macro

1) The Core Concept (Most Important)

Macroinvertebrates are small animals without backbones that are visible to the naked eye and live in water.

They are used to measure ecosystem health because different species have different tolerance levels to pollution.

Why they’re useful:

They reflect long-term water quality, not just a single moment.

That’s a classic APES idea:

  • Chemical tests = snapshot

  • Macroinvertebrates = long-term conditions

2) Examples You Should Recognize

From the table on page 1, these organisms are categorized by pollution tolerance:

Pollution-sensitive (clean water indicators)

  • Stoneflies

  • Mayflies

Moderately tolerant

  • Crayfish

Pollution-tolerant (dirty water indicators)

  • Leeches

  • Aquatic worms

The table on page 1 shows that stoneflies and mayflies are listed as intolerant, while worms and leeches are tolerant of pollution.

Translation for quizzes:

More sensitive species = healthier water

More tolerant species = polluted water

3) What Indicates Healthy vs. Degraded Water

This is very testable.

Healthy water:

  • High biodiversity

  • Many species present

  • Includes pollution-sensitive organisms

Degraded water:

  • Low biodiversity

  • Few species

  • Mostly pollution-tolerant organisms

The packet explains that samples with only tolerant species or very little diversity suggest a degraded waterbody.

4) Factors That Affect Macroinvertebrates

These are the big environmental drivers listed on page 2:

Natural factors:

  • Temperature

  • Dissolved oxygen

  • Streamflow

  • Habitat

  • Substrate (river bottom material)

Human impacts:

  • Pollution

  • Sedimentation

  • Habitat destruction

  • Nutrient runoff

  • Toxic chemicals

Important cause-effect from the packet:

Excess nutrients

→ Algal bloom

→ Decomposition

→ Oxygen decreases

→ Macroinvertebrates die

That links back to your dissolved oxygen section again.

5) How Scientists Measure Them (Short but Testable)

From the diagrams on page 3:

They:

  • Collect organisms with nets

  • Identify them in a lab

  • Count species and abundance

Then they calculate an index called:

MMI — Multimetric Index

This number reflects overall ecosystem health.

You don’t usually need to calculate it — just know what it represents.

6) Limitations (Sometimes Tested in APES)

Macroinvertebrates:

  • Are affected by many factors

  • Don’t identify a specific pollutant

  • Can vary naturally

The packet explains that their presence alone doesn’t always prove water quality because natural conditions also influence them.

These five points will likely cover most quiz questions:

  1. Macroinvertebrates indicate long-term water quality

  2. High biodiversity = healthy water

  3. Low diversity = polluted water

  4. Sensitive species mean clean water

  5. Tolerant species mean polluted water