Brown algae

Rugulopteryx okamurae is a species of brown algae with a yellow-brown to dark brown coloration, native to the Northwest Pacific but now invasive in parts of the Mediterranean Sea. Its thallus is flat, leathery, and irregularly branched, often forming bushy clumps. Fronds are usually 5–25 cm long, with a smooth to slightly undulating surface, and can cover large areas of the seafloor when it grows densely. It forms dense mats on both natural and artificial hard substrata, including piers, ropes, buoys, and boat hull, outcompeting native species and altering marine ecosystems.