Sampling Strategies and Life History of Non-Insectan Freshwater Invertebrates
Life history of benthic freshwater invertebrates, excluding insects, may influence a number of features of sampling programs, such as the environment sampled, sampling technique or equipment used, frequency and timing of sampling, and mesh sizes of nets or sieves. Consideration of the life history should increase the effectiveness of the program and, in the extreme, may allow one to recognize artifacts that would otherwise lead to incorrect conclusions.Aspects of life history that influence sampling programs are (1) direct or indirect embryonic development and the extent to which young are sampled simultaneously with adults during the breeding season, (2) times of year when various developmental stages are present, (3) differences in size between various life stages necessitating use of more than one sampling method during the year, (4) change in habitat due to migrations or assumption of a pelagic, parasitic, or aerial existence for part of the life cycle, (5) change in mobility over the life cycle, (6) sex differences in size or behavior, and (7) adaptations to adverse conditions. Examples of ways in which life history affects sampling are based on the literature and on original data on the opposum shrimp, Mysis relicta, and the crayfish, Orconectes virilis.We recommend that quantitative studies of benthic invertebrate communities be started with a pilot study employing at least two complementary sampling techniques and sufficiently frequent sampling times to allow the development of a reliable strategy for the objective. Key words: life history, sampling, benthic invertebrates, Crustacea, Mysis relicta, Orconectes virilis