As the day’s f irst rays of sunshine
filter down through the water to bathe North Lighthouse Bommie in muted early-morning light, the site is obscured by fish.
A ROW OF BROWN SWEETLIPS is backed up along the sand at the base of this coralcovered structure just west of Lady Elliot Island, their noses pointing into the current. It’s a school of a dozen adults that would have been foraging overnight for crustaceans, fish, sea urchins and molluscs over the sandy f loor away from the bommie.
But early-morning light triggers crepuscular predators into action, including sharks, which need light to hunt because they rely on eyesight, but use the shadows of dawn and dusk to hide from wary prey. It’s a dangerous time in the ocean for anything that’s not top of the food chain and these sweetlips are among a throng of f ish staying close for now and remaining watchful. Hovering off to one side is a small school of orangetailed surgeonf ish, which graze on algae. To the other side a group of adult motherin-law f ish, also known as painted sweetlips, are just waking up and will soon be heading out to forage across the sea f loor for small f ishes and invertebrates.
Above them a mixed school of plankton-eating fusiliers and drummers has assembled, using the bommie as camouf lage while also relying on the safety-in-numbers approach. Both strategies make them seem less like hundreds of manageable bite-sized morsels and more like one large formidable creature that any potential predator would baulk at approaching. Another school of just drummers hovers above the bommie, facing into the current, which suggests they’re feeding, picking up tiny creatures passing in the plankton. A school of small black damself ish is also up in the water
column doing the same. These little reef f ish are highly territorial and this would be their bommie. They’ll aggressively defend against other small fish looking to move in and take advantage of the site’s hidey-holes and crevices, which provide shelter at night or whenever there’s a threat. They’ve obviously judged that the passing plankton is a good enough feed to risk exposure. They need to be careful, though, because a couple of coral trout are lurking around the periphery. These often solitary predators will take on any fish smaller than themselves and damselfish make a perfect meal. A group of bottom-feeders – including a goat f ish sporting a pair of sensory barbels, and a moon wrasse, coloured gorgeously green with red stripes and a bright pink and blue head – is foraging off to one side picking invertebrate prey from the sand.
This site has been within a Great Barrier Reef Marine Park (GBRMP) Green Zone since 2004. That means it’s a no-take area, where f ishing or collecting is not allowed without a permit. Long-time Australian Geographic specialist underwater photographer Darren Jew has been diving in these waters since the mid-1980s and recalls local f ish populations booming after the restrictions were introduced.
He’s chosen this location to trial, with AG’s support, a unique way of documenting marine life by using extended time-lapse photography to create a f ilm capturing A Day in the Life of the GBR. It shows what life is like on a healthy, well-protected patch of reef and has captured the sort of activity occurring daily at thousands of sites throughout the marine park’s 344,400 sq.km.
NORTH LIGHTHOUSE BOMMIE SITS at a depth of almost 16m and, as one of the area’s most popular ‘cleaning stations’, is attended by a steady stream of manta rays throughout the day. There are two species of manta and the one that visits here is the smaller one often associated with reefs – Mobula alfredi. The f lattened body of this relative of sharks can reach more than 5m across.
Despite their huge size, mantas are gentle f ilter-feeders that eat by swimming with their mouths open sifting plankton from the water. As many as six individuals will visit this site today, each identif iable by different pigment patterns on their white bellies. They swoop in like huge, slow-f lapping graceful birds to be attended to by an army of cleaner wrasse that fuss about picking off external parasites. These parasites can be annoying and, if their numbers get too great, can compromise a manta’s health.
It shows what life is like on a healthy, well-protected patch of reef and has captured the sort of activity occurring daily at thousands of sites across the marine park’s 344,400sq.km.
Once the pretty moon wrasse that was feeding on the bottom during the morning spies visiting mantas, it shifts its behaviour to become a cleaner. Opportunism is always a useful tactic in the ocean.
Bommies like this are often massive old corals that have died but have a second life as a hard substrate where other invertebrate marine f lora and fauna can settle and f lourish and in turn underpin an extensive diversity of f ish and other vertebrates. This one may have been here for hundreds of years. As the f ish slowly disappear with increasing light levels, they expose a rather drab-looking, boulder-like site. But a closer look reveals it’s seething with sedentary life forms: sponges, colonial ascidians (plant-like animals distantly related to vertebrates including humans) and different forms of corals including encrusting, branching and digitate types with a stubby fingerlike appearance. Microalgae also grow among the coral.
A couple of very healthy-looking juvenile green turtles cruise by and so does a whitetip reef shark, but it doesn’t seem to be on the hunt. Like most sharks, these fish-eating fish need a good feed only every few days and this one seems not to be interested in feeding. The songs of nearby humpback whales and the chatter of dolphins filter through the water throughout the day. And during the morning one of the whales, a juvenile humpback, cruises overhead, seemingly setting out early on its southward migration towards summertime feeding grounds in Antarctica.
THE PROGRESSION of fish species continues through the day. A long, thin flutemouth passes by, its small oral opening indicative that its prey are tiny morsels it picks from the water or from sites such as the bommie. A few individuals of another species of benthic wrasse, this one coloured yellow and white, appear. And a tiger shark – perhaps a female or a juvenile male and also apparently not looking for a feed – swims past at about the same time a human diver appears in shot. High in the water column a batf ish – another plankton-feeder that’s always associated with reefs – makes an appearance and so does a lone mackerel and a small pod of bottlenose dolphins, not far from a group of snorkelling humans.
Late in the afternoon a couple of mantas appear with remoras in attendance. Remoras, which can grow as long as 75cm, are f ish that hitch rides on larger creatures, such as mantas. They attach to them using strong ventral suction cap-like appendages created from pectoral f ins that have become fused and modified through evolution. When remoras follow carnivores such as sharks, they get to feed on their scraps. But there’s no such bonus hanging with mantas. Instead they feed on their faeces. Sometimes they’ll even burrow up into a manta’s cloaca – combined urino-genital opening – to feast on waste before it’s expelled.
Early in the morning, a black sea cucumber began a feeding ‘dash’ across the sea f loor. By late afternoon it’s covered little more than a metre.
As the sun begins to set and light levels again drop, activity close to the bommie starts to pick up once more. The brown sweetlips are back. So too are the coral trout. And the evening crew begins to assemble and settle in for the night.
AG, Karen and Darren’s team thank the staff and management of Lady Elliot Island Eco Resort for their assistance with this story and the film and Project Manta’s Dr Kathy Townsend from the University of Queensland for her assistance in identifying species and behaviour.
Bommies like this are often massive old corals that have died but have a second life as a hard substrate where other invertebrate marine flora and fauna can settle and flourish.