Is This Reef Dead? | The Denver Diver
A diver’s attempt to understand why familiar reefs increasingly look pale, brown and empty—and the living partnership hidden inside every coral colony.
Is this coral dead? THE DIVE ITSELF / CORAL REEFS What I Thought Bleaching Meant—and What I Had Wrong THE QUESTION: If bleaching is not warm water simply cooking coral to death, what are we actually seeing? Doomscrolling is never good for me. My wife Trista has pointed this out—more than once—with the weary patience of someone married to a man who reads bad news and then feels compelled to talk about it aloud. But when my brother CB recently sent Ella and me an article about coral reefs running out of time to recover, I had to read. Not to mention my daughter Ella was heading to Turks and Caicos to study the very questions I was reading about, I kept going. For once, the doomscrolling came with assigned reading. The story landed differently because I have already seen the change. I have surfaced from dives feeling sad even when the dive itself went perfectly well. The reef looked drained of color and life: white coral, brown growth, broken pieces and fewer of the small movements that make a reef feel busy. I could describe what I saw. I could not explain it. Everything simply looked dead. I thought the coral was being cooked I assumed coral bleaching was exactly what it sounded like: warming water was basically cooking the color—and eventually the life—out of the coral. Grim, certainly, but easy enough to understand. I had it wrong. Ella explained that coral is not a colorful underwater rock with an unfortunate sensitivity to warm baths. A coral colony is made of tiny animals called polyps. Most tropical reef-building corals live in partnership with microscopic photosynthetic algae inside their tissues. The coral gives the algae a protected place to live. The algae use sunlight to make food and supply much of the energy the coral needs. They also contribute to the colors we associate with a healthy reef. It is not decorative algae growing on the outside. It is a living partnership operating inside the coral. Bleaching is the partnership breaking down When prolonged heat stresses that partnership, the coral can lose many of its algae or their pigments. Because the coral’s living tissue is mostly transparent, the bright white calcium-carbonate skeleton underneath becomes visible. That is what we call bleaching. The coral has not necessarily been cooked to death. It has lost the partner responsible for much of its energy and is now trying to survive without its usual food supply. That is scientifically more accurate, although not especially comforting. If the heat eases soon enough, the algae can return and the colony may regain its color. If the stress continues, the coral can run short of energy, become more vulnerable to disease and eventually die. THE DISTINCTION ELLA TAUGHT ME: White may mean a coral is alive and severely stressed. Brown or green growth over its old shape may mean the living tissue is already gone. Why a reef can still look dead A reef is both a living community and a physical structure built over generations. After coral dies, its skeleton can remain standing. From a few feet away, the reef can keep its familiar branches, ledges and shapes. Up close, the living surface may be gone and algae may be moving in. We are looking at the architecture and assuming the building is still occupied. The reverse can also fool us. A shockingly white coral may still be alive. Color returning to one colony, however, is not the same as an entire reef recovering. The broader community may have lost living coral, young recruits, structural complexity, reproductive capacity or heat-sensitive species. The numbers matter because recovery needs time The Global Coral Reef Monitoring Network reports that satellite-observed sea-surface temperatures over coral reefs rose approximately 0.81°C between 1985 and 2025. Less than one degree sounds small because it would be small in my shower. Many reef-building corals already live close to their upper heat limits, so a modest increase in the baseline makes damaging heat events easier to reach. In many regions, major bleaching disturbances are now arriving roughly every four to six years. Research in Palau found that some coral communities needed at least nine to twelve disturbance-free years to recover after severe bleaching. That is the part I cannot shake: another punch can land before the reef has finished getting up from the last one. What this means for the dives we love Understanding the biology does not make a damaged reef less sad. It makes the sadness specific. I can begin to separate bleaching from death, standing skeleton from living coral, and one colony regaining color from an ecosystem truly recovering. It also explains why a familiar site can suddenly feel empty. When living coral and physical complexity decline, we lose color, texture and hiding places. Fish communities can change. The reef may retain its outline while losing much of what made it feel alive. A recreational diver cannot diagnose the health of an entire reef from one dive. Lighting, depth, species and local conditions can fool the eye. But we can learn to describe what we saw more carefully and ask better questions: Was there recent heat stress? Has bleaching or mortality been measured? Are young corals appearing? Is living coral cover returning? Why I am excited about Ella’s next chapter I can describe what a changing reef looks and feels like to a diver. Ella is learning how to investigate what is happening beneath that first impression. That is why I am so excited about her program in Turks and Caicos—and why I want the next article in this series to belong to her. Beginning this fall, Ella will spend 15 weeks at the School for Field Studies’ Center for Marine Resource Studies on South Caicos. The program combines classroom study with fieldwork in marine ecology and conservation. Students conduct coral and fish biodiversity transects, document bleaching and storm damage, analyze field data and complete directed research tied to local conservation priorities. When she has the time and field experience to answer in her own words, I want to hear what she observed, what her team measured, what surprised her and what genuine recovery looks like through the eyes of someone learning to study it. For now, I know this much: bleaching is not as simple as coral being cooked white. It is the collapse of a partnership—and whether that partnership can be restored may help determine what the reefs beneath our future dives will look like. Science trail The science is here for readers who want to go deeper; the story above remains grounded in what a diver can actually observe. Status of Coral Reefs of the World: 2025 — Global Coral Reef Monitoring Network / International Coral Reef Initiative. Daily Global 5km Satellite Coral Bleaching Heat Stress Monitoring — NOAA Coral Reef Watch. What is coral bleaching? — NOAA National Ocean Service. Drivers of recovery and reassembly of coral reef communities — Gouezo et al., Proceedings of the Royal Society B (2019). Marine Resource Studies — The School for Field Studies, Turks and Caicos Islands.
Home · Published articles
Enable JavaScript to use signup forms and interactive features.