Although coral reefs have had periodic moments of distress and bleaching in the past, these events were frequently isolated to a given weather anomaly, most often El Nino. Unfortunately these events have become increasingly more common in the recent decade forming a troubling, yet predictable trend that can no longer be ignored. The importance of coral and the reefs they form cannot be understated; the mass death of coral will not simply increase the probability of oceanic bio-diversity loss, but rather guarantee its loss; a loss that will be a death knell for the oceans themselves.
It is important to understand the elements of the problem before suggesting a course of action. In large part coral is comprised of a colony of genetically identical polyps. After a significant amount of growth these polyps extend vertical calices that sometimes form a new basal plate; the formation of enough basal plates give rise to coral reefs. While coral can procreate either through asexual reproduction or sexual reproduction, sexual reproduction is typically favored. The release of gametes characterized by sexual reproduction fosters faster new colony construction whereas asexual reproduction typically strengths colony foundation and maintenance through coral head expansion.
Coral has the capacity to catch small animals like fish and plankton, but most coral have evolved to form a symbiotic relationship with zooxanthellae algae. This symbiotic relationship is why most coral are found in very shallow water (no less than 60 meters, but normally 2-10 meters) so that sunlight can be utilized by the zooxanthellae in order to undergo photosynthesis providing food for the algae and coral. Also while the calcium carbonate skeletons usually give coral a chalk white color on their own, their resident algae host a wide variety of colors which give coral its noteworthy color arrangement. Note that coral can also demonstrate a non-white color scheme on its own based on its protein synthesis pattern. Not all corals share a relationship with algae, but most of these non-algae coral specimens also do not commonly associate with reef formation and are typically found at much greater oceanic depths.
There are many different ways that coral can die, but the two reasons that seem to be the most associated with the recent bleaching trend are higher ocean temperatures and an increase in ocean acidity. Higher temperatures produce excess thermal stress on the coral which cause them to eject their algae in effort to reduce overall stress. While the algae has helpful attributes it also lives within the coral creating additional stress, thus when faced with a change in environmental conditions that increases stress further, the coral acts to lower stress to increase survival percentage and the easiest way to do that is to remove the algae. If the environmental change is only temporary then once environmental conditions return to ‘normal’ levels the coral typically reacquires the algae. Higher ocean acidity results in the inability of the coral to form and maintain their calcium carbonate exoskeletons lead to skeleton deformation and collapse. Coral responses to a reduced ability to form calcium carbonate structures is still unclear beyond the fact that such a situation eventually leads to premature coral death.
Unfortunately there appears that little can be done about increasing ocean acidity beyond dramatic reductions in human derived carbon emissions. One of the bigger problems with ocean acidity is that it is fairly uniformly distributed relative to ocean temperature (ocean temperature is important because the temperature of a liquid directly determines the solubility of a gas like CO2). Although an idea for a technological stop-gap for ocean acidity has been proposed on this blog here, addressing localized temperature flux may be a more effective strategy in the near-term if the goal is to increase coral lifespan within detrimental environmental conditions.
Local environmental cooling may be possible because of the natural uneven distribution in water temperatures relative to depth. Most of the threatened coral species are near the surface of the water exposed to higher temperatures than those creatures that live at a greater depth. Based on that principle if a device could be developed which could ferry water from a lower depth and deposit it closer to coral reefs cooling the region near the coral could be possible. Note that because the colder deep water would not be able to effectively mix with the warmer surface water the overall system could be thought of as similar to a fountain. Water is pumped up from a specific depth and then that water is released near the surface in close proximity to the coral reef where conduction briefly lowers the surface water temperature before the water descends once again.
One possible design for such a device could be to develop a buoy which would float on the surface of the water almost directly above the coral bed. Within the base structure of the buoy would be a pump and associated tubing that descends about 800 ft. below the surface. The reason 800 ft is selected is to focus on water collection beyond the thermocline ensuring a significant temperature differential between the collected water and the water surrounding the coral. Water would be pumped up to the buoy where it would be released back into the water near the surface. The release methodology should probably favor sparse droplets instead of a stream to avoid unnecessary damage to the coral due to excess water pressure/force. Power could be provided to the pump and any other electrical elements through a solar power panel and lithium-ion battery storage.
The biggest problem with this strategy is that a huge volume of water will need to be displaced to generate any significant cooling. At first glace the difference in total volume of displacement seems insurmountable, but the continued incessant movement of water over the course of months and on into years could generate a meaningful change. Remember that the purpose of this device is not to regionally eliminate the temperature increases threatening the coral, but slow the increase to buy time for humans to reduce carbon emissions and positively reverse the ocean from a sink to a source temporarily (over a few decades) returning ocean CO2 load to recent generational normalcy (CO2 concentration in the 1700s). A useful attribute of this system is that it is testable, especially in conjunction in the Argo float systems, can be isolated to a single environment without damaging other non-related environments and does not require any special systems.
While determining an exact price for a single system is difficult, estimation of cost seems to be reasonable. The overall pressure change between the surface of the water and the final location of the pipe at 800 ft. should be about 352.8 psi, which is not so excessive that a special material will be required. However, it may be necessary to include some form of filter on the receiving end of the tube to prevent certain lifeforms from clogging the tube and/or killing those lifeforms. As previously mentioned, the release end of the tube would probably have some form of spray attachment to break the water stream up into droplets. The solar cell/photovoltaic system only has to power a single pump plus any other necessary electronics to draw up the water, so it would probably be smaller than the ‘for home use’ systems that are currently available. Finally the battery is probably the most expensive addition to the standard buoy, but one could state that with the coming popularization of electrical vehicles, battery prices should drop slightly reducing the overall cost of lithium-ion batteries for other devices such as this one.
In closing whether or not the above system is effective at reducing local water temperatures to theoretically increase coral survival time is not the main issue. Although it would be excellent if it did, the overall point is the realization that human effort to curtail carbon emissions is not progressing faster enough to have any real level of confidence that a vast majority of coral will survive the coming decades. To save the coral it is becoming more probable that humans will have to deploy a non-emission reduction strategy. While it is not guaranteed, such a strategy will probably involve some form of technological intervention, so it is important to begin with both the research and the testing as soon as possible.