Cleaner wrasse (Labroides dimidiatus) not only help reef fishes get rid of ectoparasites, their very presence can help them grow bigger and increase the diversity of the reef habitats they inhabit.
This is the conclusion made in a study by Peter Waldie and colleagues published in a recent issue of the online journal PLoS ONE.
The authors investigated the long-term effects of cleaner wrasses on fish communities at Lizard Island (in the Great Barrier Reef) for more than eight years, making it the longest study of its kind.
The basis of this study was formed by the exclusion of cleaner wrasses in two patch reefs at the study site for 8.5 years.
The authors determined the effects of cleaner wrasses on client size by surveying two resident common client species, the Lemon damselfish (Pomacentrus moluccensis) and the Ambon damselfish (P. amboinensis).
Given that the lifespans of these two species are less than the period in which the reefs had been experimentally manipulated, many of the individuals had thus experienced the experimental conditions their entire lives.
The authors also recorded the abundance and species richness of residents, juvenile visitors, and adult visitors on experimental removal and on control reefs.
The authors found that the two damselfishes were significantly smaller in the reefs in which the cleaner wrasses had been excluded. The absence of cleaner wrasses also reduced the abundance and species richness of resident species and adult visitor species and the abundance of juvenile visitors.
Resident fishes were 37% less abundant and 23% less species rich per reef, compared to control reefs, while visitors were 23% less abundant and 33% less species rich per reef. Visiting juvenile fishes and herbivores (surgeonfishes) were also noticeably less abundant in the experimental reefs, being 65% and 66% less abundant respectively when compared to control reefs.
It can be seen that the cleaner wrasses exerts profound ecological effects on the reef far beyond their diminutive size and low density. Recruitment to the reef habitat may be significantly affected in the absence of cleaner wrasse, as may the prospects of the reef being overrun by algae (because of the removal of herbivores).
Given the importance of the cleaner wrasse, conservation and management strategies may need to also focus on the protection of this key species.
For more information, see the paper: Waldie PA, SP Blomberg, KL Cheney, AW Goldizen and AS Grutter (2011) Long-term effects of the cleaner fish Labroides dimidiatus on coral reef fish communities. PLoS ONE 6, e21201. doi:10.1371/journal.pone.0021201
Why not take out a subscription to Practical Fishkeeping magazine? Check out our latest subscription offer.