One of the biggest problems facing coral reef ecosystems is coral bleaching, a condition which occurs when the symbiotic algae inside coral expels itself from the host coral. This condition leads to the deterioration of the reef and possible death. This is very concerning for a country like Belize as coral reefs provide a coastal barrier to currents and an entire ecosystem for fish. Coral Reefs also mean big money. In 2007, Ninety percent (US$150-$195 million) of Belize’s tourism revenue came from snorkeling and reef related activities (Belize,United Nations).
The main culprit for this phenomenon is increasing ocean temperatures due to a creeping change in climate. The year 2016 is shaping up to be a real nasty year for coral reefs with climatologists predicting it to be the hottest year on record. Considering the importance of temperature in coral reef sustainability, my travels in the Belize Barrier Reef made me curious about local and global differences in coral thermotolerance determined by their location in the sea. I hypothesize there is little variation in temperature tolerance in local coral populations but great variation in distant populations.
I began my thermotolerance investigation looking at potential differences between reefs that are closer to channels versus reefs that are farther away. Snorkeling in the warm channel of Hol Chan inspired this hypothesis; however, no literature was found. So, I went back to books and researched if there are temperature tolerance differences between coral that resides in the shallow water (inshore) where it might heat up quicker versus deep water (offshore) coral where the sun’s influence is less potent. Turns out that at least in the Florida Keys, there is a noticeable difference between the two groups. To get to this conclusion, a group from the University of Texas, led by Dr. Matz, performed a common garden experiment where they took samples of mustard hill coral from an inshore patch reef and an offshore reef and placed them into a communal lab environment where they experienced heat stress. After six weeks of heat stress, it was found that coral inshore experiences less instances of bleaching and faster growth compared to their offshore kin (Kenkel et. al 2013).
Take note: the coral species the researchers used were exactly the same. Although they might look identical to the naked eye, differences in genetic expression or long term acclimation may have been the cause for the significant differences in the two populations. A similar experiment looking at in- and offshore thermotolerance differences was conducted in the Vietnam reef. Like Matz et al, this report produced similar results with inshore Porites lutea coral displaying greater energy production than their offshore counterparts (Faxneld, et. al 2011). On the flipside, these reports do not necessarily mean inshore coral is inherently the thermotolerant one since in another species these researchers looked at (Galaxea fascicularis), the inshore variant displayed lower energy output compared to the offshore coral.
We have observed thermotolerance on a local level but what about a global scale? Is there any variation if they share the same great sea and longitudinal lines? Unsurprisingly there are differences in thermotolerance with a specific research interest in the Arabian Gulf, the hottest coral reef in the world. The average coral reef temperature ranges from 73° to 84° Fahrenheit (23°–29°Celsius) while the Arabian Gulf coral tolerates temperatures as hot as 97° Fahrenheit (36° Celsius) (NOAA). Because the symbiont algae is what determines if they will expel themselves from the coral, researchers have taken increased interest in discovering if the algae in Arabian Gulf coral has any genetic similarities to other algaes.
Out of seven species of coral sampled from an Abu Dhabi reef, all of the symbiont algae belonged in the same phylogenetic clade C3, suggesting they all come from a similar common ancestor (Hume et. al 2013). This brings the possibility of propagating gulf coral into other parts of the sea but like every other biological puzzle, the phylogenetic similarity is not a silver bullet into cracking the global bleaching problem. A recent report in Nature has shown that if you took the temperature-hardy Arabian Gulf coral into less saline environments that are common outside of the gulf, they perish faster than if they were in their native environment (D’Angelo et. al 2015).
The bottom line is that yes, there are significant thermotolerance differences between coral reefs that are only miles from each other and corals that are oceans away. Although the research is only in it’s infancy, there is a spark of promise that coral may exhibit some resistance to the rising temperature in the oceans. The question, and controversy, still begs the question can or even should humans find a way to intervene with the rising coral bleaching rates? It is not the heaviest concern for me right now. Ask again later when my Old Kentucky Home becomes a beach house in 2500.
Belize. United Nations. UN Secretary. Belize Country Report on The Protection of Coral Reefs As It Relates to The UN Secretary General Report.
D’Angelo, Cecilia, Benjamin CC Hume, John Burt, Edward G. Smith, Eric P. Achterberg, and Jörg Wiedenmann. “Local adaptation constrains the distribution potential of heat-tolerant Symbiodinium from the Persian/Arabian Gulf.” The ISME journal (2015).
Faxneld, Suzanne, Tove Lund Jörgensen, Ngai D. Nguyen, Magnus Nyström, and Michael Tedengren. “Differences in physiological response to increased seawater temperature in nearshore and offshore corals in northern Vietnam.”Marine environmental research 71, no. 3 (2011): 225-233.
Hume, B., C. D’angelo, J. Burt, A. C. Baker, Bernhard Riegl, and Joerg Wiedenmann. “Corals from the Persian/Arabian Gulf as models for thermotolerant reef-builders: prevalence of clade C3 Symbiodinium, host fluorescence and ex situ temperature tolerance.” Marine pollution bulletin 72, no. 2 (2013): 313-322.
Kenkel, C. D., G. Goodbody‐Gringley, D. Caillaud, S. W. Davies, E. Bartels, and M. V. Matz. “Evidence for a host role in thermotolerance divergence between populations of the mustard hill coral (Porites astreoides) from different reef environments.” Molecular ecology 22, no. 16 (2013): 4335-4348.
NOAA. “In What Types of Water Do Corals Live?” In What Types of Water Do Corals Live? Accessed May 22, 2016. http://oceanservice.noaa.gov/facts/coralwaters.html.