Lesser knob coral

The lesser knob coral (Cyphastrea serailia) is not one of the reef's showy giants, yet it is worth learning to recognise: its encrusting or cushion-like, sometimes knobbly colony is covered in tiny round corallites barely 2 millimetres across, rising from the base tissue as little bumps. It is usually brown, cream or olive-green, and the rims of the cups are often paler, giving the surface a finely speckled look – as if someone had scattered it with pinheads.

Cyphastrea also lives in symbiosis with zooxanthellae: the photosynthesising single-celled algae in its tissues supply most of its energy, so it needs light – but the genus is famously tolerant of dimmer conditions and murkier water, thriving in spots where many other corals would give up. It grows slowly, thickening only a few millimetres a year, and reproduces by mass spawning: on summer nights it releases gamete bundles into the water, and the larvae readily settle even on shaded, vertical surfaces.

Around Hurghada you can discover it on the lower, shadier parts of reef slopes, under overhangs and even on the metal surfaces of wrecks – you have a good chance of finding colonies around the El Mina wreck and on the walls of Umm Gamar, though it also occurs on shallow reef tops, so it may cross your path while snorkeling. Its very modesty makes it easy to grab or kneel on by accident: don't. Every touch damages the living tissue, and a 30-centimetre colony can represent decades of work – hover, look, photograph, but leave it untouched.