| Bubbles
from the Naturalist Jerry's tank - by Jerry Ligon |
 |
The
following is my original observations and deductions, and perhaps a new discovery
on this unique adaptation and the reasons behind it. I hope to put together
a video that can be seen on YouTube later.
One of many interesting things about parrotfish is a behavior that leads to
the death of the males. Anytime a behavior leads to the death of one of the
breeding adults, time after time, it is a behavior that is so striking that
it totally occupies biologist's minds to try to find out why. Do the males have
a "Death Wish"?
If my observations and deductions were contained solely within the mind of a
marine biologist, then I would know that all parrotfish are born female but
have the ability to change sexes to males. Biologists call this Hermaphroditism.
But the question goes begging-Why would this behavior have evolved?
If, on the other hand, my observations and deductions were of a dedicated bird
watcher, then I would know that Ospreys are specially adapted for securing fish
and male parrots are especially snatched out of the shallow water were they
come in to feed. In the excellent book "Birds of the Netherlands Antilles",
printed in 1983 by Prof. Dr. K. H. Voous, there is a documentation of a blue
parrot being captured in Curacao and on its back was the talons of an Osprey.
The fish being so large that it dragged the Osprey into the ocean and it drowned,
however the Osprey did not loosen its talons because they are adapted with grooves
along the bottom of each claw and the Osprey has trouble letting go when a fish
has been captured. But the question goes begging. Why do male parrots risk death
by feeding in such shallow water. But put the two different views together and
with some time spent analysing the factors, some patterns begin to develop.
Something drives the males to have a differential mortality rate much higher
than the females. This factor would cause an adaptation within parrotfish to
develope in which females could transition into males when the male was killed,
thus assuring that reproduction could continue, despite this death wish by the
males.
Competition among the numerous algae feeders on the reef is keen, driving many
special adaptations among the species to be able to survive. Competition is
what drives evolution. Without competition there would be no need for species
to change.
Parrotfish have peculiar arrangement in the jaws allowing them to secure as
much energy as possible from the algae that they eat. There is a second pair
of jaws called the pharyngeal mill which can be thought of as a special parrotfish
pestal-and-morter arrangement whereby the larger chunks of substrate containing
bits of algae material that help hold the algae on the bits of coral rubble
that are bitten off by the fused teeth of the primary jaw, and the mill grinds
up these fairly large chunks into smaller pieces allowing a larger surface area
for digestion within the stomach. Divers see the release of these plumes of
fine sand from parrotfish but do not realize the size differences of the fine
sand being pooped as being much different than the size of the substrate when
it was ingested.
This is a great adaptation that has allowed parrotfish to survive in a highly
competitive world. So where is the problem that accounts for the Death Wish
of the male parrotfish?
Male and females require different volumes of algae in order to secure enough
energy during a day of grazing. Females are able to secure enough energy by
grazing in the deeper reef rubble zones and do so by grazing almost constantly
all day long. This algae is eaten by a large number of other algae feeders and
is constantly nipped off, but because of intensity of sunlight, re grows almost
immediately, and again is nipped off. This food source never gets to develop
into larger volumes thereby acquiring more nutritious energy-laden elements.
THus the need for specialized jaw adaptations in order to secure as much energy
from the algae as possible.
Now, lets look at the life of the male parrotfish. It almost goes without too
much thought that males require larger volumes of the not-so-nutritious algae
out on the reef where every algae grazer feeds, or, in the amount of time that
they have to feed, they can look for more nutritious algae somewhere that the
other grazers are not feeding. Besides the "normal" energy requirements,
males larger body size requires more energy than the females, and males must
defend their harems from always opportunistic free males trying to acquire their
own harems. You see the males chasing other males on almost every dive on Bonaire,
but only if you are aware of what is going on. Also, males must acquire more
energy because they must reproduce with the females in their harem whenever
they are gravid with mature eggs. This behavior you also see on almost every
dive on Bonaire but, again, you must be aware of what is going on or otherwise
you totally miss the male up high in the water column, with an arched tail,
and swimming over the backs of his harem,perhaps 10-15 feet below, and then
one of the females began's to rise up to the male and in a coordinated, side-by-side
rush toward the surface, they both slap their tails together and separate and
that is the precise moment when sperm and egg are released into a cloud of gamets.
I am alerted to the spawning of the parrotfish on my dives whenever I see a
tight cluster of Sargeant Majors who are feeding on these nutritious bundles
of energy, even before fertilization has had an opportunity to take place. On
a dive one August, I saw one male Stoplight Parrot, up high in the water column,
and knew to watch and was amazed to see him mate with that spawning rush toward
the surface with seven different females, all within 40 seconds.
So the male is forced to acquire his algae in shallow water where his body length
determines how close he can feed to shore depending on the effects of the tides.
The changing tide depths assures that the males do not overeat in just one depth,
but acquire more nutritious algae that has had periods of changing tides that
allow for the algae to recover form the grazing.
As you observe male Stoplights, male Queen and often Yellowtail and Redtail
Parrotfish up in the shallow waters along the waterfront here on Bonaire, you
now have an idea what they are doing, that they are at a high risk of being
a meal for an observant Osprey. This behavior is occurring all along Bonaire's
coastline and along the coasts of all the islands in the Caribbean. Unless you
put all the afore-mentioned details together and look through the eyes of both
Marine Biologist and Bird-watcher, never will you arrive at the reason behind
the Death WIsh of the male parrotfish.
Male Stoplight Parrotfish grazing in shallow water.
Photo taken of jaw sections from a known frequent site where a known Osprey feeding area is located along the northern coastline, revealing the lower jaws of 3 different individual parrotfish. This lower jaw is just half of the pharyngeal mill that parrotfish use to maximize their grazing by grinding up the larger segments of crunched substrate that also contains algae. Divers and snorkels can hear this crunching.
Male Stoplight Parrotfish in shallow water along Bonaire's waterfront.
Osprey after capturing a parrotfish. Ospreys will catch by opportunity, putting
more mortality on male parrotfish. Photo by Marijke Wilhelmus