Submarine canyons play an important role in maintaining high levels of biodiversity of small invertebrates in the seafloor sediments of the main and northwestern Hawaiian Islands, according to research from the University of Hawaiʻi at Mānoa.
What’s more, scientists have used this data to draw new connections between the levels of faunal diversity and the heterogeneity of submarine canyon landscapes at various spatial scales.
“Submarine canyons encompass myriad habitat types,” said Fabio C. De Leo, a doctoral graduate from UH Mānoa’s Department of Oceanography and the lead author on a new paper that was recently published in the scientific journal Deep Sea Research Part II. “This heterogeneity at the landscape-scale helps to enhance local biodiversity in canyon seafloor sediments.”
De Leo and colleagues, including Oceanography Professor Craig Smith, the study’s principal investigator, conducted 34 submersible dives into six underwater canyons and their nearby slopes. Plumbing depths of up to 1,500 meters (~5,000 feet), their study area ranged across the Hawaiian archipelago, from the main Hawaiian Islands through Papahānaumokuākea Marine National Monument in the Northwestern Hawaiian Islands.
The scientists evaluated and mapped landscape metrics of each canyon habitat, including the roughness of the seafloor and the steepness of canyon walls. At depths of 350, 650, and 1,000 meters in each location, they collected sediment core samples on the canyon floor.
They found that submarine canyons can serve as species oases in the sea by channeling ocean currents, capturing and trapping sinking particles, funneling migrating animals, and generally providing a varied physical landscape. As a result, canyons promote high species diversity.
Researchers say this is the first study of its kind to thoroughly examine submarine canyons on island margins. The research effort had previously yielded reports of high species diversity of fish and large invertebrates, the so-called megafauna, in Hawaiʻi’s submarine canyons. This corroboration led them to conclude: “Canyons may be particularly important in the Hawaiian islands, in part because they supply organic matter to the typically food-limited deep sea,” De Leo said. “When there’s more food, there’s more life.”
The scientists have already documented four new species discovered during the course of their research dives, including three new types of crustaceans. Up to 60 percent of the species that taxonomists identified in the submarine canyon seafloor samples are only recognized to the family level.
“There is room for discovery of many more new species,” De Leo said. “The deep sea fauna of Hawaiʻi is poorly sampled and poorly understood. Every time we go to sea and sample a new area, it’s likely that we’ll find a new species.”