GARDNER PINNACLES — Although both are constantly present, aggressive ulua have been a bigger problem than sharks for the 20-member marine science team on this research trip to Northwestern islands.

On their first dive at the Garden Pinnacles, the scientists had to use spears repeatedly to fend off attacks by the ulua.

The aggressive behavior from the big predatory fish came a day after an ulua took a research diver's hand in its mouth at French Frigate Shoals, leaving cuts and scratches.

So far, the sharks have been curious and close, but no attacks in the first week of this 25-day trip to explore the Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve. The area is being considered for designation as a national marine sanctuary.

The research team, which is conducting some of the basic scientific investigation intended to support sanctuary designation, is traveling aboard the NOAA research vessel Hi'ialakai.

While the attack at French Frigate Shoals was on a diver collecting coral samples, divers most affected at Gardner were collecting reef fish for genetic studies. The ulua, some of them huge, seemed to be attracted to the fish in the collection bags.

"(Ulua) came at me four or five times in rapid succession, then it came at me again. I think it was on Randy (Kosaki, the cruise chief scientist) more than on me," said researcher Brian Bowen.

Fellow diver Jill Zamzow snapped a photo of Bowen, holding his spear like a lance to keep the 4-foot, roughly 100-pound ulua away.

Marine biologist Luiz Rocha said three or four big ulua tried for his fish bag. One got through his defenses and snapped at his midsection. There were no injuries to the divers.

Sharks were present, too, mainly Galapagos and gray reefs, constantly patrolling around where divers were collecting corals, invertebrates like crabs, and select reef fishes.

There's not much to tiny 5-acre Gardner. It has two rocks, one a rugged pyramid and the other a smaller stack of basalt.

Gardner is the last bit of volcanic rock to pierce the surface in the Hawaiian archipelago. It lies between French Frigate Shoals and Maro Reef in the Northwestern Hawaiian Islands. It has weathered down from a much larger island to just these monoliths, and the weathering has given them many faces.

From one angle, it looks just like an 'opihi clinging to the surface of the ocean. From another, a turtle chugging across the sea. In its cliffs and slopes are skulls and lions, and one view is the spitting image of a Rapa Nui moai, one of the Easter Island stone statues.

Scientists are a little in awe of the isolation, and the risk.

"We're diving on these rocks standing out in the middle of the Pacific Ocean," said coral researcher Stephen Karl.

The islands are so small that waves and winds whip right around them, providing little shelter for boats and divers.

"People think of the Northwestern Hawaiian Islands, they think of a kind of paradise. But some of it is elemental to the point of being dangerous," Bowen said.

"I'm always amazed that they (marine plants and creatures) can get here, that they can find it. Of course, that's one of the big mysteries we're trying to solve."

For both Karl and Bowen, it was the first time diving at Gardner.

"I thought it would be more lush than it was. There were a lot of bare rocks," Karl said.

Bowen noted a large number of plant-eating fishes, which he said may be a function of the seabird droppings on the top of the island running down the sides in rainfalls and fertilizing a dense lawn of algae.

"Here and at Nihoa, I noted a dominance of grazers, especially the surgeon fishes. It's got to be a direct link to the guano," he said.

Coral researcher Greta Aeby, who has dived at Gardner before, said there is comparatively little coral, in part because the island is exposed to the tremendous power of North Pacific storms, which wipe out all but the hardiest corals. But there are lots of big boulders around the island.

"Boulders provide habitat that the corals would provide in a normal Northwestern Hawaiian Islands environment," Aeby said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.