Challenges and solutions for measuring taxonomic richness of aquatic invertebrates in wetlands

Abstract

1. Measurements of biodiversity are crucial to assessing the ecological integrity of ecosystems. However, adequately describing the range of organisms existing in habitats can be challenging, especially for the taxonomically rich invertebrates. 2. We analysed six large datasets designed to describe the taxonomic richness of aquatic invertebrate assemblages in depressional freshwater wetlands from various regions or locations (in North America, southern Africa and South America). Three of the datasets targeted large numbers of wetlands (57-163 sites), sampled once and the other three datasets repeatedly sampled over longer time periods (5-23 years), but targeted a smaller number of wetlands (10-18). 3. We estimated the total number of invertebrate taxa that likely existed for each target area (Chao estimator), as opposed to how much of that richness was actually collected by each effort (using taxon-accumulation curves). The most ambitious effort (17 wetlands, 23 years, 5-6 samplings per year) captured 95% of the aquatic invertebrate taxa projected to occur in the study area; none of the other five efforts captured appreciably more than 80% of the projected total richness per study area. 4. Findings suggest that capturing 90% or more of regional taxa is truly laborious and should not be a primary goal for efforts to sample the invertebrate fauna in wetlands. Objectives for sampling wetland invertebrates should be tailored to address what is realistic, knowing that as much as 30% of taxa may be missed by even ambitious efforts. 5. As a potential solution, we suggest setting feasible objectives for wetlands macroinvertebrate assessments. We recommend researchers try to reach a 70% study area richness target by sampling 60-80 wetlands once or smaller sets of wetlands for 2-3 years.