The continued dependence on fossil fuels for power has increased carbon emissions in the atmosphere. One of the many greenhouse gasses, carbon dioxide in the atmosphere traps heat as it radiates out from the planet. This “greenhouse effect” is essential for life on earth, but with too much carbon dioxide in the atmosphere more and more energy from the sun is being trapped, causing increased temperature to the delicate ecosystems of Earth. Although the actual rise in temperature over ninety-nine years, from 1904 from 2005, has been 0.95°C (IPCC), this has a very negative effect on most life forms, and has substantially increased over the last fifty years. This subtle heightening of temperature has, among other things, caused melting polar icecaps, desalinization in northern oceans, and increased sea temperatures, which represent potential dangerous for undersea life. Coral reefs are complex ecosystems that include not just the corals themselves, but a multitude of fish and other marine organisms. They are an important part of human life, ranging from tourism attractions to medicine development and animal habitats.

Experimental Design

For the experiment five 10 gallon aquariums were set-up and the temperatures adjusted using the 50W heaters in each tank. Temperatures were adjusted in the tanks to 76, 78, 80, 82, 84 and monitored daily.

C. viridis and the A.glauca fragments were placed on plastic racks in the tanks. Each was placed on a cement square and the corners of the squares were cut to denote which coral was which for counting purposes.

Growth and health of the corals was assessed based on polyp counts. At the end of the experiment, the average growth for each of the tanks were calculated for both species.

Aquarium Conditions

The experiment was conducted in 10 gallon glass aquariums. The tanks were lit with a Current Nova Extreme T-5 lighting system (4 x 54W 10K bulbs). Each tank contained a 50W Visitherm Stealth Heater and a Maxijet 600 pump for water flow. The specific gravity of the tanks was maintained at 1.023 g/ml. Temperatures within the tanks was adjusted using the heater and ranged from 76 to 84. (fig 1)

The Coral Studied

There were two different species of coral used in the experiment. The first one, Clavularia viridis , is a soft coral, that is phototropic, and consist of small green polyps that extend from a purple rubbery mat. (fig 3) The second coral species is Anthelia glauca, another phototrophic soft coral that has large polyps ranging from white to pink, with mat-like tissue connecting them (fig 2).


Although the overall pattern of the two graphs appears to indicate an increase in growth as the temperature increases, the lines are far from linear. (fig 6) The 84ºF tank shows the highest growth rates for both coral species tested. The 76ºF tank shows that the temperature in lower levels might stunt the growth rate of both coral species. Observations of the individual corals tested suggest that higher temperatures may stress the corals. Two of the three A.glauca in 84ºF water were a pale green in color(fig 5) , as opposed to the white A.glauca in the cooler tanks. The C. viridis in the 84ºF water were white instead of green like normal C.viridis, and in other corals white denotes bleaching, or very stressed out corals.(fig 4)The rubbery mat was also very stiff compared to the colder temperature C. viridis, which made them break easier.


The data collected for this experiment suggests that A.glauca will is a fairly temperature tolerant species, still growing in even the 84ºF tank. Qualitative observations of the corals suggest that the corals, despite the growth, were more stressed by the increased temperatures. The C.viridis also shows tolerance to higher temperatures, again showing growth in the 84ºF tank. Again, observations of the corals suggest stress from the increased temperature.

Further work

This study suggests that increased temperature does not have an adverse effect of growth of these two coral species but a longer study period may be beneficial to see if the bleaching and other signs of stress will kill the coral colonies in the long run. More study is needed to look at these signs of stress as well in terms of their effect on the coral species studied. Work could also be done with other species of corals, over longer periods of time.


The experiment was conducted as part of the E. O. Smith High School Coral Aquaculture Project. The project was funded by a Toyota Tapestry Grant and grants from the E.O. Smith Foundation.