Lab8:Stream Lab Series Part III: a Survey of the Macroinvertebrate Population

BIOLOGY SEMESTER ONE

LAB 8

Lab8:Stream Lab Series Part III: A Survey of the Macroinvertebrate Population

Lab format: this lab is delivered though lab kit

Relationship to theory: In the textbook (Reece et al., 9th ed.), this lab is related to the following unit:

Learning Objectives

At the end of this laboratory, you should be able to:

Identify the major animal groups in the macroinvertebrate population of your stream site.
Identify which organisms are pollution-tolerant or pollution-sensitive.
Calculate a diversity index and state its importance in evaluating water quality.
Synthesize the data collected from your stream site during Labs 6-8 and provide a written assessment of the water quality and diversity of life in the stream.
Make a statement concerning the quality of your stream site, based on the data collected.

Introduction

The diversity of life in an aquatic ecosystem varies considerably. Aquatic biologists classify organisms in aquatic environments mostly based on where they live: neuston are surface dwellers (water striders; duckweed);plankton are distributed through the water mass (microscopic organisms such as diatoms and protozoa);nekton are the free swimmers (fish, insects); and benthos live on or in the bottom substrate.

In this laboratory activity you will concentrate your efforts on studying the benthos. The benthos that you will study are classified as macrobenthos; specifically, the macroinvertebrates (macro = large, invertebrate = no backbone). These are defined by biologists as aquatic animals that can be seen with the unaided eye and that can be retained by a sieve with openings approximately 0.6 mm square. The major taxonomic groups making up the macroinvertebrates are insects and their larval (immature) forms, crustaceans (isopods, scuds), annelids (segmented worms), nematodes (roundworms), mollusks (clams, mussels, snails), and flatworms (planarians).

Flowing-water ecosystems place great demands on the organisms living there. The major physical parameter that influences their lives is the rate of flow of the water. In particularly fast streams, organisms either are washed away or have adapted to life in the fast current. These adaptations assume several forms: for example, many organisms have very flattened bodies (mayflies); others are not only flat but have claws or hooks to hold on to the substrate (riffle beetles, sow bugs); and some even build nests and anchor them firmly to a rock or other substrate (caddis flies). Slower streams have more sediment, and it is possible to find organisms that burrow into the silt or mud, such as nematodes (roundworms), annelids (segmented worms), and certain species of mayfly and dragonfly nymphs. Others, such as freshwater shrimp and Daphnia, are able to swim in the more slowly moving water and are not dependent upon special adaptations to keep from being washed away.

(Note: Larvae and nymphs are often confused. Insects with complete metamorphosis produce a “worm-like” larva which develops into a pupa and eventually an adult insect; insects with incomplete metamorphosis produce an immature adult - a nymph - which develops into the adult form, e.g., caddisflies, mayflies, dragonflies and stoneflies all produce nymph forms.)

The macroinvertebrates are very sensitive to stress in the environment and are useful for determining the health of a stream. The diversity of species in the macroinvertebrate population provides a wide range of response to environmental stress, and a change in water quality will readily cause a shift in population density of one or more species. Stream benthos can be classified into three categories according to their tolerance to pollution.

Pollution-sensitive (mayfly nymphs, stonefly nymphs, some flies, some snails, caddisfly nymphs, water penny beetles).
Moderately pollution-tolerant (aquatic sowbugs, crane fly larvae, scuds, hellgrammites, dragonfly nymphs, fingernail clams, crayfish, damsel fly nymphs).
Pollution-tolerant (aquatic worms, midge larvae, black fly larvae, some snails, flatworms, leeches, beetles).

Although representatives of all three groups may be present in a stream, environmental stress can be detected by observing an increase over timein the population of organisms in groups 2 and 3 and a decline in the organisms in group 1.

The idea of biological diversity was introduced in Laboratory Activity 6. In this activity you will extend this concept to include a mathematical calculation of a diversity index and use it as a more formal measure of the stress (if any) your stream is undergoing. The basic premise of a diversity index is that undisturbed biological communities have a large number of species (high “species richness” with no individual species predominating (termed a high level of “evenness”. Conversely, in a stressed environment, the number of different species is reduced (i.e. you have a low species richness), and there is a tendency for only a few species to assume a dominant role in the community structure (low evenness).

To calculate a diversity index for your stream site, you will need to place the macroinvertebrates that you collect into look-alike groups. Although a greater level of detailed information can be gained from classifying your organisms to the species level using taxonomic keys, this level of detail is not required for this laboratory. A “look-alike” classification scheme will save you considerable time and is a reasonably accurate way to classify organisms to the taxonomic level of class, family, genera, and, in some cases, even species.
equipment

Spatula/scraper
70% ethanol
collecting jar
ice-cube tray
large shallow tray (or cake pan)
D-ring net
Stick or trowel
Camera / small bucket (about 2 L)
Forceps
Disposable pipette
Turkey baster
Magnifying glass
Pocket microscope
Calculator with natural log function

Procedure

At the stream Site

Position the D-net downstream of the area you plan to sample. Work through your site, scraping off the organisms and other material from the bottom of the larger rocks by rubbing them with your hands. Be careful to ensure that any debris dislodged is collected in the net.
Return the rocks you disturbed in the stream to their original position.
Using a stick, gently stir the sediments about 50 cm in front of the D-net so that any debris that is dislodged is collected in the net.
Empty the contents of the net into a small bucket; cover with stream water.
Repeat the process at two or three more sites.
At the stream edge sort your organisms. Spread a portion of the organisms from the bucket onto a shallow pan and study them carefully. Only study a small amount at a time.
Using the ice-cube tray, remove and group the organisms by appearance; sort by colour and size. You probably will have more than one species of a particular type of organism (such as a caddis-fly larva) so sort them as carefully as you can and segregate the various types or species. Try not to lump them into a single category.
Study each organism, noting its size, shape, and colour. If necessary, use a magnifying glass to examine each specimen. It may be helpful to photo-document the different species.
List the number of different groups of organisms you obtained from your stream site. For each group, count the number of individuals. You will need this information for data analysis.
Sacrifice one individual from each group and place it in a small vial of 70% ethanol. Return the remaining organisms back to the stream to minimize your impact on the macroinvertbrate fauna.

In your home lab

Make a sketch of a representative organism from each group (Figure 9.4). Just outline the major features of the body; don't get bogged down in detail. Reviewing a benthic macroinvertebrate key will help you determine what important features distinguish the species groups.The sites listed below are a good start, but check your local library as well.
Identify the organisms to Phylum and Class, using the information in Figure 9.1. For organisms of the Class Insecta, further identify them to Order, using the information in Figure 9.2 as a guide. The following are links to helpful identification sites and information

List the groups of organisms by number and name in Table 1. Using the information in the Introduction and materials made available in the laboratory, indicate whether they are tolerant, moderately tolerant, or sensitive to pollution.

Calculating the Diversity Index

Species that live and grow together, as in communities, are said to coexist. The degree to which coexistence occurs in a community is referred to as diversity. Species diversity is a measure of the number of different species (species richness) and their relative abundance (species evenness). Considerable debate surrounds the measurement of diversity and this has led to the development of a numerous indices and models for measuring diversity. Diversity is difficult to measure because it consists of the two components, richness and evenness. The precise way in which these components are incorporated into diversity measurements (i.e. the weighting or importance given to each of the two measures)has a significant effect in terms of interpretation.

A diversity index is a mathematical measure of species diversity in a community. Diversity indices provide more information about community composition than simply species richness (i.e., the number of species present); they also take the relative abundances of different species into account by providing important information about rarity and commonness of species in a community. The ability to quantify diversity in this way is an important tool for biologists trying to understand community structure and health.

A formula known as the Shannon-Weiner diversity index allows you to calculate the diversity of your stream site. This measure of diversity produces values from 0 to 4. A diversity index between 0 and 1 indicates an aquatic system of poor health (water quality); values between 1 and 3 are indicative of intermediate health; and values above 3 are typical of good health. The Shannon-Weiner index assumes that all of the organisms have been identified as species.

Where:

S = the number of species

pi = the relative abundance of each species, calculated as the proportion of individuals of a given species to the total number of individuals in the community. This is calculated by: pi = ni/N

ni = the number of individuals in each species (abundance of each species)

N = the total number of all individuals

The most important source of error for this index is failing to identify all individuals to their specific epithet (genus species). This can be done either by not observing all species in a community or lumping several species together (e.g. all limpets). This type of error tends to generate an index value that is somewhat lower than if it were done correctly. Because you are not an experienced taxonomist, your identifications will probably not be this exact. If you examine the organisms closely when you arranged them into look-alike groups, however, the margin of error may not be significant.

1.Calculate the Shannon-Weiner index for your stream site and record your results in Table 9.2. Below is an example to assist you.

Sample Calculation

A community of organisms collected from a steam has the following composition:

Organism A = 25
B = 17
C = 37
D = 5
Total = 84

Figure1: Sample Shannon-Weaver Index Calculation

Organism / Frequency
(Pi) / Natural log
(ln Pi) / (Pi)(- ln Pi)
A / 25 = 0.298
84 / - 1.211 / 0.361
B / 17 = 0.202
84 / - 1.598 / 0.323
C / 37 = 0.440
84 / - 0.821 / 0.362
D / 5 = 0.060
84 / - 2.821 / 0.169

The Shannon-Weiner index is the sum of the products of the last column, i.e., H' = 1.225, indicating, in this case, a stream community of intermediate diversity (and hence water quality).

H' = 1.225

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BIOLOGY SEMESTER ONE: LAB 8

Figure 2 Description of Major Benthic Phyla and Classes

Phylum

Class

Body shape

Colour

Locomotion

Habitat

Diagram

Platyhelminthes (flatworms) / Turbellaria (free-living flatworms) / Flat, elongated, unsegmented, 5-10 mm long / Brown, gray-black / Gliding / Under submerged plants and rocks /
Nematoda (roundworms) / Cylindrical, elongated, unsegmented, less than 1 cm long / Colourless to blackish, often translucent / Constant, rapid, whiplike / In organic material and debris /
Annelida (segmented worms) / Oligochaeta (aquatic earthworms, Tubifex) / Cylindrical ringlike segments, about 1-30 mm long / Varies, often red / Crawling / In organic material and debris /
Hirudinea (leeches) / 32 segments, 3-5 groves per segment, suction disks at anterior and posterior ends / Brown / Crawling / Attached to submerged objects, logs, and plants /
Arthropoda (jointed appendages; hard, chitinous exoskeleton, segmented body) / Crustacea (crayfish, shrimp, sow bugs) / 2 pair of antennae, usually numerous paired appendages, considerable variation in size—from microscopic to 10 cm / Varied / Swimming, crawling / Attached to submerged objects, logs, and rocks /
Arthropoda (continued) / Insecta (immature forms) / Segmented body (head, thorax, abdomen), thorax with 3 pairs of jointed legs, 1 pair of antennae on head (see key to aquatic insect larvae) / Brown, black, green / Crawling / Attached to submerged objects, logs, rocks, and plants
Arachnida (water mites) / Globular to oval in shape, 8 legs, 0.4–3.0 mm long / Brightly coloured / Crawling / Attached to submerged objects, logs, rocks, and plants /
Mollusca (soft body in 1 shell or 2 calcareous [calcium carbonate] shells / Gastropoda (snails) / Body enclosed in 1 coiled spiral shell, may be ocone-shaped, 2–70 mm long / Gray or black shell / “Walking” with foot / Attached to submerged objects, logs, rocks, and plants, or buried in mud /
Pelecypoda (clams, mussels) / Body enclosed in 2 shells joined by elastic hinge, 2–25 mm long /

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BIOLOGY SEMESTER ONE

LAB 8

Figure 3 Representative Aquatic Insect Nymphs and Larvae

Figure4: Macroinvertebrate Sample from Stream Site

1
Common
Name______
Phylum ______
Class______/ 2
Common
Name______
Phylum ______
Class ______/ 3
Common
Name______
Phylum ______
Class______
4
Common
Name______
Phylum ______
Class ______/ 5
Common
Name______
Phylum ______
Class ______/ 6
Common
Name______
Phylum ______
Class ______
7
Common
Name______
Phylum ______
Class ______/ 8
Common
Name______
Phylum ______
Class ______/ 9
Common
Name______
Phylum ______
Class ______
10
Common
Name______
Phylum ______
Class ______/ 11
Common
Name______
Phylum ______
Class ______/ 12
Common
Name______
Phylum ______
Class ______
13
Common
Name______
Phylum______
Class ______/ 14
Common
Name______
Phylum______
Class ______/ 15
Common
Name______
Phylum______
Class ______

Table1: Pollution Sensitivity of Macroinvertebrates

Group / Name
(if possible) / General Characteristics / Pollution Sensitivity
(Tolerant/Moderately sensitive/ Sensitive)

Table2: Shannon-Weaver Diversity Index of Stream Site

Organism / Frequency (Pi) / Natural log (ln Pi) / (Pi) (- ln Pi)

Shannon-Weaver index: H' =

Laboratory Report

Using the data you have collected from your stream site over the past few weeks, you must write an overall assessment of the diversity of life in the stream and the quality of the water. Your report should have the following elements:

Physical Overview of Stream Site – Write several paragraphs describing the location of your stream site, indicating stream origin and confluence ( where it joins another stream). Identify any remarkable qualities about the stream. Indicate the type of topography through which it flows and what type of land use is undertaken in the watershed. Be sure to include all the physical data you collected during Lab 6 in a data table. (5 marks)
Water Chemistry – Write a paragraph or two assessing the water quality of your stream, based on the analyses you carried out during Lab 7. The analysis of the data collected should be done by researching the literature on limnology and water quality. Be sure to include the results of all the tests you carried out and indicate the normal range of values for each parameter. (5 marks)
Living Organisms – Write a paragraph or two on the diversity of living organisms you observed in your stream. Correlate the types of organisms you observed with the water chemistry and surrounding land use in the area. Are there parallels? Be sure to include all information you collected while examining the macroinvertebrates. (5 marks)
Write a concluding paragraph regarding the overall health of your stream. Identify what features might cause your stream to be healthy or unhealthy. (10 marks)
You should have the following tables and figures in your report (30 marks):

Table 1 – Physical Stream Data (from lab 6)
Figure 1 – Stream Site Map (from lab 6)
Table 2 – Water Chemistry (from lab 7)
Figure 4 – Macroinvertebrate Diversity (from lab 8)
Table 1 – Pollution Sensitivity of Macroinvertebrates (from lab 8)
Table 2 – Shannon-Weiner analysis (from lab 8)

Produce your own Tables and figures rather than using the pages from the lab manual. Each table and figure should have an informative title and be referred to in the report. Any photographs, or information that might be useful in your analysis, should also be included at your discretion.
This report encompasses the efforts completed for Labs 6-8 and so is a significant component of your course mark.

Total Laboratory Marks: 55 marks + 30 marks for Lab 6 +15 marks for lab notes= 100.

Bibliography

Hodgson, C. (2005). Laboratory manual for Bio 102, Principles of modern Biology, 6th Ed. Courtenay: North Island College.

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