Environmental Conditions

Corals have specific environmental conditions that they require in order to survive. These determinants limit wherein corals can live. In this unit, we will learn around the abiotic determinants that corals need to thrive.

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These environmental problems are referred to as biotic and also abiotic factors. Remember, us can malfunction the native abiotic:

a bioticwithout life

Therefore, abiotic means without life. Abiotic factors are non-living materials of an organism’s environment. Do you psychic what biotic means? It method life. Biotic factors are life or as soon as living components of a community.

Coral reefs are facility ecosystems. There are many different biotic factors that impact coral reefs. They will certainly be discussed throughout different units. Because that now, us will emphasis on the abiotic factors that impact corals.

Can you think of any kind of abiotic factors that may impact coral reef ecosystems?

Here space some examples:

Abiotic Factors
Ocean depth
Inorganic nutrient (phosphorus, nitrogen, etc.)
Dissolved gases – oxygen (O2), nitrogen (N2), carbon dioxide (CO2), etc.
Aragonite and calcium carbonate saturation(we will discuss an ext about this in later on units)

Abiotic Factors

Figure 8-1. Abiotic factors

There are multiple abiotic determinants that affect coral reefs (figure 8-1). The number in the diagram exchange mail to the numbered explanation below. Here are the optimal parameters because that corals to live in:

Light: Corals require a moderate quantity of sunshine in order come survive. Light is rapidly took in by seawater and does not penetrate to an excellent depths. If over there is too tiny light, then the zooxanthellae will not have the ability to photosynthesize and produce food for corals. Too lot light, specifically ultraviolet (UV), may reason corals to expel zooxanthellae, bring about them to bleach. In later units, we will certainly learn more about coral bleaching.

Salinity deserve to be measure by using a hand-held refractometer (figure 8-2). When using this tool, a tiny drop the seawater is placed between a measure up prism and also a cover plate. Light passes v the sample and the irradiate is refracted through the prism come the scale. By looking with the eyepiece, the salinity deserve to be read. There are various other tools, such together hydrometers and also conductivity meters, the are additionally used to measure up salinity.


Figure 8-2. The light (red arrow) bends v a refractometer offering a salinity reading, i beg your pardon is seen v the eyepiece.

Corals need clear water (water v low turbidity) so the the light have the right to penetrate through the water column, allowing the zooxanthellae to photosynthesize. When there is high turbidity, light can’t permeate through the rely particles. Additionally, corals deserve to be smothered by sediments or corpuscle that resolve on top of the corals. Eventually, this could lead to the coral dying.

One method to measure turbidity is to usage a Secchi disk. A Secchi decaying is regularly an 8 customs (20.3 centimeter) round disk the has alternating black and white quadrants (figure 8-3).

Secchi disks space lowered into the water v a rope. Light shows off that the peak of the Secchi disk. When the Secchi disk is no much longer able to it is in seen, the human being stops lowering the rope. Then they record the depth that is marked on the rope. Making use of the Secchi depth, scientists can calculate the turbidity of the water.


Figure 8-3. Secchi decaying pattern.

Nutrients: Corals like low nutrient water. Nutrients encompass phosphorus (P) and also nitrogen (N). When there are lots of nutrients, this may cause algae and phytoplankton to grow. This procedure can block out the light the zooxanthellae should survive. Also, algae can overgrow coral while competing for space. If the coral cannot obtain light, then it will certainly die.

Figure 8-4. PH scale

Corals like seawater to have actually a pH level in between 8.0–8.3, i beg your pardon is the standard pH of saltwater. It is very daunting for corals to grow in acidic conditions. We will learn more about this topic and how that is connected to s acidification in later units.

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On a coral reef, space can be very restricted and corals must compete with sponges, macroalgae (seaweed), and even other coral species. When room becomes limited, most corals can’t choose up and move. Instead, they battle it out v their neighbors. Part coral polyps perform this by extending their mesenteries from their stomachs. Climate the fight begins. The mesentery strands sheathe the intruder types and the coral publication digestive enzymes that begin to devour their neighbor. This fight for territory deserve to be viewed in the Coral Nighttime Battle. Click on video #5 to view.

Remember the these are general parameters and also that there space corals that have adapted to different conditions. Because that example, Siderastrea radians, the lesser starlet coral, has adjusted to living in really stressful conditions in Florida bay (Lirman et al. 2002). This large body that water is one estuarine area where seawater mixes through freshwater. The average depth in Florida only is 5 feet (152.4 centimeters), which is just one of the factors that environmental problems fluctuate greatly. During the dried season, when there is tiny to no rain and also evaporation prices are high, salinity levels deserve to reach hypersaline conditions (greater than 40 ppt). It has likewise been recorded that certain basins in Florida only reach over 70 ppt. This would certainly be a very difficult place come live if you were a coral. Remember that many corals have the right to tolerate 23–42 ppt.

In an additional example, American Samoa corals have adjusted to high temperatures the can easily exceed 89.6°F (32°C) for multiples hours and also days at a time (Craig et al. 2001). This offers us hope that some corals will certainly adapt to climate adjust and warming seas.

There are other abiotic factors that affect coral reefs. We have currently learned exactly how currents can influence distribution the coral reefs in Unit 7: Distribution. There are other abiotic factors that we will certainly learn much more about in later units (see Unit 9: Coral Growth). We will also learn about the biotic determinants that impact coral reefs as well (see Unit 16: Food Webs, comes soon).

Next Course



Figure 8-1. Sun. 2014 via Clipart Panda. http://www.clipartpanda.com/clipart_images/sun-clipart-medium-5602503.

Figure 8-1. Thermometer. N.d. Via Teacher’s Files. http://www.teacherfiles.com/clip_art_thermometers.htm.

Figure 8-2. Refractometer adjusted from CEphoto, Uwe Aranas , 29 Oct 2013 via Wikimedia Commons. https://commons.wikimedia.org/wiki/File%3APortable-Refractometer-03.jpg.

Figure 8-3. By User: Mysid (Own work) , 1 Nov 2005 via Wikimedia Commons. http://upload.wikimedia.org/wikipedia/commons/0/0b/Secchi_disk_pattern.svg.


Craig, P., Birkeland, C., & Belliveau, S. (2001). High temperatures tolerated by a varied assemblage of shallow-water corals in American Samoa. Coral Reefs 20: 185-189.

Dubinsky, Z. & Falkowski, P. (2011). Light together a source of information and also energy in zooxanthellate corals. In: Dubinsky, Z. And Stambler, N. (eds.) Coral reefs: an ecosystem in transition, Springer, Dordrecht.

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Lirman, D., Orlando, B., Marcia, S., Manzello, D., Kaufman, L., Biber, P., Jones, & Tahzay, J. (2002). Coral neighborhoods of Biscayne Bay, Florida and nearby offshore areas: diversity, abundance, distribution, and also environmental correlates. Aquatic Conservation: Marine and Freshwater Ecosystems 13(2): 121-135.