Undersea canyons teeming with life
By Diana Leone
Advertiser Staff Writer
Undersea canyons surrounding Hawai'i appear to be "hot spots of biological diversity" that may serve as nurseries to replenish less abundant areas, Hawai'i researchers say.
Submarine canyons 1,000 to 5,000 feet deep support abundant fish, shrimp, crabs sea cucumbers and urchins, including 41 species not seen elsewhere in the Islands, according to a paper by University of Hawai'i-Mānoa and Hawai'i Pacific University scientists published in the March edition of Marine Ecology.
The article by Eric W. Vetter, Craig R. Smith and Fabio C. De Leo summarizes some of what the team learned from 36 submersible dives off the islands of O'ahu, Moloka'i, Nihoa and Maro Reef between 2003 and 2007. It was the first such study of Hawai'i's undersea canyons.
"What we found is these valley-like features underwater tend to concentrate nutrients" that originate from land or nearshore waters, said Vetter, an HPU marine biology professor. Nutrients from decaying leaves, wood, algae and even kukui nuts provide food for a variety of animals. Food sources are especially important in water deeper than light penetrates.
For instance, in one deep water canyon, the scientists "with sonar could see big tumbleweeds of algae rolling down the canyon," Vetter said. "It simply wasn't present outside the canyon."
Working inside the UH submersibles Pisces IV and Pisces V, the scientists brought chunks of fish as bait and watched as "clouds of shrimp came in," Vetter said. "There's an enormous abundance of life."
Vetter, the lead author, had previously studied sea canyons off the California coast. By comparison, Hawai'i's deep canyons do not have as much marine life, but they definitely have more abundance than surrounding Hawai'i waters, he said.
The difference is marked enough that Vetters, UH oceanography professor Smith and UH doctoral candidate De Leo recommend that undersea canyons be candidates for marine protected areas.
"These canyons are subsidizing the areas around them," Vetter said.
One of the surprises of the research was finding some species inside the narrow canyons — just 50 to 300 feet wide — that weren't present in the areas outside them, said Smith.
"Quite a few species are potentially new to science and many may well be endemic to canyons," Smith said.
The canyons were a mile to three miles offshore from the islands studied.
For his doctoral thesis, De Leo will continue to study the source of nutrients found in the canyons, tracing them back to land, nearshore or deep ocean sources using carbon and nitrogen isotopes.