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Trophic* Relationships. This way to define organisms within an ecosystem is based, simply put, on what they eat and who eats them. * Greek for nourishment. With respect to trophic levels, marine organisms can be grouped into 3 categories:.

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Trophic relationships l.jpg

Trophic* Relationships

This way to define organisms within an ecosystem is based, simply put, on what they eat and who eats them.

* Greek for nourishment


With respect to trophic levels marine organisms can be grouped into 3 categories l.jpg

With respect to trophic levels, marine organisms can be grouped into 3 categories:

1. Primary producers form the basis of life by producing food using energy from the sun or chemical substrates. Primary producers comprise the lowest, or first, trophic level.


The sun fuels photosynthesis l.jpg

The sun fuels photosynthesis—

This type of primary productionisaccomplished by

algae (tiny aquatic plants, such as the diatom pictured here)

macroalgae (big aquatic plants, such as kelp)

and

photosynthesizing bacteria


Chemical substrates fuel chemosynthesis l.jpg

Chemical substratesfuelchemosynthesis—

This type of primary productionis accomplished by,

for example,

bacteria found at deep-sea hydrothermal vents

(hydrothermal vents are a type of underwater volcano).

University of Victoria

Canada


With respect to trophic levels marine organisms can be grouped into 3 categories5 l.jpg

With respect to trophic levels, marine organisms can be grouped into 3 categories:

1. Primary producers form the basis of life. These organisms produce food using energy from the sun or chemical substrates. Primary producers comprise the lowest, or first, trophic level.

2.Consumers, as you can guess, eat other organisms. Consumerscomprise the second and higher trophic levels.


Consumers can be divided into two groups l.jpg
Consumerscan be divided into two groups:

1. Herbivores

eatprimary producers, such as algae, and occupy the second trophiclevel. Common marine herbivores are copepods, small crustaceans that are usually a few millimeters long and very abundant in coastal waters. This copepod is about 5 mm long.


Consumers can be divided into two groups7 l.jpg
Consumerscan be divided into two groups:

2. Carnivores

eatherbivoresand other carnivores, thus occupying the higher trophic levels. Common marine carnivores are fish, although some copepods are also carnivorous.


With respect to trophic levels marine organisms can be grouped into 3 categories8 l.jpg

With respect to trophiclevels, marine organisms can be grouped into 3 categories:

1. Primary producers form the basis of life. These organisms produce food using energy from the sun or chemical substrates. Primary producers comprise the lowest, or first, trophic level.

2.Consumers, as you can guess, eat other organisms. Consumerscomprise the second and higher trophic levels.

3. Decomposersare non-photosynthetic bacteria and fungi; they derive energy from taking up detritus (pieces of dead cells) and waste products from other organisms.


Decomposers l.jpg

Decomposers

Bacteria are the most abundant living organisms in the ocean

and

are key components of ecosystems with respect to

energy and carbon cycling.

Marine fungi are less studied than marine bacteria.

This photomicrograph is terrestrial fungi.


Food chain l.jpg
Food chain

These relationships can be represented graphically as a

food chain.

Consumer (carnivore)

*

(This fresh-water

ostracod resembles

marine ostracods;

they are small

crustaceans.)

Consumer (herbivore)

Decomposer

Primary producer

* The photo of the grouper is from VersAquatics Co. USA © 2004.

herbivoresand carnivores eat organisms in trophic levels below them; Decomposers take up detritus and waste from all trophic levels.


Energy transfer within food chain l.jpg
Energy Transfer within food chain

Energy transfer between trophic levels is quite inefficient, on the order of 6-20%, with 10% commonly used in calculations. Thus, the number of trophic levels in a given ecosystem tends to be small.

Furthermore, the food chainis a model, an oversimplification of interactions occurring in the real world. Most marine ecosystems are more complex than a simple chain. For example, most organisms eat more than one type of food, and some organisms occupy different trophic levels at different life stages.


Food web l.jpg
Food web

Antarcticfood web

http://octopus.gma.org/surfing/human/foodweb.gif

Thus, food chains are often more correctly described as

food webs,

which have many interactions.


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