Posted on: Monday, June 13, 2005
 |
By Jan TenBruggencate
Advertiser Science Writer
On the rocks and shelves of the Hawaiian seashore, there apparently is a supportive relationship between two animals that you might think would compete.
The animals are the 'opihi, the limpet prized as a condiment at Hawaiian meals, and the ha'uke'uke, a compact sea urchin alternately known as the helmet urchin, shingle urchin or armored urchin.
Both creatures are uniquely designed to survive in the high-energy environment of the zone where surf crashes on the shore.
And, "it appears the ha'uke'uke can increase the growth rate of the 'opihi," said University of Hawai'i researcher Chris Bird.
Hawai'i's four species of 'opihi, three of which are found only in Hawai'i, are dominated by a hard, wide shell in a low cone shape. The most obvious feature beneath the shell is a muscular "foot" that grips the rocks.
The 'opihi cruise along the boulders, using a raspy tongue to feed on filmy algae and cyanobacteria.
The ha'uke'uke is reddish-purple in color, and unlike most urchins, it lacks pointed spines. Rather, its mound-shaped back is a series of overlapping bony features. At the edges of the "helmet" are flattened finger-like spines that press tightly down on the rocky surface. It eats seaweed.
The two animals have in common their low profile, which gives waves little opportunity to knock them free. That helps them thrive in an environment where most other animals would be quickly washed loose.
What they also have in common is that — if they haven't been fished out — you can often find more and bigger 'opihi in places where the ha'uke'uke grazes than in surrounding areas that lack ha'uke'uke.
Bird, a botanist, said he believes that's all about the algae. While both species eat algae, it seems they eat different kinds.
The 'opihi feed on the lowest-growing organisms on the rocks, ones that form a thin film on the surface and make coastal rocks slippery. The ha'uke'uke feed on taller algae, although they might still be less than an inch tall. It appears that by grazing down these larger algae, the ha'uke'uke actually creates habitat for the 'opihi, which otherwise could not travel through the seaweed beds.
Bird is still studying the relationship to see if there are other connections between the two species.
If you have an issue, question or concern about the Hawaiian environment, drop a note to Jan TenBruggencate, The Advertiser's Kaua'i Bureau chief and its science and environment writer. Reach him at jant@honoluluadvertiser.com, (808) 245-3074 or P.O. Box 524, Lihu'e, HI 96766.
