Hundreds of spider crabs occupy water around tiny SA town

ABC NEWS (Australia)

A cluster of giant spider crabs has descended on Coffin Bay in South Australia with one local fisherman describing it as a 'big invasion'.

Transcript

00:00So there could be hundreds if not thousands of spider crabs here in Keleti Bay.

00:07So we're in Keleti Bay.

00:09It's the home of the world famous Coffin Bay oysters and we're here with a local oyster

00:15grower who actually made the discovery.

00:17So I'll let him explain what's happening.

00:19Lester Marshall, when did you make the discovery of the spider crabs?

00:23Well we sort of found them in our lease about two weeks ago, but I didn't realise that we

00:29had so many up until only really, well two days ago when Mark put his drone up and flew

00:35over our farm and he went, my goodness have a look at this, there's thousands and thousands.

00:40We knew there was mobs of two or three hundred, four hundred coming out there but, which I've

00:46never seen here before, it's quite unusual, but when we saw it from the air we went, there

00:51is a, there's literally thousands and thousands and we didn't know what they were doing and

00:55yeah, we'll have to watch the noise behind me.

00:58We've got the oyster boat, she's coming up, they've been out harvesting this morning so

01:04they've had to put their wetsuits on and go and grab a heap of oysters, sorry about the noise, but.

01:12And what do you think could be causing the spider crabs to come in?

01:17Well I reckon it's moulding, safety numbers they seem to think, so yeah, so we, as far

01:25as we know, there's a lot of soft ones and then there's a lot of hard ones, hard shelled

01:30and so what we're trying to do is understand a bit more about them.

01:34I mean we've seen them on and off throughout the years but never the amount of numbers

01:39we've seen, I've never seen them just here, in these numbers ever, so whether it's tied

01:44in with this upwelling we were talking about before and the amount of food that's been

01:48in Coffin Bay since mid-January, I'm not too sure, but certainly it must have some connection

01:54you would think, but yeah, no, they're an interesting animal, something we never take

01:58much notice of, they're not a commercial species, nobody eats them, I tried one back many, many

02:04years ago and it was nothing to rave about, so, but yeah, so I think they just come here

02:08to try and moult and in protection of the shallows, the unusual thing we're finding

02:14is that's what they get in groups, the hard ones that aren't moulting protect the ones

02:19that are softer underneath or on the sides and then they must all, once they've worked

02:24out what they're doing, they all then say, yep, let's get out of here and they vamoose

02:28and head out to the, where they go, the continental shelf or where they can, nobody knows.

02:33And has it been a bumper year for oysters?

02:36It has, no, look, it's been phenomenal, the amount of food has been, the nutrients, the

02:42big upwelling, the water temperature normally is 18 degrees out, 16 to 18 out in the ocean

02:47and it was down around 13 and that was all from the upwelling of the cold water which

02:52brought the nutrients and all the algaes and was up, you know, 4.2 million algae cells

02:58per litre and it was, the oysters just took off, as did the barnacles and look, you know,

03:04it's had to have a flow on effect with other marine creatures, you would think.

03:08So it remains a mystery what they're doing and why they've arrived in Coffin Bay?

03:12Yeah, and that, so, excuse me, so what's happened, there's a lady called Elodie Camprazi

03:19from Port Phillip Bay, now she's only, she started studying, got money to study spider

03:23crabs in Port Phillip Bay, they have the same thing happens over there but it's only been

03:27going for two years and she does one day a week on it and they put little acoustic things

03:33on their back and they've got listening devices, posts around Port Phillip Bay to try and track

03:38where they go but once they leave the bay, they disappear and they have no idea where

03:41they go, what they do and look, she didn't even know they existed here in South Australia.

03:46So I mean, as far as oyster farmers and locals, we've been saying, oh, well, we've seen spider

03:49crabs here for years and years, what's the big fuss?

03:52But she's going, well, actually, no one knows anything about them and I went, oh, well,

03:56that's interesting and which, you know, I think we touched on before, this oyster reef

04:01restoration project that we're looking in Coffin Bay to enhance the biodiversity in

04:06Coffin Bay, that's just starting to get some legs and that's some of these native Angarzi

04:15oysters that, these are the old ones that were harvested back in the 1800s and they're

04:19literally tens of thousands of kilos.

04:23So anyway, we think that the oyster reef restoration project is, with its biodiversity slant, will

04:32add some, what's interesting as far as the aggregation of the spider crabs and what

04:38the connection that they have with the bay and why they come here.

04:41And I think there'll be a lot of other sea creatures.

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