What does it look like?
Adult crabs can grow up to about 12 centimetres across the shell (carapace). The shell is covered in fine hairs, although these aren’t always easy to see.
A key identifying feature is the row of six sharp spines on each side of the shell, just below the eyes. Each claw also has five prominent spines on its upper surface. Colour can vary, ranging from pale green or olive green through to a deep chestnut brown, often with purplish markings on the shell.
In their native range in South East Asia, Asian paddle crabs live in intertidal and subtidal areas, down to depths of around 15 metres. They’re found on sandy, muddy and rocky reef habitats.
In New Zealand, they are most commonly found in estuaries, particularly where the seabed is made up of firm sand, muddy fine sand, or muddy shelly sediments. Asian paddle crabs are generalist predators, feeding on a wide range of prey including shellfish, other crustaceans, fish and polychaete worms.
Why is it a problem?
Asian paddle crabs are highly aggressive and can out compete native crabs for space and food. They also prey on a wide range of native species, including shellfish, fish, other crustaceans and polychaete worms, which can disrupt local ecosystems.
They are particularly successful invaders because of their life cycle. Asian paddle crabs grow quickly, mature fast and reproduce in large numbers. They’re also very adaptable, tolerating a wide range of environmental conditions and feeding on many different types of prey.
An adult female can produce tens of thousands of eggs at a time, releasing them several times each year. The larvae are especially good at spreading and they can survive in different water temperatures and salinity levels and drift in the water for three to four weeks. During this time, tides and currents can carry them long distances, allowing the species to spread rapidly.
Control methods
You can help prevent the spread of marine pests by:
- Regularly cleaning your boat’s hull – keep fouling growth to no more than a light slime layer.
- Applying a thorough coating of antifouling paint and keep it in good condition.
- Ensure your hull is clean and free of fouling before you travel to a new area.
- Clean and dry any marine equipment (e.g. ropes, lines and pots) before using in a new area.
- Inspect areas on your boat that retain water for signs of marine life.
- Check for aquatic weeds tangled around anchors, trailers and other equipment.
Related links
Management Programme
Unwanted Organism
An unwanted organism is any organism that's capable of causing harm to natural or physical resources (like forests and waterways) or human health. A number of introduced pests in New Zealand are classed as unwanted.
