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Oceanography
An Invitation to Marine Science, 7th
Tom Garrison
Chapter 16
Marine Communities
Chapter 16 Study Plan
• Marine Organisms Live in Communities
• Communities Consist of Interacting
Producers, Consumers, and Decomposers
• Marine Communities Change as Time
Passes
• Examples of Marine Communities
• Organisms in Communities Can Live in
Symbiosis
Chapter 16 Main Concepts
• A community is comprised of the many populations of
organisms that interact at a particular location. A population is a
group of organisms of the same species occupying a specific
area.
• A habitat is an organism’s “address” within its community, its
physical location. Each habitat has a degree of environmental
uniformity. An organism’s niche is its “occupation” within that
habitat, its relationship to food and enemies, an expression of
what the organism is doing.
• Physical and biological factors in the environment determine
the location and composition of a community.
• A stable, long-established community is known as a climax
community. This self-perpetuating aggregation of species tends
not to change unless disrupted by severe external forces.
• More than half of the animal species known to science are not
free-living. Most are actively involved in close symbiotic
relationships with at least one other life-form in their community.
Communities Consist of Interacting
Producers, Consumers, and Decomposers
• What are some terms used to describe
organisms and their environments?
• Habitat - an organism’s physical location in
its community
• Niche - an organism’s role in the community
• Biodiversity - the variety of species in a
given area
Physical and Biological Environmental
Factors Affect Communities
• A proper balance of physical and biological
factors is important for the success of each
organism and the community.
• Different organisms have different tolerances for
specific factors.
• Steno- is a prefix meaning “narrow”. It can be
used to describe organisms that have narrow
tolerances for specific factors
• Eury- is a prefix meaning “wide”. It can be used
to describe organisms that have wide tolerances
for specific factors
Physical and Biological Environmental
Factors Affect Communities
Range of tolerance to a physical factor – in this
case, temperature – for a population of organisms.
Growth Rate and Carrying Capacity Are
Limited by Environmental Resistance
The J-shaped curve of
population growth of a
species is converted to
an S-shaped curve
when the population
encounters
environmental
resistance.
The physical or
biological conditions
responsible for the
cessation of growth are
called limiting factors.
Population Density and Distribution
Depend on Community Conditions
(above) Random, clumped, and uniform population distribution patterns. The clumped
pattern is most common in nature; uniform is the rarest.
A random distribution implies that the position of one organism in a bottom community
in no way influences the position of other organisms in the same community.
Clumped distribution occurs when conditions for growth are optimal in small areas
because of physical protection (in cracks in an intertidal rock), nutrient concentration
(near a dead body lying on the bottom), initial dispersal (near the position of a parent), or
social interaction.
Uniform distribution with equal space between individuals, such as the arrangement of
trees we see in orchards, is the rarest natural pattern of all.
Marine Communities Change As
Time Passes
• Marine communities change through time.
Changes can occur slowly due to climate
cycles or seafloor spreading, or quickly due
to factors such as volcanic eruption.
• A climax community is a stable, long
established community.
• If a climax community is disrupted, it may be
restored through the process of succession.
The Ocean Supports Many
Distinctive Marine Communities
• What are some examples of marine
communities?
• Rocky intertidal communities
• Seaweed communities
• Sand beach and cobble beach communities
• Salt marsh and estuary communities
• Coral reef communities
• Open ocean communities
• Deep sea floor communities
• Hydrothermal vent and cold seep communities
Rocky Intertidal Communities Are Densely
Populated despite Environmental Rigors
Although the rocky shore looks like a very difficult
place for organisms to make a living, the rocky
intertidal zone - the band between the highest
high-tide and lowest low-tide marks on a rocky
shore - is one of Earth’s most densely populated
areas.
A Pacific coast tide pool and intertidal shore. (left) A
diagrammatic view. (right) Key
Rocky Intertidal Communities Are Densely
Populated despite Environmental Rigors
The relationship between amount of exposure and vertical zonation in a rocky intertidal
community. (a) A graph showing intertidal height versus hours of exposure. The 0.0 point
on the graph, the tidal datum, is the height of mean lower low water. (b) Vertical
zonation, showing four distinct zones. The uppermost zone (I) is darkened by lichens and
cyanobacteria; the middle zone (II) is dominated by a dark band of the red alga
Endocladia; the low zone (III) contains mussels and gooseneck barnacles; and the
bottom zone (IV) is home to sea stars (Pisaster) and anemones (Anthopleura). The
bands in the photograph correspond approximately to the heights shown in the graph.
Coral Reefs Are the Most Densely
Populated and Diverse Communities
The coral reef habitat.
(a) A diagrammatic view.
(b) Key
Hydrothermal Vents and Cold Seeps
Support Diverse Communities
The path of water associated with a hydrothermal vent. Seawater enters the fractured seabed near an
active spreading center and percolates downward, where it comes into contact with rocks heated by a
nearby magma chamber. The warmed water expands and rises in a convection current. As it rises, the
hot water dissolves minerals from the surrounding fresh basalt. When the water shoots from a weak
spot in the seabed, some of these minerals condense to form a “chimney” up to 20 meters (66 feet)
high and 1 meter (3.3 feet) in diameter. As the vented water cools, metal sulfides precipitate out and
form a sedimentary layer down-current from the vent. Bacteria in the sediment, in the surrounding
water, and within specialized organisms make use of the hydrogen sulfide (H2S) in the water to bind
carbon into glucose by chemosynthesis. This chemosynthesis forms the base of the food chains of
vent organisms.
Bottom current
Precipitation
FeO(OH) MnO2
Chimney
Precipitation
CaSO4 FeS
Sedimentation
Seawater seepage
H2S in water
Basalt
Basalt
Precipitation
FeS, FeS2, CuFeS2
350ºC
(660ºF)
350ºC
(660ºF)
Stepped Art
Fig. 16-21, p. 453
Organisms in Communities Can
Exist in Symbiosis
• Symbiosis is the close interaction of the
lives of two species.
• What are some types of symbiotic
interactions?
– Mutualism – both organisms benefit in these
relationships. An example is sea anemones and
anemone fish.
– Commensalism – one organism benefits, the
other is not helped or harmed.
– Parasitism – one of the organism benefits, but
the other is harmed.
Chapter 16 in Perspective
In this chapter you learned that organisms are distributed throughout the marine
environment in specific communities: groups of interacting producers, consumers,
and decomposers that share a common living space. The types and variety of
organisms found in a particular community depend on the physical and biological
characteristics of that living space.
Any community is a dynamic place, growing and shrinking and changing its
composition as residents respond to environmental fluctuations. The growth and
distribution of organisms within communities depend on the often subtle interplay of
physical and biological factors. The relative numbers of species and individuals in a
community depend in part on whether its environment is relatively easy and free of
stressors, or relatively hard and full of potential limiting factors. A few prominent
marine communities were compared and contrasted in this chapter, and some
representative adaptations of their residents are discussed. The main principle: Why
do organisms live where they do?
In the next chapter you will learn about the range of marine resources, from
physical resources such as oil, natural gas, building materials, and chemicals;
marine energy; and biological resources such as seafood, kelp, and pharmaceuticals
to non-extractive resources like transportation and recreation. World economies are
now dependent on oceanic resources, but we find that we cannot exploit those
resources without damaging their source.