BIOL 2390 - Topic 3

Aquatic ecosystems coverage

They cover 75% of the planet, making them the most dominant habitats

Subdivisions of aquatic ecosystems

1.) Freshwater (low solutes, such as lakes and streams)

2.) Marine/saltwater (high solutes, such as oceans)

Division of aquatic ecosystems is based on…

It is based mostly on abiotic factors, such as depth, flow, substrates, and the type of dominants organisms that live there

Importance of water

1.) All living things contain between 75-95% water

2.) Most physiological/biochemical processes depend on water

Water structural propoerties

Water is a polar molecule with partial charges, which gives it the ability to attract neighbouring molecules, via hydrogen bonding

Partial charges of water

It is caused by oxygen greediness for the electrons, creating a partial negative charge on the oxygen and a partial positive charge on the hydrogen

Water characteristics

1.) Has high specific heat

2.) Has a lattice structure in its solid state

High specific heat of water

1.) Its high specific heat allows it to hold and store heat energy, while also resisting temperature changes and regulating climate

2.) This is because the hydrogen bonds pull everything together, preventing them from moving and increasing the heat

Lattice structure of solid water

1.) Its solid state has a lower density than its liquid form, which is uncommon for most solids

2.) This leads to ice floating and acting as an insulating barrier during winter

Significance of ice forming an insulating barrier

It prevents cold temps from freezing the entire body of water, allowing for the ecosystem below to survive

Cohesion

The ability to resist external forces that should break the hydrogen bonds

Cohesion results in…

It results in high surface tension, caused by the stronger attraction of water molecules to each other, rather than the air

Surface tension advantage

It is used by some organisms to escape predators or catch prey, but it depends on their weight

Viscosity/density

It is caused by the hydrogen bonds of the molecules being pulled together

Effect of high viscosity

It has streamlined adaptations in many aquatic organisms, so that they are able to move rapidly and efficiently through the viscous water

Buoyancy

The ability to float in water with little to no energy, as a result of your density matching with the water

Buoyancy advantage

It reduces the amount of skeleton needed, since the organism does not require that much strength from bones to move

Factors affecting light in water

1.) Surface reflection

2.) Absorption of light

Surface reflection

Refers to when light bounces off the water surface, with the amount varying depending on the time of day and season

Absorption of light in water

1.) Refers to when light is dispersed or absorbed by water molecules and particles suspended in the water, and then generates heat

2.) The depth of light absorbed depends on the turbidity of the water

Light penetration into the water

1.) It only penetrates the first 100 meters, even less when the water is turbid

2.) Different wavelengths are also absorbed at varying depths

Photic zone

The 100 meter depth that light is able to penetrate through

Wavelengths absorbed by light

1.) Blue shift occurs the deeper you go, because all the other colours get filtered out

2.) The first to be filtered out are red and orange

3.) Only the green and blue light actually reaches the 100 meter depth

Why does only green and blue light go deep?

Because there is less energy available the deeper you go

Light availability effect on organisms

Light availability shapes species distributions and their adaptations

Algae/plants and sunlight

1.) Photosynthesis is limited to the upper layer of the photic zone, since that’s where a majority of the sun is

2.) As a result, herbivores are mainly restricted to areas with plant and algae growth (i.e. at the upper layer)

Deep ocean life (more than 200m)

1.) Many of the deep organisms depend on sinking organic matter, mostly dead organisms from the photic zone

2.) Some predators migrate upwards at night to feed in the photic zone, such as squid

3.) Some have unique adaptations that allows them to catch their prey deep below, such as Angler fish

Why would organisms, such as squid, live deep below in the first place if they feed in the photic zone

To avoid predators

Angler fish adaptation

1.) Their looks have adapted towards living in the deep ocean

2.) They have adapted to catching prey by having bioluminescent light, which attracts prey straight to their mouth

Stratification

Separation of water into different layers, as a result of big density and temperature differences

Formation of stratification

1.) Light absorption warms the surface, causing a temperature decline, decreasing exponentially with depth

2.) Wave and wind action mixes the surface, distributing heat vertically, but this can become limited due to stratification

Epilimnion

The upper water later, which is warm and have low-density

Thermocline

“Temperature slope”, a rapid temperature transition zone that separates the epilimnion layer from the hypolimnion layer

Hypolimnion

Below water layer, which is cool and have high-density

Where does stratification occur?

In non-flowing or slow-moving water

Stratification in temperate climates vs. tropical

1.) Temperate climates have different seasons and therefore temps, therefore stratification only occurs in the summer

2.) Tropical climates are pretty stable all throughout, therefore they have stratification year round

The stratification layers act __________ from one another

Independently

Seasonal changes in water stratification in temperate climates (spring)

Ice melts and wind-driven mixing causes turnover

Turnover

It is important for nutrient and oxygen recycling

Seasonal changes in water stratification in temperate climates (summer)

1.) Increased light drives stratification, with no mixing between the layers occurring

2.) The epilimnion grows to a maximum depth at the peak of summer

Seasonal changes in water stratification in temperate climates (fall)

Cooling of temperatures reduces stratification, allowing turnover to occur

Seasonal changes in water stratification in temperate climates (winter)

Ice forms, thereby blocking light, resulting in no stratification or turnover to occur

Why does no stratification or turnover occur during winter

The ice blocks both light and wind from reaching the water below, therefore no mixing occurs.

Ecological consequences of stratification for oxygen and nutrients

Water does not mix when it is stratified, resulting in high O2 but low nutrients in the epilimnion and low O2 and high nutrients in the hypolimnion

Effect of the no water mixing on animals

It results in slow growth and low productivity, which means it is primarily a problem in tropical waters, where stratification is constant

What results in the separation of O2 and nutrients in the stratification layers

1.) Most photosynthetic organisms are in the epilimnion, causing them to eat up most of the nutrients in the layer while they are producing O2.

2.) Dead organisms fall down to the hypolimnion layer, resulting in the release of nutrients, but decomposition requires the use of O2.

Water as a solvent

1.) The polarity of water allows it to act as an excellent solvent

2.) This is because minerals and organic substances are attracted to the partial charges of water

Freshwater solutes

1.) Rainwater is nearly pure, therefore making it low in solutes

2.) It gains minerals and organic matter as it moves through the soil

Oceans solute

It is when freshwater continuously gains solutes over time, causing it to be high in solutes

Solubility limits of the ocean

1.) Solubility limits vary depending on the mineral, such that phosphorus has a different solubility limit than magnesium

2.) This limit prevents infinite accumulation

Oxygen (and other gases) _________ into water

Diffuses

Temperature effect on solubility of gases

High temperatures decreases the solubility of gases

Salinity effect on solubility of gases

High salinity decreases the solubility of gases

Atmospheric pressure effect on solubility of gases

High atmospheric pressure increases the solubility of gases

Varying amounts of oxygen

Oxygen amounts vary depending on the time of year, due to varying temperatures

Oxygen in shallow water

Oxygen fluctuations in shallow water can be large, because it usually does not have stratification

Effect of oxygen fluctuations in shallow water for fish

1.) Water heats up during the day and retains this warmth at night

2.) At night photosynthesis stops, but respiration continues, causing oxygen levels to drop dangerously low

3.) This causes fish and other aquatic organisms to gulp up air

Linkage of marine and freshwater environments

All marine and freshwater environments are linked by the water cycle

The water cycle is driven by…

Solar radiation

Water cycle process

1.) Solar radiation evaporates water directly

2.) Snow/ice sublimates directly into water vapour

3.) Transpiration (evaporation) from vegetation releases water vapour into the air

4.) Water then condenses and falls from the atmosphere

Surface water

1.) It may collect in waterways

2.) It may enter soil, becoming part of the ground water

3.) It may enter deep storage