MARION REEF - SNAKES ALIVE

With a flick of its forked tongue the snake tested the water, was there prey in the hole or was it empty? The snake slivered into the hole, disappearing for a few seconds. After a brief look inside the dark hole the snake emerged, then turned towards more interesting prey, me! Another flick of the tongue and it darted forward, heading between my fins, then around my legs. I lost sight of the sea snake and remained still, not in fear though, I was more worried I would squash this inquisitive snake. Suddenly another sea snake swam over to see what was happening. I was in heaven, surrounded by serpents in this Garden of Eden.
    We were diving Marion Reef, one of Australia ’s famous Coral Sea reefs, which is home to thousands of sea snakes. Located 400km off the Whitsunday Coast , Marion Reef is far beyond the Great Barrier Reef . The reef is 40km long by 20km wide, dominated by a deep lagoon and surrounded by the very clear waters of the Coral Sea . Marion Reef was once one of the most popular of the Coral Sea reefs, visited by dive charter boats in the 70s and 80s, but for the last two decades has rarely seen a diver. Fortunately divers can once again explore this amazing reef with Dive Nomad on their liveaboard vessel Odyssey.
    Diving Marion Reef is a magical experience. The reef edge offers canyons, channels, caves and walls to explore, while the lagoon is filled with thousands of bommies. The corals we saw were healthy and exquisite, including large gorgonians and lovely soft corals. Invertebrate species abound, reef fish are prolific and good populations of pelagic fish are seen on every dive. Marion Reef also supports a large shark population, while spinner dolphins frolic in the lagoon and dwarf minke whales are common in winter. Not to mention the visibility is usually 30m to 60m. However, of all these wonderful attractions our lasting memory of Marion Reef will be of its spectacular sea snakes.
    We knew there would be abundant sea snakes at Marion Reef before we arrived, as this part of the Coral Sea supports one of the biggest populations of these serpents on the planet. On a previous trip to nearby Saumarez Reef, we had encountered dozens of sea snakes on every dive, and being sea snake fanciers we couldn’t wait to see what Marion Reef had to offer.
    On the first dive it took us about a minute to see the first snake, a very sleepy turtle-headed sea snake (Emydocephalus annulatus) curled up in the coral. After a few photos the snake woke up and became curious of two photographers blasting it with strobe light. Fortunately the strobe didn’t seem to worry the snake, it was more interested in its own reflection in our camera ports.
    Every dive at Marion Reef was a sea snake dive, from the reef edge to the shallow lagoon. On most dives we saw up to a dozen sea snakes, either sleeping in the coral or searching the coral for prey. While we were search for sea snakes, we also had them searching for us, as many of them would follow us around, curious of these bubble blowing aliens in their liquid world.
    Sea snakes are fascinating reptiles that we have always found entertaining to observe and photograph. Seventy species of sea snake have been described and they are limited in their distribution to the Indo-Pacific region, with 14 species found on the Great Barrier Reef and Coral Sea . Sea snakes evolved from terrestrial snakes around 135 million years ago and are split into five family groups.
    The Laticaudids, or sea kraits, are represented by five species and are the only group that regularly return to land and the only group that lay eggs, on land naturally. The Acrochordids, or file snakes, are found in freshwater and estuaries, are non-venomous and consist of three members. The Natricids, or salt marsh snakes, are represented by three non-venomous species found in salt marshes. The Homalopsids, or mangrove snakes, comprises of nine species found mostly in mangroves. Of these snake species only the sea kraits are regularly seen by divers, especially in Asian waters.
    The largest family of sea snakes, and the one divers encounter in Australian waters, are the Hydrophiids, or true sea snakes. This group is represented by 54 species that evolved 30 million years ago. These snakes are generally highly venomous, have fixed front fangs and spend their whole lives in the sea.
    Though looking superficially like a terrestrial snake, except having a paddle shaped tailed, sea snakes have developed a few other special adaptations to survive in the marine environment. They have one very long cylindrical shaped lung that extends for almost the entire length of the body, which allows them to remain underwater for up to two hours, between breaths of air at the surface. But they can also absorb oxygen through their skin while underwater. Sea snakes also have unique nostril valves that prevent water entering the lung. Living in a salty environment, sea snakes expel excess salt via a gland under their tongue.
    During our week at Marion Reef we encountered four species of sea snake. The most common were the olive sea snakes (Aipysurus laevis), which are also the most curious. These snakes are quite large, up to 2m long, and were most often seen poking their head into every hole looking for potential prey. They would also check us out, following us around, peering into our masks or camera ports when seeing their reflection. Also very common was our favourite species, the turtle-headed sea snake. This species is non-venomous and eats only fish eggs. They have a very cute turtle like head as the scales around the mouth have formed into scraping plates. These snakes were most often found either sleeping in the coral or with their head poking into a hole looking for those tasty fish eggs.
    Around the shallow bommies we also found several juvenile turtle-headed sea snakes, which actually had a banded skin pattern, which we first thought was another species. We also found several Dubois’s sea snakes (Aipysurus duboisii) in the shallows, which have distinctive pale eyes. This species may only feed at night, as all the ones we saw seem to be asleep during the day. The final species we saw were the horned sea snake (Acalyptophis peronii), which appeared to use an ambush strategy to catch prey. These snakes were observed lying on the bottom with the head near the entrance of goby holes. We waited a while to see what would happen, the snake was dead still, not interested in us at all, but we didn’t see any gobies emerge.
    Many of the sea snakes we saw had algae growth on their skin. Like all snakes, sea snakes regularly shed their skin, about every two to six weeks. This is not only so they can grow, but also to rid them of any growth that has started to form on their skin. We have yet to observe a sea snake actually shedding its skin, but have seen them ready to moult with milky coloured eyes, or partly through a moult with patchy skin hanging off them.
    Diving with the sea snakes at Marion Reef in June they were very placid, but when the water warms in summer they become more agitated as it is the breeding season. When we dived Saumarez Reef it was the start of the breeding season and we regular saw groups of snakes chasing each other around, or balled together in a group on the bottom. They would also check out divers regulator hoses, thinking it was another snake.
    Male sea snakes have two penises, which are covered in hooks and spines, ouch! Once a receptive female is found the male curls around her and inserts one penis, this then locks into place. This sounds very painfully for the female, but she gets the last laugh, as with the penis locked in until the business is done he is at the mercy of the female. She literally drags him around by ‘the balls’ only allowing him to breath when she heads to the surface for a breath of air herself.
    The young snakes are born four to eleven months later, alive and underwater, and must fend for themselves immediately. The young snakes have to be careful as they can fall prey to large fish and sharks, as can adult snakes. Studies of olive sea snakes discovered that they live for ten years and breed every second year, with litters numbering from four to 16.
    Sea snakes seem to spend a lot of time looking for food; they feed on fish, eels, shrimps, crabs or worms depending on the species. Once prey is located the snake bites the victim, gripping it with its sharp teeth and injecting venom with its fangs. The fast acting venom stuns or kills the prey allowing it to be safely consumed without damaging the snake. Sea snakes can eat fish bigger than their heads by dislocating their lower jaw; the prey is then swallowed whole. It is quite common to observe sea snakes with a large bump in their slender bodies, evidence of a recently consumed meal.
    There are a few myths concerning sea snakes and why they are not dangerous to divers. It has been said that they have small mouths or small teeth that couldn’t possibly penetrate a wetsuit. This may be true for a few species, but the majority of snakes have a mouth large enough to bite a diver and teeth long enough to penetrate a 3mm wetsuit. The main reason that sea snakes don’t pose a threat to divers is that they are not aggressive, and would rather flee that bite something they are not going to eat. They will bite to defend themselves, but even then they rarely inject venom with a defensive bite. Most deaths attributed to sea snake bites have occurred to fishermen pulling them out of their nets.
    The best way to avoid getting bitten by a sea snake is not to provoke them. Sea snakes are generally placid creatures, but they do have a very curious nature. It is always interesting to watch a divers first encounter with a sea snake; the diver generally swims away, sometimes in quite a panic as if the snake is going to eat them. We have even seen divers kicking sea snakes with their fins, which isn’t very nice and a sure way to provoke an aggressive response from the sea snake. Sea snakes tend to follow divers that are fleeing from them, because they are curious as to what you are. The best advice is to stay still, let the sea snake check you out and it will go on its way. Of course once you have encountered a few, like you will at Marion Reef, you either start to ignore them or have fun following them around and watching them stalk the reef.
    It has been found that some sea snakes have a very limited home range, possibly only 150m in diameter, which means that the sea snakes we encountered on this trip will hopefully be on the same bommies when we return to Marion Reef with Dive Nomad to explore more of this Garden of Eden overflowing with serpents.

MARION REEF DIVE SITES
Marion Reef is a massive reef system and offers incredible Coral Sea diving. In the few trips that Dive Nomad have done to Marion Reef they have found some wonderful dive sites and we had a chance to find a few more on our recent trip. At Groper Channel we enjoyed a fast paced drift dive in a 25m deep reef channel, seeing an abundance of pelagic fish, such as big eye trevally, dogtooth tuna, red bass and silver drummer. A feature was the corals here, walls lined with gorgonians and a bommie encrusted with multi coloured soft corals. Zipping along with the current we also encountered coral trout, Maori wrasse, reef sharks and the usual sea snakes.
    Another interesting channel dive was at the Southern Channel where we encountered reef sharks, several moray eels and more pelagic fish. In the shallows were a maze of coral heads that formed endless caves and passages, in one of these was a large tawny nurse shark.
    At the Northern Channel we almost had a close encounter with three dwarf minke whales, which are common at Marion Reef over the winter months. But unfortunately the whales didn’t hang around, unlike on previous trips when the whales have circled divers for up to an hour. Here we explored canyons, caves and bommies in depths to 30m seeing reef sharks, schools of stripey snapper, a hawksbill turtle, giant moray eels, barracuda, parrotfish, jobfish, coral trout, sea snakes and some lovely coral growth.
    The Dive Nomad crew have found some interesting dive sites on the outer edge of Marion Reef. One site we didn’t get to dive was The Cinema, which we were informed had a barren bottom, but divers here watched an endless procession of pelagic fish and reef sharks. At the Southern Canyons we explored deep gutters and walls decorated with brilliant hard and soft corals. A shy Maori wrasse avoided us, but we saw coral trout, anemonefish, batfish, reef sharks, trevally and sea snakes.
    We did some exploratory diving at the northern end of Marion Reef and found one dead patch of coral, but also some lovely hard coral gardens. The best was a site with endless coral ridges in 20m to 30m, where we found caves packed with gorgonians and abundant reef fish. On several dives here we saw giant moray eels, sea snakes, a black-blotched stingray, reef sharks, schools of pyramid butterflyfish, stripey snapper, dogtooth tuna and a huge giant trevally. The highlight was discovering a 10m high bommie undercut with ledges and decorated with soft corals, sea whips and gorgonians. Swarming around the top of this bommie were stripey snapper and fusiliers, but when we were circled by hundreds of chevron barracuda we knew we had found a special dive site. We called this site Barra Bommie.
    Some of the best diving we did at Marion Reef was on the bommies in the lagoon. We would just pull up at a bommie and jump in to see what was there. The bommies in the shallows, in less that 10m of water, looked barren but were covered in critters. We found shrimps, hermit crabs, pipefish, sea stars, nudibranchs, moray eels, dragonets, gobies, blennies, mantis shrimps, molluscs and the usual sea snakes.
    At Big Eye Bommie we discovered schools of big eye trevally, dogtooth tuna, reef sharks, fusiliers and sea snakes. This bommie is a tower of coral rising from 25m to 5m and cut by ledges and caves. Doing slow circuits around the bommie we saw mackerel, nudibranchs, sea stars, wonderful reef fish, colourful corals and a very curious grey reef shark.
    Goat Mountain was another bommie we found on our trip that was a spectacular dive. Rising from 30m to almost the surface this bommie was home to sweetlip, Maori wrasse, moray eels, coral trout, fusiliers and plenty of reef fish. However, the highlight was a wide patch of cabbage coral swarming with hundreds of yellow-finned goatfish.

Article appeared in Sportdiving No.142 Oct/Nov 2010