Freshwater Animals

Note Ctenophores and Echinodermata are marine phyla; all other phyla have representatives in freshwater.

Phylum Porifera: The sponges

• Sponges are mainly marine but there are ~25 freshwater species described.

• Primitive multicellular animals; do not have organs, but do have specialized cells for feeding, digestion.

• Filter feeders; sieve particles from the water as it flows into pores.

• Some species have symbiotic algae (similar to corals), mainly green algae

Chlorella

.

Can be important consumers of microbes as small as bacteria

Cnidaria: Celenterates (Hydra & Jellies)

• • Most species marine; all display radial symmetry and possess nematocysts (defense cells).

Hydra

is probably most common freshwater cnidarian: – May have symbiotic algae,

Chlorella.

– Most often sessile; epiphytic

Platyhelminthes and Nemertea:

• Turbellaria (free-living flatworms) are most common in freshwater benthic habitats or epiphytic.

• Some planaria acquire nematocysts for defense by ingesting hydra (marine forms do so as well).

• Trematoda (flukes), a major group of animal parasites; some with aquatic phase in life cycle.

• Schistosomiasis is a disease of the human intestinal tract caused by a

Schistosoma

fluke. A similar fluke causes swimmers itch in humans we get infected as an alternate host (normally water fowl).

• Nemertea have an anus and closed circulatory system.

Schistosoma

life history:

•

Nematoda: The roundworms

Non-segmented roundworms; common in all kinds of aquatic habitats (damp soil, freshwater, marine).

• Generally benthic infauna (within sediments).

• Feeding strategy varied: detrivores, herbivores, carnivores (including predation on other nematodes).

• Some species are common and important parasites of animals (including humans), often using insects as host vectors. (e.g. “river blindness”, onchocerciasis transmitted by blackfly (

Simuliidae).

(and rotifers)

Rotatoria (Rotifers)

• 2000 freshwater species, more diverse than in marine habitats!

• Possess an advanced digestive system including mastax (to grind food down), stomach, intestine, anus. Possess a nervous system and sensory organs (eyes).

• Sexual reproduction produces a dormant cyst and several species can survive years of drought.

• “Wheel organ” is ciliated and creates a whirlpool-like flow to bring prey to mouth. Some modified for ambush capture.

• Predators of bacteria and small protists like nanoflagellates.

• May be planktonic or attached by “foot” (with “toes”).

Mollusca

Soft-bodied, unsegmented; possess a head, muscular foot, stomach/viscera, and often grow a calcareous shell.

• Class Gastropoda : snails and limpets – 500 species of freshwater snails – One-piece shell and a

radula

(file-like structure) that is used to scrape food from surfaces Spiral shell – Snails are important grazers of periphyton (epilithic algae, bacteria, etc.) but also feed upon detritus, macrophytes, and dead tissue

• Class Bivalvia : clams and mussels – Bivalves have a shell with two halves and gills specialized for filter feeding.

– Found in the benthos, either burrowed in sediments or attached to substrate.

– Adults can withstand periods of drought by closing shell.

– Some have specialized larval stages with interesting dispersal characteristics.

– Some bivalve species are important invaders of North American aquatic systems (alien species: Asiatic clam, zebra mussles) with serious ecological implications.

Annelida: Segmented worms

• Tubular, segmented body with specialized digestive system, terminal mouth and anus. Familiar representatives include oligocheates, leeches.

• Oligocheates (like familiar earth worms): benthic, burrow through sediment.

– Most ingest organic particles in sediments (important connection in food chain); some algal grazers or predators.

– Resistant to low oxygen and polluted conditions (good indicator species; Tubifex).

– Vectors of some important parasites, e.g. Whirling Disease

Hirudinea (Leeches)

Whirling Disease of Trout

Tubifex

sp.

Myxobolus cerebralis

Arthropoda

• Ubiquitous in all continental surface waters.

• Important in linkages of ecosystems. (aquatic and terrestrial) • All arthropods characterized by:

– Chitinous exoskeleton – Stiff jointed appendages (mouth, legs, etc.)

Arachnida: Mites and Spiders

• No true aquatic spiders; some able to utilize the environment on occasion.

• Water mites are diverse and inhabit most surface waters.

• Mostly benthic, but some pelagic species in lakes.

• Almost all predatory (mainly on insects) but some parasitic (often in larval stage).

Fused cephalothorax and abdomen Mouth Six pairs of appendages, 4 pairs of legs most conspicuous

Subphylum Insecta

• Ten orders contain aquatic species; majority are aquatic as larvae, emerge as adults.

• Characterized by: – body divided into head, thorax (three segments), and abdomen – Single pair antennae, compound eyes, specialized mouthparts • Order Collembola (springtails): Not true insects.

– Wingless, often eyeless.

– Mostly terrestrial or semiaquatic, often in lakes – Poorly studied

Order Plecoptera

• Stoneflies most common in streams; some predators and others detritivores.

• Sensitive to pollution and low oxygen levels, therefore used as an indicator species.

• Similar in appearance to mayfly larvae except only have two cerci (filaments) on posterior end, and tend to be mostly flattened.

• Incomplete metamorphosis

Incomplete Metamorphosis

Order Ephemeroptera: Mayflies

• Aquatic only as larvae; common in streams and in lake benthos. Feed by scraping, collecting, some predatory • Many species, typically divided by habitat interaction or behavior: swimmers, clingers, crawlers, burrowers. Body shape reflects lifestyle: – Clingers flattened dorso-ventrally – Swimmers round & streamlined – Burrowers often have tusk-like mandibles – Crawlers have more streamlined gills than burrowers Gills Three filaments

Mayfly life cycle : 1) Eggs hatch in water, larvae grows.

2) Larvae swims to surface and emerges; metamorphoses into sub-adult (subimago) form.

3) Subimago matures into adult. Adult mates, female lays eggs in water, dies.

Order Odonata: dragonflies, damselflies

• Aquatic as larvae in both streams and lakes (more in lakes and slow waters). Important predators of other insect larvae.

• Move by crawling, some by swimming. Prefer thick aquatic vegetation for cover, debris/litter, rocky cobble, or burrow in sediments.

• Three-stage lifecycle similar to mayflies. This lifecycle is termed

incomplete metamorphosis.

Order Trichoptera

• Caddisflies mostly lotic, a few lentic species; aquatic as larvae and pupae • Variety of lifestyles habits: – Some build protective cases from materials in the environment, crawl and graze on periphyton or leaf litter – Some construct nets for filter-feeding – Others free-living, predatory

Complete Metamorphosis

Order Megaloptera

• Dobsonflies, alderflies; aquatic as larvae, pupae • Often large larvae with large mandibles; all predators.

• Aquatic period of life cycle can last several years before emerging as adults.

• Occur in both lotic and lentic systems.

Order Heteroptera

• The true bugs are mostly terrestrial; aquatic species live either on surface or submersed.

• Inhabit both lentic and lotic environments; many possess specialized appendages adapted for swimming or to facilitate air breathing.

Order Lepidoptera

• Very few aquatic species of moths or butterflies; usually associated with ponds with dense macrophyte populations. Some lotic species grazers of periphyton.

• Complete metamorphosis.

Paired, filamentous gills

Order Coleoptera

• Though only about 3% of beetles aquatic, there are so many species of beetles that this still represents a significant order of aquatic insects.

• Some submerge water bubbles for air breathing.

• Includes predators, periphyton and macrophyte grazers.

Order Diptera: True Flies

• Largest group of aquatic insects, dominated by family Chironomidae (midges).

• Also includes nuisances like mosquitoes, black flies… • Some midge larvae possess hemoglobin as an adaptation for survival in low oxygen environments.

Subphylum Crustacea

• 4000 species of crustaceans found in freshwaters; although most are marine.

• Includes many important food chain links: – Zooplankton species are key as primary consumers (plankton grazers) – Benthic omnivores which feed upon detritus, carrion, etc.

• Characterized by: – Respiration across gills or body surface – Chitinous exoskeleton, two pairs antennae, paired and jointed appendages

• • • •

Ostracoda

“Seed shrimp” are benthic species covered by carapace made of mix of chitin and calcium carbonate.

Mostly graze algae or eat detritus.

When ostracod dies, carapace resists dissolution; can be found in sediment cores, fossils.

Isotopic composition of recovered carapace can reveal past climate patterns (temperature).

Copepoda

• Important pelagic zooplankton, but other species also benthic in streams, lakes and groundwater, or parasitic.

• Sexual reproduction, characterized by a many-staged development process divided between 6 naupliar (analogous to larval) and 6 copepodite (juvenile) stages.

• Interesting patterns of diverse morphology, adaptations and speciation.

Branchiopoda

• Diverse group including Cladocera, tadpole shrimp, brine shrimp, etc.

• Usually found in lentic environments. Some benthic, some planktonic.

• Many species have an egg stage that is resistant to drying and can withstand long periods out of water.

Decapoda

• Includes many large (macroinvertebrate) species such as crayfish, shrimp, crabs.

• Inhabit lentic and lotic environments, including caves, groundwaters, wetlands.

• Some species have high value as food for humans; these are often cultured and harvested.

• Crayfish are omnivorous and important benthic consumers; shrimp are primarily grazers or detritivores.

• Important as both consumers and as prey for larger vertebrates.

Isopoda

• Pillbugs, sowbugs; terrestrial, marine and freshwater species.

• Often found in clean, oxygenated water (springs, streams, groundwaters).

• Detritivores and scavengers.

Amphipoda

• Scuds and side-swimmers; resemble isopods but are flattened laterally, not dorso-ventrally.

• Omnivorous scavengers; some important shredders of CPOM; mainly benthic.

The Vertebrates

• In freshwaters, fish are considered the most important vertebrate species.

• Most diverse aquatic vertebrates, over 24,000 species described; ~ half found in freshwater.

• Dominant classes: – Superclass Pertomyzontiformes, jawless fishes (lampreys) – Class Chondrichthyes, cartilaginous fishes – Class Osteichthyes, bony fishes

• Fish can be found as predators, grazers, scrapers… • Body form is adapted and specialized toward certain lifestyle / behavior: –

Streamlined

fishes are specialized for near constant swimming for locating and pursuing prey – – Benthic species often mouths

flattened

dorso-ventrally, with under-slung –

Deep-bodied, ventrally flattened

fish are specialized for maneuvering in tight quarters –

Elongate, torpedo-shaped

fishes specialized as sit-and-wait ambush predators; built for burst speed.

Eels

are adapted for moving through narrow spaces

Tetrapods

Other aquatic vertebrates include amphibians, reptiles, birds and mammals.

• Amphibians

include salamanders, frogs; mostly predators but some are algal grazers and detritivores (especially as larvae).

– Amphibians have recently gained much attention as indicator species of aquatic pollution and environmental changes.

– Recent evidence suggests a worldwide decline in amphibian diversity; some correlations to climate change, global warming processes.

Reptiles, Birds and Mammals • Many familiar representatives including:

– Turtles, Water snakes, Crocodilians – Pelicans, ducks, some raptors – Dolphins, bats, beavers, hippopotamus These animals are often of interest as high-order predators, or for ways in which they alter their environment.

Mostly associated with shallow habitats and aquatic terrestrial interface.