Sunday, 15 February 2015

Narooma Hermits

The first weekend of February, after school had resumed and the crowds at the coast had mostly dispersed, we had a family long weekend at Narooma, on the New South Wales south coast. Narooma is a coastal town of 8,500 people and is situated between the surf beaches to the east and Wagonga Inlet which stretches westwards into the hills. The main body of Wagonga Inlet is connected to the ocean by a strongly tidal channel that at low tide has some extensive patches of sand/mud flats which are good for shorebirds. It's a lovely place, in an idyllic location, and I've been there quite a few times. It's also the launching place to go to Montague Island, some 7 km offshore, where I've been several times to participate in shearwater surveys.

On this occasion we stayed in a cabin at the caravan park on the ocean beach rather than at the Big 4 on the inlet. Our getting up early on the first morning was rewarded with a truly magnificent sunrise.

Sunrise over Montague Island, NSW  (7 Feb 2015)

Glasshouse Rocks sunrise, Narooma, NSW  (7 Feb 2015)

I could put up 100 more sunrise photos, all different, but this post is about hermit crabs - the biggest I've ever seen. I've seen plenty of hermit crabs in various places, mostly in warmer waters than the NSW south coast, but they have generally been fairly small and I haven't tended to try to photograph them. One exception was a cute little guy James and I found at Woody Head (Bundjalung National Park) near Iluka in northern NSW in 2007...

A hermit crab from Woody Head on the the north coast of NSW, July 2007.
Possibly a species of Dardanus, Family Diogenidae?

These Narooma ones, however, were huge. They were exposed at low tide right in the muckiest corner of the Narooma boat harbour, still just catching the late afternoon sunlight, and were within a few metres of the harbour wall. They were quite accessible if you were prepared to jump the two metre drop and squelch about the rocks, and oysters. 

There were at least a dozen or so of them visible in this little muddy corner and I ended up with photos of eight of them. It seems they are Stridulating Hermit Crabs Strigopagurus strigimanus

#1 Stridulating Hermit Crab Strigopogurus strigimanus - Narooma NSW, 7 Feb 2015

#2 Stridulating Hermit Crab Strigopogurus strigimanus - Narooma NSW, 7 Feb 2015
#3 Stridulating Hermit Crab Strigopogurus strigimanus - Narooma NSW, 7 Feb 2015

#4 Stridulating Hermit Crab Strigopogurus strigimanus - Narooma NSW, 7 Feb 2015

#5 Stridulating Hermit Crab Strigopogurus strigimanus - Narooma NSW, 7 Feb 2015

#6 Stridulating Hermit Crab Strigopogurus strigimanus - Narooma NSW, 7 Feb 2015

#7 Stridulating Hermit Crab Strigopogurus strigimanus - Narooma NSW, 7 Feb 2015

#8 Stridulating Hermit Crab Strigopogurus strigimanus - Narooma NSW, 7 Feb 2015

It wasn't until I was cropping the photos for this post that I realised some of the white spotting on crab #8 was in fact several small goose-barnacles attached to its legs. A variety of marine encrustations on the shells is expected, but I wonder if the crab is aware of these goose-barnacles and what impact they might have if they grow larger. I assume they are out of reach of the crab's powerful nippers. 

My understanding is that hermit crabs will use whatever shells are available to them that are of appropriate size (and are vacant!). Given the size of these crabs, I'm surprised there are enough large shells to go around. I don't know a lot about shells, but the ones used by these crabs appear to be some species of large spindle or tulip shell (Family Fasciolariidae), possibly Pleuroploca australasia. The hermit crab from Woody Head in the first of these hermit crab photos is using a species of triton from the Family Ranellidae.

Stridulating Hermit Crab #8 has a crop of small goose-barnacles growing on its legs.

Stridulating Hermit crabs grow to a length of 130 mm. They eat both plant and animal matter, including shellfish, and are found from shallow coastal waters to depths of 200 m around the southern Australian coast (from Bunbury WA to Sydney NSW). One reference (Edgar,2000) says they are common on shallow Tasmanian Reefs but uncommon in diveable depths around the mainland. I don't think these crabs have read that book! 

They're called stridulating hermit crabs because they can produce a noise by flexing and extending parts of their claws, supposedly to scare off predators and deter other crabs from encroaching on their patch. 

This would presumably explain their scientific name, Strigopogurus strigimanus, which means "furrow-handed furrow-crab" [striga: Latin - ridge, furrow or groove; pogouros: Greek - crab; and manus: Latin - hand], the ridging of the claws enabling the stridulation noise to be made.

There are two families of hermit crabs - the Paguridae and the Diogenidae. The latter are also sometimes called the left-handed hermit crabs because the left chela or claw is usually enlarged (rather than the right as in other hermit crabs). The stridualting hermit crab is one of the 430 or so species of Diogenidae worldwide.

As far as I can deduce, Strigopogurus strigimanus was first collected from Tasmanian waters by someone called Gunn in 1838 while on the 'Voyage of H.M.S. Erebus & Terror, under the command of Captain Sir James Clark Ross, R.N., F.R.S., during the years 1839 to 1843'. It was described and named several years later (in 1847), by Adam White, as Pagurus strigimanus, based on the specimen by then housed at the British Museum. 

Adam White was an assistant at the Zoology Branch of the Natural History Division of the
British Museum for 28 years from 1835. He left a prodigious scientific output, including many works on crustacea. 


Australian Marine Life - The Plants and Animals of Temperate Waters. Graham J. Edgar, 2000. Reed New Holland, Sydney.

Seashells of South-East Australia. Patty Jansen, 2000. Capricornia Publications, Sydney.

A Handbook to Australian Seashells - On Seashores East to West and North to South. Barry Wilson, 2002. Reed New Holland, Sydney.

1 comment:

  1. It's remarkable how often wildlife doesn't bother to read the field guides. I have that problem all the time.