The Constant Gardener
IT’S THE PERFECT LITTLE chubby face, snub-snouted and Disney-cute. She’s adorable, but my wish to stay and stare in my state of bliss is tempered by awareness that she’s not happy with the invasion of her personal space. We love anemonefish to death.
I remember being delighted and slightly hypnotised by that face on my first dive 25 years ago off Oman’s Musandam peninsula, and that delight has never gone away.
I still find it amazing that this little fish will stand its ground to me – a bubble-blowing monster literally a thousand times her size – seeming to puff out her chest and open out her flag-like fins to appear bigger.
It’s a strutting, waddling squaring-off gait, waving the tail from side to side, pushing out the shoulders and spreading and sculling with her golden pectoral fins, to intimidate me with her size.
Then you blink, and all the fins have folded back flush against the body, and the fish has becomes a teardrop-shaped bullet, darting across to the other side of its tiny territory.
Then it plunges through the anemone’s tentacles for a wiggle through to re-affirm the host-guest bond, mixing the anemone’s skin slime with that of the fish.
Safely nestled in the tentacles of her home and garden, she wriggles vigorously and watches intently with those clear, unblinking eyes.
My longtime buddy Simona calls them “pigfish” for their little round nostrils, jutting jaws and attitude.
I’ve been chased several metres from a host anemone a few times by particularly aggressive anemonefish (that – not coincidentally – had particularly massive and healthy-looking host anemones) and been butted, grabbed and shaken hard, like a giant rat by a tiny but fearless dog.
She was chasing me – as she would any other intruder – away from her home and her shelter. The anemone protects her family with its stings, and the fish in turn act as minders for the anemone by seeing off potential “tentacle-nibblers” such as butterflyfish.
Anemonefish will chase away fish up to the size of small grouper, and even the rather aggressive triggerfish. Usually, however, anemonefish retreat from large-mouthed predators (which, after all, do not eat anemones but might well eat the fish) and will usually back down from something as massive as a diver.
The richest part of the reef
Both anemonefish and their anemones choose to live on the richest and most competitive part (the reef crest) of the most biologically productive and competitive environment on earth (Indo-Pacific coral reefs).
If you’re going to live there you have to accept intense competition for prime space – of which the anemone requires rather a lot, and for which its tough little orange minder fights.
Get close to an anemone and it can get a bit noisy, the fish giving out threat chirps and pops to protect the anemone, usually followed up with charges, occasionally headbutts and bites.
The anemone may be an animal but in many ways it behaves – and is treated like – a crop of plants with the fish as farmer or gardener.
The fish occasionally directly feed the anemones by dropping mouthfuls of prey, but by far the majority of what they provide the anemone – or, more particularly, the anemone’s symbiotic guest algae – is the fishes’ nitrogen-rich faeces.
The constant wafting and swimming through by these fish aerates the anemone, and they also actively clean out sediment and sand.
It’s still not clear how much the bright colours and frantic swimming of the fish might lure other fish to be stung by the host anemone’s tentacles and become prey. Like their distant cousins the corals, however, it is the algae living within their tissues that provide most of the food for these giant anemones.
The biggest anemones on Earth
Almost all anemonefish live in carpet anemones. Heteractis and Stychodactyla form their own small family, 10 species of by far the largest anemones on Earth.
On the hyper-rich reef crests of Bali’s Menjangan or North Sulawesi’s Bunaken I have seen several over a metre across.
As well as the carpet anemones, three species from the regular anemone family, including the bubble-tip Entacmaea quadricolor, also host anemonefish.
All the anemones that host “minder” fish are unwieldy, soft, fleshy animals, which are less aggressive, have less-potent stings and are more vulnerable than “normal” anemones.
Indeed, these anemones may have become so big because the anemonefish’s protection from marauding butterflyfish and other potential predators have allowed these few types of anemones to spread and widen, taking over precious areas of the reef crest, the most prime location in the ocean.
Anemones lack the protective cup skeleton of their tiny coral cousins but they live similarly. Like corals, they thrive on sunlight on the more productive parts of Earth’s richest eco-system.
I arrived at Marsa Shagra in Egypt one year just after a very warm spell. Environmental manager Sarah O’Gorman said a few local corals and anemones had bleached (a stress response to high temperatures – ejecting their algae).
Sure enough, there were a couple of pure white anemones, and I was fascinated to see that the anemonefish living in these were almost pure orange.
The dark-brown smudged sides that most clownfish species have to greater or lesser degrees had apparently been lost along with the host anemone’s algae.
Living in a nettle field
The anemones can and do sting, and it is a powerful enough sting to kill small fish, including anemonefish that have not spent a bit of time acclimatising to their host.
The mucus produced by anemonefish skin doesn’t set off the anemone’s stings as readily as normal fish mucus, but it can and will trigger the stings. An anemonefish thrust into the middle of an unfamiliar anemone will be stung and killed.
A gradual introduction or settling of a fish into the anemone is necessary, starting with brushing by the tentacle tips, taking a little time before the fish can safely immerse and swim through the anemone, and even then needing constant contact to keep it up.
Something in the anemone mucus is taken up by the fish mucus, which stops the fish from being stung.
The big girl and her boys
The largest and dominant anemonefish in a group is usually the only female. Next-largest is her mate, the only fully developed adult male.
The others in a colony are in most cases juvenile males, their reproductive organs and development held in a kind of pre-pubescent state by the presence of the alpha female.
Some anemones can attract a dozen
or more tiny males, settling in from the plankton, brought in sometimes over great distances.
Once they settle they join the bottom of the pecking order, their growth and social position stunted by the hormones of the dominant female, waiting until she dies before each male takes a single step up the social ladder.
It can be a long wait. The youngsters can grow pretty fast, up to 5mm a day when they’re small, and theoretically could reach adult size after a couple of months, but the female can live several years (rarely to 30) and even when she dies only the next-largest male gets to grow and mature – as the existing breeding male changes gender and reaches her final adult size.
All the rest remain stunted at 3-7cm, depending on species, until a position becomes available for one of them.
If conditions are right the female will produce several hundred eggs every fortnight, spawning a week before the full and new moon.
Photographers seek out the clusters of eggs, laid on a patch of bare rock near the anemone’s rim and cared for by the adult male.
He fans them, blows water over them and cleans them, eating any dead ones and seeing off any potential predators for a week while they develop.
Then at night on or just after the full or new moon – when the tidal currents will disperse the hatchlings the most widely – the eggs hatch.
Of course most of the larvae will not survive the journey, but those that do will settle a week or so later on a distant anemone at a little less than 1cm long, joining a small community of boys waiting for the weeks, months or years to be able to step up and mature.
The limiting factor in the wild is probably the number of host anemones. As long as they have a clear reef environment, anemonefish are a success – they have plenty of food, picking at zooplankton and a bit of algae (and occasionally nibbling a bit of tentacle from their host anemone), can grow and mature rather fast when they need to, and can produce hundreds of young every couple of weeks year-round.
It’s a good job they reproduce so well, because they’re by far the most popular and heavily exploited aquarium fish in the world, and in particular “Nemo”, the clown anemonefish (Ampiphrion ocellaris).
One recent study estimated that 140,000 are taken for aquaria per year from Indonesia. This means several million dollars for local fishermen, perhaps three times this amount for middlemen.
This level of take has a clear and measurable impact on the densities of anemonefish on natural reefs – most of the reefs on which we dive contain perhaps a third of the natural numbers.
|The anemone community|
Thirty species of anemonefish live in 12 species of host anemones, ranging from the Red Sea across the Indian Ocean and tropical Pacific down to temperatures of about 20°C. All but one belong to the genus Ampiphrion, with a single species, the giant burgundy spinecheek anemonefish (Premnas biaculeatus) in its own genus.
Clark’s clownfish (Ampiphrion clarkia) has the widest range – both in terms of numbers of host anemones (10 species) and of range, and is also the most variable in colour patterns.
Other species vary in their habitat preferences. Saddleback anemonefish (A. polymnus) familiar to anyone muck-diving in Indonesia, Malaysia and the Philippines, and the rather similar Sebae clownfish (A. sebae) from the western Indian Ocean seem to do well on sandy slopes a little away from the richness of the reef crest.
Saddlebacks are unusual in that the secondary male is about as large as the matriarch.
The smallest and most slender anemonefish are the two rather successful Nemo species – the clown anemonefish (A. ocellaris) and (A. percula), both preferring large anemones at reef crests.
The large anemones that host anemonefish also support a somewhat broader community. Anemonefish are not the only members of the damselfish family that live in association with anemones – other fish that do so include cardinals and gobies, and several species of reef shrimp and porcelain crab.