Pheromones are chemical communication signals between organisms of the same species. A sender emits minute amounts of pheromone into the environment, and a receiver detects the signal in specialized olfactory receptors. Pheromones deliver information about food, domination, sex, and territory. Their advantage is that they can be transmitted in the dark and around obstacles. In addition, a small amount lasts for hours or even days, and has a good range. A disadvantage of pheromones is that they depend on diffusion or currents for transmission and that can be a slow process.

Many types of seaweed use pheromones for sexual reproduction. When an egg breaks out of the female sex organ, oogonium, at the tip of the plant, it sinks to the ocean floor and secretes pheromones into the water. Drifting parcels of sperm detect the chemical signal, burst open, and release the sperm. The male gametes swim toward...