| back to shell index |
Snorkeling over Sand
At first glance, there don't seem to be many sea shells
around the Hawaiian Islands. Visitors from the Pacific coast
of North America probably are accustomed to an abundance of shells
littering the beach and an abundance of live sea snails in and near
the water, from rocks in Puget Sound covered with elegant frilled
dogwinkles and leafy hornmouths to the steep windward shores of
Catalina Island covered with large wavy tops and Kiner's whelks.
The visitor from the East coast will find that Hawaii is not a
Pacific version of Sanibel Island. Except for periwinkles,
clusters of black nerites, and scattered Hawaiian limpets
(opihi), the sea snails of the Hawaiian Islands tend to be
either out of sight or so well camouflaged that they might as well
be. The snorkeler searching the rocky shores or reefs for the first
time looking for sea snails probably will be disappointed.
I
recall , for example, a boatload of snorkelers dumped from a
catamaran into one of my favorite coves for sea snails on the
west coast of Maui. After about twenty minutes of exploring,
several of them came over to me and complained that there was
nothing to see; they had expected to find sea shells everywhere.
In addition to an amazing array of tropical marine
fish, the cove had large numbers of cones, including spiteful cones and
golden-yellow cones, both of which seem to be abundant
on rocks and reefs throughout the main Hawaiian Islands, plus a
large, local population of penniform cones and an abundance of
small snails such as horns, miters,
whelks and turrids.
The problem is that any newcomer will
require time to learn where to look and, more important, what
to look for. To see through the camouflage of sea snails,
the snorkeler must develop search images, some sort of mental
templates that are tested against the underwater scene
and, in response to one of the many similar and seemingly shapeless
lumps, trigger the messeage "hey, there's a shell." In the same
cove that seemed so bare to the snorkelers from the boat, I saw
another snorkeler bring up a giant triton's trumpet from a depth
of about six feet. Once its cryptic coating of wildlife was removed,
the shell was beautiful. In spite of its size, none of us
who frequented the cove had seen it before, and many of us undoubtedly
had looked right at it. We had not developed a search image for
the triton's trumpet.
For the visiting snorkeler who wants to find some sea snails in Hawaiian
waters but does not have time to develop a large repertoire of search
images, and for the local resident who is a newcomer to searching for
sea snails, I recommend the bare white sand. There are many
experienced divers and snorkelers who will tell you that an open,
sandy bottom is not the place to look for fascinating sea life.
I used to be one of them. Fortunately for me, the graduate student
of a neurobiology colleague at UC Irvine happened to be from Hawaii
and educated me on the point just before I left for the Islands
on my first sabbatical leave. In the years that have passed since that time,
the bare white sand, not only in Hawaii but in many other places,
has provided some of my most interesting snorkeling. What can
one find in the sand? Part of the answer is that, usually, the sea snails
that you find will be clean (without the calcareous
algae and other extraneous material that obscures
the shapes and color patterns of shells found on underwater
rocks and reefs). The rest of the answer depends very much on
where in the Islands you are snorkeling. The answer I shall give you
in this essay applies to the beaches along the southwest corner of
Haleakala (Maui). You can have the pleasure of discovering the
answer for your own beach.
Close to shore, in water knee-deep and clouded with sand stirred
by the surf, a gleaminmg dark object about one inch long appears
through the haze. If you are alert and quick, you may snatch it as it
rides past in the eddies of the surf. Open your hand and you will see the
inconstant auger, a pretty relative of the cone, with a slender, sharp-pointed,
glossy shell.
Pressing your facemask close to the bottom, you may see these animals
working with the currents and the sandy bottom. At least in the
gentle waves in which I have watched them, inconstant augers do not
drift far before they settle to the bottom and begin to
burrow into the sand, their shells aligning with the current so
that the sharp tips point downstream and the rounded front ends
face the brunt of the flow. Each of these augers possesses a large foot
that presumably helps anchor the animal against
the currents. It has been suggested that the animal also uses the foot as
a sail in the eddies of the surf as it moves about foraging for
food (small polychaete worms).
The foraging journeys of another snail, the hectic auger,
carry it beyond the edge of the water, where it occasionally
is found cast by the surf onto the wet sand of the beach.
Watching the hectic auger resist the waves as they wash over it, one can
propose candidate adaptive values (selective advantages) for its slender,
tapered shape and its extraordinarily large foot. The streamlining and anchoring that
they provide may well allow the animal to exploit a domain that
is inaccessible to its competitors. On the other hand, the presence of
shell collectors and other predators patrolling the beaches
suggests selective disadvantages to this mode of operation as well.
I have yet to find a hectic auger that still has an unbroken apex (sharp tip)
on its shell, and what remains of the tip always seem to be scoured, perhaps
reflecting the rigors of life at the surfline and, possibly, some interesting
mode of action involving the tip of the shell. I do not recall ever seeing
a living inconstant auger with a broken or scoured tip.
All of the hectic augers that I have seen on our white-sand Maui beaches
seem to have changed their color pattern abrubtly as they grew. The
earliest, unscoured whorls have extensive, rich-brown markings on
a creamy-white background (creamy-white also being the color of the
scoured shell). The next few whorls are predominantly creamy-white,
with small flecks of rich-brown; and the last whorl or two is
pure creamy white. Camouflage is
one possible adaptive value of a creamy-white shell on white sand, but
what might the advantages of the brown markings be (or have been to the
younger animal)?
There are other beautiful augers to be seen, but many of them are in
slightly deeper water and buried in the sand. In the morning, before
the tradewinds have begun to stir the sea and make the inshore water
cloudy, as you snorkel out from shore into water about six to ten
feet deep, you will see long tracks in the sand, as if someone had come out
ahead of you and run her littlest finger along the bottom. At one end of
each track you should see a small mound, and beneath the mound you should
find a lanced auger, or a pencilled auger, or Verreaux's auger, or any of several other
surprises. Although it seems to be more abundant in slightly deeper
water, a flea cone might
be lurking beneath one of the mounds. In the process of digging up one
of these cones, at least one snorkeler has been stung on the hand.
Although the pain in that case was not severe and disappeared
in about thirty minutes, there remains the possibility that another victim
might be more sensitive and suffer more serious consequnces. Therefore,
you might consider using a heavy glove (I do not believe that the
standard cotton diving glove would block the tooth of a cone)
or a small seive or diver's catch bag to sift through the mounds of
sand. If you come up with a cone, remember to handle it by the large end.
You also should remember that its proboscis (carrying its stinging tooth)
has a long reach. If I carry a cone without a catch bag, I keep my eye on
it constantly. Even a catch bag with a metal ring and handle is kept at
arms length when there are cones aboard.
Snorkeling into deeper water, ten to twenty feet, you will find
larger tracks, as if the snorkeler ahead of you had run her index finger
through the sand. In the mounds here you will find the larger, Gould's
auger. Often at these depths, sometimes in even shallower water, you will
encounter large schools of goatfish (weke), swimming along the bottom
with their barbels, or whiskers, touching the sand and evidently serving
as sensors as the fish search
for food. Occasionally you will see a spotted Eagle Ray
winging its way past as though it were a large underwater bird.
Another bird-like fish to look for here is the flying gurnard. Resting
on the sand with its blunt nose and tapered body, this fish looks somewhat
like a large version of the little blennies that are common in Hawaiian
tidepools. Closer inspection reveals enormous pectoral fins (forefins),
folded over the sides of the body like Count Dracula's cape. If you
disturb the fish, as it swims away from you its cape becomes a pair of large
wings on which it will glide back to the sand, not far away.
It is interesting to contemplate the possible adaptive value of
those wing-like fins. The flying gurnard is not a member of the
flying fish family, and evidently does not glide in the air above the water's
surface.
An animal you are much more likely to see is the lizardfish, although
you may have to look carefully because this fish often is buried
literally up to its eyeballs in the sand, waiting in ambush for prey.
When resting on the surface of the sand, it is lizard-like indeed--
in its shape, its scaly appearance and its posture, alert and propped
on its pectoral fins.
Now push on until the water is between twenty and thirty feet deep.
Here you will begin to see large star-shaped patterns in the sand,
a few large mounds of sand, some small tracks, and some very big
tracks. If you are up to the dive to the bottom, you will find a
huge starfish (possibly of the genus Luidia) beneath the star-shaped
pattern, perhaps a tiny octopus (sand octopus) in the center of a large mound,
a flea cone at one end of a small track, and a marlin-spike
auger at one end of a large track. The flea cones often will be dragging
little trailers of seaweed
on the surface of the sand. The marlin-spike augers commonly will have
shells with broken tips, but a few will have flawless shells with
remarkably sharp crowns. It is interesting to speculate about the
activities or circumstanes that lead to seaweed trailers or
broken shells in the middle of this sandy expanse. Regarding the latter,
one must remember that large waves will stir the bottom even in water
this deep, and occasionally this presently peaceful place is
under very heavy surf.
Probably as a consequence of such stirring of the bottom in even
deeper water, the usual home of the Kona crab, after
a storm one may find those animals half buried in the sand in
water twenty to thirty feet deep Although the legs of these crabs are too small to have
much meat, their bodies are not. The meat is delicious, especially as stuffing in
Maui avocados. The rear legs of the Kona crab are flat, as are
those of many sand-dwelling crab species including the
Dungeness crab of the North Pacific, an
adaptation that suits the habitat well, allowing the animal to
burrow rapidly backward into the sand.
If you try to grab it as it goes, you are almost certain to be
left with nothing more than a handfull of sand. If you are
bare-handed and unfortunate enough to get ahold of the crab,
its sharp carapace almost certainly will slice your hand (unless
you have happened on a crab that has recently molted).
How does one catch a Kona crab? One method
is simple, but takes two snorkelers. While one dives to a position
about fifteen feet ahead of the animal and holds its attention
by waving his hands or otherwise looking preposterous, the other
dives to the floor of the sea about twenty five feet directly
behind the crab. The diver behind the crab carries a
standard diver's catch bag with its heavy wire ring wide open,
forming a device that looks like a butterfly net without a handle.
This diver swims slowly along the bottom toward the crab and then thrusts the ring of
the catch bag deep into the sand directly behind the crab. More
times than not, the crab will burrow right into the catch bag. It
is interesting to contemplate the possibility that the Kona crab has
an attention that one is able to hold. What does that imply
about its nervous system? I don't believe the answer lies merely in the visual field
at the level of the compound eye.
Pushing on to water between thirty and forty feet deep, you will continue to
find mounds, stars, and marlin-spike augers, but you occasionally will find
large spindles. If you plan to free dive (dive without SCUBA gear)
in water this deep, I have three suggestions for you. First, do not
hyperventilate before you descend. Although hyperventilation may reduce
the urge to breath, it is very dangerous. After hyperventilating, some divers have passed
out as they started their descents (as a consequence of a sudden, reflexive
drop in blood pressure), and others (fooled by the lack of carbon-dioxide
stimulus) have overstayed their oxygen reserves and passed out
before ascending. It is best to avoid hyperventilation and to dive
within your own comfortable breath-holding capacity. My second
suggestion applies to old-fashioned face-plate style masks. If you use such a mask,
be sure to keep it pressurized as you descend;
blow a little air into it through your nose. Otherwise the mask will
compress and the glass plate may push against your nose hard enough
to start a nosebleed. My third suggestion is to plan a slow ascent.
If you exhaust your breath-holding capacity at the bottom,
then rush for the surface, the rapid change in (thoracic) pressure may
produce short-term arrhythmia (erratic beating) of the heart. Even
if you are not an avid diver, if you are in good health and, like
the farmer lifting the calf each day as it grows, you have
snorkeled and dived in deeper and deeper water, spending a few
days with the smaller augers, a few more with Gould's augers, and
so on, then you soon may be up to diving for spindles.
The last adventure over the sand that I want to relate is at the
forty to fifty foot level. Here, on a calm day, the bottom will be
clearly visible, but the small tracks and snails will be too far
away to be seen easily from the surface. If you look carefully,
among the scattered pebbles of coral on the bottom you may see an
oak cone. In fact you may
see several, because these large cones tend to
congregate on the surface of the sand. By this time, you
may have begun to wonder why different species seem to favor
different water depths on the bare white sand. This zonation
effect is not as strict as it may seem; oak cones and marlin-spike
augers, for example, occasionally move into shallow water (a bit
more than knee deep), and the inconstant auger sometimes is found
in the calmer water behind the surf. Nevertheless, there do
seem to be strong tendencies to divide the turf. This may
have to do with the locations of different food sources (which
merely pushes the question of "why" to another trophic level), or
it may be a result of various adaptations of form among the
sea snails of the sandy bottom, allowing each of them to
operate most effectively at depths with a particular (normal)
degree of wave action, or (most likely) it may be the result
of a set of interesting circumstances that will provide
enjoyable research for a future investigator and surprises
for the rest of us.
On my favorite Maui
beaches, if you have reached water forty to fifty feet deep, you
are approximately 500 yards from shore. Snorkeling along the
surface, seemingly able to see forever in every direction, one
feels suspended in space, drifting over a quiet world of
bluish water, sand, and scattered small, deep (patch) reefs.
If one puts on SCUBA gear and descends to the bottom, this feeling of
suspension disappears; the sand and reefs close in, and the
awareness of the expanse of water above is attenuated. Nevertheless,
for most of us mortals, SCUBA is the only way to explore the bottom
beyond these depths.