Sampling and Processing Aquatic and Terrestrial Invertebrates in Wetlands

Abstract

Obtaining unbiased samples of aquatic and terrestrial invertebrates from wetlands provides unique challenges due to the varied life history strategies of invertebrates as well as the heterogeneity present within a wetland. Many sampling devices are useful in more than one sampling environment within a wetland but the effectiveness of most methods varies among and within wetlands as well as between users. In this chapter, we emphasize field collecting techniques and address laboratory sorting methods. When possible, the advantages and disadvantages of each method are listed and suggestions are provided to reduce bias and unwanted variability in sample collection. Sampling devices for benthic (grabs, single and multiple cores, nets, and artificial substrate), water-column (open cylinder, emergence trap, activity trap, sweep net), epiphytic (box samplers, quadrat samplers), flying terrestrial (aerial net, flight intercept trap, light trap, malaise trap), and non-flying terrestrial (sweep net, aspirator, vacuum sampler, Berlese-Tullgren funnel, mist net) invertebrates are presented and discussed.

Student Exercises

The following are some brief ideas for introducing students to wetland invertebrate sampling, identification, and ecology. If you are a wetland invertebrate specialist, you probably already have your own favorite classroom, laboratory, and field exercises. However, if invertebrates are not your main forte, the following ideas may provide you with a starting point for incorporating invertebrates into your wetlands course. These can be used as presented or modified to suit your individual needs.

5.1.1 Classroom Exercises

5.1.1.1 Classroom Exercise 1: Understanding Taxonomy

The following exercise known as the “Nuts and Bolts” lab was adapted from Dr. Robert Whitmore’s Vertebrate Natural History course at West Virginia University. The exercise is designed to acquaint your students with development and use of a dichotomous key. This assignment is most appropriate for introductory courses or for interdisciplinary courses where students may not have a solid background in biology. Assign students to work in a group and provide each group with a jar containing various small articles. You can populate each jar with the same set of items or make unique sets for each group. Examples of items might include rubber bands, dice, pebbles, small pieces of cloth, etc. Assume that each article is a wetland invertebrate. Students should examine these animals very carefully, and compare each piece with every other piece. As they examine the differences and similarities among the “organisms,” they should decide on their degree of relationship.

Part 1 : Instruct students to place these “species” in some type of “classification” where they would show a degree of relationship based on their shape or “morphology” (the function of each article may also be used as a classification character). Classifications should reflect “true relationships”. Have the students address the following questions.

• 1. List the characteristics used to group and split the taxa, and explain why you placed these species together in a given taxon at a given rank.

• 2. What makes some characters more important than others in your classification?

• 3. What characters do you consider trivial/awkward if any? Why?

• 4. Are functional or nonfunctional characters useful in determining relationships?

• 5. To what extent did arbitrary decisions and criteria influence your results?

Part 2: After the students have decided on a classification scheme, they should construct a dichotomous identification key. This key should be a ready identification of your “species”. The dichotomous key, meaning forking regularly into two nearly equal branches or segments, is based on an orderly elimination of the characters that do not fit the case in hand. This particular key considers only two possibilities at one time.

The key should be arranged to give the user the choice of two alternatives. In arriving at a choice, one should carefully read all of the characteristics that apply to both choices and then decide which of the alternatives best fits the animal. When they decide which choice to follow, they should proceed with it to the next alternative which is indicated by the number at the right of the page. Below is a very simple example.

5.1.2 A Simple Key for Identification of a Few Biological Objects

1A	Vascular plant	2
1B	Vertebrate animal	3
2A	Leaf margins without obvious indentations; total length greatly exceeds maximum width	Fescue (Grass)
2B	Leaf margins indented; total length equal or less than maximum width	Red Maple
3A	Feathers present	4
3B	Feathers absent	7
4A	Beak length greater than 4 times the width	5
4B	Beak length equal to or less than 4 times beak width	6
5A	Toes connected to each other by skin (webbed)	Gull
5B	Toes not webbed	Heron
6A	Dominant color red	Cardinal
6B	Dominant color blue	Blue Jay
7A	Body mostly covered with hair	Squirrel
7B	Body not covered with hair	Turtle

Classes that already have the fundamentals down regarding use of dichotomous keys (but are not adept at identifying invertebrates) can skip the jars containing artificial contents and go straight to vials containing real specimens. Specimens can come from previous collections or research or from the field laboratory exercises below.

5.1.2.1 Classroom Exercise 2: Selection of Sampling Devices and Creation of Study Design

As we have learned in this chapter, there are numerous methods and techniques for collecting invertebrates from wetlands. Each method has its own biases and the advantages and disadvantages of each technique will vary greatly under the particular circumstances. For each of the following scenarios, identify an appropriate sampling device and a study design. For the study design, think about number of samples, sample location, timing, and frequency of sample collection to meet objectives. Justify your choice of technique and design. Are there any potential biases or issues with your technique and design?

• (A) You work for a state wildlife management agency within their wetland mitigation program. Your boss wants you to evaluate function of created wetlands in comparison to natural wetlands. In particular, your objective is to obtain an unbiased estimate of food availability (invertebrates) based on biomass and density for red-spotted newts (Notopthalamus viridescens) inhabiting these natural and created wetlands. Red-spotted newts generally select prey items within the water-column, on vegetation, and in the substrate. Each of the wetlands you choose to study (5 of each) has an average water depth of 50–60 cm and varies from about 0–125 cm deep. Wetlands are primarily covered in broad-leaved cattail (Typha latifolia) with about 10 % open water.

• (B) You are in charge of developing the first dragonfly and damselfly atlas for you state or province. The atlas should provide the distribution and relative abundance of each species on a county-by-county basis. In essence, for each county you are recording and documenting a species’ presence and their relative abundance (rare, uncommon, common, abundant) based on criteria that you will set.

• (C) Little whirlpool ram’s-horn snail (Anisus vorticulus) is a rare gastropod species that occurs in wetlands throughout a number of European countries including England, Germany, and Poland among others. In England, they have been identified as important umbrella species for their relation to high quality wetlands and their association with other invertebrates (Osmerod et al. 2009). Even though they can be associated with high quality wetlands, they are known to occur in highly altered systems including drainage ditches designed to drain wetlands to facilitate grazing by livestock. However, much of their basic life history remains unstudied. Develop a sampling methodology to better understand their population dynamics within these altered wetland systems.

  Osmerod SJ, Durance I, Terrier A, Swanson AM (2009) Priority wetland invertebrates as conservation surrogates. Conserv Biol 24:573–582

• (D) You work as a biologist on a national wildlife refuge located along a major migratory pathway for spring migrating shorebirds. The refuge has water control capabilities on eight impoundments totaling about 1,200 ha of wetlands. These wetlands are managed as moist-soil management units. Thus, they are primarily vegetated with annual plants and by the time you start your spring drawdowns there is less than 5 % vegetative cover. You want to experiment with drawdown timing and water management to maximize shorebird use and invertebrate foods (benthic invertebrates). You have already designed a strategy to sample shorebird use every other day for an 8-week period. How will you sample their food sources?

5.1.2.2 Classroom Exercise #3: Understanding Species Diversity Through Sampling

Species diversity is a common measure of species composition and numbers in a community. Higher species diversity exists when many equally or nearly equally abundant species are present. A higher diversity also indicates a more complex community with more species interactions. This classroom exercise is designed for student to calculate and understand species richness and diversity with data sampled in different ways.

In this exercise, Margalef’s species richness index (D _a ) and Simpson’s species diversity index (D _s ) will be used. Students are advised to use hypothetical data sets provided below.

	Number of individuals collected with different sampling methods (Hypothetical data set)
Species	Method 1	Method 2	Method 3	Method 4
n1	100	100	10	10
n2	100	90	10	10
n3	100	80	10	10
n4	100	70	10	10
n5	100	60	10	10
n6	100	50	10	10
n7	100	40	10	10
n8	100	30	10	10
n9	100	20	10	10
n10	100	10	100	10

Species richness: Margalef’s species richness index is calculated as,

$$ {D_a}=\frac{(s-1) }{{\log N}} $$

where s is number of species and N is number of individuals.

Species diversity: Simpson’s species diversity index is calculated as,

$$ {D_s}=1-\frac{{\sum {{n_i}} ({n_i}-1)}}{N(N-1) } $$

where n _i is number of species i and N is number of individuals.

Based on calculations of indices, examine the effect of sampling methods on species richness and diversity indices. Also, discuss about advantage and disadvantage of using Margalef’s species richness index (D _a ) and Simpson’s species diversity index (D _s ) to compare structures of different communities or compare different sampling methods.

Further study: students are encouraged to examine the data sets further with other indices. Diversity indices are well presented in many ecology books, and a list of references below may be helpful for students to understand the indices.

• Cousins SH (1991) Species diversity measurement: choosing the right index. Trends Ecol Evol 6:190–192

• Peet RK (1974) The measurement of species diversity. Annu Rev Ecol Syst 5:285–307

• Maurer BA, McGill BJ (2011) Measurement of species diversity. In: Magurran A, McGill B (eds) Biological diversity: frontiers in measurement and assessment. Oxford University Press, Oxford

5.1.3 Laboratory Exercises

5.1.3.1 Field Laboratory Exercise #1: Using a Diversity of Sampling Devices

The purpose of this exercise is to allow students the opportunity to use and understand how to operate a variety of different wetland invertebrate sampling devices. Obtain examples of all the aquatic and terrestrial samplers that we described in the chapter. Go to a wetland that has varied topography and structure so a variety of sampling sites are available such as open water, emergent vegetation, trees, shrubs, and mudflats are available. Have each student deploy and operate each sampling device within the appropriate circumstances. Each student should collect multiple samples to ensure that they have the procedure down. Samples can be deposited back in the wetland if not needed or a few samples can be kept and preserved in the field or brought back to the laboratory for processing and use in other lab exercises. Setting up stations with one or two devices and having groups of students rotate among stations often works best with larger class sizes. After using a device students should write a few notes on their perceived advantages and disadvantages of using each device. Students should type a report comparing and contrasting each device’s effectiveness.

5.1.3.2 Field Laboratory Exercise #2: Epiphytic Invertebrate Sampling

Epiphytic invertebrates present particularly unique challenges in sampling invertebrates due to the complexity that the plant shoots, water, and substrate provide. Assign students to work in pairs or small groups and select two or three different sampling methods for epiphytic invertebrates such as a box sampler, stovepipe sampler, quadrat, throw trap, or D-frame net for them to use. Have them collect an equal number of samples using each assigned method from a homogenous stand of vegetation within a wetland that has standing water. Remove the invertebrates from the sampling device and preserve in ethanol. Use one vial for each sample. Be sure to label all containers with all relevant information. Take the samples back to the laboratory or do an analysis in the field depending on logistics. Depending on the identification proficiency available within the class you can conduct: (1) total counts of invertebrates captured, (2) separate into morphological types or major categories (worms, snails, bugs), or (3) identify to family or genus. After counting and recording data, place the samples back in the vials, and add new ethanol. These vials of specimens can be reused later in more formal identification labs if desired.

5.1.3.3 Field Laboratory Exercise #3: Terrestrial Invertebrate Sampling in Wetlands

This exercise is performed over a several day period, and is especially appropriate for long field trips. The purpose of the exercise is to highlight how different collecting techniques are appropriate for collecting different target taxa. As mentioned in this chapter, there are a multitude of methods for collecting terrestrial invertebrates within dry wetlands, and each method is particularly useful for collecting certain terrestrial invertebrate groups. Divide students into small groups and assign each group a different collecting technique. We suggest pit fall traps, beat sheets, malaise traps, pan traps, and berlese funnels (soil sampling). Each group should then deploy their traps in the field. It is best if all methods are deployed in the same type of habitat, though this is not absolutely necessary. Other sampling methods, such as light trapping, may be very good for highlighting the lessons of this exercise, but be sure to consider the logistics of using such methods when teaching a class.

After a predetermined amount of time (3 days–1 week will be adequate), have the students collect the specimens from the traps and bring them into the classroom. Now the groups can count the number of specimens collected in their traps (abundance) and identify them to order (diversity). Gather the data from each group and share it with the rest of the class. The students should notice which traps collect the most terrestrial invertebrates and which traps collect a large number of specimens from a certain order (such as Diptera in pan traps). As a follow up to this exercise, you may have the students write a short report on why they think certain collecting techniques are more effective for collecting certain taxa.