Sunday, January 13, 2013

Dive if you dare - the reef at night

As the little sister of two mischievous brothers, I’ve been subject to my fair share of practical jokes. So when many years ago, one of them suggested that we go night snorkelling, I thought “Ha! I’m not falling for it this time, what a ridiculous idea, we won’t see anything”. Then I was given an underwater torch and proved completely wrong.  The reef never sleeps; the familiar faces of the day are swapped for weird and wonderful creatures of the night. Jump in about half an hour before sunset and you’ll see the changeover, the fish take on a new lease of life, rushing around like maniacs, chasing each other and catching their dinner before bedtime.

Twilight feeders have an advantage; their light-loving prey cannot see properly in the fading sunshine, and their own nocturnal predators have not yet woken from their slumber. There is a word for this - Crepuscular- it sounds like some sort of disfiguring disease, but no, it’s used to describe an animal active mostly at twilight.  (Predictably it’s derived from Latin, which was absolutely my worst subject at school. Latin is annoyingly used extensively in Biology so my advice to mini Marine Biologists is to stay awake during Latin classes - they’re not lying, it’s useful!)

Groupers are often crepuscular feeders; if you stand on the jetty near our Park Hyatt Maldives Hadahaa sign you will often see the big daddies terrorising schools of innocent baitfish peacefully resting in the shallow waters.  Sharks have excellent night vision too and are particularly fun to encounter in the dark; like thieves in the night their eyes glow with menace. They have a reflective layer behind the retina called the “tapetum lucidum”, consisting of lots of tiny little plates covered in the splendidly shiny substance “guanine”. This multitasking molecule is not only found in sharks’ eyes, but it’s responsible for shiny things the world over, from the sheen of the shiniest fish to cosmetics. Even more incredible, it’s a vital component of DNA; does this mean that DNA is sparkly? Sadly I think not.

Nocturnal fish are usually carnivores, particularly if they feed on zooplankton. After dark, the bigger more delicious plankton rises from the deep, you can see it twitching and wriggling around in the beam of the torch. Herbivores such as parrot and surgeon fish are almost always diurnal, probably because finding food is easy but they need to be able to see what is edible and what is not. At night parrotfish really do bed down for the evening; they hide by wriggling into cracks in the coral and thanks to their lack of eyelids they fall into what looks like a “zombified” trance.  Some species of parrotfish sit inside a gooey bubble of mucus which is thought to prevent their scent from traveling through the water and also wards off the attack of blood sucking isopod parasites.  

Ugly squelchy things seem to prefer the cover of darkness too. Yesterday we saw the Maldivian sponge snail, and last week we came across a pair of mating sea-hares – giant slugs which can reach up to 30cm in length.  Many armed monsters such as imperial urchins and delicate feather stars emerge from hiding and little shrimps chirp away, their eyes glistening from the crevices. Part of the fun of night diving or snorkelling is that it allows you to focus your attention to only the small patch of reef illuminated by your light; so invariably you notice the detail of things.  Bioluminescent plankton produce the most magnificent magic trick of all; if you were to turn off your torch and flap your arms around in the dark silky water, little flashes of light no larger than pin pricks start appearing all around you - a truly beautiful reminder of the wonder of nature and how much life and excitement there is to find in the ocean.  
Twilight diving on the Hadahaa house reef

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