AQUATIC BIOMES
CHAPTER 4 SECTION 4
SC B-6
STUDENTS WILL DEMONSTRATE
AN UNDERSTANDING OF THE
INTERRELATIONSHIPS AMONG
ORGANISMS & THE BIOTIC &
ABIOTIC COMPONENTS OF THEIR
ENVIRONMENT
Aquatic Biomes
 charaterized primarily by their physical environment
rather than be climate
 often layered with regard to
light penetration
 temperature
 community structure

Zonation in Aquatic Biomes
 light absorbed by water itself + photosynthetic
organisms so…light intensity decreases rapidly with
depth
 Photic Zone: sufficient light for photosynthesis
 Aphotic Zone: little light penetrates
 Pelagic Zone = photic zone + aphotic zone
Zonation in Aquatic Biomes
 Abyssal Zone:

2,000 – 6,000 m deep
 Benthic Zone:

the bottom of all aquatic biomes, shallow or deep
 Benthos:

communities of organisms that live in sand &
sediments of the benthic zone
More Definitions
 Detritus:

dead organic material that “rains” down from
photic zone; food source for benthos
 Thermocline:
narrow layer of water where there is an abrupt
temperature change
 separates the more uniformly warm upper layer
from the uniformly cold deeper water
 many temperate lakes undergo a semiannual
mixing of their water

Lakes
 lake environment generally classified on basis of 3
physical criteria:
1. light penetration

photic / aphotic
2. distance from shore / depth of water

littoral / limnetic
3. open water / bottom

pelagic / benthic
Lakes
 standing bodies of water range from ponds a few
square meters in area to lakes covering thousands of
square kilometers
Lakes: Oligotrophic
Lakes: Eutrophic
Lakes: Photosynthetic Organisms
 Littoral Zone:
shallow, well-lit waters close to shore
 rooted & floating aquatic plants

 Limnetic Zone:
waters too deep to support rooted plants
 phytoplankton, including cyanobacteria

Phytoplankton
Lakes: Heterotrophs
 Limnetic Zone:

small, drifting heterotrophs or zooplankton
(graze on phytoplankton)
 Benthic Zone:

assorted invertebrates (species depends on O2
content)

Fishes live in all zones that have sufficient O2
Zooplankton
Wetlands
 habitat that is inundated by water (at least part of
the year) & supports plants adapted to watersaturated soil
 due to high organic production by plants &
decomposition by microbes: water & soil of wetlands
periodically low in dissolved O2
 *high filter capacity: both nutrients & pollutants
Wetlands: Autotrophs
 among most productive biomes in world
 water-saturated soils great for plants
Lily pads
 Cattails
 Sedges
 Tamaracks
 Black spruce

Wetlands: Heterotrophs
 diverse community of invertebrates, birds, reptiles,
amphibians, and mammals
 Herbivores:
crustaceans
 aquatic insect larvae
 muskrats

 Carnivores:
dragonflies
 frogs
 alligators
 herons

Streams: Physical Environment
 most prominent characteristic: their current
 stratified into vertical zones
Streams: Physical Environment
 Headwaters:
 generally
cold, clear
 turbulent, & swift
 Downstream:
 generally
warmer
 more turbid
Estuary
 a transitional area between river & sea
 when high tide: salt water flows up estuary channel
 higher density sea water stays below lesser density
freshwater
Estuary: Chemical Environment
 salinity varies from that of freshwater  sea water &
with rise & fall of tides
 nutrients from rivers make estuaries some of most
productive biomes
Estuary: Photosynthetic Organisms
 saltmarsh grasses & algae (including phytoplankton)
are major producers
Estuary: Heterotrophs
 abundant #’s of worms, oysters, crabs, & many fish
 many invertebrates & fishes use estuaries as
breeding grounds
 crucial feeding grounds for birds & some marine
mammals
Intertidal Zones
 are periodically submerged & exposed by the tides,
2x daily on most marine shores
 upper zones exposed to air for longer periods 
greater variation in temp & salinity
 changes in physical conditions from upper to lower
zones limits the distribution of many organisms to
particular strata
Intertidal Zones: Chemical Environment
 O2 & nutrient levels generally high & renewed with
each turn of the tides
Intertidal Zone: Photosynthetic
Organisms
 high diversity & biomass of attached marine algae
inhabit rocky intertidal zones
 much lower diversity & biomass in sandy intertidal
zones with vigorous wave action
 sandy intertidal zones in protected bays or lagoons
have rich beds of grass & algae
Intertidal Zone: Heterotrophs
 animals here have multiple structural adaptations
 rocky
areas: ways to attach to hard surfaces
 sandy areas: many bury themselves
 feed on what tides bring them
Ocean Pelagic Zone
 open blue waters
 mixed constantly by wind & ocean currents
 photic zone extends deeper here (water is clearer)
Oceanic Pelagic Zone: Chemical
Environment
 O2 levels generally high
 nutrient levels generally lower than in coastal waters
 tropical oceans: thermally stratified all year
 temperate & hi-latitude oceans have spring & fall
turnover so generally nutrients renewed in photic
zone
Oceanic Pelagic Zone: Geologic Features
 covers ~70% Earth’s surface
 average depth = 4,000 m
 deepest point: 10,000 m
Pelagic Zone: Photosynthetic Organisms
 phytoplankton (including photosynthetic bacteria)
dominate
 due to vast area this zone covers: ~50% of all
photosynthesis on Earth by them
Pelagic Zone: Heterotrophs
 zooplankton most abundant group in this zone
 graze on phytoplankton
 includes:
 protists
 worms
 copepods
 shrimp-like
krill
 jellies
 small
larvae of invertebrates
Pelagic Zone: Heterotrophs
 also include free-swimming animals:
 large
squid
 fishes
 sea turtles
 marine mammals
Coral Reefs
 formed largely from the calcium carbonate skeletons
of corals
 in photic zone of relatively stable tropical marine
environments with high water clarity
 sensitive to temps < 18 – 20° & > 30°C
 found in deep seas 200 -1,500 m deep
 as
much diversity as shallow reef
Deep Sea Coral Reef
Shallow Coral Reef
Coral Reef: Chemical Environment
 require high O2 levels
Coral Reefs: Photosynthetic Organisms
 unicellular algae live w/in tissues of corals in
mutualistic relationship: provides corals with
organic molecules
 diverse multicellular red & green algae growing on
reef also photosynthesize
Coral Reef: Heterotrophs
 dominant
heterotroph: corals
are a diverse group of
cnidarians
 also high diversity of
fishes & invertebrates
 overall nearly as
diverse as tropical
rainforest