AS A STUDENT OF LIFE UNDER THE SEA, I’m always curious about behaviors. So when, on a dive, I saw a pack of little yellow initial-phase bluehead wrasses streaking toward a distant point, naturally I followed them. They were almost certainly on an egg raid.
Blueheads are notorious for plundering the egg nests of other species of fish, particularly damsels and blennies.
BLUE HEADS & YELLOW BODIES
To be clear, bluehead wrasses get their name from the distinctive coloring of their terminal-phase males, or supermales. But only a small percentage of a bluehead population make it to supermale-dom.
Most are the little yellow juveniles and initial-phase guys we see all the time in the Bahamas/Florida/Caribbean basin. This happened to be at Flower Garden Banks National Marine Sanctuary in the Gulf of Mexico, off Galveston – the “Texas Caribbean.”
Juvenile blueheads are all yellow. Initial-phase’s have yellow heads and backs and white bottom halves, separated by a dark band. Actually, when they’re transitioning, it’s more complicated.
Some are males but most are females. If a supermale disappears, one of them – male or female – transitions to take his place. But initial-phase’s are adults and engage in broadcast spawning with each other as well as with the supermales.
For a more detailed look at bluehead wrasses, read “Bluehead Wrasses – An In-Depth Spotlight” here.
FEISTY FISH FIGHT FEEDING FRENZY
In this case, the target of their egg raid was a nest belonging to bicolor damselfishes (Stegastes partitus), the little black and white fish that seem to be ever-present on the reefs in the Tropical Atlantic/Caribbean basin. They’re nesting spawners, optimally creating egg nests in less-visible spots like crevices and holes. Hopefully, that makes the nest more egg raid resistant, but clearly not always.
I have to admit that I’ve always thought of bicolors as shy, innocuous little bystanders on the coral. Whenever I try to approach them, they always seem to drift behind a ledge or into a crevice.
THE BLUEHEAD PLAN – OVERWHELM WITH NUMBERS & CHAOS
In fact, as this egg raid shows, they’re ferocious little guys who fight mightily to protect what’s theirs, darting and nipping at the plethora of attackers.
Here, it seems likely that the several dozen wrasses overwhelmed the half-dozen or so bicolors and gobbled up a good quantity of eggs. While the bicolors are distracted by the chaos of the ever-moving blueheads above the nest, others are darting in and snatching eggs.
THE BICOLOR BACKUP PLAN – LAY MORE EGGS
Enough eggs must survive. Bicolors add eggs to their nests every day, and there certainly is never a shortage of bicolor damsels on the reefs.
Unfortunately for them, the same is true of bluehead wrasses.
PRINCIPAL SOURCES: Reef Fish Identification Florida, Caribbean, Bahamas, Paul Humann, Ned DeLoach; Reef Fish Behavior, Ned DeLoach; Peterson’s Field Guide to Atlantic Coast Fishes, C. Richard Robins, G. Carlton Ray, John Douglass; “Thalassoma bifasciatum,” Encyclopedia of Life; “Thalassoma bifasciatum,” University of Florida Museum of Natural History.