Underwater close up shot of a decorator crab with seaweed on its back, walks along the sandy bottom that is covered in green and white seaweed

algea seaweed seabed intertidal pollution undersea carcinus maenas underwater ecology sea murky north sea acstrandkrab crustacean crab shell clearity water fishing ocean muddy wildife floor bubbles ripples nature depletion temperate animal stock rock sandy protection wild claw netherlands close up brown decorator light follow walking no people dapple