Life in Freshwater
Lecture 3
Phylum Mollusca
- Class Gastropoda (snails/limpets)
- Ubiquitous
except in acidic, grossly polluted waters
- Associated
with solid substrates, mostly in shallow areas
- Much
of taxonomy based on shell morphology since rest of animal is usually
quite soft
- Snails:
spiral or discoid coiled shells
- Limpets:
low conical shells
- 2-70
mm diameter
- muscular
“foot” projects from snail, ventral surface is flat, head at anterior end
bearing two tentacles, mouth in ventral and anterior, shell on dorsal
side
- Nutrition
- Most
are vegetarians: eat periphyton algae and
incidental amounts of organic matter, bacteria, and microanimals
- Some
are scavengers and omnivores
- Mucous
trail left by snail as it move traps and fertilizes microbes and snails regraze areas
- Have
radulae (teeth for scraping)
- Reproduction
- Sexual:
hermaphroditic in some families, dioecious in
others
- Eggs
laid in spring, # variable, gelatinous mass on substrate
- Development
occurs within the egg and hatches as a small replica of adult
- May
live 2-4 years
- 1-3
generations per year
- Asexual
- Parthenogenesis
is uncommon, but known
- Class Pelecypoda (bivalves: clams and mussels)
- 2-250
mm long
- benthic,
most common in larger streams and rivers
- shell
has 2 values attached by elastic hinge ligament
- valves
gape slightly to permit foot and siphons to protrude
- no
tentacles, head, eyes
- Nutrition
- Feed
chiefly on seston: suspended organic matter
including living microorganisms
- Can
remove down to 1 um particles, food particles driven over mucous in
gills, mucous driven by ciliary action to
mouth
- Reproduction
(varies by family)
- Sphaeridae
- Hermaphroditic/self-fertile
- Young
develop in grills
- Released
fully formed up to 1/3-1/4 adult size
- Unionidae
- Separate
sexes
- Young
only retained for a short time
- Released
as “glochidium”: 0.05-0.5 mm, obligatory
parasite with chintinoid valves
- Must
attach to specific fish species with a few days or die
- Larvae
clamp to fish & fish tissue overgrows
- During
encystment little increase in size, but
development proceeds to near final internal structure
- Breaks
out of cyst, falls to bottom, burrows in bottom and starts to grow as a
filter feeder on seston
Phylum Arthropoda
(jointed legs, chitinous exoskeleton)
·
Class Arachnida (water
mites)
o Appear
to be minute spiders – eight legs
o Cephalothorax and abdomen fused
o 0.4-3.0
mm long
o Nutrition
o Carnivorous
or parasitic
o Small
crustacean, worms: body pierced, fluid sucked out
o Reproduction
o Dioecious/separate sexes
o Eggs
fertilized as released
o Extruded
into groups of 20-400 onto surfaces
o Larvae
become attached to aquatic insects as parasites
o Chironomids are most frequent hosts: 10-20 per insect
o Metamorphosis
occurs within larval exoskeleton and nymph emerges
o Nymph
is free-living, looks similar to adult except not reproductively mature
·
Class Crustacea
o Most
body segments bear jointed, paired, biramous
appendages
o 2
pair of antennae
o Respire
through gills or body surface
o Most
crustaceans go through a naupliar stage
o SubClass Eubrachiopoda
o 2-100
mm
o inhabit
temporary ponds
o filter
feed moving through water eating plankton and detritus
o Three
small orders:
·
Anostraca (fairy
shrimp): wavelike beating of legs
·
Notostraca (tadpole
shrimp): may feed on larger items
·
Conchostraca (clam
shrimp): enclosed in clamlike shell, fall on side
when swimming stops
o Reproduction
·
Asexual: parthenogenesis is common
·
Sexual
o Separate
sexes
o Eggs
carried for a few days
·
Summer: thin-shelled
·
Resting: thick shelled
o Resting
eggs survive freezing and drying
o Brine
shrimp (Artemia) is a fairy shrimp
o Order
Cladocera (water fleas)
o 0.2-3.0
mm long, except Leptodora
o no
clear segmentation/thoracic & abdominal regions covered by a secreted
shell/carapace
o large
compound eye, small 1st antennae on head
o second
antennae are large, laterally inserted near posterior margin of head, used to
swim
o mouthparts
near head/body junction
o 5-6
pairs of lobed, leaf-like thoracic legs used for food gathering
o large
post-abdomen (no abdomen)
o Nutrition:
·
Filter feeding or scraping of particles from
solid substrates
·
Algae, protozoa, detritus, bacteria
·
Filtered by setae from thoracic legs, shunted
into groove and then into mouth
·
A few are predaceous (Polyphemus,
Leptodora)
o Reproduction:
·
Asexual:
o parthenogenic during much of the year
o 4-10
parthenogenic eggs per clutch
o eggs
carried in brood pouch until next molt
o eggs
hatch into small replicas of adult (neonates)
·
Sexual
o Males
(smaller) produced late in population cycle, stimulated by crowding
(accumulation of excretory products), decrease in food, etc.
o Similar
conditions cause females to produce sexual eggs which are produced only one or
two at a time
o When
fertilized, develop into resting or “ephippial” egg
o Ephippial eggs sink to the bottom, are resistant to dessication and temperature extremes, will hatch later when
conditions are right
o Order
Copepoda
·
0.3-3.2 mm, most less than 2 mm
·
gross morphology more homogeneous than cladocera
·
3 basic types: calanoid,
cyclopoid, harpacticoid
o baed on body shape, antennule
length, # of egg sacks
·
Nutrition
o Harpacticoids:
·
Bottom feeders – scrape, size, or rake food off
the bottom or other solid substrates
o Calanoids:
·
Filter plankton using maxillae (mouthparts), eat
mostly phytoplankton
o Cyclopoids
·
Always raptorial, seize and bite individual
particles such as protozoa, small metazoan, organic debris
·
Reproduction
o Only
sexual in almost all species
o Male
and females about the same size
o Male
clasps female, sometimes even before final molt
o Sperm
are deposited in female, eggs fertilized as they leave female and pass into egg
sack
o Egg
hatches into nauplius, molts 6 times and becomes copepodid which molts 5-7 times into adult male or female
o Order
Ostracoda (seed shrimp)
·
Maximum size 8 mm, but most are < 1mm
·
Animal is enclosed in a lime-impregnated valve
o Adductor
muscle allows tight closure
o Valve
opens and appendages protrude through when active
o Body
segmentation lost
o 1st
antennae – digging/climbing or swimming
o 2nd
antennae – locomotion, feeding, clasping female
·
Nutrition
o Mostly
benthic and substrate associated
o Eat
bacteria, fungi, algae, fine detritus
o Large
specimens: scavengers
o Kick
up currents, strain particles from water
·
Reproduction
o Asexual:
parthenogenesis
o Sexual
·
Males and females are similar in size
·
Males have largest sperm in animal kingdom
·
Eggs deposited on underwater substrates
singularly or in clumps
·
Eggs remain viable for long periods of dessication
·
Egg hatches into shelled nauplius
and after 8 molts into adult
o Order
Mysida (Opossum shrimp)
o Mostly
marine
o 3
US species, not
widely distributed
o Mysis relicta
·
Found in cold deepwater lakes
·
Restricted to hypolimnion
in summer
·
Good food for lake trout
·
Feeds on cladoceran
when present
- Order
Isopoda (sow bugs)
- 5-20
mm long
- mostly
marine, 130 fw US
species
- benthic
organisms, many in springs, streams and hyporheic
- strongly
dorsoventrally flattened
- “head”
= cephalothorax
- 7
thoracic segments w/appendages
- 4
abdominal segments + telson
- locomotion
by slow crawling
- Nutrition
- Scavengers:
dead, injured animals and live vegetation
- Reproduction
- Sexual
- Male
grasps nearly mature female before or during last molt and deposits
sperm
- Eggs
released in broods of 20-250 into marsupiumm
retained for up to 30 days which includes hatching
- 1st
instar looks like miniature adult, 5-8 preadult molts
- Order
Amphipods (scuds)
- Chiefly
marine, 150 fw US
species
- 5-20
mm
- body
is laterally compressed
- cephalothoras – 2 pr of antennae
- 7
thoracic segments
- 6
abdominal segments and small telson
- 1st
two pair of thoracic segments adapted for grasping
- crawl
and walk
- shallow
benthic habitats
- Nutrition
- Voracious
feeders on all kinds of plant and animal material
- Do
not normally kill live animals, may feed on periphyton
and detritus
- Reproduction
- Male
grasps immature female and holds up to 7 days, when female sheds her
exoskeleton, mating occurs
- Female
releases eggs, they are fertilized and go into the marsupium
- After
1-8 days they hatch into miniature adults and are released on the next
molt
- 9
instars to adult
- Order
Decapoda (crayfish, shrimp)
- Most
are marine
- In
US freshwater, crayfish (2 families), shrimp (16 species), 1 crab in Florida
- Crayfish:
10-150 mm, cephalothorax & 6 abdominal
segments
- Nutrition
- Omnivorous,
sometimes predaceous, may eat vegetation
- Reproduction
- Male
and females roughly the same size
- Male
flips female over and deposits sperm
- Eggs
are released by the female, but remain attached to her legs “in berry”,
10-700 eggs/female
- Newly
hatched young look like crayfish, remain attached to female for 2
instars
- 3rd
instar leaves intermittently, then permanently
- normal
lifespan < 2 yrs, but some 6-7 yrs
- Class
Insecta
- Includes
orders that are aquatic in all life stages and some that are only aquatic
in juvenile stages
- Insect
life cycle may be characterized as:
- Ametabolous: non-metamorphic, slowly increase in
size, never have wings
- Hemimetabolous: egg --à
nymph -à adult
- Larva
is a nymph, looks similar to an adult and gradually attains complete
adult morphology and function
- Last
molt has wings and is reproductively active
- Holometabolous: egg à
larvae -à pupa -à
adult
- Larva
and adult very different in form and habitat
- Most
larvae are “wormlike”, feed actively, and increase greatly in size
- Pupa
is a development stage where individual moves from the active growth
stage (larva) to the reproductive stage (adult)
- Adult
is mostly a reproductive and dispersal stage
- See
Table that lists the type of metamorphosis, aquatic stages, habitats, trophic niche for each of the following orders of
insects
- Collembola (springtails)
- Plecoptera (stoneflies)
- Ephemeroptera (mayflies)
- Odonata (dragonflies)
- Hemiptera (true bugs)
- Megaloptera (hellgrammites, dobsonflies)
- Neuroptera (spongilla
flies)
- Trichoptera (caddisflies)
- Lepidoptera
(aquatic caterpillars)
- Coleptera (beetles)
- Diptera (two-winged or “true” flies)
Phylum Chordata/Subphylum
Vertebrata
- Class
Pisces (fishes)
- Life
history:
- Eggs-à Larvae -à
Juvenile -à male and female adults
- Most
fish reproduces annually, usually at a fairly standard time producing a
cohort
- Reproduction
often occurs in spring or early summer in temperate areas
- Eggs
hatch fairly rapidly and larvae progress to juveniles over a few weeks
- Larvae
are generally poor swimmers: may be in a nest (eg.
sunfish) on the bottom or just cast into the water (planktonic)
(eg shad, striped bass)
- Larvae
feed on small zooplankton (rotifers, cladocera,
nauplii)
- Sexual
maturity (adult) reached in 1-3 years
- Some
representative groups (families)
- Lampreys
(Petromyzontidae)
- No
hinged lower jaw
- Larvae
(ammocoetes) burrow into soft bottoms, strain
for organic matter and microbes
- Transform
into adults (may or may not be parasitic on other fish)
- Sturgeons
(Acipenseridae)
- Most
primitive bony fishes
- Elongate
body/extended, hard snout
- Economic
importance – caviar and meat
- Can
be very large: several hundred pounds
- 14-20
years to maturity
- predators
on large benthic invertebrates
- Gars
(Lepisosteidae)
- Long
slender fishes with cylindrical body covered with plate-like scales and
snout with sharp teeth
- Voracious
predators, slowly stalk and wait
- Feed
primarily on other fishes
- Can
survive low DO because of “lung”
- Can
be very large, up to 8 ft long, 350 lbs
- Bowfin
(Amiidae)
- Lowland
streams
- Prefers
quiet clear water w/vegetation
- Predator
on other fishes and crayfish
- Large,
up to3 ft long, 20 lbs.
- Eels
(Anguillidae)
- Catadromous: spawn in Atlantic
near Bermuda, larvae (elvers)
find their way back to the coast and migrate well upstream
- Bottom
feeders and scavengers
- Very
slippery
- Found
in small creeks to larger rivers
- Herrings
(Clupeidae)
- Large
family of silvery, slab-sided, schooling fishes
- Many
are marine or estuarine, but migrate into freshwater
- Spring
spawners, no nest, no parental care
- Shad
& herring: feeds on minnows, aquatic insects
- Gizzard
shad: feeds on plankton, sieve with gill rakers
- Small
species are important forage for larger fish
- Trout,
salmon (Salmonidae)
- Coldwater
fishes, freshwater and marine
- Commercially
important
- Feed
on aquatic insects and small fish
- Pike
(Esocidae)
- Valuable
predators on sunfish, gizzard shad
- Duck’s
bill snout
- Lie
in wait in weedbeds or other cover
- Northern
pike: up to 4 ft, 40 lbs
- Muskellunge:
up to 5 ft, 70 lbs
- Minnows,
carp (Cyprinidae)
- Largest,
most widely distributed fish family (1500 spp)
- Many
are quite small, some such as carp are large
- Most
are herbivorous/periphyton scrapers/small
inverts
- Valuable
forage fish
- Suckers
(Catostomidae)
- Bottom-dwellers,
fleshy protusible lips
- High
dorsal ray fin count
- Anal
fin further back than cyprinids
- Range
from creek chubsucker (9”/0.5 lb) to buffalo
(3 ft/68 lbs)
- Benthic
feeders: algae, protozoa, crustacean, oligochaetes,
insect larvae and nymphs
- Serve
as forage for other fish
- Killfish, topminnows (Fundulidae)
- Small
fish: 2-6 inches
- Adapted
to low DO waters, can uptake O through head
- Favor
aquatic vegetation and shallow water
- Eat
terrestrial insects, small aquatic animals
- Live
bearers (Poeciliidae)
- Mosquitofish (Gambusia)
- Internal
fertilization/sperm storage
- Bear
live young
- Tropical
species (guppies, mollies, etc.)
- Introduced
for mosquito control, but may displace small native fish
- Silversides
(Atherinidae)
- Surface
& midwater species
- Small
slender fishes, generally less than 4 inches
- Forage
for other fish
- Zooplankton/chironomids, small insects
- Important
food for larger surfaces & littoral fishes
- Temperate
basses (Moronidae)
- Popular
game fishes
- 2
dorsal fins, large mouth/forked caudal fin
- random
spawners
- 1
lb to 50 lb (striped bass)
- predacious:
young eat crustaceans and insects, adults each small fish
- Sunfish/basses/crappie
(Centrarchidae)
- Deep,
compressed bodies
- Nests
constructed by males, circular depressions in the substrate
- Males
guard eggs and larvae, may herd the fry
- May
become stunted when food supply is limited
- Sunfish
(Lepomis)
- Feed
mainly on invertebrates
- Highly
flattened, up to 10 inches, 2 lbs
- Bass
(Micropterus)
- Sleeker,
larger, up to 15 lbs
- Eat
larger invertebrates, other fish
- Perches
(Percidae)
- Darters,
walleye, yellow perch
- Darters
are native only to E. North America: 2-4 in max
- Sand
darters: remain buried in sand, dart out after passing aquatic insects
- Sauger: river species up to 8 lbs, predator
- Walleye:
rivers, reservoirs, up to 22 lbs, predator
Kingdom Plantae
- Nutrition
- Photoautotrophs
- Obtain
mineral nutrients from sediment or water column
- Reproduction
- Asexual
- Fragmentation
- Runners,
bulbs, tubers
- Spores
(ferns, mosses)
- Sexual
- Divisions
differ in structural and reproductive characteristics
- Bryophytes
- No
vascular tissue
- Gametophyte
dominant, sporophyte grows on it
- Vascular
plants
- Vascular
tissue (xylem, phloem)
- Progressive
reduction in size and complexity of gametophyte
- Ferns
is small, heart-shaped, freeliving
- Angiosperms
is pollen grain in male, 7 cell/8 nuclei tissue in female
- Aquatic
plants group conveniently into three types
- Emergent:
photosynthetic tissue extents into the aerial environment
- Submersed:
whole plant underwater
- Floating
leaved: mostly underwater, but leaf blades float on the surface
- Review
major taxa
- Angiosperms
discriminated mainly by reproductive structures