1. The Effect of High Temperature on Coral Symbiont Densities
Pratima Rosen
Introduction :
Climate change and anthropogenic threats, such as destructive fishing practices, pollution, excess nutrients, etc., are increasing and coral reefs are getting decimated.
Reefs are dying due to coral bleaching—a break in the symbiosis between the coral host and their symbiotic algae caused by increased ocean temperatures.
Review of Literature:
Thomas Oliver and Stephen Palumbi in 2011 found that corals naturally growing in the Highly Variable (Pool 300) pool resisted heat stress, while those corals from the Moderately Variable (Pool 400) suffered high mortalities.
A reason for the higher tolerance could be explained by Logan’s experiment in 2014 that discovered that, possibly, coral exposed to constant higher temperatures developed mechanisms that allowed them to respond to the heat stress and were less likely to get bleached
Dan Barshis in 2013 posited that some species may go through constitutive front loading, allowing them to maintain physiological resilience during frequently encountered stress. Constitutive front loading means that the coral already have high expression (activity) of genes important in the stress response.
Oliver and Palumbi in 2011 proposed that among the corals that were able to host multiple types of symbionts, most showed higher proportions of this clade D symbiont in the hotter habitat.Therefore, corals that host clade D may be a mechanism that helps the coral respond to the heat.
Data/Results:
Table 1. Sample of Symbiont Concentration Densities
Hypothesis:
In this experiment, it was hypothesized that highly variable (HV) pool corals are more bleaching resistant than moderately variable (MV) pool corals, across multiple species.
Background:
Two species of coral, Acropora aspera and Acropora formosa were collected from Ofu Island in American Samoa. Nubbins were collected from two distinct back-reef pools that experience variation in levels of temperatures, pH, and oxygen driven by tidal fluctuations.
The two pools are labeled as pool 300 and pool 400. Pool 300 is the highly variable (HV) pool in terms of greater fluctuations in temperature. Pool 400 is the more sensitive neighboring pool and is classified as the moderately variable (MV) pool.
Methodology:
Species
Date
Time
Tank
Pool
Treat-
ment
Conc (symb/cm2)
A. aspera
25-Aug-11
21:00 2
300
control
1.81E+06 4
2.36E+06
27-Aug-11
8:00
2.39E+06
1.55E+06
16:00
2.14E+06 1
heated
2.04E+06 3
2.64E+06
2.23E+06
A. formosa
1.61E+06
400
1.03E+06
5.76E+04
1.18E+06
1.52E+06
1.36E+05
All coral fragments placed in a tank
Temperature of tanks 1 & 3 were raised in increments over a period of time
Bleaching signs/incidents were recorded
Selective coral fragments were collected to be studied
Heat Stress
Treatment
A. aspera had a lower symbiont concentration in pool 300 (HV), thus it would not be as heat tolerant as A. formosa to heat stress
Filtered Salt Water
A coral fragment was placed into a plastic bag and blasted with filtered sea water
It was blasted until the fragment was completely bleached (white)
The tissue and filtered sea water were poured into falcon tubes
Obtaining Coral Tissue
A. formosa had a higher symbiont concentration in pool 300 (HV) in comparison to pool 400 (MV)
Discussion
There is a strong correlation between symbiont concentration and the heat variability of pool 300 and 400
The coral fragments that had higher concentrations from pool 300 (HV) was most probably due to being pre-exposed to fluctuating temperatures, allowing them to develop mechanisms
The data and results seemed to have a great amount of variability most likely due to imprecision of the measurement of the surface area technique—the wax dipping method or an inconsistent Symbiodinium count
This experiment should be repeated so that the various mechanisms that can help coral species better withstand heat can be further investigated
Centrifugation
Process
Pellets were diluted based on abundance of symbiodinium to make haemocytometer reads easier
Haemocytometer
Count
References:
Barshis, D. J., Ladner, J. T., Oliver, T. A., Seneca, F. O., Traylor-Knowles, N., & Palumbi, S. R. (2013). Genomic basis for coral resilience to climate change. Proceedings of the National Academy of Sciences of the United States of America, 110(4),  
Logan, C. A., Dunne, J. P., Eakin, M., & Donner, S. D. (2014). Incorporating adaptive responses into future projections of coral bleaching. Global Change Biology, 20(1),
  Oliver, T. A., & Palumbi, S. R. (2011). Many corals host thermally resistant symbionts in high-temperature habitat. Coral Reefs, 30(1),
Oliver, T. A., & Palumbi, S. R. (n.d.). Do fluctuating temperature environments elevate coral thermal tolerance? Reef Resilience. s y 
Wax Dipping
References, cont.:
Buchheim, J. (2013). Coral Reef Bleaching. Retrieved September 6, 2013, from Odyssey Expeditions website:
"Coral Reef: Threats." World Wild Life. N.p., n.d. Web. 10 Mar aboutourearth/blueplanet/coasts/coralreefs/coralhreats/