2002 Sea Shells
Catalogue of Indo- Pacific Mollusca
Most people's idea of a sea shell is a dead specimen. Neville Coleman relates just how the living animals of sea shells have fascinating, unbelievable life styles and behaviour beyond the credibility of science.....
Indeed, molluscs (the animal and the shell) are an extremely important group in the web of life in all our oceans and their continued presence supports major commercial industries and millions of humans as a food source.
For eons in time molluscs of the shoreline have been a staple diet for peoples who lived along the coasts of many countries. I was one of those people and as a small child was brought up on scrounging oysters and mussels from the shore lines of the Lane Cove River in Sydney just to help feed the family. At that stage of my life I could only relate to oysters and other bi - valves as food. Even today I still enjoy a dozen or so oysters on special occasions. ( photo: Neville Coleman)
Many years hence I have learned that oysters are a luxury to most and a plate like this may cost up to $40.00 at some restraunts.
Molluscs feed on other molluscs, worms, crustaceans, echinoderms, fish, birds and marine mammals and even more so by humans. Many aquatic creatures are dependent on chitons, univalves, bivalves and cephalopods for their daily sustenance.
Local and imported Helmet shells, Baler shells and Strombs along with many other univalves have been collected in their millions to be converted into objects and ornaments for sale to tourists as genuine products of Australia. Few people would know that many of the species being promoted as products of Australia are actually species imported from the USA, Philippines and Mexico.
Some of the Indo - Pacific species are protected in Australia, yet the same species imported can be legally sold. Which really makes a farce of our protected species laws, because who can tell the difference?
In the past to the present, divers and intertidal collectors have searched out rare shells and sold them as a commodity like any other fishing enterprise. Natural resources such as scallops, abalone, oysters, mussels, clams, trochus, pearl shell, pipies etc. have been exploited by humans as food, bait, ornaments and precious stones in the form of pearls and pearl shell ornaments.
Professional shell collectors are few and far between in Australia. To my knowledge their are only 9 professional shell diving licences at present in Western Australia. Scuba diving for shells in shallow water can reduce populations of the some of the rarer species of Cowries that reproduce by direct development. However, most of the vulneable species also exist in deeper water and this makes fishing for them much more limited. ( photo: Neville Coleman)
Australia's population has increased over the last 40 years with people's from many countries that no longer have any intertidal resources left. Australia's intertidal shores have since been decimated by thousands of local and visiting shell collectors and sustenance collectors combing the inshore reefs for everything that is saleable, or edible. Many of our inshore Marine parks are visited on a regular basis by sustenance collectors working in teams to collect for the local Menu's.
Even in this modern day world when everybody is so aware of the natural environment and the fact that many of the ocean's resources have been plundered beyond recovery we still tend to only think of shells as inanimate objects to be collected, or used as road fill, or ornaments such as lamp shades, or door stops.
Little thought is ever given to the living animals that have lives and histories and are capable of unbelievable behaviours and wonderful abilities.
Few can understand that these incredible life forms are far more than meets the eye and that humans can improve the well being of their lives just by understanding that NATURE has the key to all our problems and we can learn so much if only we slow down a little and bother to look around us.
Shell collecting has been a worldwide "fishing business" and vast areas and species have been all but wiped out by the insatiable appetites of souvenir/collectors.
While in my day, divers collecting Helmet Shells to be killed and used for doorstops was "normal", today it is hoped that we know and care a little more. ( photo: Neville Coleman)
Horned Helmet Shells
The Horned Helmet shell Cassis cornuta is a large (350 mm) carnivorous Gastropod, which lives in the shallow waters of lagoons, on sandy sea floor along the northern reaches of the Great Barrier Reef, and across the Indo - Pacific. This mollusc is generally found in colonies, although individuals may be dispersed over a wide area.
Due to heavy collecting for the tourist trade to be used as door stops and lampshades through the years, this species is now completely protected within Australian waters. ( However, this only came about because it was supposed to feed on "Crown of Thorns" sea stars?) Crown of Thorns sea stars are not the normal food of Horned Helmet shells but who cares? We have one more species on the protected lists and I am sure everybody who reads this story would agree, it was well done , even if it was not well meant?
During the day most of these molluscs are dormant, lying partly buried in the sand in depths of 5 to 20 m. Their food consists almost entirely of heart urchins, which they attack by rasping a hole through the test of the urchin with their radula and using their proboscis to suck out the soft parts.
Sexual dimorphism exists, with the males being smaller in size and having fewer but larger knobs on the shoulder of the shell, while the female is more rotund, is larger shelled, and has uniform smaller knobs on the shoulder of the shell.
A small brown chitinous operculum is present on the foot, but this seems of little use for protection as it only covers about one quarter of the total aperture length.
Horned Helmet shells use two methods of digging. One is to burrow ahead at an angle, using the wide flanges of the shell aperture to push away the sand. At other times they will rise up on their strong foot and bring the shell down hard on to the bottom, displacing the sand around and forming a depression. By repeating this process they are able excavate a shallow hole.
At night the Horned Helmet is quite active, crawling over the sand and low profile
reef in search of prey. As with other prosobranch molluscs, the eyes are not capable of forming clear images and merely act as light receptors. All other functions and senses are thought to be similar to other prosobranchs.
This small amount of text contained most of the information known about living Cassis cornuta in Australia at the time.
A Giant Horned Helmet shell bulldozing its way across the sandy bottom searching for heart urchins buried below.( photo: Neville Coleman)
Not so long ago we raped, pillaged and destroyed nature in all its forms as if it was our "God given right" Indeed, on the Bible I was brought up on, dominant male humans were encouraged to utilize or destroy anything they saw fit, especially if it did not bow to their beliefs. This is also a familiar theme in other religions I made it my business to reason with in my younger days.
Due to the new age of concern about nature and the health of the planet in general (and the fact that we have already destroyed a huge amount of the planets living resources) our attitudes are slowly giving way to becoming a bit less plundering.
Getting sorted at Samaurez
17/09/74 Samaurez Reef, Coral Sea 6.30 pm to 9.30 pm.
While carrying out my normal recording functions underwater, I was on my way back from my third shallow-water dive of the day (7 m) when I passed three Horned Helmet shells in close proximity to the charter boat.
At the time I took little notice other than to assume that some other divers had collected them, taken them on board, and that the skipper had ordered that they be thrown back, as they belonged to a protected species. (This later proved to be correct.)
The shells had landed in a triangle such that each shell was about 5 metres away from the others. Two of them had landed with their right side up, but one had landed on its anterior end and the entire front was buried in the sand. It never occurred to me to stop and turn this shell over, as my mind was full of an hour's observations, in which I had taken two rolls of film on behaviour involving several new records, and I had a new species in my collecting bag.
Two Giant Horned Helmet shells combining to excavate sand from around their stricken co specific. What is unbelievable about this is that it was being done in tandem; in pitch-black conditions without the benefit of eyes or any other form of communication we lowly humans can even understand.( photo: Neville Coleman)
I was also anxious to change film, have my tank filled and get back into the water. It was just coming on to change over time and I wanted to be back under water at dusk to see what happened in this area when it got dark. Little did I know that by ignoring that shell and swimming past it I would set the scene on one of the most exciting observations of my (then) sixteen years in the sea.
Within the hour I was back in the water and as I swam up to the anchor line there was still enough light to see that the two shells were crawling towards to the buried one.
I continued the dive and an hour later, low on air and with only two shots left in one camera, I retraced my way to the anchor line and froze at what the torchlight revealed.
The two Horned Helmet shells were now in tandem and were crawling around the shell that was partly buried in a tight circle. They had furrowed a depression around the immobile shell, having dug away the sand with the front flanges of their shells as efficiently as if they were a pair of miniature bulldozers.
MY MOST EXCITING AND UNBELIEVABLE EXPERIENCE
In the sixteen years of working underwater I've seen a thousand impressive sights and a thousand new ones, but nothing like this. I could hardly believe what was happening, but took the pictures anyway. Lying on the bottom in the dark, barely daring to breathe, I watched two unintelligent, unemotional invertebrates, without vision, or any known form of communication, with pea-sized brains and no reasoning mechanism that we are aware of, combine their actions to assist another of their species in trouble.
By the time I swam on to the duckboard of the charter boat I was shaking from head to toe, my hands wouldn't work and my feet had a will of their own. Those who saw me thought I'd had a scare. Scared wasn't half of it. I was awe-struck. The tears poured from my eyes and sobs wrecked my chest.
But why? Why should I let this example of innate behaviour response, triggered by some unexplained stimuli, affect me so much.
I don't know. Maybe because I'm human.
UNKNOWN SURVIVAL TECHNIQUE
Here was a survival technique unheard of in marine invertebrates. What if, because of the effects of storms and cyclones, Horned Helmets couldn't right their own shells
from certain positions on the sand and depended upon a special 'Mayday' chemical
release which others in the immediate vicinity could pick up and respond to!
All hypothetical, of course, but it did provoke thought. Thought or not, the clashing of tanks and equipment brought me quickly to my senses; several other divers were getting their gear ready to dive later that evening. Realising what affect the presence of other divers might have on the concluding stages of this epic; I quickly had my tank filled, changed films in the cameras, and, while the others were having tea, I once again rolled off the duckboard into the cold black depths.
By digging out a trench around the fallen shell and pushing it along from behind and the side, the two larger Horned Helmet shells were successful in turning the smaller one over onto its base.( photo: Neville Coleman)
The scene had entered another phase. Both working shells were now actively engaged in pushing the partly buried shell along on its side from behind. With slow methodical determination they had manoeuvred it into a position where it could be turned it back onto its normal underside. I watched enthralled as one reared up on to the turned shell's back and pushed from a higher aspect, providing the leverage that eventually righted the upturned shell.
The sequel to one of the most moving events I have ever witnessed in the sea. The three Giant molluscs (all males) have come all come together after the drama, in a siphon to siphon group, as if they were bonding or providing assurance to the smaller one? ( photo: Neville Coleman)
THERE IS A LOT MORE TO NATURE THAN MEETS THE EYE!
I watched for as long as my air lasted and with my last frame, exposed a final record of the three shells, now all right side up. There were two big males and one little male, almost siphon to siphon, and the little one had burrowed a few centimetres, perhaps seeking the familiar security of the sand after several hours of exposure. Three molluscs just touching, just being, for a moment in time that was mine.
At that instant I didn't care too much for computer analysis, innate behaviour mechanisms, or key stimuli. I hated what my brain would eventually do to that scene. I cursed every bit of cold calculating behavioural biology I'd ever learned, every critical realism, and casual analysis. I hated beyond hate, science, my self, and the world in general, because I knew in my heart that this, like a thousand other encounters in the animal world must fade into the objectiveness of a thousand unknowns.
Because science has strict and exacting principles, of which feelings play no part, one is not supposed evaluate animal behaviour in terms of human experiences, behaviours and emotions. To do so is termed to be anthropomorphism-the ascription of human characteristics to that which is not human- and if science were a religion, then anthropomorphism would get you excommunicated, to say the least.
Nevertheless, regardless of how, or why, I saw two 'lowly' invertebrates spend several hours saving the life of another 'lowly' invertebrate and nobody on this planet is going to convince me otherwise.
PS: Since this story was published many years ago science has conducted experiments and found these facts to be true. Fancy that!
We have really advanced very little in regard to our knowledge of the interactive behaviour of sea creatures. If, as admitted, we only have 1% of the oceans of the world recorded then there is still a lots of exciting 'stuff' to keep many thousands of scuba diving underwater naturalists enthralled for the next couple of hundred years.
I for one, hope I can scrounge out a few more years in the wonderous World of Water and share the results with all.
Copyright Neville Coleman