Unit 8C Notes:
Freshwater Habitats and
Organisms
Freshwater
Macroinvertebrates
A. General Characteristics
• Freshwater macroinvertebrates are
animals without backbones that live in
or near the bottom of freshwater
ponds, lakes, streams, and rivers for all
or part of their life cycle.
• They are very important indicators of
the health of these bodies of water,
reflecting the quality of the water and
the conditions of the habitat.
General Characteristics
• Freshwater insects are a large group within
the macroinvertebrates found in bodies of
freshwater. They make up 90% of the
organisms living at the bottom of a stream.
• Organisms that live on the bottom are called
benthic. Of the 2 million known insect
species, there are over 80,000 species that
fall into the macroinvertebrate category.
Examples:
• Examples in insect macroinvertebrates
include mayflies, dragonflies, and
beetles.
• Other benthic macroinvertebrates that
do not fall into the insect group include
crayfish, clams, snails, worms, and
leeches.
B. Aquatic Adaptations
• Freshwater macroinvertebrates are
usually grouped by three characteristics:
– how they move,
– how they feed,
– their tolerance to pollution
How They Move:
• In order to adapt to the aquatic environment, macroinvertebrates
have to be able to move or maintain their position in the water.
Type
• Skaters -
Description
-Adapted for movement on the
water’s surface
-Scavenge on organisms caught in
the surface film
How They Move:
Planktonic May float and swim in open water or
float at the surface to get oxygen or
food; can dive when alarmed
Inhabit open water (limnetic zone) of
lakes, ponds, and bogs (lentic systems)
How They Move:
Divers
Can swim by rowing with the hind legs
in lentic habitats and lotic pools
How They Move:
Swimmers Adapted for fish-like swimming in lotic
and lentic habitats
How They Move:
Clingers
Construct shelters, have long claws
and flattened bodies for attaching to
rock or other surfaces in lotic riffles
and wave-swept rocky littoral zones
How They Move:
Sprawlers Live on the surface of floating aquatic
plants or fine sediments
Adaptations include long legs
How They Move:
Climbers
Live on overhanging branches, logs,
roots, or aquatic macrophytes
Adapted for climbing plants or debris
How They Move:
Burrowers Inhabit fine sediments of streams
(pools) and lakes
Adapted for digging
How They Feed:
Feeding
Food Preference
Feeding Habits
Group
Shredders Live or dead aquatic Chew, bore, or
plant material
gouge
How They Feed:
Feeding
Group
Food Preference
Feeding Habits
Collector- Small bits of
Gather deposits
gatherers decomposed organic from the bottom
matter
How They Feed:
Feeding
Group
Food Preference
Feeding Habits
Collector- Small bits of
Filter matter out
filterers
decomposed organic of the water
matter
How They Feed:
Feeding
Group
Food Preference
Feeding Habits
Scrapers
Algae, diatoms,
bacteria, and fungi
found attached to
plants or rocks
Scrape food
from the
surface it is
found on
How They Feed:
Feeding
Group
Food Preference
Feeding Habits
Piercers
Live aquatic plants
Pierce into the
plant and suck
fluids out
How They Feed:
Feeding
Food Preference
Group
Predators Live animals
Feeding Habits
Engulf whole
animals, or
pierce into the
animal and
suck fluids out
Pollution Tolerance
• Aquatic macroinvertebrates are also put
into categories based on their tolerance
to pollution. Tolerance values range
from 0 to 10 with 0 being the least
tolerant, and 10 the most tolerant.
• Tolerance values are assigned to those
organisms used as pollution indicators.
Pollution Tolerance
• Freshwater macroinvertebrates are used as
indicators of pollution for many reasons:
–
–
–
–
Important part of all aquatic ecosystems
Found in all types of aquatic habitats
Fairly easy to collect
Have different levels of tolerance to an
environmental disturbance
– Most live or stay over a small area
– Life cycles of most groups are well documented
Why are macroinvertebrates
bioindicators of stream health?
•
•
•
•
•
•
•
•
Spend up to one year in
the stream.
Have little mobility
Generally abundant
Primary food source for
many fish
Good indicators of
localized conditions
Diversity = healthy
stream
• Easy sampling
techniques
• Potential threats to
macroinvertebrate
diversity
– Sedimentation
– Habitat loss
– Chemical pollution
Group I: Generally sensitive to
pollution. Large numbers of these
types of organisms
• normally indicate GOOD WATER QUALITY.
Water Penny Beetle Larva
Stonefly Nymph
Riffle Beetle Adult
Gilled Snail
Mayfly Nymph
Hellgrammite
Non-Net-Spinning Caddisfly Larva