>Burrow building — practiced by jawfish, tilefish and a scattering of gobies — is nature's go-to solution for life on the sand. Three small wrasses, however, including rosy razorfish (our most recent fish of interest), have taken an alternate route to survival: By developing heads as hard and sharp as cleavers, they can power dive beneath the sand when threatened. Minutes later, after the coast clears, the slender 5-inch fish slip out of the sand and calmly go about their business picking plankton from the currents overhead.
>After a bit of sleuthing, we learn that the rosies' colony — an ever-morphing mosaic of contiguous territories — spreads across several hundred square feet of featureless terrain. The prime real estate consists of 4-foot territories near the center, each dominated by a large breeding male along with three to five smaller females with which he attempts to exclusively mate. A cabal of eager young bachelors relegated to the outskirts, however, has other ideas.
>Rosies, like most wrasses, are protogynous hermaphrodites that are born as females into a hierarchical system where size and sex mean everything. Later, when growth and social status dictate, some females change into males — the pinnacle of reproductive prosperity in fishdom. This life-changing transformation initiates a growth spurt and later bestows the yellow-green coats of male maturity. Such a competitive social system fosters bickering, so throughout the day females nip at underlings, while dominant males vigilantly guard invisible borders from encroaching males that are primed and ready to try to usurp a female or two.
>One morning from a distance we see a large yellowtail snapper circling high above the colony. A hundred sets of eyes, along with ours, track the predator until it fades from view. The snapper soon returns, makes two low passes, vanishes, returns, circles twice, cuts high across the colony and disappears once again. The threat lurks for 10 minutes until the snapper strikes from out of the blue with the speed of a missile, taking out one of the colony's largest males with a blow that leaves the fish dead on the sand. The loss of such a high-ranking colleague creates a power vacuum, setting into motion a time-honored struggle for dominance far too nuanced for our eyes to decipher.
>Afterward, the rosies become increasingly lethargic, until one by one they bed down for the night by diving into the safety of the sand as the sun sets.
>Watch this video to learn more about rosy razorfish.
>© Alert Diver — Q3 Summer 2019