• Add to new collection

    An interactive activity in which students construct the ideal habitat for crab larvae to resettle.

    You will need the Adobe Flash Player to view this.

    Rights: University of Waikato. All rights reserved. Published 31 August 2016 Referencing Hub media

    Can you build the ideal home for crab larvae to resettle? In this interactive, you need to select the ideal conditions for the rocky shore habitat for your crab larvae to resettle. They are swimming in from way out at sea, so it’s important to build just the right habitat.

    You will need the Adobe Flash Player to view it.


    Your goal is to build the ideal marine habitat for a crab.


    Build the ideal home for a crab. On each screen, make the best choices for your home and drag these into your environment. Sometimes there will be only be one correct choice, other times there may be up to three.

    Select your senses

    Imagine you are trying to find your way home. What senses would you use? Most likely, you would use your eyes. What senses do scientists think crab larvae use to find their way home? Choose two senses.


    Touch is very limited, you can’t touch things a long way away so it’s probably not a very good sense for finding your way over long distances. Scientists don’t think crab larvae use touch to find their way home.


    Vision is very important to humans. Most people would be able to find their way home using familiar sights. However, scientists think that vision is less important for crab larvae.


    Taste isn’t really used to help us find our way around. It is important when we eat, but we wouldn’t find home using our sense of taste. Scientists don’t think that crab larvae use taste to find their way.

    Smell (olfaction)

    Smells can help us find our way around. You might know you’re getting close to home when you can smell your mum’s cooking. Smell is very important to crab larvae in the sea and can help them find their way to a reef habitat.


    Humans don’t use our sense of hearing very much to navigate, but it is very important to crab larvae. Sounds of the reef, such as kina, shrimp and waves, can help the larvae find their way home.

    Select your animals

    Select the animals that belong in the ideal environment for a crab. Choose three animals.


    Kina live on a reef and make noises that attract other species such as crab larvae.

    Snapping shrimp

    Snapping shrimp live on the reef. The sound of their front pincer snapping attracts crab larvae to the reef.


    Reef sharks live on reefs throughout the Pacific but rarely visit New Zealand waters – it’s too cold. They eat fish and crustaceans such as crabs.


    Trout are found in freshwater streams and rivers throughout New Zealand. They don’t live on reefs or in salt water.


    Eels live in shallow water, both fresh and salty. Moray eels live on reefs around northern New Zealand. They eat crustaceans such as crabs.


    Pāua live on rocks just under the water surface. They feed on seaweed. Pāua are very picky and like clean water. They are a sign of a healthy reef.

    Select your vegetation

    Select the vegetation that belongs in the ideal environment for a crab. Choose three plants.


    Mosses are plants that grow in shady spaces on land. They are not found in a reef habitat.


    Kauri trees are found on the land in northern New Zealand. They are not found in reef habitats.


    Kelp is a type of seaweed that likes reef habitats. Kelp provides food for a range of species including kina, which help attract crab larvae to the reef.

    Lily pads

    Lily pads are the leaves of freshwater plants called water lilies. Water lilies are found in tropical climates and are not native to New Zealand.


    Flapjack is a type of seaweed found on New Zealand reefs. It provides food and camouflage for a range of reef species. This seaweed is important for a healthy reef.

    Wire weed

    Wire weed is a type of seaweed that is important for a healthy reef. It lives in the shallow water of the reef and provides food and habitat for a number of species.

    Select your substrate

    Select the substrate that belongs in the ideal environment for a crab. Choose one option.


    Sand is found on beaches and shallow bays. It is not a good habitat for crab larvae.

    Underwater rocky surface

    Rocks just under the water surface form reefs that are ideal habitats for crab larvae. The rocks support a range of animals and plants that help the crab larvae develop into an adult.


    Mud is associated with estuaries where freshwater rivers meet the sea. This area is very tidal and varies in salt content. It is not ideal for crab larvae.


    Concrete is a man-made material that should not be in the sea. It is not a very good habitat for crab larvae.


    Soil is found on land and is important for growing healthy plants. It is not found under water on reefs.


    Coral are small animals that group together to form colourful structures in tropical waters. They need to be warm, so there are no coral reefs in New Zealand.

    Select your water quality

    Select the water quality that you think crab larvae would like the most. Choose one option.

    Healthy clean water

    Healthy water isn’t polluted with rubbish or chemicals. Crab larvae will survive much better in clean water.

    Very polluted with sewerage

    Sewage is very toxic, it kills animals such as crabs. Crab larvae would prefer to live in nice clean water without pollution.

    Very polluted with rubbish

    Crab larvae need clean, clear water. They won’t survive in water that is full of rubbish.

    Select your water salinity

    Select the water salinity that you think crab larvae would like the most. Choose one option.

    Super salty water

    Too much salt will harm the crab larvae. Not many things can live in very salty water.

    Salt water

    All the world’s oceans and seas contain salt. This is the perfect habitat for a crab larvae.

    Fresh water

    Fresh water is found in lakes and rivers. Many plants and animals like to live in freshwater, but crabs need to live in the sea, which is salty.

    Select your sounds

    Select the sounds that belong in the ideal environment for a crab. Choose three sounds.

    Feeding kina

    Kina make noise while feeding. This attracts crab larvae to the reef and may be a very important cue in settling the reef habitat.

    Snapping shrimp

    When shrimp snap their front pincer, together they make a sound. This noise helps crab larvae find their way to the reef habitat.

    Water turbines

    Water turbines can be put under water to generate electricity for human use. They are noisy and can interfere with the sounds from the reef. The presence of water turbines will likely cause crab larvae to get lost.


    Speedboats are used by people to go fishing or for exploring the bays around the coast of New Zealand. The motor makes a lot of noise that can confuse crab larvae trying to find their way home.


    Waves make different noise if they are crashing on the rocks of a reef or splashing gently on a sloping beach. The crashing waves of a reef will help attract crab larvae.

    Rock music

    Rock music is made by humans and shouldn’t be found around the reef. Crab larvae are unlikely to be attracted to the sounds of rock music playing.

    Image acknowledgment: Alison Perkins