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