Study
of new parasitic coral reef species advances understanding of factors
influencing disease transmission in oceans
President Barack Obama has one. Comedian
Stephen Colbert has one. Elvis Presley has one. Even computer software magnate
Bill Gates has one. And now, Bob Marley--the late popular Jamaican singer and
guitarist--also has one. So what is it that each of these luminaries has? The
answer: they each have a biological species that has been named after them.
Paul Sikkel, an assistant professor of
marine ecology and a field marine biologist at Arkansas State University,
discovered and just named after Marley a "gnathiid isopod"--a small
parasitic crustacean blood feeder that infests certain fish that inhabit the
coral reefs of the shallow eastern Caribbean. Sikkel named the species Gnathia
marleyi.
All of the life stages of Gnathia marleyi
are described by Sikkel and his research team in the June 6th issue of
Zootaxia. This research was partly funded by the National Science Foundation
(NSF).
Sikkel said, "I named this species,
which is truly a natural wonder, after Marley because of my respect and
admiration for Marley's music. Plus, this species is as uniquely Caribbean as
was Marley."
Gnathia marleyi is a new species within
the gnathiid family, and the first new species to be described in the Caribbean
in more than two decades.
By concealing themselves within coral
rubble, sea sponge or algae, juvenile Gnathia marleyi are able to launch
surprise attacks on fish and then infest them. Sikkel explained that adult
gnathiids do not feed at all. "We believe that adults subsist for two to
three weeks on the last feedings they had as juveniles and then die, hopefully
after they have reproduced."
There have been increasing numbers of
reports that the health of Caribbean coral reef communities is declining due to
diseases. "We are currently researching the relationships between the
health of coral reef communities and gnathiid populations," said Sikkel.
"Gnathiids, in general, are the
most common external parasites found on coral reefs and are ecologically
similar to land-based blood-sucking ticks or disease-carrying mosquitoes,"
Sikkel said. "Gnathiids live on the ocean floor from pole to pole, and
from shallow reefs to the abyss--and everywhere between. They are also the most
important food item for cleaner fishes and thus key to understanding marine
cleaning symbioses."
Sikkel explained that his research group
is interested in the combined ecological effects of fishing pressure and reef
degradation. "We suspect that coral degradation leads to more available
habitat for external parasites to ‘launch attacks' on host fishes," he
said. "And as the number of potential host fish decreases, each remaining
host will become more heavily parasitized."
"Our current work is focused on how
changes in coral reef environments, such as coral bleaching, influences
interactions between hosts and parasites," said Sikkel. "We're
including in our studies any effects on cleaning organisms that remove parasites
from hosts."
About 80 percent of all organisms found
on coral reefs are parasites. The gnathiid isopods are among the most
ecologically important of them, according to biologists, because many diseases
afflicting desirable fish are either caused by, or are transmitted by
gnathiids. In addition, the immune system of fish also depends on the overall
health of coral reefs, which are known as the "rainforests of the
sea" because of their vast biodiversity.
At the end of the day, it comes down to
simple oceanic economics: the more parasites there are, the fewer fish there
are--at least until the parasites run out of hosts to infect. And fewer fish in
the sea can cause significant losses to the populations that depend on them.
Studying the effects of changes in
sea-bottom communities associated with coral and sponge diseases and their
interactions among other species will advance knowledge of blood-borne
pathogens. Sikkel suspects that Gnathia marleyi may be a vector in transmission
of these diseases.
Sikkel says his team's current funding
through NSF's Ecology and Evolution of Infectious Diseases (EEID) initiative
and Biological Oceanography is enabling the team to study precisely which
species of Caribbean reef fish harbor these blood parasites. "We are
determining the role of Gnathia marleyi, which will help us understand the
impacts of changes in coral reef habitat on the transmission of a fish disease
called haemogregarines--a type of fish malaria that may weaken their immune
systems through a reduction in certain blood cells."
"Disease ecology is a rapidly
maturing field in marine science," said Michael Lesser, a program director
in NSF's Biological Oceanography Program. "To advance this field,
scientists must identify which organisms are the main players in disease
transmission in oceans."
Lesser continued: "With so much
marine diversity yet to be described, parasitic species don't always get the
attention they deserve. But Sikkell and his team have taken an important step
by helping to analyze the ecological effects of a parasite on Caribbean coral
reef fish populations by describing this previously unknown species."
Sikkel initially discovered Gnathia
marleyi about 10 years ago in the U.S. Virgin Islands where it is relatively
common--so common, in fact, that Sikkel had assumed for years that the species
had previously been described. Nevertheless, compelled by a hunch, Sikkel
ultimately sent a specimen of the species to Nico J. Smit of North-West
University in South Africa, a member of Sikkel's research team, who confirmed
that the species had, in fact, previously been overlooked by taxonomists. With
the help of Whitney Sears, one of Sikkel's students, the research team raised
the isopod from its juvenile stage through adulthood, a laborious task that was
necessary because most taxonomy descriptions of gnathiids are based on adult
males, which usually differ in appearance and other ways from juvenile
gnathiids.
Specimens of Gnathia marleyi will be
housed indefinitely at the American Museum of Natural History in New York City.
"We are currently discussing with AMNH the possibility of creating an
exhibit featuring this species that could be viewed by the public," said
Sikkel.
Sikkel's research team includes Charon
Farquharson of the University of Johannesburg in South Africa and Smit.
And by the way, if you are wondering,
President Obama has a lichen named after him; Colbert has a beetle; Gates has a
flower fly, and Elvis has a wasp.
-NSF-
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