While scuba diving at Koloa Landing a few days ago with some friends, we came across a very unusual sight.
Sea stars are commonly called starfish, but they are not a fish at all but an invertebrate called an echinoderm. Sea stars are very common throughout the Pacific Ocean, but quite rare in Hawai‘i.
Along the West Coast of the United States you might see 50 sea stars on one scuba dive and you also see them in tide pools. Most of the sea stars are from 2 inches to 15 inches across and they come in a variation of colors, but here in Hawai‘i seeing a single sea star on a dive is unusual.
Hawai‘i has 20 known species of sea stars, but most of them live in deep waters and are rarely seen.
We were scuba diving at about 30 feet deep and up ahead of us I saw what looked like a man-made object sitting on the seafloor. At first I thought it was a steering wheel from a boat. As we got closer I noticed it was bright purple in color and about 18 to 20 inches across.
Once we were right on top of it, I could tell it was a very rare purple velvet sea star with five long arms that looked like pieces of rope. I have seen these rare sea stars in deep water off of Ni‘ihau, but they were only about a foot wide and this one was giant! What was it doing in 30 feet of water at Koloa Landing?
Most sea stars have a head surrounded by five arms. They have tube feet on the underside of each arm and they pump seawater into the arms and out through these hydraulic tubes to crawl slowly along the seafloor.
They feed on dead plants and animals, and also other slow moving creatures they can catch. When they have captured a prey item with their tube feet, they eject their stomach outside of their body and digest their food right on the spot.
It turns out that the very first purple velvet sea star ever observed in Hawai‘i was at Koloa Landing, but after doing more than 200 scuba dives there I have never seen one up until now. The largest recorded size of a velvet sea star is 15 inches wide. The one we found was much larger at almost 20 inches wide.
Sea stars breed in two ways. One is by emitting eggs and sperm into the water and producing fertilized swimming larvae that drift in the currents until they grow big enough to settle on the bottom. Maybe the colony of velvet sea stars on Ni’ihau produces babies that float over to Kaua‘i. The other way they breed is by dropping off one of their legs, which will grow into a whole new sea star!
Hawai‘i still has many unique and rare marine life species we know nothing about. Why would we find one giant purple starfish at Koloa Landing in shallow water when we usually see them way out at Ni’ihau in deep water?
Maybe someday there will be deep water unmanned rovers that can explore the seafloor between the Hawaiian Islands and see if our sea star species crawl from one island to the next way below the sea surface.
The Hawaiians use pe‘a as the general name for sea stars. More than likely more specific species names were not used because the sea stars are poisonous, so they can’t be eaten and they were not used for cultural practices. So, they more than likely were just ignored.
You can see some of our unique sea stars in action in my documentary movie about marine life at Koloa Landing up on my webpage at www.underwater2web.com.
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Terry Lilley is a marine biologist living in Hanalei Kaua‘i and co-founder of Reef Guardians Hawai‘i, a nonprofit on a mission to provide education and resources to protect the coral reef. To donate to Reef Guardians Hawaii go to www.reefguardianshawaii.org.
