One Reef, Two Weeks Apart: What Hurricane Lowell Left Behind
In September 2026, Hurricane Lowell sent a powerful swell across Hawaiʻi’s shoreline. On one reef we had surveyed in detail just two weeks earlier, 125 of the 145 coral colonies we had mapped were gone when we returned.
The viewers below let you see that change for yourself. Each one shows the same patch of seafloor, photographed on 31 August and again on 16 September 2026, lined up so the two dates sit exactly on top of each other.
The Reef’s Densest Corner
The second viewer zooms into a 5 by 4 meter corner of the plot, marked on the small map in its top corner. This corner held 81 of the 145 colonies we mapped: more than half the plot’s coral, packed into about a seventh of its area.
It was also where the losses were heaviest. Of those 81 colonies, 6 remain in place: 2 of 18 branching corals and 4 of 63 mounding corals. Zoom in and you can see clusters of lobed mounding corals and finger-like branching corals that are simply no longer there.
One area here was a dense mat of small mounding colonies growing too close together to outline one by one. It is shown as a single outlined patch, so the true number of colonies lost in this corner is higher than the count shows.
Why These Corals Matter
Coral reefs are built slowly by living colonies, and they give a great deal back. They break incoming waves before they reach the shore, shelter the fish and invertebrates that feed island communities, and hold deep cultural meaning in Hawaiʻi.
The two kinds of coral highlighted here grow, and break, in different ways:
- Branching corals grow as clusters of short branches or fingers, such as cauliflower coral. They grow relatively quickly and create sheltered spaces for small fish, but their branches snap easily in heavy surf.
- Mounding corals grow as solid lobes and domes, such as lobe coral. They are sturdier but grow slowly, often a centimeter or so a year, so a large mound can represent decades of growth.
Losing both at once means losing the reef’s fast-growing shelter and its slow-built foundation together.
How The Imagery Was Made
Each image is an orthomosaic: a single, map-accurate picture of the seafloor stitched together from hundreds of overlapping underwater photographs. Software matches features across the photos to rebuild the reef in 3D, then produces a top-down view in which every pixel sits at its true position.
Both surveys were processed onto the same map grid, so the before and after images line up to within a few centimeters. The versions shown here are at 2 millimeters per pixel, sharp enough to see the outline of individual coral colonies.
To map the corals, each colony in the before image was located and outlined, then labeled as branching or mounding. Each one was then checked against the after image and marked as still in place or gone. Our team reviewed and corrected these outlines by hand. Colonies smaller than a few centimeters were not counted, so the true totals are likely higher.
What Happens Next
This reef is part of an emergency response led by the Restore with Resilience partnership: Ocean Alliance Project, Mālama Maunalua, and Protect and Preserve HI. The work has three stages:
- Assess the damage. Survey the wider area to understand how far the losses extend.
- Restore quickly. Stabilize and replant surviving coral fragments before they are lost too.
- Monitor the recovery. Return to the same plot over the coming years to track how the reef responds to restoration.
Few reefs are ever surveyed this closely both before and after a major storm. By continuing to monitor this site, we hope to learn what restoration approaches work best after a disaster, so that communities can respond faster and more effectively when the next one comes.