At Jarvis Island the coral skeletons were still standing — but they were dead, and covered in pink calcareous algae. The 2015 El Niño had brought the largest warming event yet observed on a coral reef, and a catastrophic die-off. When NOAA divers returned, they swam the reef looking for juvenile corals growing among the remains, and swapped out a temperature logger that had been recording there for three years, through the warming.
That search was one stop on a two-and-a-half-month expedition by the NOAA Ship Hiʻialakai to the Pacific Remote Islands and American Samoa. NOAA scientists have surveyed Pacific coral reefs since the early 2000s, to learn how reefs vary from place to place and year to year — reefs that are packed with life and give millions of people coastal protection, food and livelihoods — and so to inform how they are managed.
Searching for new corals among the skeletons left by the 2015 die-off, Jarvis Island. (Photo: NOAA Fisheries, Courtney Couch and Brittany Huntington)
The route
| Leg | Stops | Along the way |
|---|---|---|
| 1 | Howland and Baker Islands, then Swains Island | 7 days' transit from Honolulu; a U.S. Fish and Wildlife Service team camped on Howland while the divers worked |
| 2 | Tutuila, Ofu and Olosega, Taʻu, Rose Atoll (American Samoa) | nine straight days of rain and wind, then sun |
| 3 | Jarvis Island, Palmyra Atoll, Kingman Reef (Line Islands) | 5 days from Tutuila to Jarvis; 14 diving days across the three |
Smooth sailing from Honolulu toward Howland Island. (Photo: NOAA Fisheries, Morgan Winston)
What a reef survey measures
- Pictures. Divers photograph the corals to assess the reef's health, and fly a camera rig over it to take hundreds of images that are stitched into a 3D model.
- Counts. Fish-team divers count and size every fish — hard work when a school of purple anthias hovers over the coral, or thousands of convict tangs cruise through the survey area.
- Measurements. Coral colonies are measured along a transect line, and a core drilled from a coral head carries a record of its history and, possibly, of ocean conditions over time.
- Water. Bottles of seawater show the ocean's dissolved inorganic carbon; instruments fixed above the reef track how the reef and the water's chemistry affect each other — knowledge that may help respond to local effects of ocean acidification.
- Heat. Temperature loggers at different depths show how heat exposure drives change in the reef community.
- The small things. Autonomous reef monitoring structures (ARMS) soak on the reef for three years, then come up full of crabs, snails, nudibranchs and shrimps.
Photographing the corals to assess reef health. (Photo: NOAA Fisheries, Louise Giuseffi)
Measuring coral colonies along a transect on Baker Island's reef slope. (Photo: NOAA Fisheries, Morgan Winston)
Extracting a core from a coral head. (Photo: NOAA Fisheries, Hannah Barkley)
A manta ray watches Ariel Halperin fly the camera rig for a 3D model, Jarvis Island. (Photo: NOAA Fisheries, Courtney Klepac)
A sample of the small animals found in the monitoring structures. (Photo: NOAA Fisheries, Evan Barba)
Who lives there
The reefs were busy. At Baker Island a school of black jacks swam through a field of branching Acropora corals; at Swains Island a curious young gray reef shark came in close during a fish count, and blackfin barracuda swarmed in daytime schools — unlike their relative the great barracuda, which cruises alone. Off Tutuila, young orangefin dascyllus sheltered in an anemone. Jewel damsels "farm" plots of algae and chase off other fish, and even divers. At Rose Atoll the reef is pink and purple with crustose coralline algae, which thrives there and can survive being exposed at low tide; blacktip reef sharks patrol the lagoon so shallow their fins show from shore. Off the west side of Taʻu, a giant coral head the scientists call "Big Momma" is estimated to be more than 750 years old. At Kingman Reef, giant clams crowd the shallow lagoon.
Black jacks over Acropora at Baker Island. (Photo: NOAA Fisheries, Jeffrey Milisen)
A juvenile gray reef shark at Swains Island. (Photo: NOAA Fisheries, Jeff Milisen)
Blackfin barracuda at Swains Island. (Photo: NOAA Fisheries, Jeff Milisen)
Crustose coralline algae at Rose Atoll. (Photo: NOAA Fisheries, Samantha Clements)
"Big Momma," off Taʻu. (Photo: NOAA Fisheries, Evan Barba)
Giant clams at Kingman Reef. (Photo: NOAA Fisheries, Ari Halperin)
Life aboard
Most of the diving is done from small boats, which the ship's davits lift back into their cradles to be locked down for the night; on one run the boat Metal Shark took the team into rough weather, rain showers and rainbows included. After an hour or so of surveying, every diver makes a safety stop — three minutes at 15 feet — to adjust to the change in pressure before surfacing. The expedition ended where it began, in Honolulu.
A safety stop off Tutuila. (Photo: NOAA Fisheries, Evan Barba)
The Hiʻialakai home in Honolulu. (Photo: NOAA Fisheries, Tomoko Acoba)
Sources
- NOAA Fisheries, Sea Tales of Deep Dives and Shallow Reefs.
Licence: CC0 1.0 (public domain) · Adapted from www.fisheries.noaa.gov
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