The soft one has fronds that are dark green, soft, and velvety, like green velvet or soft sponge. They are cylindrical, branching, and finger-like, often growing in dense, cushion-like clumps. The texture is soft and spongy, you can press it with your finger and feel it give. It looks comfortable, inviting, almost polite. It is the alga of the velvet surface, the one that is soft to the touch and easy to like. What makes it special is the invasion. The sea velvet is a model citizen in its native waters, but a troublemaker elsewhere. It has been introduced to Europe, North America, and South Africa, probably in the ballast water of ships or attached to imported oysters. In those places, it spreads rapidly, smothering native seaweeds and seagrasses, changing the character of the reef. It is the polite one with bad habits, the one that is a friend at home and a bully abroad, the one that reminds us that context is everything. The sea velvet is a green alga, a member of the Codiaceae family. It is made of thousands of tiny, finger-like filaments, packed together so densely that they form a solid, velvety mass. Each filament is a single cell, a long, thin tube with many nuclei. Under a microscope, the filaments are beautiful, a dense forest of green tubes packed tightly together. Biologically, the sea velvet reproduces by releasing spores from specialised structures on its fronds. It also reproduces by fragmentation, a piece broken off can grow into a whole new plant. This is why it spreads so easily, why a single fragment can colonise a new reef, why it is so hard to stop once it gets started. To find sea velvet is to find a soft, green cushion on the rock. It looks soft, feels soft, seems polite. But it is the one with bad habits, the one that causes trouble elsewhere, the one that proves that the most successful species are often the ones that are soft on the outside and tough on the inside.