alleni (Everglades crayfish) and P. fallax (swamp crayfish) inhabit the Everglades. Some researchers have previously confused identification of these species and it was not until 2000 that P. fallax was officially documented in the southern Everglades. Field collections indicate that swamp crayfish have been present in the southern Everglades and in coastal Broward County since 1985. More recent studies suggest that although these two species occur in sympatric and occasionally syntopic distribution, P. alleni may prefer shallow water and short hydroperiod conditions, whereas P. fallax prefer more permanently flooded conditions. Elsewhere in Florida, where P. fallax was found within the range of P. alleni, P. fallax appeared to be the more successful competitor. Because of their critical roles in the trophic structure of Everglades wetlands, shifts in relative abundance of these two species may have significant effects on wetland communities and overall availability of crayfish as food for other organisms. Researchers are now recognizing the critical importance of crayfish in Everglades wetlands, as bio-indicators to assess effects of hydrology, fire, and nutrient enrichment; as intermediates in food webs; and as ecosystem components in community sampling studies. More studies have been conducted on the biology and ecology of P. alleni than on P. fallax and P. alleni was proposed as an indicator species to monitor progress of Everglades restoration programs. Only two previous studies examined life history and ecology of both P. alleni and P. fallax. The two species appear to differ in reproductive strategies, growth and maturation rates, and migration and burrowing behavior patterns. The sparse information available centers on adults rather than juvenile crayfish. Current Research. Three experiments were conducted on juvenile P. alleni and P. fallax under laboratory conditions that simulated conditions in South Florida wetlands. Adult crayfish of both species were obtained from various areas, including wetlands that were historically connected to the northern Everglades. Young crayfish were hatched from berried females captured in the field or bred in the laboratory. In the first experiment, growth, survival, and development of hatchlings were monitored to three months of age, under stable conditions. In the second experiment, effects of biotic and abiotic factors (water levels, food, density and competition) on growth and survival of hatchlings were examined during three months. In the third experiment, behavior patterns and substrate choice were observed in the presence of an adult arthropod predator. Under stable conditions, juvenile P. fallax had significantly higher survival than P. alleni. P. alleni had significantly greater weight and total length than P. fallax, however, at a given length, P. fallax was heavier than P. alleni. More P. fallax than P. alleni developed gonopods 1 and 2 within three months. In conditions simulating different water levels, P. alleni survival was impacted most by low food levels, high density, all three water levels, and intraspecific competition. The highest survival occurred with high food levels, and low density. Lowest survival of P. fallax occurred in low food levels, high density, and low water levels, while high food levels, low density and drying conditions enhanced survival. P. alleni grew larger than P. fallax in all conditions tested. Growth of P. alleni was most impacted by low food levels, drying conditions, high density, and intraspecific competition. The best conditions for growth of Everglades crayfish included high food levels, low water levels, low density, and interspecific competition with P. fallax. Growth of P. fallax young was most impacted by low food levels, high density, and high density interspecific competition. P. fallax grew largest in conditions of high food levels, low density, and low density interspecific competition. P. fallax grew to the same size in all three water levels. With or without an arthropod predator present, both species spent the most time in Utricularia foliosa and Panicum hemitomon, and the least time in Typha domingensis and on sand. With a predator present, juvenile Everglades crayfish were exposed on sand more at night, and more than P. fallax. P. fallax spent significantly more time secluded in bladderwort than P. alleni. In the absence of an arthropod predator, feeding was the primary activity of both species during the day. P. alleni was more mobile at night, whereas P. fallax spent more time resting and less time feeding. In the presence of the predator, movement by both species was reduced and juveniles fed more during the day and rested more at night. P. fallax spent more time resting then P. alleni during day and night, but P. alleni wandered around twice as much as P. fallax at night. Both species exhibited diurnal behavior patterns. Because of its larger size, P. alleni may have a competitive advantage in resource holding potential, and by producing more eggs. P. fallax grow more slowly, but compared to P. alleni are heavier at a given length, reach maturity at a smaller size, and may reproduce throughout the year. In Everglades wetlands, P. alleni are more abundant under fluctuating conditions and may survive better during dry periods. Juvenile P. fallax have higher survival under stable conditions. If survival and growth strategies of P. fallax are enhanced by long hydroperiods and appropriate depths, then P. fallax could have a considerable competitive advantage over P. alleni in survival, growth, and development. Research Needs. A more holistic approach is needed to understand the role of crayfish populations in Everglades ecosystems that integrates laboratory, field and modeling studies. Detailed, long-term information is needed about most aspects of the life history and ecology of P. alleni and P. fallax, to determine nutritional needs, life span, reproductive strategies, and predator-prey cycles in Everglades environments. Studies of water depth, hydroperiod, and water quality are also needed, to understand how P. alleni and P. fallax can coexist, on a microhabitat level. Little is known about tolerances of either species to water quality factors such as oxygen, temperature, salinity, turbidity, or pH for different stages of the life cycle. Water managers must consider that even small changes in hydrology may significantly alter crayfish populations and community structure over large areas and at multiple trophic levels in Everglades ecosystems. Depth, delivery and timing of water may favor either species of crayfish, to the detriment of the other. Conservation strategies should consider the need to provide crayfish habitat that will allow balanced distributions of P. alleni and P. fallax populations that maintain floral and faunal biodiversity, and optimize the roles of crayfish as predators, prey, and habitat managers in southern Florida wetlands. Peggy, VanArman, Palm Beach Atlantic College, PO Box 24708, West Palm Beach, FL , 33416, Phone: 561-803-2287, Fax: 561-803-2390, peggy_vanarman@pba.edu, Ecology and Ecological Modeling Directory: papers papers -> From Warfighters to Crimefighters: The Origins of Domestic Police Militarization papers -> The Tragedy of Overfishing and Possible Solutions Stephanie Bellotti papers -> Prospects for Basic Income in Developing Countries: a comparative Analysis of Welfare Regimes in the South papers -> Weather regime transitions and the interannual variability of the North Atlantic Oscillation. Part I: a likely connection papers -> Fast Truncated Multiplication for Cryptographic Applications papers -> Reflections on the Industrial Revolution in Britain: William Blake and J. M. W. 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