Processes and patterns of plant destruction by crayfish:: effects of crayfish size and developmental stages of rice

Interference by crayfish on the establishment of rice plants was evaluated in this study. Two experiments were performed in outdoor containers with wet-seeded rice. The purpose of the first experiment was to determine if crayfish size has a significant impact on plant destruction. Two different scales of habitat size were analysed. The second experiment was designed to determine the influence of crayfish on different developmental stages of rice and to obtain data on the type of destruction caused by crayfish. Remaining dry weight, number and dry weight of the rice seedlings (intact + damaged) and number and dry weight of the seeds (intact + damaged) were quantified in the first experiment. The second experiment quantified: (1) number of viable seeds or seedlings, (2) dry weight of the remaining rice biomass; (3) number of viable seeds; (4) number of non-viable seeds; (5) height of any damaged seedlings, (6) number of seedlings damaged, (7) height of intact seedlings, and (8) number of intact seedlings. Our findings indicate that: increasing crayfish size results in larger negative effects on rice plant establishment; and consumption is the most important cause of destruction although the effect is reduced as plants grow. Crayfish left only a very small portion of the seedlings intact at 3 and 6 days of plant development. Thus, practical implications for management are that any crayfish control mechanisms being used are expected to be particularly effective during the first 6 days of rice growth.