Invertebrates and Plants: methods and applications

Document Type


Publication Date



Invertebrates and plants are among the most ubiquitous and abundant macroscopic organisms in aquatic ecosystems; they dominate most habitats in both diversity and biomass and play central roles in aquatic food webs. Plants regulate and create habitats for a wide array of organisms (Cooke et al. 2005). Snail grazing and bivalve filtering profoundly alter habitats and communities (Harvey and Hill 1991; Vaughn and Hakenkamp 2001). Aquatic habitats in North America support extremely diverse floras and invertebrate faunas; groups such as crayfishes and freshwater mollusks reach their highest worldwide diversity here. Crayfishes are important economically for human food, fishing bait, and the aquarium pet trade industry (Nielsen and Orth 1988; Huner 1997). Freshwater mussels have been exploited heavily in North America since at least the mid-1800s for freshwater pearls, button production, and currently for cultured-pearl bead nuclei (Anthony and Downing 2001). Macroinvertebrates and aquatic plants are the foci of many fisheries studies because of their importance in aquatic ecosystems, the imperiled status of many species, and the increasing presence of harmful invasive species. A disproportionate number of aquatic plants and invertebrates are imperiled relative to terrestrial species. For example, more than 50% of the 579 plant species considered of special concern in Pennsylvania are aquatic (Cronk and Fennessy 2001). Freshwater mussels and snails are among the most imperiled animals in North America (Strayer et al. 2004); about 35 mussel species and 40 snail species have become extinct in the last 50 years (Neves et al. 1997). Although only four species of crayfishes are federally listed as endangered in the USA, about half of the 363 species in the USA and Canada are considered imperiled (Taylor et al. 2007), illustrating the frequent disparity between formal conservation status and actual conservation risk. Conservation status of aquatic insects is poorly known; however, the local extinction rate of aquatic insects in Illinois exceeds that of fishes and mussels (DeWalt et al. 2005), and stoneflies may be comparable to mussels and fishes in their degree of imperilment (Master et al. 2000). Moreover, invasive aquatic plants and invertebrates have jeopardized the integrity of many aquatic ecosystems (Pimentel et al. 2000; Holeck et al. 2004). This chapter provides an introduction to sampling and study methods for freshwater macrophytes and macroinvertebrates. The term macrophyte refers to all macroscopic aquatic vegetation and does not apply to microscopic plants such as phytoplankton and periphyton (Cooke et al. 2005). We do not cover zooplankton or phytoplankton; these organisms are treated separately in Chapter 9 because of their fundamental importance in aquatic systems and because their pelagic habits require specialized sampling approaches. Lowe and LaLiberte (2006) describe methods for sampling periphyton. We limit our coverage of macroinvertebrates to groups that are commonly 2 chapter 10 of interest in freshwater fisheries studies, such as nonplanktonic crustaceans, aquatic insects, and mollusks. Information on sampling other aquatic macroinvertebrates (e.g., sponges, annelids, nematodes, flatworms, mites, and meiofauna) can be found in Smith (2001), Thorp and Covich (2001), and Hauer and Lamberti (2006); however, many of these groups can be sampled with the methods described in this chapter. The scope of this chapter is huge even when focusing on freshwater ecosystems; therefore, we were forced to exclude marine ecosystems even though many methods used in freshwater are applicable in marine habitats. Chapters 6 and 7 describe trapping methods for commercially important marine invertebrates. We suggest the following sources as an introduction to the literature on sampling marine macroinvertebrates and plants: Caddy (1989), Raffaelli and Hawkins (1996), Jamieson and Campbell (1998), Little (2000), Eleftheriou and McIntyre (2005), McLachlan and Brown (2006), Bakus (2007), and Gray and Elliott (2009). We focus on the following objectives common in fisheries management and research: (1) identification of organisms, (2) sampling to estimate diversity, spatial distribution, abundance, and biomass, (3) sample handling and marking of individuals, (4) quantification of life history or population parameters such as age, growth, and fecundity, and (5) use of macroinvertebrates and plants as bioindicators. We limit our discussion of life history and population parameters to decapod crustaceans (crayfishes and shrimps) and mollusks because these organisms are often the primary focus of fisheries studies. In contrast, fisheries biologists are rarely called upon to study life history parameters of aquatic insects, even though estimating insect abundance is often a primary goal in fisheries studies. Methods for life history study of other groups can be found in references cited in Table 10.1.