Scientists are having trouble identifying the crabs and say they've not seen anything like it before.
Presenter: Geraldine Coutts
Speaker: Dr Andrew Rossiter, the director of the Waikiki Aquarium
ROSSITER: They're very small, very hard to identify and there's not a lot known about the larval stages of crabs, so it's a pretty tough thing. The way we're approaching it at the moment is we've collected a bunch of them, we've got them behind the scenes and we're trying to rear them up to adulthood so that we can be sure of what they are.
COUTTS: How far into that are you, how big do they get?
ROSSITER: They actually grow to about six inches in size. At the moment they're probably a little bit bigger than peas so you can imagine they've got quite a way to go.
COUTTS: Well trying to identify these crabs, are they unnamed or have you given them a working title?
ROSSITER: Yeah we think they're what's called 7-11 crabs or also known as the spotted reef crab, but that's a best guess it's not a strong statement.
COUTTS: So what do you do now to try and absolutely identify them? Do you put it out to the world scientists to say have you seen this critter?
ROSSITER: We've actually got somebody at the university doing a DNA analysis on them, but that's only good enough, it's only of any use if there's already a sequence of that species. But it's a step forward.
COUTTS: And if that is the case where have they come from?
ROSSITER: If it is the 7-11 crab they're found here naturally, they're found right through the Indo-Pacific, the Red Sea, Japan, China, Australia. So when they spawn, when they breed the eggs and larvae are washed offshore, they live in the plankton, they grow up to about pea-sized and then they move onshore, but never in such huge numbers as this.
COUTTS: Well why do you think they are such huge numbers? But before we get to that it makes it more curious if they're actually indigenous to the area?
ROSSITER: Right, right. There was a case in 2004 I believe where a significant number were washed up, but nothing on this scale. For something of this magnitude to happen it has to be environmental or ecological, so people have said it's a slug of cold water come in, a slug of warm water, pollution. But if it were any of those it would affect other species as well. So what I think has happened is that it's been an exceptionally good year for the breeding of this species, there's millions of them offshore and an onshore blow has probably aggregated them and swept them onshore all at one time.
COUTTS: Well what do you do now, are you going to try and maintain the population so that they stay there?
ROSSITER: We've got some behind the scenes but in terms of on the reef itself the little fishes are having a feast, so I think it's self-regulating.
COUTTS: Now to ask this question is a must actually, have you popped any into the pot, what do they taste like?
ROSSITER: These things are about pea-sized, the shells are pretty soft, I would imagine dipped in breadcrumbs and fried they'd be delicious, but I haven't tried yet.
COUTTS: And do you think that they'll be sustainable, they won't be wiped out, that they'll live on happily in this cycle that you've described?
ROSSITER: Yeah given the numbers that have come in some of them have bound to have settled out, so I would suggest that probably in three or four years they'll be a lot of adults of this species present once they reach adulthood.
COUTTS: And most of them are dead when they arrive anyway in this particular population?
ROSSITER: No actually most were alive, it's only when some of them got washed up onshore that they died. So in some places there are bays around the shore and the water was absolutely purple with these things, and people were swimming in there and they said they were absolutely covered in them and the little buggers were pinching them as well.
COUTTS: Well that sounds like a lot, can you put a number on it, how many have actually swum ashore?
ROSSITER: Probably millions.
COUTTS: Wow, and are many of them making it ashore, are they nipping the people on the beaches as they're trying to get a suntan?
ROSSITER: It's only in certain parts of Oahu and they're also on the big island as well. And there was a hurricane passed by here about two weeks ago so we think that may have caused an onshore blow because they're only on one side of the island. So they're not everywhere and the numbers have gone down now, there's not many being washed up at all.
COUTTS: So how does this leave you with the Waikiki Aquarium, is it the kind of thing you'd like to maintain and have in the aquarium or you're quite happy for it to be cyclical?
ROSSITER: Yeah we've got some in the aquarium, we're going to grow them up and then we'll put some on display for sure. But it's all part of the pattern of nature so some years are good for some species, some years are bad, and this is a good one for the 7-11 crab.
COUTTS: And are you working with the university or is this something that you're doing at the Waikiki Aquarium?
ROSSITER: We're actually part of the University of Hawaii.
COUTTS: Alright so they're doing the testing for you?
ROSSITER: We're doing it altogether yeah. And the mission of the aquarium is education, conservation and research, so something like this is right up our alley/
COUTTS: How long will it be do you think before they grow to that six-inch diameter that you were talking about earlier?
ROSSITER: Again nobody knows how quick they grow but I would guess within three or four years they'll be at least three or four inches.
COUTTS: Well for the Waikiki Aquarium is this actually exciting or is this just ho-hum for you?
ROSSITER: I think it's brilliant.
COUTTS: And what about the spectators or the visitors to the aquarium, do they think it's pretty cool too?
ROSSITER: Yeah they're surprised, they're absolutely amazed that there are so many of one species all present at one time.
COUTTS: Is it drawing extra numbers for you through the gates?
ROSSITER: I think the first day that there were a lot of crabs on the shore there were increased numbers in the aquarium and that's because people didn't want to go in the water. So instead of lying on the beach they came to the aquarium instead.