Tales from the Reef

Tuesday, August 27, 2013

The Coral Eating Starfish - Crown of Thorns

Although the Crown of Thorns Starfish (COTS), Acanthaster planci, is not something to be excited about in the slightest, it is worth blogging about, as they are quite interesting creatures. There are actually over 2000 different species of starfish or sea stars. Most have the remarkable ability to consume prey outside their bodies and they can also regenerate entire limbs! The general consensus about starfish though, are that they are nice, pretty, colourful little animals, but the COTS is far from it. The second largest starfish in the world, it has a diameter of up to 3 feet and up to 21 arms! There bright colours make them quite beautiful and nice to look at, but beneath their fortress of protective poisonous spines is something quite deadly and destructive.

Crown-of-thorns starfish are one of the most damaging creatures of tropical coral reefs. They are corallivores, preying on living coral polyps! COTS especially like to eat the fast- growing Acropora species, particularly table corals. With hundreds of sucker-like tube feet they climb onto living corals and then throw out their stomach through their mouth to digest the coral tissue alive so it can be absorbed! Not so nice! This leaves a white scar of dead coral skeleton. One starfish can consume up to 6 square meters of living coral reef per year. Natural numbers of these starfish on the reef are not a huge problem, however, if there is a huge population boom, whereby their numbers are increased in their hundreds, well they can ultimately devastate entire reefs.

So it was not the best news when one of the dive instructors reported seeing many of them on the outside reef of the atoll! What to do? COTS do have natural predators, titan trigger fish, napoleon humphead wrasse and the huge triton snail, but not so many on the reef as to eat all the starfish. We decided the best plan of action was to collect and remove the starfish from the reef before they wipe it out for themselves. It was the right thing to do. During a 5 minute swim along the reef I counted 300 of them. I have never seen so many before, it was shocking. They had devoured part of the reef leaving just the white skeletons of dead corals in the wake of their feeing path. Our mission was on.... we did back to back dives and managed to collect most of the them so not bad for a days work!!

Though scientists do not know for certain what causes COTS outbreaks, there are a number of possibilities:

the outbreaks are part of a natural cycle
overfishing and the decline of the starfishes natural predators
human disturbance such as agricultural run-off of nutrients from land leading to phytoplankton blooms which provide more food for the starfish larvae.

Hopefully that will be the last we see of them for a long time. This is definitely one animal that i do not feel guilty about digging a hole and tossing them all in!

COTS devouring a large table coral. The white skeleton is the dead coral and the brown is still living, for the time being anyway!

Mission on - collecting as many as possible. We used fins or sticks to pick them up as they are covered in protective venomous spines which can give a nasty sting

So many on the reef consuming all the coral in their paths. It was heartbreaking :(

Greedy buggers! The coral has no chance...

Their sucker tube like feed to move around with a mouth in the middle

A dead white coral skeleton, Acropora clathrata, which use to be beautiful and alive!

All the dead white coral skeletons. It was like swimming over a grave yard!

Bringing them up to the surface

Whoop whoop, mission accomplished. They dont smell too good on the surface though

We collected about 250 all together. Was a great team effort

Sunday, August 4, 2013

My First Oceanic Manta

I’m very happy to report that I saw my first oceanic manta a few days ago!! It was nice to see a manta at all as manta season is usually from December to April but sometimes you get the odd one passing by.

Manta rays are cartilaginous fish which means they are closely related to all other rays as well as sharks. Until quite recently there was only thought to be one species of manta ray and in 2009 they were re-classified into two separate species; the resident reef manta (Manta alfredi), and the giant oceanic manta (Manta birostris). Oceanic mantas are the bigger of the two species reaching a wing span of up to 7m while resident mantas grow to about 4m.

We were diving at Bodu hithi Reef which is an important manta spot during the season. However, we were not there to look for mantas… a tiger shark had been spotted at the same reef a few days before so although it was unlikely to see it again it was worth going to check out as you just never know. I have always wanted to see a tiger shark or any big shark will do, you probably think I’m mad, but sharks are such fascinating and impressive creatures, and well I’m bored of seeing black tips and grey reefs now… I want to see something big!!!

Well I did see something big, not a tiger shark but a 4m giant oceanic manta ray will do. I was in the middle of a fish survey which unfortunately got binned when this huge manta swam over my head. It was pretty curious and circled around us all twice while we were hovering in the blue captivated by its pure magnificance and grace. At first I was like that’s a pretty big manta and then when I looked closely I realized it was an oceanic. Although I have never seen one before I knew how to recognize the different markings on the body. Just to make sure I sent it to my friend Guy Stevens who has been researching and identifying mantas in the Maldives for over 10 years now. Oceanic mantas are not spotted too often, they spend their entire lives cruising large distances across open oceans, so he would be happy to hear about this elusive giant. You can identify each individual manta by the spot pattern on their bellies so I was interested to know whether this one had been sighted before….. and she hadn’t, she was a first sighting which is great and it means I get to name her.

She was spotted just past the cleaning station so maybe she was on her way to be cleaned!! Cleaning stations are certain areas on a reef, usually a prominent reef outcrop or coral bommie, were small cleaner fish hang out. These cleaner fish are usually members of the wrasse family. They have a very important job as they clean all the fish that come specifically to visit these stations. Obviously fish don’t have hands so they cannot clean themselves… instead these cleaner wrasse do it for them. They eat all the dead skin cells, parasites and algae that cover their clients so essentially they get a “free” meal while their clients gets cleaned. It’s almost like going to the doctors or dentist or even your local spa! In the Maldives, there are hundreds of known manta ray cleaning stations were mantas will come to visit just to be cleaned but Bodu Hithi is definitely one of the best spots were you can have a reliable encounters with these magnificent animals, and it’s only a 25 minute boat ride away :)

All of the above are photos of my first giant oceanic manta, luckily i had my camera!

A resident manta pictured above and below. You can see the different markings on the dorsal surface compared to the oceanic manta but they are quite subtle!

This one was at a cleaning station

Resident manta hovering at a cleaning station

Manta rays are solitary animals but they come together at cleaning stations, so as well as being cleaned its also a good place to hang out!

Thursday, May 23, 2013

The first green turtle nest of 2013

Yesterday morning I received a call earlier than usual. A turtle had been spotted on North beach…. I was out of bed and out the door in a flash but sadly not quick enough. By the time I arrived the turtle had disappeared into the sea. She left lots of tracks all over the beach though so it must have been a long night. Coming up the beach can be quite exhausting for her, a turtles flippers are ideal for the sea but not really for the land!! And after all her effort coming up the beach we didn’t find any nests…. We call this a "false crawl" - the female has attempted to nest but returns to the water without laying her eggs.

Not good for the turtle as it meant she would have to return to the beach again to lay another nest that she failed to lay before, but good for me as fingers crossed I might actually get to see a turtle nesting on the beach, a sight I have yet to see. However, there are 12 beaches at Reethi Rah and although turtles usually nest on the same beach, she could easily nest on another beach on the island especially when there are 12 to choose from, so it was best to check them all.

We started at 1230am first checking the beach were she made a false crawl the night before but no signs of a huge green turtle. We found tracks on the last beach we checked, Sunrise beach, but unlucky for us there were tracks coming out of the sea and tracks going back in. She had escaped us again…. we were gutted to say the least. Even worse we think we missed her by just half an hour!! The question is though… Did she leave a nest this time?? Yes she did :) Behind the villa in the bushes, Wade, my turtle nest finding expert, managed to find her nest. The turtle had made a huge mess so it was hard to locate it with all the sand everywhere. There were only 50 eggs in the nest so this would have been the last nest she laid for the season. Turtles generally lay 2 or 3 nests during a nesting season with the last nest having fewer eggs. We carefully took the eggs and have relocated them to another beach were they can be monitored more closely. We expect them to hatch within 50-60 days so more sleepless nights to come but it is so worth it...

Turtle tracks on north beach (false crawl)

Green turtle tracks close up

Nest found on Sunrise beach

Tracks on sunrise beach - coming up and going down

50 eggs (last nest from the female)

Relocating the eggs

50 - 60 days till the hatchlings emerge :)

Saturday, May 18, 2013

Swimming with Turtles at Reethi Rah

I thought it was about time I blogged about the amazing Turtle Adventure trip that we do here… I even made a video

Reethi Rah is lucky enough to have a Hawksbill turtle feeding ground very close by known as “Turtle Reef”. It’s a beautiful site, amazing fish life and of course the turtles. Out of all the places I have snorkeled and dived over the Maldives this reef is truly unique. Not only can you guarantee seeing turtles in their natural habitat but you can really have some up close and personal encounters with these ancient marine reptiles. Most of the turtles are very relaxed, the shy ones will swim away but the ones that are not phased by people will sometimes swim along with you, or even come up for a breath of air right in front of you, a very cool sight to see.

The lifecycle of a turtle is pretty straight forward, when the hatchlings crawl out of the nest and first enter the water, they swim out to the open sea. They will spend the first couple of years out in the open ocean to avoid predators, and to basically eat and grow, and then when they reach dinner plate size they return inshore to a feeding ground. The turtle will spend most of its life at this feeding ground just leaving periodically to mate and nest.

Most reefs were you might happen to see a turtle, well generally the turtle will take one look at you and take off very quickly…. but not at Turtle Reef. As it’s a feeding ground and home to the majority of the turtles that we see, I think that they don’t feel threatened when they see people, and therefore they don’t swim away. They are nearly always eating, using their long beaks to probe into spaces between corals to find sponges and invertebrates to eat. Turtle Reef is covered in a green zooanthid, an invertebrate, which the turtles love to eat. When they are eating, they really don’t seem bothered by all the people looking down at them. Sometimes the turtles will look up at you, as if to say, “not these crazy people again”… and then just carry on eating!!

I do like to think I know some of these turtles personally now, I recognize the common ones I see and now many of them have names. Turtles have a unique scale pattern on each side of the head, kind of like a finger print so you can identify them, but I also recognise them by the patterns of encrusting coralline algae growing on their shells. All the turtles I see are photographed and uploaded into a photo identification database to try to establish their population size, foraging sites and migration patterns. So far I have identified over 60 different turtles from Turtle Reef and then about 25 different turtles from another reef called West Point.

The majority are female turtles, Spot, Ringo, Crush, Samha, Reina, to name a few of the regulars, then there are only 3 males that I have recorded, Marvin, Badhur and Ali. The males have a long tail which is how you can tell them apart from the females, well we all know it’s not really a tail!!! There are also lots of juveniles on the reef as well which is great, they are so cute, there is Junior, Kurumbas, Mona, Bear, Noah…. Generally every month I see one or two new turtles as well, sometimes they may stay a while or sometimes they are just passing by.

So out of the thousands of photos I have of these turtles, here are some of my favourite shots of the common turtles that I see, I wonder if they recognise me as much as I recognise all of them…