The Big Island of Hawaii, where we live, is volcanically active. Kilauea Volcano, in the southern part of the island, has been erupting continuously since 1983, sending lava down its flank and into the ocean. Mauna Loa, another active volcano on the island, erupted most recently in 1984, and could erupt again at any time.
The coastline at Puako, where we dive most often, was formed by an old lava flow from Mauna Loa. The layers of hardened lava flows run well beyond the shoreline, extending seaward below the surface of the ocean to form the volcano's submarine flank. The old lava flows also form the substrate for the wonderful coral reef that fringes that particular section of the western coast of the Big Island.
Molten rock -- called magma -- moves along constantly underground beneath the volcanoes, and far below the reef and the sea floor. Here and there, cracks have formed in the substrate beneath the reef. When that happens, sea water seeps down and mixes with hotter fluids closer to the magma. That warmed sea water then rises back up toward the surface.
About 15 years ago, we discovered a couple of spots on the reef at Puako where this geothermally heated water rises up through chimney-like vents in the reef, creating warm springs. The photos on this page show one of those vents. I know it doesn't look very impressive, especially in the first in the photo, but we find these sources of volcanically heated water on the reef quite fascinating. [Click on any of the photos for a larger view.]
We first noticed this one, and another about 50 meters away, by their appearance. These vents are relatively small, but they are eye-catching to divers. They are situated in a broad coral garden dominated by a certain species of finger coral (Porites compresa). In fact, in that area, that species of coral is so dense that it uniformly and completely covers the substrate for acres.
Amidst that large stand of finger coral a couple of spots stand out, because they look different. There are deep holes, literally, in that dense forest of finger coral, and the holes are surrounded by a crust of very different looking corals.
It was the unexpected interruption of the field of finger coral that first caught our eye. We swam over to have a better look at these anomalies, and that's when we discovered that the crusty looking corals actually were arrayed around holes in the reef. When we hovered directly over the holes to peer inside, we felt the warm water emanating from below. We understood right away that these holes were venting geothermally heated water. It was an exciting find.
On one occasion, we showed the vents to a marine biologist friend who was visiting and diving with us. When she returned to Honolulu, she in turn told some oceanographer friends about these geothermal vents in Puako Reef. The news traveled through the grapevine, I guess, because we then got a call from someone at NOAA who asked if we would be willing to serve as dive guides to some researchers who wanted to have a look at the vents the next time they visited the Big Island.
We agreed, of course, and a party of three divers arrived in Puako several weeks later. We led them to the vents, where they took some photos, and some water samples. Once we were back on shore, they said these vents probably were not very important. In any case, they did say that they would let us know what was in the water samples, but then we never heard from them again.
We concluded from the silence that, indeed, 'our' little geothermal vents were not scientifically important. Still, we always have enjoyed this little underwater curiosity on our reef.
In this final photo, at left, our friend Dan is poking his head and shoulders into the larger of the two vents. I had asked him to pose for a photo near the mouth of the vent, to provide a reference for the size of the opening. Dan decided spontaneously that this posture would demonstrate the size better than simply posing beside it! (Thanks, Dan.)
In fact, the photo also demonstrates something besides the size of the vent opening. It should tell you that the water emitting from the vent is warm, but not hot, else Dan would not be able to actually enter the space like that! Using the temperature indicators on our dive computers, we have measured the temperature of the water coming out of the vents on many occasions. It varies, but always is in a range between 27-29 C (about 81-83 F). In other words, it is always several degrees warmer than the ambient water temperature, which typically ranges from about 24 C (75 F) in late winter to 27 C (80 F) in late summer.
Some of the reef critters seem to have discovered these vents. On numerous occasions we have spotted sea turtles hanging out around the edges of the vents. We also have seen any of several species of crab, and even the odd slipper lobster, snuggled down into the hole, clinging to the stony side of the vent, and at times we have seen clusters of sea urchins ganged up along the rim.
We, too, have taken advantage of this relative warmth, especially after long, deep dives. Making our way to our exit point, we can choose a route via one of the vents, and take turns hovering in the warm water for a few minutes. Ahhh.
Cowrie shells are prized by collectors for their shiny china-like surface, and beautiful colors. Hawaii has many cowrie species. Some are endemic -- found only in Hawaii -- while others are more widely distributed around the Indo-Pacific region. Curiously, though, a number of the cowrie species that are found elsewhere as well as in Hawaii happen to grow to a larger size in Hawaii. One of those is the Mole Cowrie (Cypraea talpa), pictured at left.
Decades ago, on an early dive trip to the Red Sea, I had found a small Mole Cowrie shell and added it to the collection. Back home in Hawaii, we found pieces of broken Mole Cowrie shells with maddening frequency, so we knew they were around, but for the longest time we never could find a whole Mole Cowrie -- dead or alive.
One day, finally, we saw a large Mole Cowrie shell, all by itself on the surface of the sand. We hurried toward it, anxious to pick it up and examine it to see if it was alive. But before we reached it, a Spotted Eagle Ray appeared out of nowhere, swooped down, and snatched the Mole Cowrie from the sand. The ray quickly swam off, still munching its snack, and expelling sand and broken pieces of shell through its gill slits! Of all the nerve!
This time our disappointment was short lived. Just a few weeks later we were heading back to the reef after another deep dive out on the sand flat at Puako. We began to gradually ascend as we swam shoreward. As we passed over a large boulder that we used as a landmark on our route, I was amazed to see beside it a large, whole Mole Cowrie shell. Since we had begun our ascent, we were already a good 5 meters above the rock, but I couldn't resist dropping back down to check out the Mole Cowrie.
Since I had my camera in hand, the first thing I did was take a photo of the Mole Cowrie where it sat on the sand, without distrubing it. That's it in the photo on this page. A nasty looking Viper Moray eel that was hiding in a crevice near the base of the big rock poked its head out as I snapped the photo of the cowrie shell. The eel -- mouth open, eyes glaring -- looked right at me as I reached for the shell. I wondered if the eel would grab the shell, just as the Eagle Ray had done weeks before. But no, the eel tucked itself back into its crevice, so I picked up the shell. As I picked it up, I could tell that it was very light: it was empty!
I looked up at Jerry who was still hovering 5 meters above where I knelt and gave him the 'okay' sign. I popped the shell into my trusty little mesh bag and we swam back to shore with our new treasure.
Like most cowries, the Mole Cowrie forages at night. When the snail is active, it slides its fleshy mantle up over the outside of the shell until it is completely covered. The secretions from the mantle are what keep the surface of the shell so smooth and shiny. Here is a link to a photo of a live Mole Cowrie with the mantle extended, so you can see what it looks like.
Over the years we have become quite adept at finding shells underwater, but some species that we wanted for our collection were elusive for a long time. There were some we had seen in books or displays that we just never came across in the ocean. In other cases we had found the shell, sometimes on numerous occasions, but only ones that still had the critter living inside.
As I mentioned in an earlier post about shell collecting and diving, we do not take live shells that we find in the ocean, so we are especially delighted when we come across an uncommon or particularly beautiful shell that also happens to be empty. In the previous post, we told the story of finding an Arabian Cowrie in the Red Sea. In this post and the next, we'll tell the stories of a few more very special seashell finds.
The shell on this page is a Hawaiian Stromb (Strombus vomer hawaiensis), a very rare Stromb subspecies endemic to Hawaii. [Click on the photos for a larger view.] Not only does it exist only in Hawaiian waters, the Hawaiian Stromb only dwells at depths below 25 meters (more than 80 ft), so the likelihood of finding it on a beach is nil, and snorkelers will never get to see it in the water, either.
The find was quite accidental: we weren't even looking for shells at the time. We were doing a deep dive -- on a mission to photograph some cerianthid tube anemones that lived on a sand flat at Puako at a depth of about 40 meters (around 130 ft) and below. Not wanting to rack up any more decompression time than we had planned and prepared for, we had descended quickly to the sand flat, and we were hustling to the spot where we knew the anemones lived.
The surface of that particular sand flat is relatively barren terrain, with very few rocks or other features -- just hard-packed sand and mud, gently sloping into the deep for as far as the eye can see. For that reason, things that stick up out of the sand -- even small things like the cerianthids we were there to photograph -- are relatively easy to spot. In this instance, what Jerry spotted as he swam along was the pointy tip of the Hawaiian Stromb shell protruding from the sand.
As Jerry tells it, he recognized immediately that it was a piece of shell, but he figured it probably was a broken shell. He dug it up, curious to see what kind of shell it might be, way out there in the middle of nowhere. I watched him uncover what turned out to be a whole shell, not a fragment.
When Jerry picked it up and brushed the sand away with his glove, I heard him shriek and saw his eyes widen behind the faceplate of his dive mask. He held out the shell to me, and it was my turn to shriek when I realized what species it was. The aperature of the shell was packed with sand, indicating that there was no animal inside. What an exciting find!
This Hawaiian Stromb was a bit crusty from having been buried in the sand for who knows how long, but it cleaned up very nicely. Our specimen is 7 cm (2.8 in) long. It has become one of the greatest treasures in our seashell collection.
More seashell stories to come, after Wordless/Watery Wednesday...
Here's a special cowrie shell from our collection. The shell pictured at right is an Arabian Cowrie (Cypraea arabica). Jerry found this one in the Red Sea many years ago, and it is the only one we've ever seen, except in pictures.
I had to tell about this one today, since I'm writing this on Easter. As it happened, we had gone on a dive trip to the Red Sea over the Spring holidays one year, and Jerry found this shell on Easter Sunday. We always joked that the Easter Bunny must have put this egg-shaped cowrie shell there for him to find that morning.
As cowrie shells go, this is a fairly large species. The Arabian Cowrie shell pictured here is 6.5 cm (about 2.5 in) long.
The first photo shows a dorsal view of the shell. Below are two more views of the same shell, so you can see its interesting markings. First is a side view:
And here is what the base of the shell looks like:
Here is a link to a photo of a live Arabian Cowrie on Wikipedia. You can see the pale colored mantle of the snail that manufactures the shell and lives inside. There was no snail inside the Arabian Cowrie shell that Jerry found.
In a recent post, we introduced our readers to Cone Shells, and the snails that make those shells and live in them. We mentioned that the Cone Shell snails have a venomous sting, making them potentially dangerous to handle when they are alive.
Unlike some other mollusks, which eat algae, the animals that inhabit Cone Shells are carnivorous , and they use their venom, which is a neurotoxin, to immobilize or kill their prey. Some Cone Shell snails eat other mollusks, while others eat marine worms. A few Cone Shell species, like the one on this page, actually eat fish!
This is the Striated Cone (Conus striatus), a relatively large Cone Shell species. The one pictured here is from our shell collection. We found it in a sandy patch at a depth of about 6 meters (20 ft) off the coast of Puako, Hawaii. It is 10.4 cm in length (about 4.25 in). The Striated Cone is uncommon -- that is, it is not abundant in most locations. At the same time, though, it is widely distributed. It can be found in many different locations around the Indo-Pacific region, from the Red Sea all the way to Hawaii.
The Striated Cone is one of the Cone Shell species considered to be potentially dangerous to humans. For one thing, its venom is among the most potent. For another, the snail is amazingly flexible and agile. Its siphon and proboscis (where the stinging radula teeth are located) can be extended nearly the length of its shell. Thus, even if you are careful to hold a live Striated Cone Shell by the widest end, it still may be possible for it to sting you.
The Striated Cone snail hunts primarily at night. A wily predator, its method is to sneak up on a small fish that is 'sleeping' on the bottom and sting it, injecting it with venom. The neurotoxic venom paralyzes the little fishy. Once the prey is thus immobilized, the snail literally engulfs it.
You might imagine that it would take quite awhile for a snail to engulf a fish. In fact, the snail's proboscis (mouth) expands and it hoovers in the prey in a remarkably short time, swallowing it whole.
Don't believe me? Have a look at this video of Striated Cone Shell snail attacking and consuming a little fish: .