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Marine Communities
Basics
 Community: Organisms in a specific group of
interacting producers, consumers, and recyclers that
share a common living space.
 Population: A group of organisms of the same species
that occupy a specific area.
Organisms Within
Communities
 Dependent on the availability of energy
 Habitat: an organisms “address” within a community.
Its physical location.
 Niche: An organisms “occupation” or “job”. Its
relationship to its food and predators.
 Example: Small fish in a coral reef share the same
habitat, but each species has a different niche. Each
population has a different “job” based on its shape,
size, color, behavior, and feeding habits.
Influence of Physical and
Biological Factors
 Physical Factors include:
 Temperature
 Pressure
 Salinity
 Biological Factors include:
 Crowding
 Predation
 Grazing
 Parasitism
 Lack of sunlight
 Generation of wastes
 Competition for oxygen
Limiting Factors
 A a factor that limits and organisms success in a community.
 Prevents organism from feeding, growing, reproducing,
defending itself, or sensing danger.
 Stenothermal Species: Affected greatly by temperature
 Eurythermal Species: Not affected by temperature
 Stenohaline: Affected greatly by change in salinity
 Euryhaline: Not affected by changes in salinity
 What does Stenobaric mean? Eurybaric?
Competition
 Availability of resources such as a food and light
determine the number and composition of populations
within a community.
 In a stable population, two species cannot occupy the
same niche for long. One will outcompete the other
and force one to extinction or to leave.
 Sometimes this is very simple: Fore example, in a
rocky intertidal community, one species of barnacle
lives on the upper portion of rocks and the other lives
on the lower portion of rocks.
Growth Rate and Carrying
Capacity
 If there were no competitors for food or space, then growth
rate is exponential or J-Shaped curve (i.e. humans,
bacteria).
 But most species have limiting factors which leads to
environmental resistance (the sum of all limiting factors).
 This creates an S-shaped curve where a species grows until
it reaches its carrying capacity and then levels out.
 Carrying Capacity: Population size of a species that a
community can support indefinitely under a stable set of
environmental conditions.
Distribution of Organisms
 Population Density: The number of individuals per unit area or
volume.
 Higher in places like coral reefs and forests than in tougher
conditions like polar regions or deserts.
 Random Distribution: Position of one organism in no way
influences positions of others in the same community. Very rare.
Abyssal Plains.
 Clumped Distribution: Conditions for growth are optimal in small
areas (like cracks in rocks) or if there is nutrient concentration.
Most common type.
 Uniform Distribution: Rarest type. Equal space between each
individual (like arrangement of trees in orchards).
Distribution Types
Random
Uniform
Clumped
Change in Marine
Communities
 Occur slower in marine communities than on land.
 However, natural catastrophes and human influence
can rapidly change communities.
 Climax Community: Stable, long established
community.
 Succession: Orderly changes of a community’s
species composition from temporary inhabitants to
long-term inhabitants.
Examples of Marine
Communities
 Rocky Intertidal
 Seaweed
 Sand Beach and Cobble Beach
 Salt Marshes and Estuaries
 Coral Reefs
 Open Ocean
 Deep-Sea Floor
 Deep Rock
 Hydrothermal Vent and Cold Seep