Big crabs are in the pacific - but they are ? mostly ? land based.  The
Coconut Crab -, /Birgus latro/,
I suspect they venture into the reef area for food as they eat most
anything from Coconut to dead crab and fish.  The
large ones are monsters - largest in the 25-30 (10-12kg)  pound range
and stretching 6' (~2m) across when captured and measured.

While the two would not likely meet, the Nautiluses we caught were in
the reef and close
by sand.  I think we only found them (foggy in the mind) after a storm.
I suspect they
were swept towards the reef by high storm currents.   We had a few crabs
on Kwaj, I rather expect
they went into a stew pot over the years along with octopus and squid
that were swept in.

Nautiluses might reside in deep reef and surface when shook out of a hole.

Exploring the outer reef wall on Kwaj would be an enlightening trip.
Lobsters were just below the edge on the ocean side.

I just opened our glassware display case and looked at our house
Nautilus. It has a W (wider than
the font) cut about 3/4" across.  It is healed over.  Might have been
two punctures or breaks.

The entire shell - the outer lip  shows  scars from banging into
something. All of them repaired
but it is consistent along the major 'cream colored' outer whorl.
Looking like only lip issues
but the W is on the inside of the whorl where a bite might be done -
across the back with the
'legs' on the outside away from the attacker.  I didn't see apposing
marks but with a new look
identified the W having rounded bottoms (as in teeth) while the other
breaks were rectangular
and across the width.   The opposing side was the deep inside curl and
maybe it is much
stronger.  Maybe this got away from a two tooth monster who broke the
other two in a bad capture.

What about barracuda as an attacker.  They get big and go where they
want, but mostly shallows.

Martin

Paul Callomon wrote:
> As Pete points out, it's not likely to be crabs attacking the
> Nautiluses, though the latter do sometimes approach the "bottom"; they
> are often seen around the sides of sea mounts and walls. To make the
> holes I'm talking about, however, something would need a gape of at
> least six inches. The biggest tropical crabs don't have claws anywhere
> near that big. In any case, crab claws cannot make fine punctures like
> this.
>
> Again: these are not bored holes, they are punctures. The holed
> Nautilus specimens we have to hand have obviously survived the attack
> by whatever caused the holes, but we have no way of knowing how many
> do not survive. My guess is that a big-mouthed fish or a shark just
> chomps down on the Nautilus, and keeps chomping until the shell is
> crushed. The fragments then fall into the abyss. If the shell stands
> up to the first chomp, however, the fish may open up again for a
> second try. At that point the Nautilus may be able to get away.
>
> On my wall I have an impressive Japanese fish print of a Napoleon
> Wrasse. They couldn't find a piece of paper big enough, so they used a
> bed sheet. This thing is five feet long and weighed about 160 lbs. It
> has a mouth that would easily engulf a Nautilus, and only four teeth -
> two upper and two lower. Napoleons are primarily deep reef dwellers
> and are active in the day (this one was taken by a spear fisherman at
> night, when it was asleep), so the question is whether they would come
> into contact with Nautiluses in the normal scheme of things. Sharks
> definitely would.
>
> PC.
>
> Paul Callomon
> Collections Manager
> Malacology, Invertebrate Paleontology and General Invertebrates
> Department of Malacology
> Academy of Natural Sciences
> 1900 Parkway, Philadelphia PA 19103-1195, USA
> Tel 215-405-5096
> Fax 215-299-1170
>
> >>> Pete Krull <[log in to unmask]> 9/28/2009 7:41 AM >>>
> In trying to solve this mystery we should keep in mind the life history of
> the chambered nautilus. It was my understanding that nautiluses are free
> swimming, at rather extreme depths most of the time. In photos of living
> specimens I have never seen any "growths" or parasites on the shell.
>
> Predation by crabs or boring mollusks or starfish seems unlikely in an
> animal that never comes in contact with the ocean bottom. Octopuses remain
> mostly near the bottom and unlikely to be able to get to nautiluses on a
> regular bases.
>
> Also, the nautilus does not have an operculum.  the soft parts are rather
> easily accessible so why would an animal bother to bore through the
> shell if
> it didn't need to?
>
> Predation by sharks or other large fish is a possibility I guess and
> perhaps
> the punctures are caused by the fish grabbing the soft parts and
> accidentally poking the shell at the same time. Squid are large and
> carniverous and might make a meal of a nautilus but I don't know how
> or why
> they would cause bored holes.
>
> Is there a possibility that the holes are bored from the inside?
> Perhaps an
> internal parasite needing a breathing hole?
>
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Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
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