Marine Ecosystem Structure and Organisms

• Ecosystem = A biotic community and its interaction with the abiotic environment.

• Flow of Energy and Cycling of Mass.

• Population & Community Controls.

• Marine Environment Zonation.

• Plankton Community

All ecosystems require energy inputs and a supply of carbon to create its living mass (biomass)

Primary Producers refer to organisms whose biomass is the ultimate source of energy and carbon for all other biota in an ecosystem; they are always autotrophs (= organisms that use energy to convert inorganic carbon (CO2) and nutrients to the organic matter of biomass; typically plants.

Solar radiation supplies the energy for photosynthesis.

Flow of energy and cycling of mass.

Some autotrophs use energy rich minerals like sulfur as their energy source for chemosynthesis

Organic matter represents energy in a chemical form. It is converted to other forms of energy, CO2 and nutrients in the process of respiration. Even plants respire in the dark.

Energy is ultimately lost to space as heat, but the CO2 and nutrients get reused, or cycled, within the ecosystem; hence energy flows and mass cycles in ecosystems.

Heterotrophs are all organisms, including bacteria, that solely depend on eating organic matter (dead or living) for energy and biomass carbon.

When heterotrophs eat other living organisms they are called consumers.

When they eat dead organic matter (detritus) they are called decomposers.

Generation of CO2 and mineral nutrients as respiration byproducts is a process called remineralization or nutrient regeneration.

Net Primary Productivity =

All the photosynthetic/chemosynthetic production of organic carbon minus the respiration of primary producers when they are in the dark.

= (Gross Primary Productivity – Respiration)

Chlorophyll a is the primary light harvesting pigment involved in converting light energy to chemical energy during photosynthesis.

It is located in cell structures called chloroplasts, as seen in this diatom cell.

Chlorophyll a content in seawater is a good estimate of phytoplankton biomass.

Global estimates of chlorophyll content measured by satellite. Note, where nutrients are found so are high levels of phytoplankton.

Energy flows up through a hierarchy of different feeding groups, called trophic levels, within biotic communities. Each higher trophic level looses 90% of the lower levels available energy, so there is less total biomass in progressively higher trophic levels; hence trophic pyramid. Typically, more small guys than big guys and they grow faster.

Simple linear links between prey and predators of progressively higher trophic levels is called a food chain. Food webs include all possible feeding relationships, which are typically more complex, yet reality.

Ecological Terms

Population = group of individual organisms of the same species residing in a specific area.

Community = many populations interacting in a habitat.

Habitat = where a population is physically located (address).

Niche = what the population does; its function or role (job).

Species richness = numbers of species in a community.

Species diversity = combines in a single index the richness and evenness of population distributions.

Physical-Chemical Factors

• An organism must live within its tolerance range for all of physical and chemical factors (e.g. temperature and nutrients)

• An organism has an optimum value within its tolerance range for each factor.

• The factor provided at a level below or in excess of an organisms tolerance range will harm the organism; we call this the limiting factor.

• What are best conditions for one organisms may not be the case for other organisms. Some organisms have strategies for coping with conditions that we humans consider extreme (limiting to our survival).

• What are the important physical and chemical factors that can limit growth?

Physical-Chemical Factors

• Temperature (ectotherms versus endotherms)

• Nutrients (nitrogen and phosphate)

• Salinity

• Dissolved Gases

• Acid-Base Balance (pH)

• Hydrostatic Pressure

• Light (not just for plants; UV light is harmful)

Harsh conditions, i.e. extreme physical and chemical factors, favor lower species diversity.

e.g. This deep-sea environment

Mild conditions, i.e. more optimal physical and chemical factors, favor higher species diversity.

e.g. coral reef environment

Population & Community Controls

• Physical & Chemical Factors (must be tolerant of all)

• Biological Factors:– Competition

• Intraspecific (within same population)

• Interspecific (between different populations)

– Predation• Co-dependence of predator and prey

• Balanced state confers community stability

– Disease (parasites)• Impacts weakened/stressed populations

• May counteract imbalances (overpopulation of a species)

• Disturbance (physical or biological in nature)

Consider these two species of barnacles in a rocky intertidal zone community. Tolerance of desiccation and competition for space and prey are important in maintaining their intertidal location. Similar interactions explain the zone of the brown seaweed, Fucus. Disturbance or predation may create opportunities for rapid colonizers of open space.

Disturbance:– Creates new habitat; thereby opens new niches for other organisms.

– The stepwise replacement of one group of organisms in a community with another over time is called succession. The process may be seasonal.

– Succession after disturbance may ultimately lead to a stable community, called a climax community that remains until the next disturbance.

Predation as a disturbance:

Predators may remove the dominant species.

Such local disturbance opens habitat for organisms of an earlier succession stage.

Marine Environment Zonation

• Pelagic Zones: water environment– By light– By depth (pressure and temperature changes)

• Benthic Zones: bottom environment – By depth

• Both zones have many different habitat types; therefore, different communities within each.

Life in the deep dark ocean (>600m) has evolved special means of communication, finding mates & detecting prey:

Echolocation, electrosensing, bioluminescence, and smell are four mechanisms for getting around in the dark.