Aquatic Biome Stratification MP 2.1 and 2.2

Light Intensity Light intensity decreases rapidly with increasing depth greatly influencing the communities that can live at each level Zones in a lake are classified by whether or not they receive light (photic) or not (aphotic)

Photic Zone Upper part of a lake or ocean where there is sufficient light for photosynthesis

Aphotic (profundal) zone Deep lower parts of oceans or lakes where no light penetrates

Benthic Zone Bottom of the lake or ocean at ANY depth Has special communities adapted to living on the bottom

Detritus The poop and bodies of decaying organisms (detritus) fall like snow to the benthos (bottom) by gravity. Benthic bacteria convert the detritus into nitrates that algae use as nutrients for photosynthesis. Currents bring these nutrients to the surface where photosynthesis can take place (eutrophication)

Thermocline Differences in temperature with increasing depth Usually gets colder quickly Effects the distribution of aquatic organisms especially fish.

Littoral Zone Part of the sea, lake or river that is close to shore Also subdivided into smaller areas. Dominated by herbivorous fish communities like Perch and Bluegill and their predators.

Limnetic Zone Part of the open water in a lake that is in the photic zone Off shore of the littoral zone and above the profundal zone. Communities would include predators like pike, trout or bass.