Deep-water Macroalgal and Seagrass Assemblages

Entry from September 6

News Release-

Exploring Hawaii's Deep-water Limu Scientists at the University of Hawaii Botany Department are using a research submersible to explore the waters off O`ahu, Moloka`i, Maui, and Kaho`olawe for limu (seaweed) in deep-water.

Limu grow wherever there is sunlight. However, in places where sunlight can penetrate beyond the normal depth range of SCUBA diving, marine botanists need to use other tools to reach these rarely encountered plants. Two graduate students from Celia Smith's laboratory are following the limu to the edges of their depth distribution using both closed circuit rebreathers and the Hawaii Underwater Research Laboratory's Pisces V submersible to answer their research questions.

"Limu research in Hawaii began when Hawaiians developed an appreciation, as well as a taste, for these marine plants. While scientists have been working to extend this knowledge for over 160 years in Hawaii, we never seem to be at loss for new discoveries," Dr. Smith commented.

On Friday, the graduate students, Heather Spalding and Kim Peyton, made their first submersible dive off Ewa Beach. Starting at depths deeper than sunlight can penetrate, the research team ascended the sandy slopes of south O`ahu. To their amazement, extensive underwater meadows appeared on an otherwise featureless sandy bottom by a limu never previously reported in Hawaii. "This is probably a species in the green algae genus Udotea," Heather Spalding reports, "We did not even know this genus occurred in Hawaii until finding it on this dive; it may be a new species. However at depths of 60 to 90 meters it is common, forming extensive meadows with hundreds of small fish darting in and out of its 8- to 12-inch tall canopy. Some of these fish may be new species to science as well."

As the submersible worked its way along a predetermined course, a second species of seaweed started to occur, intermingling with the newly discovered limu. "Every biologist gets a rush of excitement when they encounter their study organism in a new setting. There is so much you can learn when that happens. Of course when you work with invasive species your excitement is tempered a bit because you are finding them in new habitats," Kim Peyton said. The invasive alga nicknamed the leather mudweed, Avrainvillea amadelpha, already under study by K. Peyton because it is wrecking havoc on O`ahu's seagrass beds, is also associating itself with extensive meadows of the newly discovered limu, Udotea.

H. Spalding and K. Peyton will return to their new study site off Ewa Beach with closed circuit rebreathers because the shallower portions of this sandy plain are accessible using decompression diving and a few ichthyologists can join them. Using the submersible Pisces V piloted by the 25 year veteran Terry Kerby, these botanists are mapping the depth distribution of native limu, invasive seaweed and the fish and invertebrate communities associated with these deep-water plants.