Chapter 2: Understanding Ecosystems

Life on Planet Earth Earth is a medium-sized planet orbiting our Sun (a star) at a distance of approximately

150 000 000 km. Earth is home to countless organisms and habitat types. A habitat is the place where an organism lives. Habitats can be terrestrial (on land) or

aquatic (in the water). In the oceans, life ranges from colourful fish on coral reefs to strange creatures living in

the dark depths. On land, there are cacti and rattlesnakes in the arid deserts; enormous trees swarm with

insects in the tropical rainforests; or low-lying shrubs and herds of caribou abound in the frozen Arctic.

The Spheres of EarthA) The Atmosphere

Earth’s mass creates a force of gravity strong enough to hold gases near its surface. Earth’s atmosphere is the layer of gases surrounding Earth. The atmosphere

extends upwards for hundreds of kilometers. The atmosphere is made up of 78% nitrogen gas and 21% oxygen gas. The remaining

<1% of the atmosphere includes argon, water vapour, carbon dioxide, and a variety of other gases.

The atmosphere is critical to life on Earth. It acts like a blanket and moderates surface temperature. This insulation prevents excessive heating during the day and cooling during the night. Without an atmosphere, Earth’s surface temperature would drop from the 15°C average it is now to approximately -18°C.

The atmosphere also blocks some incoming solar radiation, including most ultraviolet light.

Without the atmosphere, most of Earth’s species would be unable to survive.

B) The Lithosphere The lithosphere is the rocky outer shell of Earth. It is Earth’s solid outer layer and

consists of the rocks and minerals that make up the mountains, ocean floors, and the rest of Earth’s solid landscape.

The lithosphere ranges from about 50 to 150 km in thickness.

C) The Hydrosphere The hydrosphere is all of Earth’s water in solid, liquid, and gas form. The hydrosphere includes oceans, lakes, ice, groundwater, and clouds. Nearly all the water on Earth (97%) is contained in the oceans.

D) The Biosphere The biosphere is the zone around Earth where life can exist. The biosphere is a term used to describe the locations in which life can exist within the

lithosphere, atmosphere, and hydrosphere. Earth is very large (approximately 12 700 km in diameter) but the biosphere is very thin

in comparison. All conditions required for life must be met and maintained within this thin layer of ground, water, and lower atmosphere.

All living things need space, water, and nutrients to survive. However, the supply of these resources is limited.

Introducing Ecosystems An ecosystem is all the living organisms and their physical and chemical

environment. In other words, an ecosystem is all of the living organisms that share a region and interact with each other and their non-living environment.

Biotic factors are living things, their remains, and their products or wastes. For example) Bears, ants, leaves, flowers, or decaying matter.

Abiotic factors are non-living components which include physical and chemical components of an ecosystem. For example) Wind, temperature, water, minerals, and air.

Sustainability of Ecosystems Most natural ecosystems are sustainable. A sustainable ecosystem is an ecosystem that is maintained through natural

processes. The ecosystem is able to maintain a relatively constant set of characteristics over a long period of time.

Human activities often change the biotic and abiotic features of an ecosystem. This can render a previously sustainable ecosystem unsustainable.

Sustainability is the ability to maintain natural ecological conditions or processes without interruption, weakening, or loss of value.

Other ecosystems are artificially created and maintained by human actions. To create an artificial ecosystem, like an urban park or farm, desired plants and animals are introduced and maintained. Artificial ecosystems are not usually sustainable – they require management to maintain the biotic and abiotic features deemed desirable.

Energy Flow in Ecosystems All organisms require energy to stay alive and function. The source of almost all of this

energy is radiant energy. Radiant energy is energy that travels through empty space. It is the energy that

radiates from the Sun. Earth is continuously being bombarded with both invisible radiant energy (like ultraviolet rays) and visible radiant energy, called light energy.

Light energy is any visible form of radiant energy, such as light rays that we see from the Sun.

About 70% of the radiant energy is absorbed by the hydrosphere and lithosphere and converted into thermal energy.

Thermal energy is the form of energy transferred during heating or cooling. Thermal energy is what warms the atmosphere, evaporated water, and produces wind.

The remaining 30% of radiant energy is reflected directly back into space. A small fraction of the radiant energy (a mere 0.023%) is absorbed directly by living

organisms in a process called photosynthesis. Photosynthesis is the process in which the Sun’s energy is converted into chemical

energy. Thermal energy keeps Earth’s surface warm, but it cannot provide organisms with the

energy they need to grow and function. The chemical energy that is created during photosynthesis can be stored in cells and then

released when needed. Chemical energy is used by all organisms to perform functions, including movement, growth, and reproduction. As chemical energy is used, it must be replaced.

Photosynthesis Many organisms are able to convert light energy into chemical energy using the process

of photosynthesis. This conversion of energy is one of the most important chemical processes – without it, life on Earth would not exist.

Producers are organisms that make their own energy-rich food compounds using the Sun’s energy (light energy). Producers are the type of organisms that are able to

photosynthesize. Producers are also known as autotrophs – since they get their energy directly from the Sun.

On land, the major producers are green plants, such as a tree’s leaves, grass, or shrubs. In the water, the major producers are algae, cyanobacteria, seaweed, and other water plants.

Most producers use light energy to convert two low-energy chemical compounds (carbon dioxide and water) into high-energy compounds (sugars). In doing so, they release oxygen gas into the environment as a by-product.

The photosynthesis reaction is as follows: light energy

Carbon dioxide + water → sugar + oxygen The sugar formed in this process contains stored chemical energy. This energy is stored

in the roots, stems, leaves, and seeds of a plant. Most plants convert the sugar into starch for storage.

Not all of the sugar produced through photosynthesis goes toward energy storage. Some sugars are used as building materials. The carbon, hydrogen, and oxygen in the carbon dioxide and water are like building blocks. Using light energy, they are rearranged to form sugars and oxygen gas during photosynthesis. Then, components in the sugars are rearranged to form different combinations – they may form carbohydrates (such as cellulose used in cell walls) or in combination with nitrogen in proteins.

Cellular Respiration Cellular respiration is the process by which sugar and oxygen are converted into

carbon dioxide and water, to provide energy of the cell. Remember that photosynthesis produces stored energy in the form of sugar. To make

stored energy available for use, the plant performs the complimentary reaction called cellular respiration.

As the process of cellular respiration takes place, energy is released. The plant is able to use this released energy for any of the activities carried out by its cells.

Cellular respiration occurs in the mitochondria (power-house) of the cell. The word equation for cellular respiration is:

Sugar + oxygen → carbon dioxide + water + energy

The energy originally stored in the sugar is released as a product of cellular respiration. Unlike photosynthesis, cellular respiration occurs continuously. No light energy is

required for cellular respiration. Many organisms cannot photosynthesize. Therefore, they are not able to make their own

energy-rich sugar or building blocks. These organisms are called consumers. Consumers are organisms that obtain energy from consuming other organisms. For

example) Animals and humans. Consumers are also known as heterotrophs since they must consume producers or other consumers to get energy.

To obtain energy from food, they undergo cellular respiration. While only producers can undergo photosynthesis, both producers and consumers

perform cellular respiration.

Ecological Niches

An ecological niche is the function a species serves in its ecosystem, including what it eats, what eats it, and how it behaves.

An ecological niche is the interactions that every species has with other species and with its environment. It is the role of a species within its ecosystem.

For example) An ecological niche for a black bear would be as follows: black bears feed on nuts and berries. They supplement their diet with insects and other small animals. Bears may carry seeds long distances in their digestive systems before the seeds are expelled and germinate. Bears go into hibernation during the winter. While they have few predators other than human hunters, black bears are themselves fed on by many blood-feeding insects and are hosts to a variety of parasites.

A key feature of any ecosystem is the feeding roles of each species. Types of consumers:

Feeding Role Definition Example

Herbivore Animal that eats plants or other producers.

Rabbit

Carnivore Animal that eats other animals. SharkOmnivore Animals that eat both plants and

animals.Humans

Scavenger Animal that feeds on the remains of other organisms.

Vulcher

Food Chains and Food Webs The most common interactions between species ar through feeding relationships. The

easiest way to display these relationships is with food chains. Food chains are a sequence of organisms each feeding on the next, showing how

energy is transferred from one organism to another. Food chains illustrate who eats whom in an ecosystem. It always begins with a producer,

and ends with a top carnivore. In a food chain diagram, the arrows show the direction of food and energy flow. Arrows point to who is doing the eating.

In a food chain, some of the chemical energy stored in the producer is passed through the primary consumer, and continues to make its way up to the top carnivore. In this way, food chains show how energy passes through an ecosystem. Remember that energy is continuously lost from all levels of the food chain. Only 10% of the energy is actually passed to the next trophic level – the remaining 90% is used in biological processes such as growth and reproduction, and is lost as thermal energy.

Trophic levels, or feeding levels, are used to describe the position of an organism along a food chain. Producers occupy the lowest, or first, trophic level. Herbivores occupy the second trophic level, and carnivores occupy the third and fourth trophic levels.

A trophic level is the level of an organism in an ecosystem on its feeding position along a food chain.

Food chains are very simplistic and do not actually exist in nature. They show simple feeding relationships. Food chains are part of more complex sets of relationships that exist among species.

A more accurate way to illustrate interactions is with a food web. A food web is a represention of the feeding relationships within a community. Food

webs are highly complex, with consumers feeding on many species. The large number of interactions tends to reduce the vulnerability of any one species to the loss or decline of another species. For this reason, complex food webs are thought to be more stable than simple food webs.

Food webs are useful tools to figure out what may happen when a species is removed from,or added, to an ecosystem.

Ecological Pyramids An ecological pyramid is a representation of energy, numbers, or biomass

relationships in ecosystems. They display the relationships between trophic levels in ecosystems.

The size of each layer in the energy pyramid represents the amount of energy available at that trophic level. A continuous supply of energy is essential for all living things.

As an organism consumes another, it obtains both the physical matter (nutrients) and the chemical food energy it needs to survive, grow and reproduce. However, each time energy is used, some of it is released to the environment as thermal energy (heat). For example) You can feel an example of lost thermal energy by placing your hand on your forehead.

Remember that only about 10% of the energy taken in by the individuals at one trophic level is passed on to individuals at the next level. So, species at the highest trophic level have less energy available to them than species at the bottom. This often results in their populations being much smaller than species lower in the food chain. This is why an ecosystem will have fewer predators, such as hawks, than herbivores, such as mice.

Populations that occupy different trophic levels vary in their numbers and their biomass. Biomass is the mass of living organisms in a given area. A pyramid of numbers shows the number of individuals of all populations in each

trophic level.

A pyramid of biomass shows the total mass of organisms in each trophic level.

A pyramid of energy shows the available energy in each trophic level. An energy pyramid will always decrease in size from lower to higher trophic levels.

Organisms that feed at lower trophic levels generally have much more energy and biomass available to them. This is why herbivores are usually more numerous than carnivores.

Biogeochemical Cycles Biogeochemical cycles are the movement of matter through the biotic and

abiotic environment. The particles that make up matter cannot be created or destroyed. This means that all

water and nutrients must be produced or obtained from chemicals that already exist in the environment.

This happens in a series of cycles in which chemicals are continuously consumed, rearranged, stored, and used.

Because these cycles involve living (biotic) organisms and occur as Earth (geo) processes, they are called biogeochemical cycles. Every particle in an organism is part of a biogeochemical cycle.

The Water Cycle The water cycle is the series of processes that cycle water through the environment. Liquid water evaporated, forming water vapour that moves through the atmosphere. The

vapour eventually condenses, forming liquid water or ice crystals, and returns to Earth as rain, hail, or snow.

Water falling on land may enter the soil and groundwater or move across the surface entering lakes, rivers, and oceans.

Water that is taken up by plant roots may be released from leaves in a process called transpiration.

Most of the water that is present in the water cycle is in the abiotic environment.

The Carbon Cycle The carbon cycle is the biogeochemical cycle in which carbon is cycled through the

lithosphere, atmosphere, hydrosphere, and biosphere. Carbon moves between the abiotic and biotic parts of an ecosystem. Most of the

exchange occurs between carbon dioxide (either in the atmosphere or dissolved in water) and photosynthesizing plants and micro-organisms.

Large quantities of carbon cycle through photosynthesis and cellular respiration, most of Earth’s carbon is not cycled. Instead, it is stored carbon-rich deposits. Fossil fuels, such as coal, oil, and natural gas, are the most valuable carbon deposits. They form when decomposed organisms are compressed over millions of years. Carbon is also stored for millions of years as limestone formed from dead marine organisms.

Human activities have had dramatic effects on the carbon cycle. By burning fossil fuels, human release the stored carbon into the atmosphere. The concentration of carbon dioxide in the atmosphere is now higher than it has been in at least the past 800 000 years. This is causing global climate change. Climate change can alter the most critical abiotic factors in the ecosystems: water availability and temperature.

The increase in the average temperature of our atmosphere is melting ice caps and glaciers, causing sea levels to rise, and disrupting ecosystems.

Deforestation also increases the concentration of carbon dioxide in the atmosphere. Large-scale reforestation and dramatic reduction in the use of fossil fuels are needed to

slow the process of climate change.

The Nitrogen Cycle The nitrogen cycle is the series of processes in which nitrogen compounds are

moved through the biotic and abiotic environment. Nitrogen is extremely abundant in the atmosphere. However, it is not easy to acquire

directly from the abiotic environment. Nitrogen is essential for all living things as it is a building block of amino acids which

producing proteins. Proteins are used as building blocks in our DNA, for growth and reproduction, and in our muscle and tissues.

Most nitrogen is made available for use by a process called nitrogen fixation which is the process of converting unuseable nitrogen gas into useable nitrogen (in the form of nitrates). It occurs in the presence of oxygen. Nitrogen fixation can occur through two means:

A) In nodules found in legumes and the soil. Nitrogen gas (N2) is taken from the atmosphere by certain bacteria (micro-

organisms) in the soil and converted into a variety of nitrogen-containing compounds including nitrates (NO3- ), nitrites (NO 2- ), and ammonia (NH 3- ) . Herbivores will now consume the producers (plants) and intake nitrogen.

Nitrogen gas in the atmosphere (unuseable form of nitrogen)→ammonia→nitrites→nitrates (useable form of nitrogen for plants found in the soil)

B) Lightning and ultraviolet light also fix small amounts of nitrogen. Nitrogen gas→nitrates in the soil

As well, humans add nitrogen to the soil as fertilizer. Once in the soil ecosystem, the nitrogen-rich compounds are available to producers.

After the nitrogen is absorbed, it is passed from producer to consumer and on up the food chain. Many animals consume more nitrogen than they can use and excrete the excess in the form of urea or ammonia.

A dead organism’s nitrogen-rich compounds are taken in by decomposers or are released back into the environment. The process of denitrification is when denitrifying bacteria convert nitrates back into nitrogen gas which then re-enters the atmosphere. It occurs in the absence of oxygen.

Nitrates→Nitrites→Ammonia→Nitrogen Gas

Biotic and Abiotic Influences on Ecosystems

Ideal biotic and abiotic conditions allow a species to flourish. Other conditions may lead to a species’ decline or even extinction. Both biotic and abiotic factors determine where a species can live. A limiting factor is any factor that restricts the size of a population. It is a factor

that places an upper limit on the size of a population. Limiting factors may be biotic, such as the availability of food, or abiotic, such as access

to water. Human influences often act as limiting factors.

Influence of Abiotic Factors Abiotic factors such as temperature, light, and soil can influence a species’ ability

to survive. Every species is able to survive within a range of each of these factors. This range

is called the species’ tolerance range. The tolerance ranges are the abiotic conditions within which a species can survive. Near the upper and lower limits of the tolerance range, individuals experience

stress. This will reduce their health and their rate of growth and reproduction. Within a species’ tolerance range is an optimal range, within which the species is

best adapted. The largest and healthiest populations of a species will occur when conditions are within the optimal range.

Some species have a wide tolerance range, while some have a much narrower range. Species with a broad tolerance range will tend to be widely distributed and may easily invade other ecosystems.

The key abiotic factors in aquatic ecosystems are salt concentration and the availability of sunlight, oxygen, and nutrients.

Light is abundant in shallow clear water, but rapidly decreases with increasing depths. Oxygen concentration is greatest near the water’s surface because this is where oxygen enters from the air and where most photosynthesis takes place (remember that oxygen is released during photosynthesis).

Influence of Biotic Factors While abiotic factors determine where a particular species is able to live, biotic

factors often determine the species’ success. Many key biotic factors involve interactions between individuals. Individuals are

often in competition with members of their own species and with other species. They compete for limited resources, such as food, light, space, and mates.

Key Types and Examples of Species InteractionsRelationships Definition Examples

Competition Two individuals vie for the same resource.

Foxes and coyotes both feed on common prey such as mice and rabbits

Humans and insects

compete for the same crop plants.

Predation One individual (the predator) kills and feeds on another individual (the prey).

Lynx prey on snowshoe hares.

Leeches and black flies are “micro-predators) that feed on humans.

Mutualism Two individuals benefiting each other.

Nitrogen-fixing bacteria live in the roots of certain plants. The plants provide sugars to the bacteria. The bacteria provide nitrogen to the plant.

Parasitism One organism (the parasite) lives on or in another organism (the host) and feeds on the host organism.

Tapeworms are parasites of cats and dogs.

Microbes that cause malaria live within human blood cells.

Commensalism One individual benefits and the other neither is harmed nor benefits.

Many birds nest in particular kinds of trees or in abandoned burrows.

Spanish moss lives on certain tree species.

Carrying Capacity As a population’s size increases, the demand for resources, such as food, water,

shelter, and space also increases. Eventually, there will not be enough resources for each individual.

Furthermore, as individuals become more crowded, they become more susceptible to predators and diseases.

Eventually, these other factors will result in the population reaching the upper sustainable limit that the ecosystem can support, called the carrying capacity.

Carrying capacity is the maximum population size of a particular species that a given ecosystem can sustain.

The carrying capacity can be altered through natural or human activity when resources are removed from or added to the ecosystem.

For example) Irrigation can change a desert into a lush oasis because it increases the carrying capacity of the desert.

The loss or introduction of a species can change the carrying capacity of the ecosystem for other species in that ecosystem.

For example) The removal of wolves by human hunters will increase the carrying capacity of the ecosystem of moose.

Major Terrestrial Ecosystems

On Earth, there are relatively few prominent and easily recognizable types of ecosystems. These prominent types have characteristic features that are observable even without identifying individual species.

A biome is a large geographical region defined by climate (precipitation and temperature) with a specific set of biotic and abiotic features.

Terrestrial Biomes The most important factor in determining the location and makeup of a terrestrial

ecosystem is climate. The natural landscape in Canada is dominated by 4 major biomes: tundra, boreal forest,

grassland, and temperate deciduous forest. British Columbia also contains a mountain biome as well as a temperate rainforest biome.

A) Mountain Forest:Abiotic Factors Biotic Factors

Temperatures vary with elevation Cool summers Windy conditions Heavy precipitation on leeward

side of mountains Fast-flowing rivers

Marmots Squirrels Elk Black and grizzly bears Cougar Large coniferous trees Ferns

B) Tundra: Tundra is Canada’s most northern biome. The tundra is a cold desert with an extremely

short growing season and low temperatures. Because of these harsh conditions, there is a very limited amount of plants that are able to survive here.

The rate of photosynthesis is reduced, so plants in the tundra grow slower than in other biomes.

Vast regions of the tundra have permafrost (permanently frozen ground). During the summer, the soil closest to the surface thaws and forms an active layer in which plant roots can grow.

Caribou and polar bears are some of the more popular species in the tundra. The caribou are able to travel long distances to obtain food (they feed on low-growing lichens and mosses).

Abiotic Factors Biotic Factors Low temperatures for most of the

year Short growing season Permafrost layer beneath soil Precipitation from 0-25 cm/yr Poor soil quaility

Low diversity Rapid-flowering plants Mosses and lichens Caribou Ptarmigan Lemmings Arctic foxes

C) Boreal Forest: The boreal forest is the largest biome in Canada. Rainfall and warm summers support the growth of trees.

The soil is acidic because acids are released by decomposing conifer needles. This slows decomposition and limits the variety of plants that grow in this biome.

Conifers are the dominant trees. They can withstand the harsh winters while retaining their needle-shaped leaves. Needles have a thick wax coating that reduces water loss during the winter. In addition, leaves can photosynthesis as soon as the temperature warms up in the spring.

Abiotic Factors Biotic Factors Warmer than tundra No permafrost Changeable weather Soil contains some water and is acidic Precipitation is 40 cm/yr or more

Coniferous trees (needles, not leaves) Seed-eating birds Squirrels Voles Snowshoe hares Black bears Pine martens Grey wolves

D) Temperate-Deciduous Forest: The temperate-deciduous forest biome is dominated by deciduous trees such as maple,

oak, and ash. This biome has a longer growing season. The temperatures do not reach the extreme lows found in the boreal forest region.

Therefore, decomposition rates are faster. The deciduous forest plants community is very diverse. It has a layer of canopy trees,

understorey trees, shrubs, and non-woody vegetation on the forest floor. This variety of plant life supports a rich variety of animals.

The climate of this biome has made it attractive to humans. We have replaced large portions of the original temperate forests with farmlands, roads, and cities.

Abiotic Factors Biotic Factors Longer growing season than boreal

forest Higher temperatures than tundra or

boreal forest Fertile soil Precipitation up to 100 cm/yr

Deciduous trees (leaves) and other flowering plants

Tree and ground squirrels Many insects Shrews and mice Deer Black bears Hummingbirds Weasels

E) Grassland: Canada’s natural grassland, or prairies, occurs where moderate rainfall supports grasses

but cannot support most tree species. The hot, dry summers provide ideal conditions for fires. Fires maintain grasslands

because they suppress tree growth. The black earth of the grasslands is among the most fertile of all the soils in the world. High summer temperatures promote decomposition, which releases nutrients back into

the soil. The grasslands are shrinking at a fast rate – they used to cover much of Manitoba,

Saskatchewan, and Alberta. However, humans have replaced most natural grasslands with large fields of wheat and canola.

Abiotic Factors Biotic Factors Longer growing season than boreal

forest Higher temperatures than tundra or

boreal forest Rich, fertile soil Precipitation from 25-75 cm/yr

Fescue grasses Grasshoppers Bison Voles and mice Snakes Hawks Coyotes

Major Aquatic EcosystemsA) Freshwater Ecosystems:

Freshwater ecosystems have salt concentrations that are typically below 1%. They consist of moving bodies of water, such as rivers and nearly stationary bodies of

water, such as lakes. Rivers and streams are unique among ecosystems as they are continuously flushed with

a fresh supply of water from upstream. Organisms must swim continuously against the current or attach themselves to the bottom or some kind of fixed object.

Lakes and ponds are classified based on their nutrient levels: Oligotrophic: Are bodies of water that are low in nutrients. Even with

abundant light, photosynthetic organisms have difficulty obtaining enough nutrients to grow.

Eutrophic: Are bodies of water that are rich in nutrients. Photosynthetic aquatic plants and algae grow more rapidly and support a large biomass of consumers. Eutrophic bodies of water are often clouded with suspended microscopic plankton.

Wetlands, such as bogs and marshes, are large areas of shallow water or saturated soils. They are nutrient rich and support large populations of fish, amphibians, insects, and birds. Wetlands act as huge sponges and plant a critical role in filtering water in the water cycle.

Watersheds are land areas drained by a particular river – they are also called a drainage basin. Watersheds are an area of land through which all water drains into a single lake or river. This geographical relationship is important because water always flows downhill. If a pollutant enters the watershed, the areas downstream could become polluted as well.

B) Marine Ecosystems: Oceans (or marine ecosystems) have a salt concentration average about 3%. More than 70% of the Earth’s surface is covered in oceans. Marine ecosystems are an important part of biogeochemical cycles. Most of the water

that evaporated into the air and falls as rain and snow comes from oceans. Marine algae play a critical role in the production of oxygen and the absorption of carbon dioxide gas from the atmosphere.

Must of the ocean supports very little life. The open ocean is nutrient poor and unable to support many photosynthesizing organisms. The deep ocean is a lightless environment, so photosynthesis is impossible.

In contrast, the shallow waters near the shore are nutrient rich and support abundant life. Coral reefs develop in warm shallow oceans and support a huge variety of organisms. However, coral reefs are extremely sensitive to changes in water temperature, acidity, and pollution.

Estuaries are partially enclosed bodies of water where fresh and salt water mix. They are high in nutrients and often support valuable shellfish, such as clams and scallops. For example) The Gulf of St. Lawrence is the world’s largest estuary.

Mangroves are unusual communities that occur along tropical and semitropical sandy shorelines. They contain specialized tree species that have adapted to live at and beyond the water’s edge. The prop roots of the mangroves grow out of the water. This reduces coastline erosion and creates a habitat for several marine organisms.

The Intertidal Zone: Ocean coastlines are ecosystems that are part-time terrestrial and part-time

aquatic. They are home to the unusual communities that occupy the intertidal zone – the area between the low-tide and high-tide lines.

Many coastlines exhibit a significant change in water levels approximately 4 times a day – with two periods of high-tides and two periods of low-tides.

The highest tides in the world occur in the Bay of Fundy with differences of up to 17 m between low and high tides.

Among the common species that inhabit this unusual environment are seaweeds, barnacles, sea stars, and urchins.

Organisms in the intertidal zone face many conditions: In the summer, they alternate between a life under the water and above the water, where they are exposed to high temperatures, full Sun, and strong drying winds. In the winter, they alternate between icy ocean water and exposure to bitterly cold air, snow and ice. These species must be able to withstand the daily pounding of wave action. This is why most intertidal species have protective body coatings and very tough tissues.