BLUEHEAD WRASSE: PRIVATE LIFE LAID BARE


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BLUEHEAD WRASSE: PRIVATE LIFE LAID BARE

The bluehead wrasse (or blue-headed wrasse) Thalassoma bifasciatum is a denizen of the coral reefs of the tropical waters of the western Atlantic Ocean. This bright little 4-inch fish is… a wrasse with a blue head. No more and no less. Unless it’s a juvenile. Then it is mainly bright yellow. It’s similar to BLUE TANG (aka ‘the Disney Dory’), which starts life bright yellow and grows up to be blue.

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The species may be found singly, in pairs or small groups, or in schools.  They have an important role to play in the life of the reef. They are CLEANER FISH, vital to the health and wellbeing of the larger species they attend to, and thus of the reef itself. This is ‘cleaning symbiosis’, a relationship of mutual benefit. The big fish get cleaned; the little fish have a useful function and – importantly for them – therefore don’t get eaten. 

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Having said that, blueheads are of course fair game as a snack for species that aren’t in the market for their cleaning services. And, unfairly, some species that are content to let cleaner gobies runtle around their gills and mouths are not so considerate of the wrasse. Some types of grouper and moray eel, for example.

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TELL US EXACTLY SEVEN BLUEHEAD WRASSE FACTS

  • Juveniles can alter the intensity of their colour, stripes & bars
  • The bluehead wrasse is a ‘protogynous sequential hermaphrodite’
  • All are born female**. Some change sex to male during maturation (see below)
  • Food includes zooplankton, small molluscs and small crustaceans…
  • …and parasites / other juicy bits (fungal growths, anyone?) from bigger fish
  • The main threat to the species is coral reef degradation or destruction
  • The bright colours invite aquarium use, but the trade is not a significant one

** Some sources suggest some are born male and remain male. I’m not sure which is right

A juvenile bluehead (with feather-duster worms) – mostly yellow, with a pale underside
Bluehead Wrasse juvenile (wiki)

THE REMARKABLE SEX LIFE OF THE BLUEHEAD WRASSE

This is an unavoidable topic, I’m afraid. The bluehead’s sex life is the most interesting thing about them, and this is no time to be prudish. It is the subject of extensive scientific research, not all of which I have read since I decided to write about the species last night. Like many human relationships, “it’s complicated”, but in a conch shell it boils down to this:

  • To recap, BWs are born female and as they mature, some become male.
  • Males reach an ‘initial phase’ when they can breed in groups with females
  • Some males grow even larger & reach full colouration. This is the ‘terminal phase’
  • These large males aggressively chase away smaller ones & seek females to pair with
  • Their state of readiness (as it were) is signalled by colour changes
  • This behaviour is similar to that seen in many city centres in a Saturday night
  • The smaller fish have one bonus – their sperm count is higher than a dominant male
  • Prozac tests have shown that the drug reduces a dominant male’s aggression

blue-headed_wrasse_det (wiki)

As the excellent organisation OCEANA puts it: Bluehead Wrasses may reproduce in four different ways throughout their lifetime:  1) as a female in a group spawning event; 2) as a female in a pair spawning event within the territory of a large male; 3) as a small male in a group spawning event; and 4) as a dominant, terminal male in a pair spawning event within its own territory.

A cropped still from a video I took at Fowl Cay marine reserve. I’ve looked at dozens of images online and not found one that was all blue with a yellow end to its tail fin. Maybe it’s not a BW at all. Or it’s a different type of fish completely. Or perhaps it is just an all-blue alpha male.bluehead-wrasse-fowl-cay-mr-abaco

Credits & Sources: Melinda Riger; Adam Rees; James St John; Oregon State edu / Pinterest; Wiki images; self; Oceana; IUCN; magpie pickings

A bluehead wrasse passes the time of day with a gruntbluehead-wrasse-grunt-adam-rees

ABSORBING SPONGES ON THE BAHAMAS REEFS…


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ABSORBING SPONGES ON THE BAHAMAS REEFS…

A while back I showed a collection of colourful sponges – one that you might come across with minimum equipment. Snorkel, mask, flippers. Oh, and a coral reef, if you happen to have one handy. I suspect that to quite a few people the word ‘sponge’ means soggy yellow thing, as found in the proximity of a bath. Or a scratchy nylon-based equivalent. Well, here are a few more sponges to enjoy. Some I can give you the names of, some I don’t know and am too idle busy to look up… Sorry.

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Candelabra Songe (with brittle stars attached)candelabra-sponge-melinda-riger-g-b-scubasponge-melinda-riger-g-b-scuba

Black Ball Spongesblack-ball-sponge-melinda-riger-g-b-scuba-copy

One for Valentine’s Dayheart-shaped-sponge-melinda-riger-gb-scuba

Vase Spongesvase-sponge- pink-melinda-riger-gb-scubavase-sponge-melinda-riger-g-b-scuba

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Spawning Brown Encrusting Spongebrown-encrusting-sponge-spawning-melinda-riger-g-b-scuba

All photos: Melinda Riger, Grand Bahama Scuba

PIP THE PLOVER VARIES HER DIET…


Piping Plover, West End, Grand Bahama (Linda Barry-Cooper)

PIP THE PLOVER VARIES HER DIET…

Hi guys, that’s me, Pip, in the picture above. I live in North America in the summer. That’s where I was born. I fly down south to somewhere warm for the winter. Like many migratory humans, my chosen place is the Bahamas. It’s got some great empty, safe beaches and the weather is (mostly) lovely. Unless a Big Wind happens. The tide-line is cram-full of meat-strings (these would be worms. Ed). There are great patches of weed larder to work through. It suits me very well, just like lots of other shore birds. It’s why some of us return every year.

I’ve just got one point to raise, if you wouldn’t mind. There’s a mass of plastic (and other) crap out there on the beaches. It washes in on every tide. I know it isn’t Bahamian crap, but has come from many miles away. But Mr Harbour has done some work with my portrait to identify what’s in the seaweed I’m feeding on that might be harmful. He enhanced it and picked out just the things he’s certain shouldn’t be there. All the blue bits, for a start. And who knows what else is under the weed that I can’t even see to avoid. The shoreline and the wrack line is my dining area. I might easily eat some of the small bits by mistake. I think I must do that quite often. That would be bad – too much plastic crap and I’ll be ill. Or die. There are only about 8000 of us in the whole big wide world. If 80 of us die from plastic ingestion, that’s one per cent. The loss has to be made up next breeding season before we can even begin to increase our population. 

Just sayin!

PIPL & beach crap

♦  ♦  ♦  ♦  ♦  ♦  ♦  ♦  ♦  ♦  ♦  ♦

chris-jordan-inside-albatrossPhoto: Chris Jordan, who studies birds killed by trash

HUMPBACK WHALE SEEN OFF SANDY POINT, ABACO


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HUMPBACK WHALE SEEN OFF SANDY POINT, ABACO

Dolphins are regularly seen around the coast and in the fishing grounds of Abaco. Sometimes, they make it easy by nosing into harbours and being generally adorable for a while, to the delight of onlookers. Hope Town can be a good place for this. Those aboard the “Donnies” –  the ferries that criss-cross the Sea of Abaco from the main island to the various Cays – may be in luck too. However, it is perhaps less well known that Abaco waters provide a home or a migratory passage for gigantic whales. Beside these mighty creatures, the several other whale species of the Bahamas seem relatively small. Yes it’s true: there are huge whales – humpbacks and sperm whales (cachalots) – to be found in Abaco waters, and not so very far from land either.

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The humpback whale Megaptera novaeangliae above, with its characteristic white pectoral fins, was seen about a week ago off Sandy Point (southwest Abaco). You’ll get an idea of its immense size from the photo. An adult of this BALEEN WHALE species can reach 50 feet in length and weigh 35 tons or more. Imagine watching one slipping silently past your boat… and then consider that even larger sperm whales are seen in the same area. 

For the link to report a Bahamas whale sighting, please see either link provided below

Humpback whale / adult male human in scuba gear comparison
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Humpbacks are found in oceans throughout the world. They migrate huge distances each year, from polar regions to the tropical and sub-tropical waters where they breed. These are the whales beloved of wildlife film producers and whale-watching trips, with their spectacular arched breaching in which half their length or more may emerge from the water before smashing back into the waves. 

A humpback breaches on the Stellwagen Bank (about 50 miles offshore of Boston)
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Like other large whale species, humpbacks were unsurprisingly prime targets for the whaling industry in a melancholy era of marine history that took them to the edge of extinction until a moratorium was declared in 1966. Since then the population has recovered significantly. They remain vulnerable, however: in some locations, to killing; to entanglement in heavy-duty fishing gear; to ship collisions; and to noise pollution that affects their ability to communicate long-distances underwater, as they need to do.

Finally, the Sandy Point humpback makes a last dive and, with a wave of its fluke, disappears  bmmro-humpbacks-4    bmmro-humpbacks-3

Do you have a Bahamas whale or dolphin sighting to report? Please use this link, giving as many of the details as you can. Each report makes a valuable contribution to the BMMRO’s research. 

http://www.bahamaswhales.org/sightings.aspx

As a footnote, my first whale encounter was on the Stellwagen Bank mentioned above, when I went on a whale-watching trip from Boston. We encountered a mother humpback with her calf and spent about 1/2 hour watching them interacting. I have the memories luckily – my photos were rubbish, using a very early digital camera that these days would be less effective and well-spec’d that a luminous pink plastic child’s camera now… 
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RELATED POSTS

HUMPBACK HOPE TOWN ABACO

BLAINVILLE’S BEAKED WHALES

BMMRO

SIGHTING REPORTS

Credits: Brad & his crew, and the BMMRO; Whit Wells / Wiki for the breaching whale; moi for the rotten but quite interesting archive photos from the same place; the whale for being awesome in the true sense of the word

WATCHING NURSE SHARKS: BE PATIENT…


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WATCHING NURSE SHARKS: BE PATIENT…

I last took a look at nurse sharks nearly 3 years ago HERE. Time to revisit these creatures. Indeed, time for a close-up look. If you want to know more about this fascinating species, just click the link above.

The two strange items hanging down from the upper lip are sensory barbels
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This side-view shows the shark’s relatively small mouth (for a shark anyway)nurse-shark-a-melinda-riger-gb-scuba

Admire the extraordinary texture of the the skin; and the tiny evil eye. Click or – better – double click on the image and you will see that the skin is in fact tessellated, made up of a mosaic of tiny squares and near-squares**nurse-shark-close-up-melinda-riger-g-b-scuba

This one is a baby nurse sharknurse-shark-baby-melinda-riger-gb-scuba

A juvenile nurse shark with a couple of grunts. Note the youngster’s paddle-like finnurse-shark-juv-melinda-riger-g-b-scuba

Head, mouth, jaws and teeth

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SO, THEY ARE SHARKS – ARE THESE GUYS DANGEROUS?

Not really, no. They aren’t looking to pick a fight; and they are not as territorially aggressive as the ‘bitey’ sharks are (or can be).  These slow-moving bottom-dwellers are generally harmless to humans. However, they can be huge—up to 4 metres —and have very strong jaws filled with thousands of tiny, serrated teeth. They will bite defensively if stepped on or bothered by divers who assume they’re docile. [As I said previously, “there are recorded instances of injuries caused to divers who have tried to pull nurse sharks by the tail. And serve them right, I say. Treat them with patience and respect!”] 

Nurse Shark ©Melinda Riger @ G B Scuba copy

**FUN FACT

M.C. ESCHER (the inspiration for Mr Hammer) was the master of tessellation in art. Click the link to explore the dedicated website. Maybe, sensationally, one day a shark will be found with skin like this… (Alert reader: “Actually, I think it most unlikely…”)

Escher fish

Credits: field photos by Melinda Riger, Grand Bahama Scuba; Wiki for the 4 mouth images & the Escher 

Nurse Shark ©Melinda Riger @ Grand Bahama Scuba

CHRISTMAS TREE WORMS: FABULOUSLY FESTIVE


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CHRISTMAS TREE WORMS: FABULOUSLY FESTIVE

music-notes-clip-art-png-music“Deck the Reefs with Worms Like Christmas Trees… Fal-La-La-etc-etc ” is a traditional Carol familiar to all. Well, most. Ok, some, then. Oh right – maybe with different words. Anyway, now is as good time as any to take a look at these remarkable plants creatures and subsurface symbols of good cheer.

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10 CHRISTMAS TREE WORM FACTS TO PONDER

  • The 2 colourful spirals are not the worm, but complex structures for feeding & respiration
  • The spirals act as specialised mouth extensions for ‘filter-feeding’
  • Prey is trapped by the feathery tentacles & guided by cilia (microscopic hairs) to the mouth
  • The tentacle things are radioles and act as gills for breathing as well as prey traps
  • It is not believed that prey slide down the spiral to their doom, like on a helter-skelter

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  • The actual worm lives in a sort of segmented tube, with extremely limited mobility skills
  • It contains digestive, circulatory & nervous systems – and a brain in the middle of it all
  • The worm also has a tiny drainage tube (I think I have this right) for excretion etc
  • They embed themselves into heads of coral such as brain coral. And stay there
  • And yes, the Christmas trees are retractable…

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HOW DO THE WORMS… YOU KNOW…  ER… REPRODUCE?

This is a delicate area. They don’t tend to talk about it much, but as far as I can make out they eject gametes from their what-I-said-above. There are mummy and daddy CTWs, and their respective gametes (eggs and spermatozoa) drift in the current and presumably into each other to complete the union. The fertilised eggs develop into larvae, which settle onto coral and burrow into it, build their protective tubes and the process begins again.

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LOOK, YOU DON’T REALLY UNDERSTAND THESE CREATURES, DO YOU?

I won’t lie. I found it hard to work out how the CTWs function in practice. There are plenty of resources showing them in their full glory, but that only takes one so far. Then I came across a short video that shows it all brilliantly simply (except for the reproduction part). So maybe I should have just posted this first and saved you (and me) some trouble…

The worm, invisible in its coral burrow, hoists its pair of trees. You can easily see small particles – possibly zooplankton – drifting in the water, and the radioles swaying to catch potential food. Bingo. It all makes sense! Next: the New Year Worm

Credits: Melinda Riger (G B Scuba); Adam Rees (Scuba Works); Nick Hobgood; Betty Wills; Absolutely Wild Visuals; MarineBio; Wikibits & Magpie Pickings

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FLORAL CORAL: BEAUTIFUL BAHAMIAN REEF LIFE


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FLORAL CORAL: BEAUTIFUL BAHAMIAN REEF LIFE

This post needs no commentary from me, nor my larky intrusions. These wonderful images from Melinda Riger speak for themselves. You’ll see a wide variety of soft and hard corals in the images below (prize** for the full list). If these superb photos don’t want to make you want to grab a snorkel, mask and flippers, then… well, that would be a very great shame.

coral-melinda-riger-g-b-scubacoral-melinda-riger-gb-scubacoral-reef-2-melinda-riger-g-b-scubafire-coral-melinda-riger-gb-scubapillar-coral-melinda-riger-gb-scubablushing-star-coralpurple-sea-fan-melinda-riger-g-b-scubapurple-sea-fan-melinda-riger-g-b-scuba-copy

**the prize is the usual legendary bottle of Kalik. Or do I mean mythical?

All wonderful photos by Melinda Riger, Grand Bahama Scuba. All corals also available in a wide range of colours in Abaco waters. See them there on the third largest barrier reef in the world (and in rather better nick that the greatest, by all accounts).