Reefs go through daily, tidal, and seasonal temperature changes. Different parts of a reef vary in their resilience. But the great warming may blow all of this away. That section of a reef that does better because of its proximity to the deep water (colder) channel will still die-off if the colder waters of the channel are no longer cold. That reef systems that can deal with extreme temperatures that occur 3-6 days each year, will not do so well when those extremes are reached 13-16 days each year, and they will then die-off completely when those temps are reached 23 -26 days each year.
Will they move north? Will they move north quickly enough? Can we help them move north?
The adults coral do not move, of course. But the next generation of a species of coral could be in a different place because the larvae spent time as plankton, and they settle out away from the parent coral. Whether coral reefs will survive might have to do with if these coral, generation by generation, can spread out from their current locales, fast enough.
Time as plankton:
The key to this is whether their larval survive for long periods as plankton, allowing them to settle far from their current location. Some species can spent a long time in the plankton. Acropora species (staghorn and elkhorn corals) and Orbicella faveolata (Mountainous Star Coral), two reef building species, spent up to 83 days as plankton.It turns out that many might not be viable after that extended period, viability likely decreases with time spent in plankton.
Let’s help them.
Is it possible to start a coral reef in colder waters, but water that might not be very cold for very much longer. What would we need to know to make this happen?
What coral can survive in cooler temps, or at wider temp ranges.
Species, and individuals, that can survive warmer temperatures have been detected, in Kiribati for example. This may allow survival of tropical coral reefs, and allow transplantation of reefs in the tropics. But rather than look at what species can survive warmer temps, to spread coral north or south of the tropics, we want to look at species that can survive cooler temps.
Cooler temps mean slower growing, so these reef systems may take many year to become established.
In the northern climes there are coral reefs. We are just becoming aware of deep water reefs as far north as the arctic, another blog of these soon, but these species are not going to replace the current tropical reef systems.
So we need to:
- ID corals that can live in cooler waters, or a broad range.
- These coral should be reef builders, that is hard corals that start building the structures that so many other organisms rely on.
Acropora and Porites species (staghorn/elkhorn, and finger corals) have a wide temperature tolerance: A problem here is that studies are testing their warmer water tolerance not colder water tolerance. These genera are found all over the tropical regions of the planet. Just observation is a testament to their ability to survive broad temperature ranges. In the Pacific corals Pocillopora (bush corals or cauliflower corals), have a wide tolerance.
Okay, this might be as easy as I first thought. It turns out that temperature tolerance can vary among populations of the same species. As I ponder this, this might make things easier. Just pick a species and go for it. It’s all a big experiment anyway.
3. Determine what helps coral survive transplantation?We know this, artificial reefs: These help coral become established. Let’s create artificial reefs systems, especially for coral settlement, on the US east coast these should run as far North as Cape Cod (say about 41 degrees North). Currently tropical reefs only extend to about 30 degrees North.
4. Seed the fake reefs with coral larvae.
FYI, corals do not do well in regions where large amounts of freshwater are dumped into the system. So we can avoid creating artificial reefs and transplanting corals, around large river mouths.
What about the dangers?
Oh yeah, this will mess everything up. Corals moving north along the Japanese coast have already disrupted algae beds, and the host of organisms that rely on them. But, I don’t care, I want to snorkel among the coral reefs in Maine, dammit. Let’s start Coral reefs to the North. “Welcome to Bar Harbor, to the left of the shipping channel is the Coral Gardens.”
Further Readings:
Jurriaans S, Hoogenboom MO. 2019 Thermal performance of scleractinian corals along a latitudinal gradient on the Great Barrier Reef. Phil. Trans. R. Soc. B 374: 20180546.
Miller MW, Bright AJ, Pausch RE, Williams DE. 2020. Larval longevity and competency patterns of Caribbean reef-building corals. PeerJ 8:e9705.
Potts DC, and Swart PK. 1983. Water temperature as an indictor of environmental variability on a coral reef. Limnology and Oceanography. 29: 504-516