Environmental Factors Affecting Corals and Coral Reefs
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Environmental Factors Affecting Corals and Coral Reefs. Environmental Factors Correlated with Healthy Reef Coral Growth. Warm tropical water Normal seawater salinity Appropriate solar radiation Low organic nutrients (oligotrophic) Low turbidity Low sedimentation Vigorous water motion.

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Environmental Factors Affecting Corals and Coral Reefs

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Environmental Factors Affecting Corals and Coral Reefs

Environmental Factors Correlated

with Healthy Reef Coral Growth

  • Warm tropical water

  • Normal seawater salinity

  • Appropriate solar radiation

  • Low organic nutrients (oligotrophic)

  • Low turbidity

  • Low sedimentation

  • Vigorous water motion

The Electromagnetic Radiation Spectrum

Only green and blue wavelengths pass through water a great distance.

Photosynthetically Active Radiation


(i.e., visible light)

Primary Production Limitations

  • light

  • water

  • nutrients


Photic Zone

No Photosynthesis

Aphotic Zone

Light Absorption in the Ocean

Light Intensity

  • decreases with depth

  • 100 meter = depth limit of hermatypic corals primarily a result of the overall reduction in light

  • many studies have focused upon how changing light intensities with depth affect the photosynthesis of zooxanthellae of corals

Light Penetration in the Ocean

Primary Productivity

The rate of production of organic matter by autotrophs

Primary Productivity


  • Involves the use of light energy in the conversion of inorganic carbon into organic carbon.


6H2O + 6CO2 + light  C6H12O6 + 6O2

Primary Producers

Common Name

Blue-green algae (cyanobacteria)

Red algae

Brown algae

Green algae





Primary Productivity


  • Involves the use of energy released by the catalysis of certain inorganic reaction to convert inorganic carbon into organic carbon.

Cellular Respiration

C6H12O6 + 6O2 6H2O + 6CO2 + energy


Measuring Primary Productivity in the Ocean

Standing Crop Estimates

  • weigh out total plant material

  • measure concentration of chlorophyll in the water

  • use satellite imagery

    Measure Actual Rates of Primary Productivity

  • measure oxygen production and consumption by plants (e.g., light-dark bottle technique)

Table 1. Average net primary production and biomass of aquatic habitats. Data from R.H. Whittaker and G.E. Likens, Human Ecol. 1: 357-369 (1973).

Primary Productivity

Gross Primary Productivity (GP)

  • The rate of production of organic matter from inorganic materials by autotrophic organisms

    Respiration (R)

  • The rate of consumption of organic matter (conversion to inorganic matter) by organisms.

    Net Primary Productivity (NP)

  • The net rate of organic matter produced as a consequence of both GP and R.

Primary Productivity

NP = GP + R

Note that R is a negative value because it results in the reduction of organic matter.

Plankton Sampling

Plankton Size

  • Picoplankton (.2-2 µm)

  • Nanoplankton (2 - 20 µm)

  • Microplankton (20-200 µm)

  • Macroplankton (200-2,000 µm)

  • Megaplankton (> 2,000 µm)




Plankton Sampling


5 in

Collecting bottle

Avoidance ability- this is a function of reactive distance, radius of net, speed of tow, burst of speed of larvae

To reduce net clogging:

  • pick correct mesh size

  • use longer net

  • tow at slower speeds

  • tow for shorter time

  • change configuration of net

  • Picoplankton .2-3um

  • Nanoplankton 2-20um

  • Microplankton 20-200um

Rates of primary production regulated by LIMITING FACTORS:

  • major limiting factors in ocean (inorganic nutrients, light) differ from those on land (moisture, temp, inorganic nutrients, light)

  • primary production measured via change in O2 concentrations in “light” and “dark bottles”






Light & Dark Experiments


light + 6CO2 + 6H2O C6H12O6 + 6O2


C6H12O6 + 6O2

6CO2 + H2O + ATP

light bottle


+ respiration

dark bottle



Sources of Error

  • Respiration rates are not equal between light and dark bottles.

  • The glass wall of the light bottle filters light.

  • The bottle may not be representative of the water as a whole.

Photoadaptation in Corals

Changes in pigment concentrations and algal densities in response to light intensity

A coral (Acanthastrea) under high magnification. Focus stack. Fluorescent pigments emphasized with full-spectrum lights

Colony Morphology Responses to Irradiance

Hemispherical Branching Colonies

Plate-Forming Colonies

Absorption of Ultraviolet Radiation by the Earth’s Atmosphere

Types of UV and Human Sunburn Responses

Effects of UV on Living Things

  • damage to DNA resulting in mutations

  • damage to other biological molecules

    • proteins: enzyme inactivation

    • lipids: disruption of cell membranes and membrane transport systems

Corals and UV Radiation

  • decreased growth

  • decreased rates of calcification

  • transplantation experiments (deep corals brought to the surface) demonstrate corals may be UV-sensitive (exhibit bleaching and increased mortality)

  • coral sperm appears to be UV-sensitive (note spawning normally takes place at night)

Ultraviolet Absorbing Compounds in Corals

  • mycosporine-like amino acids (MAA’s)

  • MAA’s apparently produced by zooxanthellae but stored in the animal tissues

  • concentrations greater in shallow water corals than in deeper ones

  • transplantation experiments demonstrate adaptational changes in pigment concentrations

  • positively buoyant eggs exhibit higher concentrations of pigments than do negatively buoyant eggs

Effects of UV on the Coral-Zooxanthellae Symbiosis





Coral pigment


Ozone in the Atmosphere

The hole in the ozone

Oct. 1979

Sep. 2013


  • Lethal Limits

    • <17 and > 33oC for extended periods of time

    • physiological effects = bleaching (expulsion of zooxanthellae from coral tissues)

  • Ecological Limits

    • 18 - 32oC (low limit correlates with 20o N & S latitude limit of reef corals)

    • some exceptions exist

    • reasons for differences between lethal and actual limits

      • secondary effects of temperature on feeding or on reproduction

      • synergistic effects of other environmental factors (e.g., UV irradiance)

Global Distribution of Coral Reefs



Global Climate Change

Other Factors

  • Salinity

  • Sedimentation

  • Aerial Exposure at Low Tide

  • Water Motion

  • Inorganic Nutrients

  • Currents


Nutrients and Algae Growth

Acid Rain in Marine Environment

  • reduces ability of marine organisms to utilize calcium carbonate

  • Coral calcification rate reduced 15-20%

  • Skeletal density decreased, branches thinner

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