Freshwater Eco - Diversity

ways diversity can be assessed

• Genes, genotypes, discrete breeding groups, genera, families…

6 groups of organisms based on ecology

• filter-feeders

• predators

• planktonic

• benthic

• piscivores

• herbivores

size of viruses

20 to 200 nanometers

smallest organisms in freshwater ecosystems…

viruses

important roles of viruses

• attack heterotrophic bacteria (causing daily turnover of bacteria and viruses)

• involved in biochemical cycling (release nutrients by killing microbes)

• impact population dynamics of their hosts

places viruses are abundant in freshwater ecosystems

• water column

• sediment

• eutrophic water

why is it important that viruses are more abundant in summer

leads to high encounter rates and thus helps start crop die-offs

bacteria convert … and … into …

organic and inorganic matter into energy

impact of cyanobacteria 2.5 billion years ago

started to convert the biosphere from having no free oxygen to being rich in oxygen gas

roles of bacteria in freshwater ecosystems

• Extremely important for lake metabolism...involved in mineralization
  processes and in the chemical transformation of elements between
  reduced and oxidized forms (e.g., nitrogen, sulphur)

• fast generation time

• most abundant food source for higher/larger organisms

characteristics of cyanobacteria

• lacks a nucleus and other cell structires

• pigment phycobilin used in photosynthesis

• can be colonial or filamentous

• form heterocysts

the issue with cyanobacteria blooms

• foul smell

• lower dissolved oxygen

• produce toxins

• related to eutrophication

• occur naturally

what are gas vesicles

• found in cyanobacteria

• Protein walls of the vesicles are permeable to atmospheric gases but not to water

• may collapse from high external pressure

• may occupy 30% of cell volume

role of gas vesicles

• The float/sink cycle keeps them in the water layers most suitable for their survival

• gains them access to nutrients at the top of the hypolimnion where sinking detritus is decomposing

float/sink cycle of gas vesicles

• vesicles fill with gas and move up in the water column

• now closer to the light, more photosynthesis occurs, resulting in the increased formation of sugars

• sugars increase tugor pressure in the cell, collapsing the gas vesicles

• cell becomes denser and sinks before it gets too close to the surface where light intensity is lethal

• the further the cell sinks down, the more gas vesicles form causing the cell to float upwards again

how can gas vesicles be a maladaptation to cyanobacteria

• in summer they phytoplankton levels are high causing a shallow euphotic zone

• results in cyanobacteria spending more time in low light, causing more gas vesicles to form and be stronger

• increased buoyancy causes many cells to rise to the surface but the gas vesicles don’t burst

• cells get trapped and light intensity kills the cells and causing scum to form

adaptations of fungi

• have large, sticky spores that attach to dead leaves

• parasitize higher organisms

role of freshwater fungi

• decompose plant remains (they can degrade cellulose and lignocellulose)

• vital for recycling of nutrients and energy

how do protozoa obtain nutrients

Consumers (heterotrophy) of complex organic molecules or particles such as bacteria

3 types of protozoa

1. amoebae

2. ciliates

3. flagellates

amoebae traits

• lack cell walls

• move using temporary extensions (pseudopodia)

• obtain nutrients by absorbing/enclosing food particles that stick to their surface

ciliates traits

• use cilia for locomotion and feeding

• feed on bacteria, algae, detritus, and other protozoans

• mixotrophic and/or photosynthetic

• can grow in low oxygen levels = lots in polluted waters

flagellates traits

• use flagella for locomotion

• have fewer and longer hairs than ciliates

• mixotrophic, heterotrophic, or autotrophic

• eat bacteria (control bacteria abundance)

general features of primary producers

• bottom of the food chain

• use light energy to transform CO2 into large organic substances

• photosynthetic

• green pigment due to chlorophyll

3 requirements for all aquatic plants to survive

• nutrients

• carbon dioxide

• light

3 groups of aquatic plants

1. macrophytes

2. phytoplankton

3. periphytic organisms

macrophytes refer to…

macroalgae and vascular aquatic plants

2 types of macrophytes

1. attached to substratum

2. freely floating

3 types of macrophytes that attach to substratum

1. emergent macrophytes

2. floating-leaved macrophytes

3. submerged macrophytes

conditions where emergent macrophytes are found

• water saturated or submerged soils

• water table is about 0.5 m below soil surface to where sediment is covered by about 1.5 m of water

physical traits of emergent macrophytes

• primary rhizomatous (have roots and shoots)

• some are cormous perennials (grow from tubers or bulbs)

• all have aerial reproductive organs

• may have a submerged form (heterophylly)

heterophylly

plants that have different leaf forms depending on environmental conditions

3 adaptations that emergent macrophytes have

1. Plants are typically tall so they are unlikely to become completely submerged

2. Leaves tend to be narrow which provides less resistance to wind and water movements

3. Stems tend to be tough and hollow

   
   

floating-leaved macrophytes traits

• mostly angiosperms

• attached to submerged sediments

• found at depths 0.5 to 3 m

• floating leaves on long flexible petioles or short petioles from long ascending stems

traits of free floating macrophytes

• live unattached within or upon water

• some are large with rosettes

• others are minute with few to no roots

• often the reproductive organs are aerial or floating

5 adaptations to free floating macrophytes

1. Tough leaves to withstand weather and water movements

2. Presence of chloroplasts only on the upper leave surface

3. A thick cuticle on the upper surface

4. Stomata for gas exchange only on the upper surface of the leaf

5. Air-filled cavities are usually present

   
   

traits of submerged macrophytes

• found at all depths in the photic zone

• reproductive organs may be aerial, floating, or submerged

• variable leaf morphology

• include pteridophytes, mosses, charophytes, and angiosperms

what mainly controls aquatic plant coverage

depth

horizontal patchiness of aquatic plants

• Clumps of one species or another shift in position from year to year

• May result from changing the pattern of silts, or differences in weather that
  favour one species over another, or grazing by birds

what other abiotic factors influence plant coverage

• light availability

• wave disturbance

• water pressure

why do emergent macrophytes only grow a specific depth ranges

• require CO2 from the atmosphere

• cannot take up dissolved oxygen or bicarbonate

• rely on energy stored in rhizomes over winter

periphyton traits

• grow on other plants or subtrates

• can inhibit the growth of host plant through shading

• increase production with increased fertility of the habitat

benefits of periphyton

• aquatic invertebrates will eat periphyton but not the plant host

plant adaptions to protect from periphyton

• Grow mucus

• Constantly produce new shoots

• Some produce organic substances that inhibit growth of periphyton (e.g., polyphenols)

general traits of algae

• single celled, colonial, or filamentous

• circular, spined, or flagellated morphology

• reproduce asexually

• absorb nutrients through cell wall

• sink

adaptations that help algae stay afloat

• denser than water so they need to be suspended in water by wind-generated currents (eddies)

• delays inevitable sinking

• necessary to obtain nutrients and and light for photosynthesis

how is sinking rate calculated

• stoke’s law

• Sinking (v) is related to the acceleration due to gravity (g), the radius
  of the sinking particle (r), the densities of the particle (pp) and water
  (pw), and the viscosity of the water (μ)

how do algae reduce sinking rates

• changing shape/radius without density can reduce sinking rates

• Flat plates, needle shapes with curved ends, spines, and
  projections all seem advantageous

  
  

how do algae change/decrease density

• vacuoles, gas vesicles, and ballast molecules

• respiration consumes products made by photosynthesis that weigh down algae

• mucus layer to hold water = density becomes similar to water density

what appendage helps algae change position in the water column

flagella

how do algae adapt to avoid being eaten

• large size

• spines

• mucus sheets allow them to survive gut passage

• different adaptions are successful in different environments

• adaptations can be expensive so algae may focus on growth and reproduction instead

Does Competitive Exclusion explain the diversity of phytoplankton we see in large water bodies?

• Gause’s Law predicts that the number of species equals the number of
  limiting resources

• Most phytoplankton communities are “supersaturated”, there are
  many more species than limiting resources; and there is wide swings in
  species abundances over time (system not at equilibrium)

what does Hutchinson propose about algae distribution

• Vertical gradients of light (or turbulence)

• Symbiosis

• Differential predation

• Constantly changing environmental conditions

how does Hutchinson’s proposal explain supersaturation of alage

• Chaotic fluid motion

• Size-selective grazing

• Spatio-temporal heterogeneity

• Environmental fluctuations

• Physiology that changes comp. ability

• Life history (extinction/invasion)

environmental conditions for sponges

• filter feeders

• grow on solid substrates (ex: stone, macrophytes, fallen tree branches)

• clear water habitats

how do sponges get their color

• greenish yellow color

• have symbiotic algae that have chlorophyll pigments

why do sponges need clear water

• so their symbiotic algae have access to light

• too murky water decreases their filtering capacity

hydroid traits

• freshwater jellyfish and corals

• simple body plan with central cavity

• attach to hard surfaces

• prey on small crustaceans, insect larvae, and worms

• have stinging cells

• reproduce asexually

mussel traits

• bivalves

• two valves enclose the body

• held together by an adductor (when relaxed they open)

• filter feed on particulate organic matter

mussel life cycle

• larvae are parasites on fish gills because they get more food as water rushes through the gills

• once in juvenile phase they leave their host and live on the substrate

2 key features of rotifers

• Corona (ciliated region used in locomotion and food gathering)

• mastax (crushing food)

rotifer traits

• prolific reproducers

• parthenogenetic reproduction

• solitary or in colonies

parthenogenetic

eggs develop without fertilization into a new individual, identical to mom

what phylum do crustaceans belong

arthropoda

Crustacean physical traits

• segmented bodies with 3 regions (head, thorax, abdomen)

• body covered in exoskeleton made of chitin and calcium carbonate

• shed exoskeleton as they grow and replace it with a new one

• male and female organisms

• have gills or use direct diffusion for oxygen acquisition

crustacean life cycle

• eggs hatch to a larval stage

• larvae undergo metamorphoses to produce a juvenile that is a smaller version of the adult

• juvenile grows into the adult stage

2 groups of crustacean zooplankton

1. cladocerans

2. copepods

Cladocerans feeding habits

• “grazing cattle” of lakes

• herbivores that feed on green algae and bacteria

Cladocerans reproduction

• Will form resting eggs (ephippium)

• but mostly reproduce parthenogenetically

cladocerans physical traits

• small and transparent

• disc-shaped body

• carapace protects the body like an overcoat

• one pair of antennae used as paddles for locomotion

examples of cladocerans

Daphnia, Bosmina (pelagic) and Chydorus (benthic)

how do daphnia avoid predators

• diel vertical migration (behavioral trait)

• development of spines

• change in head shape

• increased transparency

other name for daphnia

water flea - due to swimming behavior from antennae movement

daphnia reproduction

• parthenogenetic reproduction - female adult can produce males and females by themselves

• sexual reproduction: female produces haploid eggs that are fertilized by the male to produce an egg with a zygote inside

copepods feeding habits

• “hop” to attack prey

• diverse diet - can be herbivorous, predacious, detritivores, omnivorous

copepod reproduction and life cycle

• Use sexual reproduction and when eggs are fertilized are extruded in egg sacs

• Resting eggs can be produced in suboptimal conditions (food shortage or high predation pressure)

• Have 5 to 6 naupliar larval stages, then 5 to 6 copepodite stages, and then
  finally the adult appears

physical traits of mysids

• crustaceans - opossum shrimp

• designed for fast active swimming

• no gills - take up oxygen through exoskeleton, meaning they are sensitive to low oxygen

mysids habitats

• Mostly found in northern, cold, deep, oligotrophic lakes

• Migrate vertically, spending nights filter feeding on zooplankton and
  phytoplankton in shallow waters

why may mysids be an issue to some lakes

compete with juvenile fish for food

isopod traits

• ex: water louse

• flattened body

• live in weed beds

• feed on periphyton, bacteria, fungi

• food source for many predators

amphipods traits

• freshwater shrimp

• swim sideways using their legs

• opportunistic foragers (eat anything that is available)

• abundant in ponds without fish

decapod physical traits

• crayfish - look like small lobsters

• 5 pairs or legs - first pair are large pincers used for crushing food and as weapons

• largest freshwater crustacean

• carry eggs on abdomen from fall to spring

decapod feeding vs prey habits

• generalist opportunistic feeders

• consumed by fish

traits of freshwater insects

• secondary colonists (have terrestrial ancestors)

• often the adults are aerial and breathe air while the larvae or nymphs are aquatic

• require adaptations to obtain air - aqualung (air bubble)

why do larger ecosystems have more species richness

• more habitat diversity to support different species

• more stable environment - less impacted by climate and geological changes

why do colder climates have less species richness

• short growing season

• glaciation

• less light access

river continuum concept

• a model for classifying the flow of water

• river changes as more streams are added

• different organisms and materials enter the river depending on upstream vs downstream as well has how narrow the stream is

2 generalizations about pelagic cold temperate lakes

1. covered with ice over winter

2. strongly stratified in summer

events during winter in a temperate lake

• dependent on light levels which is controlled by snow cover

• green flagellated algae will be dominant - feed on dissolved organic matter that washed into the lake during late summer and fall

events during spring in a temperate lake

• spring melt and mixing

• causes longer days = growth of diatoms

• species that were low density during the winter begin to multiply = spring peaks

what are spring peaks controlled by

amount of nutrients available and timing of ice clearing

events in summer temperate lakes (beginning of summer)

• onset of stratification

• diatoms decline from nutrient depletion = diatoms sink to the bottom due to decreased mixing

• daphnia begin grazing on dead diatoms = brief clear period since phytoplankton populations are still low

• chrysophytes may be present - are able to grow in cooler water with less light like in spring

events of temperate lakes in the summer (early summer with some stratification, not full)

• water is still flowing from catchment to replenish loss of nutrients

• young fish spawned in littoral areas are moving offshore to find food

• large daphnia become scarce while rotifers and copepods become abundant

events in temperate lakes in summer (lake is fully stratified but temperature is not at peak)

• piscivores have started feeding on the new fish

• causes grazing on phytoplankton to slightly decrease

• nutrients are being recycled

• phytoplankton multiply and have more species richness

events of temperate lakes in summer (stratified and at peak temperatures)

• Higher temperature and increasing detritus stimulate bacterial activity = releasing some vitamins for phytoplankton

• layering of the epilimnion may occur - cryptophytes and cyanobacteria will favor the top because light and detritus levels are higher

events of temperate lakes in summer (stratified but past peak temperatures)

• large cyanobacteria and colonial green algae become abundant

• caused by CO2, low pH, ammonium, and phosphate in water

events of temperate lake in summer (end of summer)

• calmer conditions allow surface blooms to form

• hypolimnion increase in ammonium and phosphate levels due to high bacterial activity = only benefits phytoplankton that can move up and down in water column

• oxygen may run out in the hypolimnion if it is small or has lots of organic matter

• storms will move nutrients from the depths to the epilimnion

what does running out of oxygen cause

• Leads to more ammonium, phosphate

• Reduces iron and manganese

• Smelly hypolimnion because of more sulphide and methane production

events of temperate lakes at transition between summer and autumn

• water cools

• wind deepens epilimnion

• diatom populations return and phytoplankton mixtures decrease

• nutrient supply from catchment increases

events of temperate lakes in autumn

• late autumn storms mix lake - destroys stratification

• early mixing boosts diatoms

• late mixing will not boost diatoms

• lake is re-oxygenated = Reduces phosphate because it oxidizes with iron and manganese compounds that reform and precipitate