Lindisfarne National Nature Reserve Advent Calendar - Door number 13

It's as clear as mud.....our advent calendar door number 13 is mud! Yes we've not gone mad! Well actually it's mud and sand because they are an extremely important part of the Reserve. Without this there wouldn't be any habitat for the marine creatures and vegetation that provide food for the thousands of birds that use the Reserve. On the picture you can see the many of casts which are left behind by the worms living in the mud.