HPU Graduate Student
Rainforests are vital to our planet for many reasons, including the absorption of carbon dioxide that is critical to reducing climate change. However, there is another ecosystem in our oceans that holds even more carbon than rainforests—seagrass beds. In fact, one hectare (about 2.5 acres) of seagrass habitat absorbs almost three times more carbon than one hectare of rainforest.
In East Honolulu’s Maunalua Bay, the native Hawaiian seagrass Halophila hawaiiana once supported a rich community of species ranging from tiny sea snails to threatened sea turtles. But in the 1980’s the invasive alga Avrainvillea amadelpha, or leather mudweed, moved onto the bay’s reef flats. Forming thick mats that excluded native algae and seagrass, the invasive seaweed transformed the area from a healthy, mixed habitat to a mud flat.
Concerned about the problem and the future health of the bay, individuals and families that had lived in the area for generations formed the community group Mālama Maunalua, and in 2010 partnered with The Nature Conservancy and Pono Pacific to remove more than 27 acres of invasive algae. The project—which received $3.4 million in federal stimulus funds through the National Oceanic and Atmospheric Administration (NOAA)—uncovered large sandy areas that had once supported seagrass, clearing the way for Halophila to return.
To speed up that process, Amelia Murphy, a graduate student in marine science at Hawaiʻi Pacific University, recently took on the challenge of exploring ways to transplant the native seagrass into the newly cleared areas. The project was the subject of her Master’s thesis, with Dr. Dwayne Minton, science advisor for The Nature Conservancy of Hawaiʻi, serving on her committee.
According to Murphy, re-establishing the seagrass beds will not be easy. “Seagrass is very slow to recover due to its limited dispersal capabilities,” she explains. “Recovery to its former density could take decades, inhibiting the return of animals that rely on seagrass beds.”
For her research, Murphy attempted seagrass transplants using techniques that had been successful for other similar seagrass species—but the transplantations did not take. Realizing that not enough was known about Halophila, especially with regard to certain biological characteristics that would affect the transplantation process, Murphy looked into where growth occurred, how the seagrass responded to being cut, how cutting affected the rhizome (think of the rhizome as an under-the-sand runner, similar to how grass grows in your lawn), and where and how to collect and distribute transplants.
From what she learned, Murphy was able to propose a new approach for transplanting Halophila that she believes has a high likelihood of success. “Through trial and error, I am confident I have found a technique for transplanting that could help speed up its recovery in the bay,” she says.
Specifically, Murphy recommends the following:
• Do direct transplants with sea grass plugs instead of trying to propagate the sea grass in a laboratory first. Take a plug (seagrass and sand) from a natural bed and move it to a new location.
• Select a transplantation location carefully. The sand should be deep and the currents low. Transplants should be done on calm days so they aren’t washed away.
• Seagrass plugs should be as large as convenient and taken from the edge (not center) of an existing bed.
• If possible, put mesh down around the transplanted plug to reduce the chance of the sand washing away.
Mālama Maunalua is now looking at implementing Murphy’s transplant technique to encourage the return of the bay’s native seagrass meadows. In the meantime, volunteers, graduate students and staff from The Nature Conservancy and Mālama Maunalua continue to monitor the growth of seagrass and other native algal species, and the preliminary results are promising.
"Three years after clearing invasive algae, the native algal cover has exceeded that present before we cleared,” says Dr. Minton. “And we are also beginning to find more seagrass, but the natural recovery has been slow. Learning how to successfully transplant seagrass will speed the restoration of this area of Maunalua Bay.”September 02, 2013