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Bacteria
and fungi break down the more complex substances in the cell walls. It is
something that protists and animals have difficulty in accomplishing. Protists
search for food amongst the particles of detritus. They partly eat organic
material that is already broken down, but they primarily eat those micro-organisms
that speed up the breaking down process because the fungal and bacterial
population is kept young and quick growing. Certain animals, for example
certain shellfish and sea-urchins eat the detritus as it is, while suspension
feeders catch some of the detritus particles that whirl up.
Detritus material contains small amounts of protein. Alga
remains are composed mainly of cell walls that mainly contain carbohydrates,
e.g. celluose. There are several types of carbohydrates that cannot be broken
down by many animals, this includes a majority of the detritus eaters. When
algal detritus passes through the animals body only certain nutrients are
taken up, the ones which the animal is capable of absorbing and from the
micro-organisms that follow with the detritus. The remains that the animal
leaves in its faeces are finely ground and thus enable the access of more
bacteria and fungi to continue the breaking down process. Many of the micro-organisms
have enzyms that can break up most carbohydrates that are found in detritus,
futhermore, several of them can combine the seawater´s inorganic nitrogen
compounds with broken down carbohydrates to build proteins. Detritus eating
animals are dependant on these proteins because of their very one sided
diet when they eat algal remains. Detritus material can pass through the
animals digestive system several times before it totally broken down. Every
time the waste products are colonized by new micro-organisms.
Exposed=export - protected=import
On the exposed
rocky beach in our example, most of the larger algae´s production
is exported as detritus. The majority of micro-algae´s production
is eaten by shellfish in the same area. The large populations of suspension
feeders are sustained by external production by the fact that they mainly
eat plankton. Grazers, larger detritus eaters and suspension feeders are
assailed by meat eaters. Some of these predators are in turn attacked by
other meat
eaters.
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