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Seashore Resource |
Intro | 1.Field
Trip | 2.Rocky Shore | 3.Plankton |
4. Creatures of the Sandy Beach and Mudflat Scroll down to find information on these mudflat creatures
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Mud crabs This crab chews balls of mud, sorting and sieving out the diatoms to eat and spitting out the left-over mud as pellets. The crab’s burrow is its ‘air-raid’ shelter where it hides from enemies like the kingfisher ‘dive-bomber’ and the white-faced heron. When the tide is out the puddle in the botton of the burrow keeps the crab’s gills damp. A male crab has large front claws or pincers and a narrow tail. If you pick up a crab and carefully turn it over, you will see the tail tucked under the body, as shown in the diagrams below. |
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Note: only half the legs and none of the pincers are
drawn so you can see more clearly. A female crab carries her eggs under her tail, that’s why it’s so broad. |
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| Mud snail or
titiko I digest the diatoms and bacteria and pass out the mud. This makes LOTS OF POOHS! Mud snails are like gardeners. They sift and turn the mud and make diatoms grow better. It’s heavy shell protects the mud snail from predators. (enemies that would like to eat it) Mud snails are hermaphrodite (her-maff-ro-dite) which means each snail is both male and female. Any two snails can pair up, swop sperms and then lay eggs. |
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This circle contains up to 12,000 eggs! |
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Enough diatoms grow on a hectare of mudflat to feed half a million (500,000) mud snails! Because they need sunlight and oxygen from the air, the diatoms can only grow in the top few centimetres of mud. If you dig deeper the mud is black and stinky! Things down there live without oxygen and they make ‘rotten eggs’ gas – hydrogen sulphide. Pooh! |
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plankton soup eaters Seawater is like watery soup. In it floats PLANKTON, which is made up of tiny plants (diatoms and dinoflagellates) and tiny animals, so small you can’t see them. To get the plankton out of the seawater, you need a sieve. Shellfish that feed on plankton have special gills, adapted as sieves. |
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This is a diagram of
the inside of a cockle. The arrows show the direction seawater is moved across sieve/gills by hairs which trap the plankton then move it to the stomach. |
| Twice a day, every day of
the year, the tide brings in water full of plankton. There is so much of this tiny food
that it can feed huge numbers of cockles and pipi and tuatua. In Golden Bay, near Nelson, there are up to 200 cockles on every square metre (equivalent to 100 cockles on a school desk)! In turn, these shellfish are food for birds and fish, making a FOOD CHAIN in the estuary. Migratory birds, for example godwits, fly more than 7000 kilometres from Siberia to eat the crabs, shellfish and worms of our estuaries. |
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