Ecosystems: Aquatic Biomes

Ecosystems: Aquatic Biomes

EVPP 111 Lecture

Spring 2004

Dr. Largen

Aquatic biomes

Aquatic biomes

occupy largest part of biosphere
two major categories of aquatic biomes

Freshwater

salt concentration of <1%

Marine

salt concentration of ~ 3%

many exhibit pronounced vertical stratification

vertical stratification

based on physical and chemical variables, such as

light

is absorbed by organisms and the water

intensity decreases rapidly with depth

ecologists distinguish between 2 zones based on light penetration

photic zone

zone through which light penetrates
light is sufficient for photosynthesis

aphotic zone (profundal)

very little light can penetrate
insufficient for photosynthesis

temperature.

light-penetrated layer

warmed by heat energy from sunlight

thermocline

narrow stratum of rapid temperature change
separates a more uniformly warm upper layer from more uniformly cold deeper waters

deep waters

beyond penetration of light
are uniformly cold

benthic zone
bottom of any aquatic biome

the substrate, made up of

sand
organic and inorganic sediments

contains detritus

dead organic matter

occupied by communities of organisms collectively called benthos

for whom a major source of food is detritus

rains down from waters of photic zone

Major aquatic biomes

Freshwater biomes

Marine biomes

Freshwater biomes

salt concentration of <1%
closely linked to soils and biotic components of terrestrial biomes through which they pass
characteristics are influenced by

patterns and speed of water flow
climate of area in which its located

two categories

standing (lentic) bodies of water

lakes
ponds
inland wetlands

moving (lotic)bodies of water

rivers
streams

lakes

large, natural bodies of standing fresh water
formed when precipitation, runoff, groundwater seepage fills depressions in earth’s surface

depressions can be formed by

glaciation (Great Lakes, NA)
crustal displacement (Lake Nyasa, East Africa)
volcanic activity (Crater Lake, Oregon)

large lakes may have many of same characteristics as oceans

lakes

consist of 4 zones, defined by depth and distance from shore

littoral zone

shallow, well-lit, close to shore.
rooted and floating plants flourish

limnetic zone

well-lit, open surface water, farther from shore, extending to depth penetrated by light
occupied by phytoplankton, zooplankton, higher animals
produces food and oxygen that supports most of lake’s consumers

profundal zone

consists of deep, aphotic regions
too dark for photosynthesis
oxygen levels are low
inhabited by fish adapted to cool dark waters

benthic zone

bottom of lake
inhabited by organisms that can tolerate cool temperatures and low oxygen levels

lakes

productivity

determined by several factors

temperature
depth
nutrient content
dissolved oxygen content

dissolved oxygen content

aquatic organisms must have molecule oxygen (O₂)
enters water from

air
released as result of photosynthesis
mixing from wave action

determines types of organisms that can inhabit a lake
decomposition of organic matter by bacteria and fungi requires oxygen (as they perform respiration)

biochemical oxygen demand (BOD)

amount of oxygen used by decomposers to break down a specific amount of organic matter
greater amount of organic matter (or influx of nutrients) increases BOD and decreases amount of O₂available in water

often classified according to their production of organic matter

three general categories

oligotrophic

deep
cold
small surface area relative to depth
nutrient-poor
phytoplankton are sparse, not very productive
don’t contain much life
waters often very clear
sediments low in decomposable organic matter
example: Lake Baikal, Siberia

eutrophic

shallow
warm
large surface area relative to depth
nutrient-rich
phytplankton more plentiful and productive
waters often murky
high organic matter content in benthos

leads to high decomposition rates and potentially low oxygen

mesotrophic

moderate nutrient content
moderate amount of phytoplankton, reasonably productive.

eutrophication

process in which some oligotrophic lakes become eutrophic

occurs over long periods of time
lakes pass from oligotrophic to mesotrophic to eutrophic
occurs as runoff brings in nutrients and silt
pollution from fertilizers can cause explosions in algae population and cause a decrease in oxygen content

wetlands

an area covered with water at some point in year that supports aquatic plants

range from periodically flooded regions to soil that is permanently saturated

conditions favor specially adapted plants called hydrophytes

can be freshwater or saltwater

many types, including

marshes

usually covered with water year-round
dominant plants are emergent (stems and leaves extending above surface

swamps

dominated by woody plants

bogs

dominated by sphagnum mosses

seasonal pools

generally develop in three topographic situations

basin wetlands

develop in shallow basins

ranging from upland depressions to filled-in lakes and ponds

riverine wetlands

develop along shallow, periodically flooded banks of rivers and streams

fringe wetlands

occur along coasts of large lakes and seas
water flows back and forth due to changing lake levels or tidal action

wetlands

are among richest biomes

contain diverse communities

provide important services

water-storage basins

help reduce intensity of flooding

improve water quality by filtering pollutants

frequently destroyed or degraded by human activity

filled for agriculture and development

now protected in many areas

rivers and streams

bodies of water moving continuously in one direction
downward flow of surface water and groundwater from mountain highland to sea can be separated into

three zones

source zone
transition zone
floodplain zone

source zone

contains headwaters (headwater streams)

often begins as springs or snowmelt
cold
clear
carries little sediment
contains relatively few nutrients
channels usually narrow
current is swift
substrate is rocky

transition zone

contains wider, lower elevation streams
streams join to form tributaries
warmer
less clear
carries more sediment
contains more nutrients
channels usually wider
current is slower
substrate begins to accumulate silt

floodplain zone

tributaries join to form rivers

which empty into oceans at estuaries

warmer still
murky
carries substantially more sediment
contains substantially more nutrients
channels wider, wide mouth
current relatively slow
substrate silty from deposition of sediment

rivers and streams

nutrient content

largely determined by the terrain & vegetation of the area through which it flows
input via

adjacent and overhanging vegetation
weathering of rock
soil erosion
human activities

estuaries

areas where freshwater (stream or river) merges with ocean

freshwater meets salt water

salinity varies

from that of fresh water to that of ocean water
spatially (based on location)
temporally (due to tidal activity)

one of most productive biomes on earth due to nutrients delivered by rivers

major producers are salt marsh grasses, algae, phytoplankton

support diverse communities
are crucial feeding areas for many types of water fowl
threatened by same types of activities as wetlands

Marine biomes

salt concentration of ~ 3%
cover ~ 75% of the earth’s surface
have enormous impact on planet’s climate
evaporation of seawater provides most rainfall
ocean temperatures affect wind patterns, distribution of energy to land via currents
supply substantial portion of world’s oxygen
photosynthesis by marine algae & photosynthetic bacteria
consume huge amounts of atmospheric carbon dioxide
result of photosynthesis by marine algae and photosynthetic bacteria
communities are distributed through several zones
based on

depth of water
degree of light penetration
distance from shore
open water versus bottom

zonation in marine communities

5 general zones

intertidal zone
neritic zone
oceanic pelagic zone
benthic zone
abyssal zone

intertidal zone

where land meets water
is alternately submerged and exposed twice daily die to tides
communities are subjected to huge daily variations in

availability of saltwater
temperature

organisms are subject to mechanical forces of wave action

can be rocky or sandy
are often destroyed by pollution and human activity
vertical zonation

based on percentage of time spent submerged

uppermost zone
middle zone
bottom zone

vertical zonation

uppermost zone

submerged only during highest tides
have adaptations that prevent dehydration and overheating
inhabited by grazing mollusks, suspension-feeding barnacles, a few algae

middle zone

submerged at high tide
exposed at low tide
inhabited by array of algae, sponges, sea anemones, mollusks, crustaceans, echinoderms, small fishes

bottom zone

exposed only during lowest tides
inhabited dense cover of seaweeds, diver community of invertebrates and fishes

neritic zone

beyond intertidal
includes shallow regions over the continental shelves
in warm tropical waters, this region contains

coral reefs

dominated by structure of coral itself

formed by diverse group of cnidarians that secrete hard external skeletons made of calcium carbonate
cerates a substrate upon which other corals, sponges, algae grow

include a very diverse assortment of vertebrates and invertebrates
very productive

currents and waves constantly renew nutrients
light penetrates to ocean floor allowing photosynthesis

easily degraded by

pollution
development
high water temperatures

oceanic pelagic zone

extends past continental shelves, can be very deep, is the open water

includes most of the ocean’s water.

water is constantly mixed by ocean currents
plankton live in photic zone and are producers for this biome
nutrient concentrations generally lower than in coastal areas
includes a great variety of free swimming animals (fish, large squid, sea turtles, marine mammals )

benthic zone

ocean bottom below neritic and oceanic pelagic zones.
Substrate and temperature are very important characteristics in determining community development
nutrients "rain" down from above in form of detritus
communities consist of bacteria, fungi, seaweed and filamentous algae, numerous invertebrates, and fish.

abyssal zone

very deep benthic communities
organisms are adapted to

continuous cold.
high pressure
low to no light
low nutrients

deep-sea hydrothermal vents of volcanic origin found here.

dark, hot, oxygen-deficient environment

producers are chemoautotrophs

Aquatic biomes

Primary productivity

in aquatic ecosystems, is limited by
light
nutrients
marine ecosystems
freshwater ecosystems

marine ecosystems

light

is first variable to control primary production in oceans

since solar radiation can only penetrate to a certain depth (photic zone)

more than 50% of solar radiation is absorbed in first meter of water

even in "clear" water, only 5-10% of radiation reaches depth of 20m

since light is primary variable limiting primary production

we would expect production to increase along a gradient from the poles to the equator

but that is not the case, there is no such gradient
there are parts of the ocean in tropics and subtropics that exhibit low primary production

why are tropical and subtropical oceans less productive than we would expect?

due to availability of nutrients
nutrients more than light limit primary productivity in different geographic regions of the ocean

nutrients

nitrogen and phosphorus

most often limit marine production
are examples of limiting nutrients (nutrients that must be added for production to increase)
concentrations are low in photic zone where photosynthesis could occur
often more available in deep waters where its too dark for photosynthesis

freshwater ecosystems

limited by solar radiation and temperature
nutrient limitations also common

phosphorus is usually limiting nutrient (rather than nitrogen as in oceans)

hence shift in late 1970’s to phosphate-free detergents

cultural eutrophication

eutrophication of lakes as a result of input of nutrients from

sewage and fertilizer pollution

Aquatic biomes

aquatic primary succession

main concepts of terrestrial primary succession can be applied to aquatic ecosystems
except for oceans, over time, most aquatic ecosystems are replaced by terrestrial ecosystems

aquatic ecosystems receive continuous input of soil particles and organic matter
as sediment increases, water depth decreases

types of organisms change

The End