Increasing Intensity and Duration of Coral Bleaching Events in the Eastern Pacific Ocean, Panama

Surviving the Coming Coral Reef Apocalypse

By Dr. Bill McGraw

Introduction

Coral reefs provide an estimated 10 trillion dollars to world economies primarily through fisheries and tourism. What may be more important is that although coral reefs cover 0.1 % of the total ocean surface area, at least 25% of fisheries depend on coral reefs for survival, with a billion people depending on them for their livelihood. Reports indicate that there are about 700 species of corals providing habitat for 4,000 species of fish. Coral reefs are incredibly important for the survival of most of humanity and yet they are the most understudied and underfunded areas of scientific research.

Coral reefs are predominantly composed of hard corals which consist of an internal coral skeleton made of calcium carbonate, which is 99% of their weight, and an outer thin layer of tissue. Corals exist in a symbiotic relationship with specialized colored algae called zooxanthellae embedded in the coral tissue. The thin living part of the coral provides a home for the algae while producing carbon dioxide that is absorbed as a food source, in turn, algae release sugars and proteins utilized by the coral tissue. Corals live as individual colonies of microscopic polyps arranged in diverse shapes due to calcium carbonate precipitation, which functions as an endoskeleton.

The History of the El Niño and Coral Bleaching

Currently, there are many threats to corals, yet periodic increasing ocean temperatures due to a change in ocean currents, known as El Niño, cause the most recognizable damage through a process called coral bleaching. Average global temperatures have increased by a factor of 7x from the period of 1980 to 2017, concurrently, with more severe rising ocean temperatures due to El Niño. Although the politically intense topic of global warming has many unproven possible causes, it has been established on a scientific basis that El Niño events are the primary cause of coral bleaching.

The relationship between corals and their algal counterparts is somewhat delicate. Coral bleaching causes the ejection of necessary algae known as zooxanthellae from the coral tissue due to temperature induced stress they experience from increased algal metabolism. In other words, corals need very specific algae for very specific ocean temperatures and if higher temperatures occur then more high temperature tolerant zooxanthellae are needed, and if these more tolerant zooxanthellae are not encountered and absorbed into the coral tissue, the coral will die. Corals depend on their algal symbionts for life and can only live without them for a maximum time of about one month.

Coral bleaching has increased in frequency, duration and intensity during the last 15 years, along with expected increases in ocean temperature. During the time before the 1980s coral bleaching events were rare, although El Niño events have been recorded since the year 1900 and occur with an average frequency between 2 and seven years, these periodic events were less severe.

Current More Intense El Niño Effects

During the most extreme Eastern Pacific Ocean bleaching event ever recorded during 2014-2017, about 80% of corals worldwide also experienced bleaching with 35% unable to recover from heat stress. Coral bleaching during 2014-2017 was named the 2nd biggest major worldwide bleaching event ever and the first that lasted more than one year. Previous yearly coral bleaching events described during 1998 and 2010 were much less destructive.

The corals of the Eastern Pacific Ocean off the coast of Panama have been reported to have endured some of the highest sea surface temperature changes. During the last major coral bleaching event in 2016, before the one happening currently, I documented the temperature changes in the Eastern Pacific Ocean that caused incredible color changes due to bleaching in corals at Seca Islands, Gulf of Chiriqui, Panama (https://coralreefs.org/wp-content/uploads/2019/01/Reef-Encounter-Dec-2016-LoRes.pdf). This area consists of a small archipelago of 16 islands in the Gulf of Chiriqui, Panama (Figure 1).

Although striking and odd shaped sponges found near and on coral reefs seem to thrive with the increase in sea temperatures (https://thefishsite.com/articles/how-sponges-adapt-to-climate-change), corals reefs suffer tremendous stress when sea temperatures increase as little as 1 oC. According to data I acquired from The Smithsonian Tropical Institute in Panama City, Panama, as well as NOAA, temperatures increased on average between 1.3 to 2.0 oC, down to an ocean depth of 18 meters during the period of August 2015 to February 2016. This caused tremendous color changes in the large boulder like corals, known as Porites, from the basic algal colors of yellow and minor amounts of purple to brilliant hues of blue, green and beige. Coral tissue ejected old algae and then accepted new ones of different colors (for photos see: https://coralreefs.org/wp-content/uploads/2019/01/Reef-Encounter-Dec-2016-LoRes.pdf). Corals have a limited time to accept new algae into their tissue or die, as algae leave the coral tissue others inhabit it, but not all at once which makes the algal transfer and potential survival of corals unpredictable. This chaotic algal exchange is incredibly obvious from observing the underwater photos near Seca Islands during the more recent coral bleaching event from 2023-2026, (Figures, 2-5) discussed below.

The El Niño of 2023-2026 will likely be one the strongest ever recorded. Increased ocean temperatures have caused major stress for corals, resulting in strange color anomalies and striations in Porites coral that have not been seen at Seca Islands during the last 15 years. Incredibly, coral bleaching is currently continuing with contiguous boulder corals showing remarkable color differences (Figures 6), while the more common branching coral Pocillopora having more regular brown/olive color with no evidence of bleaching for that species during the time the photos were taken. Although sea surface temperatures increased for an average of 2 oC during a 12-month period during 2016-2017, the El Niño during 2023-2024 showed a lesser increase of 1 to 2 oC, with thermal peaks more fragmented. This more minor temperature change did cause the more common branching coral to bleach the previous year as photos taken from nearby Coiba Island during May 2025 demonstrate (Figure 7). Some Porites corals were observed to be completely bleached during May 2025, while there was no bleaching of the common branching coral seen during the May 2026 excursion to Seca Islands, indicating they had recovered. All Porites corals at Seca Islands during May 2026 were observed to be in the process of algal exchange.

The Expected Outcome

Unfortunately, temperature stress has other ill effects on coral reefs besides disrupting the delicate relationship between coral tissue and their algal counterparts. Corals typically experience a decrease of 50% in reproduction rates as well as producing weaker sperm and smaller eggs during years of El Niño. During the past decade due to the increase in intensity and duration of El Niño years, it is likely that coral reef diversity and abundance will decline during the coming decade due to decreased success in reproduction and expected mortality from bleaching. More shocking is the fact that the El Niño effect is still continuing and currently 84% of all coral reefs are currently under heat stress (https://www.nesdis.noaa.gov/news/worlds-fourth-mass-coral-bleaching-event-likely-ended-2025).

According to NOAA El Niño prediction models, sea temperatures in the Gulf of Chiriqui will increase on average up to a record breaking 3 oC during the current El Niño, potentially resulting in catastrophic coral bleaching with likely major changes to many coral species. Many sources are already citing temperature increases in the Eastern Pacific Ocean to be the most intense ever experienced. Together with the unprecedented change in ocean currents in the Eastern Pacific Ocean off the coast of Panama (Unprecedented suppression of Panama’s Pacific upwelling in 2025 | PNAS), the current bleaching and the expected dismal rates of coral reproduction, the current continual El Niño event may be later categorized as apocalyptic.

It is unknown how corals will adapt and survive this never before experienced increase in temperature, likely creating never seen before changes in coral reef ecosystems. Current and future research needs to document these changes so that conservation efforts can focus on potential adaptation strategies that can be incorporated into conservation efforts for the survival of coral reefs.

Additional Sources of Information

https://www.mcgill.ca/newsroom/channels/news/why-some-coral-reefs-resist-bleaching-365721

https://www.nature.com/articles/s41467-025-67506-w

https://www.realclimate.org/index.php/archives/2017/11/el-nino-and-the-record-years-1998-and-2016/

https://sevenseasmedia.org/saving-coral-reefs-with-biosecure-zero-water-exchange-aquaculture/

https://www.youtube.com/watch?v=bizBpw6Wjes

Dr Bill McGraw is an independent scientific consultant and researcher who lives in Panama. He has spent decades studying coral reefs, zero water exchange aquaculture systems, scalar energy, ecology, alternative medicine and Rife technology. As almost all of the work published on coral reefs during the previous 20 years has been conducted on a volunteer basis, not associated with any university or organization, he requires donations to fund his current and future work. Monetary contributions can be sent through PayPal using the email address billmcgraw29@hotmail.com. He thanks all patrons who make the sacrifice to help continue his incredibly important work for the survival of future generations. Dr Bill can be contacted using drbillmcgraw@gmail.com, 507 6205-1605.