Preventing Ecosystem Collapse: Caribbean Coral Reefs

What’s Natural ?

Guest post by Jim Steele

Media headlines have been promoting unrealistic fears of ecosystem collapse due to climate change. Such fears get supported when the International Union for the Conservation of Nature (IUCN) designates some ecosystems as endangered, such as Caribbean Coral Reefs. But reefs are resilient and the human factors threatening individual reefs can be remedied.

The Caribbean reef ecosystem consists of thousands of individual reefs spanning from the east coast of Mexico and Central America to Florida and the Bahamas and south to the coast of Venezuela. Fifteen thousand years ago these reefs did not exist because sea level had fallen by 400 feet during the ice age. Modern reefs became established 8,000 years ago by colonizing newly flooded coastlines.

Based on one IUCN criterion the Caribbean reef ecosystem was designated “Least Concern” due to the widespread occurrence of individual reefs. In contrast, the loss of 59% of total coral cover between 1971 and 2006 prompted the IUCN to designate the reef system as “Endangered”.

Coral cover naturally fluctuates with seaweeds (macro-algae). Coral are killed by hurricanes, disease or bleaching,  which allows seaweeds too colonize the vacated space. The seaweed is gradually reduced by algae-eating animals which allows coral to return to their former dominance. Coral usually recover within 15 to 20 years, but recently their recovery has been extremely limited thus reducing coral cover. Unlike the demonized sea urchins that threaten Alaska’s kelp forest, algae-eating urchins are vitally important in maintaining the balance between seaweeds and Caribbean coral. The recent lack of coral recovery is largely attributed to a new disease that devastated urchin populations in the 1980s and minimized the urchins’ consumption of seaweeds.

Caribbean corals had been decimated in the 1980s by the novel White Band disease. However, that disease only affected two coral species from the genus Acropora – staghorn and elkhorn coral. Those species are now considered endangered. Acropora’s evolutionary strategy was to quickly colonize vacated shores produced by natural disturbances like hurricanes. These coral species thus dedicated their energy to rapid growth to out compete the seaweeds. That adaptation allowed staghorn and elkhorn coral to rapidly colonize flooded coasts as sea level recovered from the last Ice Age and dominate modern Caribbean reefs. But that strategy required diverting energy from building stronger reefs or resisting disease.  

Because Acropora require shallow habitat they’re vulnerable to storm damage. So, they evolved a reproductive strategy that produced new colonies by cloning new coral from storm damaged fragments. However, cloning reduces genetic diversity which also made them more vulnerable to new diseases.

Mortality from bleaching also reduced coral cover. Bleaching from unusually warm temperatures during summer 2005 and the 1998 El Nino is often highlighted. Surprisingly, fatal cold weather bleaching is rarely mentioned. Yet in January 2010 along the Florida Keys, cold weather killed 11.5 percent of the coral, which was 20 times worse than the 2005 warm weather mortality. Understanding why both warm and cold weather causes bleaching provides insight into how coral have successfully adapted to ever changing climates over the past 220 million years.

Shallow water corals depend on photosynthesizing symbiotic algae (aka symbionts) that provide over 90% of the coral’s energy. However, those corals will remove one symbiont species and acquire a new symbiont that is better adapted to the changing weather conditions. During the winter, colder temperatures and less light reduce photosynthesis. So, coral increase their density of symbiotic algae to counteract reduced productivity. But if it is too cold, the symbionts keep their energy supply for themselves. As a result, coral remove the “freeloaders” causing bleaching. A more productive cold‑tolerant symbiont must then be acquired, or the coral die.

In contrast during the summer, more light and higher temperatures produce so much energy, coral reduce their number of symbionts. Because photosynthesis also produces potentially harmful chemical by-products, coral remove symbionts to reduce the production of harmful chemicals. That too causes coral to bleach, and unless a better adapted symbiont is  acquired, the coral will die. Despite that mortality risk, research now shows by switching their symbionts, coral can quickly adapt to warmer or cooler climates and enhance the species survival.

Studying fossil reefs, scientists determined that Caribbean corals had been declining decades before widespread bleaching and disease outbreaks occurred. Growing human populations cleared the land for farms, sugarcane and banana plantations. Resulting soil runoff reduced water clarity required for efficient photosynthesis. Increased sewage also reduced clarity and introduced pathogens. Those stressors made coral more susceptible to subsequent bleaching and disease. Soil runoff also added nutrients that tipped the ecological balance to favor seaweed growth, while overfishing removed seaweed‑eating fish that once restricted seaweed dominance.

We can, and are controlling soil runoff and treating sewage. Fishing regulations are restoring the ecosystem that had balanced seaweeds and coral. And with those protections, naturally resilient coral will steadily recover.

Jim Steele is Director emeritus of San Francisco State’s Sierra Nevada Field Campus,

authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism,

and a member of the CO2 Coalition

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Ron Long
December 18, 2020 2:50 am

Good report, Jim Steele. In the mid-to-late 1970´s Exxon Research noticed that seismic profiles from around the world, when age of sedimentary rocks is same, matched surprisingly well. They correctly interpreted this to mean that there were large movements in sea level, and Sequence Stratigraphy was born. So when the sea level was 400 feet lower in the Carribbean 15,000 years ago, the corals were not gone they had migrated some distance away to maintain the water depth they prefer, usually quite shallow. Geologists at all oil exploration companies now utilize Sequence Stratigraphy (I am certified and experienced in the discipline and use it for migrating redbed zones for copper/vanadium/cobalt/uranium exploration), and these geologists look at the claims of CAGW with a mixture of amusement and disgust.

Ian Miller
December 18, 2020 4:12 am

We are custodians of the reef and as Jim eludes, good management of reef ecosystems leads to good outcomes.

Mickey Reno
December 18, 2020 5:35 am

Jim Steele, great article, as usual. If only Michael Mann, Kevin Trenberth, Ben Santer, Josh Willis, and all those rummies at UEA-CRU had had you (or someone like you) for their undergraduate and graduate advisor. SIGH

Gary Pearse
Reply to  Mickey Reno
December 18, 2020 7:14 am

Jim Steele is a gifted honest teacher and a superb writer. I had long ago given up reading ecological/biological articles because of the heavy misanthropic angle that most perpetrate. This discipline is perhaps the most interesting of all, but it has been so severely corrupted by activist politics (eg. Paul Ehrlich and other lefty haters of the human race with their end-of-world bs) that I was suspicious that the science was bent to make ugly points (the polar bear commissariat and coral reef harangers are the worst in this regard).

I have no problem with honest assessments that human activity may be impacting ecologies and that changes may need to be made, but prescribing a new Dark Ages is more than extreme.

Thank you Jim for making the natural world readable and educational again. I think you would have a winner with a series of popular-style books surveying the natural world’s habitats and its creatures.

Reply to  Gary Pearse
December 18, 2020 4:51 pm

Thank you

December 18, 2020 5:44 am

Yet in January 2010 along the Florida Keys, cold weather killed 11.5 percent of the coral

….yep, we recorded water temps on the reefs right at 50F

BTW, it’s not called cloning…it’s fragging….rubble

December 18, 2020 7:10 am

Indeed an excellent article. As a first-hand witness to their demise, I do know that the Caribbean reefs do not suffer from a problem that cannot be remedied by simply reducing sediment/nutrient loads and prohibiting all demersal and shark fisheries for at least 10 years.

The former is straightforward but the latter will require convincing many locals to use alternative sources of protein and help the fishermen to seek alternative sources of income.

December 18, 2020 10:05 am

If we really wanted to understand how resilient coral reefs are, there would be legions of researchers poring over the Bikini Island lagoon, whose coral reefs were totally obliterated by atomic bomb testing as recently as the 1950s.

Since then, these reefs have totally re-established themselves back to their former glory, without any “management” from humans.

(on second thoughts about researchers poring over these corals, why don’t we just leave them to their own devices – they clearly know what they’re doing)

Andy Pattullo
December 18, 2020 10:21 am

Excellent and very educational summary. Many thanks.

December 18, 2020 11:28 am

Good article. Enjoyed reading it. But the photo accompanying the article was taken in the South Pacific not the Caribbean. Those are not Caribbean corals or fish.

Reply to  StevenF
December 18, 2020 11:39 am

My bad. I had simply googled ” .gov Caribbean coral reef ” figuring images from government sites had no copyright issues and that was one of the first 10 images.

December 18, 2020 1:36 pm

In recent years (2011-2019) there has been a colossal “bloom” of seaweed from the Caribbean to west Africa. Now this is hardly unprecedented given that this part of the ocean is called the Sargasso Sea.

What is the impact of this big increase in seaweed volume? Have coral communities been fouled by it?

People have attributed this seaweed bloom to increased nutrient discharge from Amazon alongside increased nutrient upwelling on Africa’s west coast. This upwelling is likely the dominant reason as the surface cooling it has caused is also a factor favouring increase volume of floating seaweed.

December 18, 2020 2:32 pm

Jim Steele has become my favorite writer in 2020. Every article is a must read that checks all the boxes of great writing.

  • Thought-provoking
  • Timely
  • Enlightening
  • Accurate
  • Nonpolitical
  • Authoritative

I always learn so much from Jim’s cogent articles as they put important issues in the proper scientific perspective.
Thank you Jim Steele, the extensive knowledge you share is greatly appreciated. Wishing you and everyone in WUWT community a great 2021!

Reply to  Eisenhower
December 18, 2020 4:50 pm

Thank you Eisenhower. You made my day!

Duncan MacKenzie
December 18, 2020 6:11 pm

When I was snorkeling around some Caribbean islands in the 90’s and was dismayed by all the bone-white coral, the locals put the blame squarely on motorboats; the concussive effect of the propellers, and the pollutants spewed into the water instead of the air. In Indonesia the dead coral around the gilis was blamed on fishing with dynamite, but that may have been local humor. I do remember one island off the coast of Flores with the most beautiful coral I’ve ever seen – denser than any aquarium, full of sealife. Locals attributed the health of that reef to strong safeguards against any boats coming anywhere near the coral. – the only dock was 100 yards offshore, a mile or more down-current from the reef.

So, are motorboats not to blame anymore?

Reply to  Duncan MacKenzie
December 18, 2020 7:49 pm

Dynamite fishing was a big one. I made a Cousteau short about it.

Last edited 2 years ago by Charles Rotter
December 18, 2020 9:13 pm

Coral islands are made out of dead coral, its not like they never died before mankind was around….a percentage of them grows too tall, and sunshine, low tide, and storm surge takes a toll every year, every “nino”, even every tide….

Duncan MacKenzie
Reply to  DMacKenzie
December 18, 2020 11:49 pm

Totally not me.

Willis Eschenbach has described convincingly on this site how atoll heights are determined by wind and parrotfish. Was pretty convincing to me, anyway.

Reply to  Duncan MacKenzie
December 19, 2020 12:54 am

We have two D MackEnzies, Duncan. He’s not spoofing you. He’s had over a thousand comments.

Chauncey Chapman
December 19, 2020 6:34 am

Mostly spot on, but seems to minimise the 1983 near-extinction event, 98% of all Diadema antillarum died in about 1 year, from Bermuda to Brazil the keystone species population was decimated. The long spine black sea urchin was the principal algae control mechanism on the coral reefs. ( Diadema is a non-discriminate algae eater, they effectively kept the reefs clean, produced astronomical numbers of larvae which the coral feed on, and cleaned the substrate for larval implement. With the Diadema population reduced to ineffective levels macro algae successfully competed with the coral for sunlight, killing the coral and over growing the coral skeleton. What was a majestic coral structure in up until the 1983 die off became a cabbage covered mound.

Last edited 2 years ago by Chauncey Chapman
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