Emergence and dynamics of cyclopoid copepods in an unpredictable environment


Grace A. Wyngaard, Department of Biology, James Madison University, Harrisonburg, Virginia 22807, U.S.A.


SUMMARY. 1. We studied species composition, abundance and population dynamics of cyclopoid copepods emerging from dormancy from the sediments of a temporary pond in South Carolina in 1985, 1988 and 1989. During a drought in 1988–89, the maximum hydroperiod was 19 days; in 1985 and late 1989-early 1990, the hydroperiods were 57 and 118 days. We also report on species present in 1984 and 1987, two years that had longer hydroperiods, and on abundance of cyclopoids in 1984.

2. Within a day after standing water appeared, fourth-instar copepodids of Diacydops haueri and D. crassicaudis brachycercus became active. These two species appeared every time the pond filled in winter, spring, or autumn. Other species, including Acanthocyclops vernalis, were usually not collected until weeks or months after the pond filled. Because the times and durations of fillings were extremely variable, species composition differed among years, with the most species (eleven) appearing in 1984, the year with the longest hydroperiod.

3. The abundances of emerging Diacydops were much lower in 1988 and 1989 (range of means from seven fillings in spring and autumn: 675–7382 animals m−2) than 1985 (range of means from three fillings in winter: 26,037–107,418 animals m−2). Low abundances of emerging animals could have been caused by poor survival of dormant animals, poor production during preceding seasons, or incomplete emergence of the dormant populations.

4. Substrate samples from the dry pond were collected in spring, summer, and autumn 1988 and winter 1989 to measure emergence of the cyclopoids in laboratory incubations. Population densities of emerging animals were much lower in 1988 and 1989 (range of means from seven experiments: 0–120 animals m−2 over the first 3 days) than in similar experiments in 1984 (Taylor & Mahoney, 1990, means from two experiments: 3630 and 6890 animals m−2).

5. Despite the low abundance of animals emerging from dormancy in late 1989, the cyclopoid populations in 1990 reached similar densities of copepodids (104−-105 animals m−2) to those reached in 1984 and 1985. These results suggest that short generation time and high reproductive capacity permit rapid recovery from population reductions.