Kaneohe turtles devour alien seaweed species


POSTED: Monday, April 20, 2009

Usually the only time seaweed gets my undivided attention is when I'm swimming and a piece touches my skin. I jump like I've been attacked, and when I see what it was—oh, just seaweed—I move on.

Then last week I read a new study about seaweed as turtle food, and these marine plants grabbed my attention. Researchers report in Pacific Science that the top three seaweeds Kaneohe Bay's honu (green sea turtles) eat are alien species.

The scientific names of the three seaweeds were listed along with the other 127 plants found in the study of turtles' crops, but they didn't mean much to me. I had to match the Latin words with pictures and when I did, I found I know these seaweeds. I just didn't know their names or that they weren't native.

This 28-year-long honu study was conducted in the Kaneohe Bay area from 1977 to 2005. During that time, researchers collected and analyzed the crop contents of 372 green turtles that died in or near the bay, an average of about 12 per year.

Turtles eat seaweed by biting off fairly uniform-sized pieces and then squeeze the water out by pressing the pieces against the roof of their mouths. After the turtle swallows, the plant bits go into the crop, a pouch in the esophagus. Researchers examined crop contents under a microscope to see what the turtles ate.

Number one is Acanthophora spicifera, also called spiny seaweed. This was accidentally brought to Hawaii from Guam in the 1940s or '50s, likely on a barge. Now spiny seaweed is the most widespread and successful alien algae in Hawaii. This highly adaptable marine plant is common throughout the warm waters of the world.

Our turtles love it. Sixty-four percent (237) of the study turtles ate spiny seaweed.

The turtles' second favorite is Hypnea musciformis, no common name. People brought this seaweed to Kaneohe Bay from Florida in 1974 to cultivate for food and as a thickener in ice cream, toothpaste, shampoo and more. The seaweed spread quickly to other islands.

Forty-one percent (154) of the study turtles had this one in their crops.

The third alien seaweed our turtles like is Gacilaria salicornia. This was first found in Hilo Bay in 1971 and was brought to Oahu in 1978. Some people eat it for its crunchiness. It's sold as robusta on Oahu.

The honu like it, too. Thirty-seven percent (138) of the examined turtles ate this seaweed.

The recovery of Hawaii's turtles since 1971 is the result of laws protecting them and researchers learning what turtles need to survive. It's also due to the turtles themselves. They found something new in their territory, ate it and thrived.

This speaks to the adaptability of these remarkable reptiles, and also to the potential value of alien species. Introduced plants and animals often aren't good for the environment, but neither are they always bad.

Unless we're mistaking them for creatures that bite, seaweeds don't spark the imagination like seaweed eaters do. But plants are the first link in the marine food chain and are, therefore, the basis of all life in the ocean.

Hawaii's seaweeds, both native and introduced, deserve respect. I just wish they had easier names.

You can match local seaweed names with pictures at www.hawaii.edu/reefalgae/natives/sgfieldguide.htm.

Susan Scott can be reached at www.susanscott.net.