Shells of molluscs were discussed in previous lessons in Cruising Helmsman; this article takes a detailed look at other interesting items that beachcombers have discovered.
The first obvious thing of interest to beachcombers is the beach itself. In spite of what people who live in the tropics say, some of the best beaches are found in southern Australia.
Most tropical beaches are made up of sand that is coarse and made up of calcium carbonate (limestone or chalk) most of which is derived from coral. Coral is continually being broken up into particles by waves and the action of predators. What they do not tell you in the travel brochures is that much of the coral sand of tropical beaches has passed through the guts of parrot fish.
There are many carnivorous animals that crush and scrape coral and the colourful parrot fishes are often the most numerous. A parrot fish has fused massive teeth with which it scrapes coral to feed on algae and the coral itself. The remains of the coral skeletons, mostly calcium carbonate, pass through the digestive track as particles and these are eventually washed ashore to form sand for tourists to lie on.
Parrot fishes must have to consume large quantities of coral to gain quite a small amount of food as, when snorkelling over coral and watching these fish, they appear to be continually evacuating clouds of coral dust from both ends.
But there are exceptions to the usually coarse coral sand of tropical beaches. Whitehaven Beach on Whitsunday Island, for example, is in the tropics and is famous around the world for its beautiful, white sand.
The renowned white and powdery sand at Whitehaven Beach is unusual for a tropical beach as it consists almost entirely of silica (silicon dioxide) derived, not from coral, but the wearing down of quartz. At the northern end of Whitehaven Beach is Hill Inlet, a large area where the tide shifts the fine sand and water to create beautiful shades of turquoise.
Other than broken down coral, sand can contain other material of a biological origin. About one third of all seafloor sediments and, in many places, beach sand consists of the remains of very tiny creatures called foraminifera; these are simple, single-celled creatures related to amoebas and have shells or tests usually made of calcium carbonate. It must be one of nature’s slyest tricks to hide her most exquisite designs in creatures that are nearly too small to be noticed.
So take a magnifying glass ashore with you when you go beachcombing.
The shell or tests of some microscopic species have exotic shapes of spheres, spikes, swirls and twists.
Most species are less than two millimetre in diameter; although some, such as Marginopora, can be much larger. This species is often so common on tropical beaches that people in Pacific islands make necklaces by threading a fine line through the central perforation. In Samoa I found that the species even has a common name: ma’a masina, meaning ‘moon stones’.
Other sandy things
Some beachcombers show me interesting spiral collars of sand they had found on the beach. What animal produced these?
Moon snails, described in a previous article as a predator of cockles and clams, are responsible. The moon snail lays her eggs and protects them by embedding them in sand and mucus.
Other related species protect their eggs by laying them in a jelly-like sausage blubber in the shape of a horseshoe. Both forms of egg container are hardly likely to be appealing to would-be predators. Eventually the eggs are released as the
egg containers break down.
Beach fleas and sea lice
Among the flotsam and the jetsam on seashores, beachcombers often find and are concerned about, small crustaceans commonly called beach fleas and sea lice.
But these are not insects. Beach fleas or sand hoppers belong to a group of crustaceans known as amphipods and they are important scavengers that feed on plants and dead animals washed up by the waves. Reference to the animal as a flea is undeserved and it is solely based on their superficial resemblance to the insects that infest places of careless human habitation.
Sea lice belong to a group of crustaceans known as isopods and are similar to the sow bugs or slaters which are found under rotting wood and damp vegetation. Very few of them can really be referred to as lice, although some are parasitic on fish such as the leatherjacket shown in the accompanying illustration.
Some species of marine isopods, sometimes called gribble, have evolved to bore into wood; causing the destruction of wharves and boats. Other species reach huge sizes, about 40 centimetres in length, in deep water.
When people swimming get an itch or a skin irritation sea lice often get the blame. But this is more likely to be small drifting stingers or fragments of jellyfish tentacles.
The crews of many vessels are keen on fishing, beachcombing to them has a more practical purpose. Fishers are hunting for bait. The best known bait is the ghost shrimp or marine yabby which is sucked out of its burrows with a hand pump in the sandy silt of estuaries.
In areas that are muddier, often in stands of mangroves, burrows of the larger mangrove lobster can be found. These can be tempted out of their burrows by passing a piece of meat across the burrow’s entrance.
There are usually several types of shore crabs to observe and these are shown in the accompanying illustration. The male fiddler crab has one outsize red claw which it waves in front of it. The ghost crab is nocturnal and burrows deep in the sand during the day and can best be seen by wandering along a tropical beach at night with a torch. Often armies of soldier crabs with their blue bodies can be seen marching across sand flats.
Many snail shells that beachcombers find are occupied, not by their original inhabitants but by hermit crabs. There are many different species of hermit crab and all have soft abdomens that are usually protected by living in the empty shell of a sea snail. A growing hermit crab seeks out progressively larger shells as it grows.
The species shown in the illustration is able to retreat into its shell and uses a claw to block the entrance.
Beachcombers often find the bleached white shells or tests of sea urchins and their relatives. These usually have beautiful patterns of perforations in the shape of a five-armed star which emphasises their relationship to sea-stars or starfishes.
In life, the sand, or heart, urchin burrows beneath the sand in sheltered bays and estuaries where it searches for particles of food. Sand dollars, also known as snapper biscuits in New Zealand, are extremely flattened sea-urchins that also burrow in the sand.
Paddling beachcombers should beware of some living sea urchins which have sharp spines. Urchin spines are covered with a thin layer of tissue and when they break off in someone’s foot, it is this tissue that rots and sends the surrounding skin septic. The only treatment is to use tweezers to remove as many of the spines as possible and soak the affected area in an antiseptic. But there is at least one sea urchin that has spines that are toxic.
When I had my boat moored near the university in Fiji, several local women often fished in the shallow water where they stood up to their waists in the sea and fished with a hook and line or a scoop net. One particular day, I moored the yacht and when I rowed the dinghy ashore I noticed that one of the Fijian fisherwomen stumbled and fell over. I rowed over to her and helped her into the dinghy; I actually had to jump overboard and lift her into the dinghy as she was a considerable size and not co-operating that much.
There were many spines from a hatpin urchin in her lower leg and, although I removed some, many of the points remained in the flesh. I left her ashore where her family wrapped her wounds in pawpaw skins that were bound onto her skin with banana leaves; green pawpaw is traditionally used to heal wounds and, not coincidentally, in cooking as an effective meat tenderiser!
The Fijian woman had strayed too close to a hatpin urchin whose needle-like spines reach over 30cm in length and contain toxins that cause a painful wound.
There is not much to eat inside a sea urchin, which is rather like a hollow globe with the gut draped around the inside, the rest is rather unpalatable. But the five-armed reproductive organs (roe), which are large in the breeding season and attached to the inside of the test are regarded as a delicacy. With a squeeze of lemon and a glass of white wine: delicious!
Items on the beach such as washed-up fishing floats often include marine hitchhikers and the most common of these are gooseneck barnacles.
When sailing back from Fiji to Sydney it was wonderful and easy sailing. The wind had been on the port quarter and the sails set at the same angle since leaving Fiji, so I did not have to touch a rope.
We had stayed on the one tack with one side of the yacht’s hull heeled over into the sea for so long that, when I eventually did change tack, I saw that gooseneck barnacles had grown well above the waterline on the side that had been submerged.
The gooseneck barnacle is a creature of the open sea and seems to be the only hitchhiker that attaches itself to a yacht’s hull on an ocean passage. The larvae of most fouling organisms, including mussels and acorn barnacles, attach themselves to yachts while they are moored near coasts where they can take advantage of water enriched by nutrients washed from the land.
Although superficially mollusc-looking, both acorn barnacles and gooseneck barnacles shown in the accompanying illustration are crustaceans in which the shell is made up of plates just like those covering a prawn or a lobster. Both have feathery appendages that trap drifting plankton.
Gooseneck barnacles are attached to hard surfaces by purple-brown stalks and beachcombers frequently find them on ocean beaches fastened to logs, old crates and fishing floats, items that may have drifted on long ocean voyages.
When paddling or swimming across the sandy floor of a tropical lagoon, sea cucumbers are often the most numerous of animals to be seen. They have an important role in clearing the sand of debris.
A sea cucumber bulldozes its way along, ingesting sand through its tentacled mouth. During digestion, organic material is removed from the sand, which is then expelled as castings at the other end. Three different species of sea cucumbers are shown in the accompanying figure.
Some paddling beachcombers are horrified to see what they believe to be sea snakes beneath their feet. Often, these are giant snake cucumbers which grow to a length of over three metres; but the mottled brown species is soft-bodied and quite harmless. Other species are much smaller with thicker and firmer bodies.
Sea cucumbers are usually marketed for their muscular body walls that are valued food items in South East Asia. In authentic Chinese restaurants there are usually items on the menu listed in English as sea cucumbers, beche-de-mer or trepang and the dishes contain slices of the body wall that are tasty and tender, quite unlike the raw product. The body wall of cucumbers contains glass-like spicules and quite drastic processing is required to make them edible.
I thought I was quite adventurous in trying local foods. I had eaten fruit bat in Palau and jellyfish in Tonga but, in Samoa, there was one local delicacy that had me beaten. This was the partially fermented guts and reproductive organs of sea cucumbers.
Samoan women collect sea cucumbers such as the curryfish and remove the internal organs through a slit in the body wall; they then return the sea cucumbers to the sea where their internal organs are believed to regenerate.
They pack the guts and reproductive organs from about 20 sea cucumbers in a large bottle of seawater and offer them for sale from the side of the road. Here the bottles sit in the sun and the gruesome contents partially ferment over the day. Samoans love the concoction and women in particular drink it as a tonic; I was told by a local doctor that it contains a lot of iron.
Once, when out in a local bar with some Samoan friends, I had a few more conventional drinks and resolved to try it. My friends bought me a bottle and I got as far as removing the plug stopper. It was like opening the hatch of a holding tank on an overcrowded yacht, the cesspit-like smell made me retch. I still have not tried it and probably never will.
Several curious beachcombers found bizarre, green-brown creatures in shallow water. When disturbed, these creatures released a smoke-screen of brilliant purple dye.
These are molluscs known as sea-hares because they have, if you have a lot of imagination, tentacles that resemble the ears of a hare. Its grotesque, often warty, appearance has given rise to the belief that these molluscs are dangerous but in fact they are quite harmless.
The danger of stinging jellyfish is usually well known by cruising sailors. In the tropics, most sailors avoid swimming in the rainy or summer season, particularly in the mouths of rivers and creeks.
But beachcombers sometimes find the remains of two brilliant blue species washed up on beaches during onshore winds. The identification of these often get confused: one is the Portuguese man o’ war which is to be avoided and the other is the by-the-wind sailor which is harmless.
In fact the Portuguese man o’ war is not a true jellyfish, which is a single individual organism, but a floating colony of polyps. It is a team of differentiated polyps: some that capture prey, others that eat and still others that reproduce! This quite amazing association of individual polyps working together enables the colony to function in the
same way as a more complex animal.
Although small specimens are often driven up on beaches by onshore winds, the tentacles of large individuals may be over 18 metres long and bear nematocysts that are capable of paralysing quite a large fish. But in spite of their powerful and painful stings there appears to be no record of any deaths in human victims.
One of my favourites is the small and harmless by-the-wind-sailor, Velella velella, which is related to stalked hydroids not to jellyfish. Each has a disc-like, blue float with a transparent ‘sail’, which enables the animal to drift on the ocean’s surface. But many may sometimes be found washed up on beaches.
According to popular belief the angle of the sail is supposed to allow the by-the-wind sailor to tack to windward like a sailing boat. However, I once observed a fleet of thousands of these driven by light northerly winds into a lagoon in Samoa; although some managed to sail at right-angles to the wind it seemed that few were able to escape the lee shore by tacking away from it.
There are many striking species of sea-stars in tropical lagoons including the common blue sea-star and the large pin-cushion star. One of them, the crown-of-thorns, is a predator of corals. It moves across corals using the small tube feet beneath its arms and pushes out its stomach to digest the coral polyps. After feeding, it moves on leaving the bleached white skeleton of the coral.
I once got spiked by a crown of thorns when I was not even in the sea. It happened while I was running an underwater survey in a Samoan community that had set up a fish reserve.
People from the community removed crown-of-thorns from the coral reef and took them ashore where they were piled up for burial; killing them at sea is difficult as some sea stars have the remarkable ability to survive and regenerate from a piece of its body. They had to be handled carefully as their seemingly ineffectual short
spines are toxic.
I was standing on the beach talking to a group of people involved in the survey when I stepped backwards right onto the pile of collected crown of thorns. Several spines penetrated my diving boot.
The skin covering the crown-of-thorns’ spines contains a toxin called saponin and when humans are ‘spiked’ the effects include intense pain, nausea and vomiting. A traditional remedy in Samoa is to turn the sea star upside down and place its mouth over the victim’s wound, the sea star is then supposed to suck out its own poison.
I was much too busy hopping around on one foot to try this and I had a leg that ached for days.
Cephalopods – Nautilus
Beachcombers often find the shells of molluscs that are neither sea snails nor bivalves. These are the cephalopods, a class of mollusc that includes squids, cuttlefishes and octopuses; yes, the plural of octopus is correct as it comes from a Greek rather than a Latin word.
These marine animals all have arms or tentacles that are used for grabbing their prey or mates.
Often beaches may be littered with white cuttlebones, these are the internal shells used by cuttlefish to aid buoyancy. Cuttlebone consists mainly of aragonite, a form of calcium carbonate or chalk.
For this reason cuttlebones are often collected for caged birds to correct calcium deficiency. Less easy to find are the delicate and transparent pens of squids; these consist of chitin, a horny substance related to cellulose. The internal shells of both a squid and a cuttlefish are shown with their owners in the accompanying figure.
Very lucky beachcombers may find the shells of two other magnificent cephalopods. In cooler waters of southern Australia, beachcombers may find the ‘shell’ of a paper nautilus or argonaut.
The argonauts are a group of pelagic octopuses and are remarkable in that the female produces a fragile and shell-like case in which she lays her eggs. The male is much smaller than the female and does not make a shell. The female has two specialised arms, which have membranous flaps that secrete and envelop the delicate egg case. The female stays in the case which is used to protect the eggs until they hatch and empty egg cases are sometimes washed ashore after winter storms.
On tropical beaches people may find the empty shells of the chambered nautilus, a living fossil that has survived in earth’s oceans for the last 550 million years, existing before there were fish, dinosaurs or mammals. What a beautiful shell the nautilus has.
In the Middle Ages, when small numbers of nautilus shells were obtained by travellers in the East Indies and beyond, they were regarded as great treasures. But, of an entire group of related and once successful animals, only the nautilus remains and its distribution is restricted to tropical waters of the eastern Indian Ocean and the western Pacific Ocean.
However, there must be large numbers of nautiluses in deep water as when I was setting shrimp traps down to depths of 800m in Fiji we often caught them. On one memorable trip we caught twelve of them in a single trap.
We caught so many nautiluses that one night at a party we decided to cook some. Now, eating an animal that in evolutionary terms is 300 million years older than dinosaurs and about 50 million years older than the first primitive fish is not something to be undertaken lightly. Perhaps it could have been blamed on the amount of alcohol consumed, a common excuse for many misdeeds.
Why is the nautilus the lone survivor of its group? Nobody knows for sure but, like all animals remaining on this earth, it had some favourable characteristics that its relatives did not have. Compared with other members of its peer group it had some attributes that prevented it becoming extinct, that is how natural selection works.
What did the living fossils taste like? They were as tough as a leather sailmaker’s palm and if humans were their only predators their survival would be assured. ≈