It was one of these early and calm afternoons during the summer months, somewhere at a dive site entry along the fringing reefs of South Sinai. The near-shore reef flat area at this site was covered with rounded boulders and smaller stones derived from ancient, massive river floods which once transported these materials there from the mountainous hinterland, many thousands of years ago. All these rocky surfaces were more or less overgrown by turf algae, partly seaweed, and who knows which variety and amount of invertebrates found shelter and feeding substrate at this very location.
While we prepared for the dive, putting on our mask and fins, some curious little fishes appeared, moving about our feet where we accidentally had stirred up the sediment, and twitching around most vividly, in obvious search for food items possibly released by our disturbance. Their body was perfectly streamlined, with a pointed head and a truncate caudal fin, and they exhibited a conspicuous colourful pattern – green on their back and head, the breast and belly being light blue to white, and with few red stripes alongside the body. In addition, dorsal areas and head showed transverse and wavelike patterns.
Many divers and snorkellers have probably tested the inquisitive behaviour of this animal which is one of the most abundant and frequently encountered fish species in the shallow-water area of coral reefs – predominantly the reef flats, crest areas and upper reef slopes: turning a stone upside down means offering access to potential food items - first hidden beneath, then exposed as a prey for the predator.
We are talking about Klunzinger's wrasse (Thalassoma rueppellii) belonging to the large family of wrasses (Labridae) and, more precisely, its subfamily Corinae (or "julidin wrasses"). More than 80 species of wrasses are known from the Red Sea. The South-German physician and zoologist Carl Benjamin Klunzinger (1834-1914) had described the species as early as 1871, paying tribute to his famous predecessor, the Senckenberg zoologist and geographer Eduard Rüppell (who had written about Red Sea invertebrates and fishes several decades before Klunzinger), by naming the species after his colleague.
Because of its scientifically confirmed high abundance in the shallow reef areas (0.5 – 20m), the survival strategies of Klunzinger's wrasse seem to be highly successful. It belongs to a genus that has existed for several millions of years. Like all other wrasses in our region, Klunzinger's wrasse is a sequential hermaphroditic species, in the sense that all females can change their sex and turn into males which both grow bigger (up to three times bigger than primary males), patrol and defend a territory (so-called territorial behaviour) and maintain a harem within the limits of this territory. Like other wrasses they release eggs and sperm in the open water (pelagic spawning) favouring the widespread dispersal of their offspring. While primary males spawn in large, mixed groups, the secondary males choose their sex partners for solitary courtship and pair-wise spawning. Possibly this mating behaviour secures the passing on of genetic material of higher quality, thereby enhancing chances for better adaptation to, and thus survival in the reef environment.
The mostly carnivorous feeding model of the wrasses also applies to Klunzinger's wrasse. They predominantly hunt small benthic invertebrates and fishes, which they pluck with their protruding canine teeth that are well-designed for this purpose. The often hard-shelled prey is then crushed by the powerful pharyngeal teeth.
The wrasse may also behave like a cleaner, and its unafraid and rather offensive prying (something which may have contributed to the species' evolutionary success) may go quite far – we can report "attacks" of plumb lines used in substrate surveys of reef monitoring campaigns, and also experienced bites into a diver's usually "exposed" hands. The species, like its relatives, is active only during daytime. At night it chooses to hide in corals rather than sleep under sand.
Apart from juveniles and sub-adult individuals, males and females are not easily distinguished from each other but their respective sizes may provide some clues. The dominant secondary males can be up to three times bigger than primary males, and females reach hardly half the size of secondary males, which may reach a maximum length of 20cm.
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