Video | Business Headlines | Internet | Science | Scientific Ethics | Technology | Search

 


Paddle Crabs; Cannibals Of The Seashore

No.2: Paddle Crabs Cannibals Of The Seashore

Ever had a crab nip your toe at the beach? The culprit is most likely the paddle crab.

This agile swimmer is found in the intertidal zone (between high and low tide marks) all around New Zealand and in southern Australia, down to depths of 100 metres. It’s one of nine species of swimming crabs in New Zealand.

“Paddle crabs prefer sandy bottoms, especially on sheltered surf beaches,” says Shane Ahyong, crab taxonomist at NIWA. They’re especially active at night and at high and low tides, although you’re most likely to see them at low tide. During the day, they spend most of their time buried in the seabed, with only their eyes and antennae protruding.

“If you’re not lucky enough to spot a live paddle crab, you’ll often see their discarded or dead shells washed up on the beach,” says Dr Ahyong.

“Paddle crabs can swim sideways very quickly using the paddles on their rear legs. They also use their paddles to dig themselves backwards into the sand, which they can do very quickly when threatened.”

Their main predators are stingrays, dogfish, snapper, and other predatory fish. Humans also fish them for meat and bait. As for their prey, paddle crabs will eat almost anything, and even cannibalise smaller paddle crabs, but their staples are shellfish and small fish.

“They are aggressive but would only attack a human in self-defence. If a paddle crab nips you, it’s probably because you stood on it,” says Dr Ahyong.

Like cicadas, paddle crabs ‘stridulate’ – producing sounds by rubbing parts of their body together. In the crab’s case, they rub one of their legs against a rasp on the underside of their claw to serenade prospective mates. Their deepwater cousins don’t have rasps, but instead have evolved iridescent patches on their bodies to signal other members of their species, says Dr Ahyong.

Species Fact File

*Common names: paddle crab, common swimming crab
* M?ori name: p?paka
*Scientific name: Ovalipes catharus
*Type: swimming crab
*Family: Portunidae
*Size: up to 15 cm across the shell
*Lifespan: 4 years
*Diet: Shellfish, small fish & crabs, whatever they can catch or scavenge
*Reproduction: Female lays fertilized eggs, from which larvae emerge. There are several larval stages.
*Things you need to know: They’re agile swimmers, can bury themselves quickly in the sand, and will only bite you in self-defence!
Something strange: When close to breeding, the male carries his mate underneath him until she moults, then mates with her.

ENDS

© Scoop Media

 
 
 
 
 
Business Headlines | Sci-Tech Headlines

 

Revenue Renewal: Tax Modernisation Programme Launched

Revenue Minister Todd McClay today released the first two in a series of public consultations designed to modernise and simplify the tax system. More>>

ALSO:

Scoop Business:
NZ Puts Seven New Oil And Gas Areas Put Up For Tender

A total of seven new areas will be opened up to oil and gas exploration under its block offer tendering system, as the New Zealand government seeks to concentrate activity in a few strategically chosen areas. More>>

ALSO:

Half Full: Dairy Payouts Steady, Cash Will Be Tight

Industry body DairyNZ is advising farmers to focus on strong cashflow management as they look ahead to the 2015-16 season following Fonterra's half-year results announcement today. More>>

ALSO:

First Union: Cotton On Plans To Use “Tea Break” Law

“The Prime Minister reassured New Zealanders that ‘post the passing of this law, will you all of a sudden find thousands of workers who are denied having a tea break? The answer is absolutely not’... Cotton On is proposing to remove tea and meal breaks for workers in its safety sensitive distribution centre. How long before other major chains try and follow suit?” More>>

ALSO:

Get More From Scoop

 
 
 
 
 
 
 
 
 
Sci-Tech
Search Scoop  
 
 
Powered by Vodafone
NZ independent news