DAY 13 – MARCH FOCUS ON NORFOLK ISLAND’S REEF
Bluestreak cleaner wrasse, Labroides dimidiatus, are important critters on our coral reefs. These fish offer a swim-through, full-body maintenance shop for other fish species – their clients. They nibble away dead skin and any nasty ectoparasites that might be living on their clients in a mutually beneficial relationship known as mutualism. The cleaner gets a meal and the client rids himself of unwanted passengers that can affect his general health and well-being. It’s a really important service when you consider that fish don’t have arms, hands and fingers to reach into those tricky spots.
I love to stop and watch the cleaner station when it’s in full swing. Fish of all different species will queue up and wait their turn as the busy little wrasse flits in a distinctive up-and-down jerky swimming motion from one client to the next. When it’s their turn, the client will strike a pose, which varies depending on what species they are. It usually involves angling the body, extending the fins and flaring the gills in readiness for a once over. In an almost trance-like state they patiently allow the cleaner to nibble away their irritations.
This relationship between cleaner wrasse and other fish species has been well studied, so here’s some quick interesting and unexpected facts: [i] [ii] [iii]
The cleaner wrasse will be busy for about four hours every day. Incredibly, in that time it can check out as many as 2,000 clients and remove 1,000 ectoparasites.
Sometimes they get a little ahead of themselves and will sneak a bite of the protective mucous that their clients produce. This is called ‘cheating’. But, interestingly, it has been shown that if they are being watched by a queue of clients they are less likely to indulge in this inappropriate behaviour because they know their clients may decide to go elsewhere for their service – in other words, to a rival cleaner wrasse.
Cleaners will prioritise their clients, attending to those with the highest parasitic load first, or those that may be at risk of travelling elsewhere – such as the larger fish species that move more freely around the reef. There is a hierarchy of service with small damselfishes and butterflyfish down at the bottom of the priority list.
Researchers have also shown that fish that are cleaned of ectoparasites are more intelligent (they solved some tasks more quickly), and therefore are generally more successful.
Research has shown that some fish if cleaned regularly (and presumably have fewer blood suckers sapping their strength) will grow bigger.[i]
Reefs without cleaner wrasse can have not only less species of fish but less total numbers of fish.[ii] [iii]·
All of these findings make sense. For example, if you have head lice, the constant irritation could drive you a bit bonkers, let alone making you more vulnerable to infections from open wounds, among other things. Why would fish be any different?
I have only seen our cleaner stations with one bluestreak cleaner wrasse in attendance at any time. Elsewhere, on other coral reefs, it has been reported that there can be one male and up to three females working together. I’ve also never seen a turtle using one a cleaning station here, which doesn’t mean they don’t, but I’ve never seen it occur.
Above: the busy cleaning station on our reef this week.
I am really interested to know the optimal number of cleaner wrasse stations for a reef the size of Norfolk Island’s inshore lagoons. I know that I used to see three of these cleaning stations along the length of the reef (both bays). But for ages I couldn’t find any – there is a gap of a full year in my photos, which bearing in mind my fascination with these places points to a distinct absence. Then on 14 November 2022 I finally found a new station. I know that date well because I took Senator David Pocock out on a swim and excitedly pointed it out to him (image at bottom).
The new cleaning station was very quiet for the first two months, and often I thought the little cleaner wrasse had shut up shop, but I persisted in visiting the spot. Which paid off, because during the last couple of weeks it has been a wonderful hive of activity.
What I have seen increasingly at other places along our reef are juvenile moon wrasse, Thalassoma lunare (and they are always juveniles for some reason) offering a similar service but not in such a formalised way. It seems to be at any mutually convenient spot rather a specific location. Usually, it is initiated by a banded scalyfin (Parma polylepsis, known locally as aatuti) striking a pose and the moon wrasse then obliging. The only other client species that I’ve seen using the moon wrasse for cleaning services are the sand mullets.
Another cleaner wrasse I have also seen, just a couple of times and both in recent weeks, are sixstripe wrasse, Pseudocheilinus hexataenia, cleaning aatuti.
There’s a lot that can be learned about a reef from watching these busy little fish, and I have many questions I’d love to answer about their behaviour and how they interact and affect the health numbers and diversity of our local fish populations. And are the moon wrasse stepping in to fill a gap in the market, or are they effectively pushing out the bluestreak cleaner wrasse?
One of the many interesting reports I read when researching for this blog post says this: ‘Our findings indicate that a single small and not very abundant fish has a strong influence on the movement patterns, habitat choice, activity, and local diversity and abundance of a wide variety of reef fish species.’[iv]
Above, from left to right: a moon wrasse cleaning an aatuti; left and right middle, cleaning sand mullet; right, a sixstripe wrasse cleaning an aatuti. (Click on the images for larger versions.)
References
Senator David Pocock checking out the cleaner wrasse’s station
[i] Long-term cleaner fish presence affects growth of a coral reef fish, Gillian E Clague, Karen L Cheney, Anne W Goldizen, Mark I McCormick, Peter A Waldie, Alexandra S Grutter
[ii] Effect of the removal of cleaner fish on the abundance and species composition of reef fish, Alexandra S Grutter
[iii] Long-term effects of the cleaner fish Labroides dimidiatus on coral reef fish communities, Peter A Waldie 1, Simon P Blomberg, Karen L Cheney, Anne W Goldizen, Alexandra S Grutter
[iv] Cleaner fish drives local fish diversity on coral reefs, Alexandra S Grutter, Jan Maree Murphy, J Howard Choat
Other works consulted:
The fish that makes other fish smarter, by Ed Yong, The Atlantic.
Exploitation and cooperation by cleaner wrasse, by Laura Vander Meiden