To be small on a reef is a hazard, but just how important are the tiny cryptobenthic fishes to reefs and reef tanks? Dr Sterling Tebbett explains.
DR STERLING TEBBETT A coral reef ecologist in Australia, with eight years of aquatic retail experience.
GLIDING OVER A tropical, clear-water coral reef and admiring the diversity of life on show is arguably one of life’s most enjoyable moments. One drawback to the experience, however, is knowing that you’re only admiring approximately half the fishes present in that location.
What are you missing? Well, the answer is nearly all the cryptobenthic reef fishes. These fishes have been historically overlooked in coral reef ecology and are potentially one of the most underappreciated groups in home aquariums. Nevertheless, they represent a fascinating assortment of species that are essential to how coral reefs function, and many of these lend themselves perfectly to life in aquaria.
Life in miniature
Cryptobenthic reef fishes, or ‘cryptos’ for short, have generally been considered as fishes that are less than 5cm long and live in close association with the substratum. However, colleagues of mine recently defined cryptobenthic reef fish families using quantitative bounds: families where more than 10% of all species are less than 5cm long.
Notably, many common aquarium fishes derive from cryptobenthic fish families such as Gobiidae (gobies), Blenniidae (blennies), Callionymidae (dragonets), and Pseudochromidae (dottybacks).
While home reef aquariums are often considered small slices of the reef, they do differ from natural reef ecosystems in a multitude of obvious ways, although one way that is often not considered is that very few reef aquariums contain anywhere near the natural density of cryptos. Indeed, on any average 1m² section of reef, researchers generally find 10-20 cryptos, mostly comprised of gobies. That represents the highest density of vertebrates in any ecosystem in the world and is equivalent to keeping approximately 20 gobies in a standard 180x60x60cm reef aquarium.
The high densities of these small cryptobenthic fishes means that, on Australia’s Great Barrier Reef, researchers have found that the average length of a fish, across all fishes on the reef, is just 4.5cm long. This is why you are missing approximately half of the fishes when you glide over the reef, they are simply too small and are hidden am
