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Vitória-Trindade Chain
a stepping stone for reef fishes
Few people know
or have even heard
of Trindade and Martin Vaz,
Brazil's most remote oceanic islands.
These islands mark the eastern end
of the Vitória-Trindade Chain,
a volcanic ridge
that extends 1200 km
in front of the coast
of the state of Espírito Santo
and the Abrolhos Bank.
The Vitória-Trindade Chain originated
after South America separated
from Africa,
50 million years ago,
and grew until 1 million years ago,
when was formed Martin Vaz.
Currently,
most of the Vitória-Trindade Chain
is hidden under the waters
of the Atlantic Ocean.
However, during the ice ages
the sea level was
100 meters below actual.
At that time, most of the seamounts
were emerged
and a linear series of islands extended
offshore of the city of Vitória.
The first expedition to study
the fishes of Trindade through diving
was in 1995,
with Sergio floeter and I
using free diving.
A year later,
we came back with a few cylinders
to do the first scuba dives
at Trindade Island.
The first studies about the
biogeography of Brazilian reef fishes,
a decade ago,
detected that Trindade
hosts many species,
more than would be expected
from its geographical isolation.
On the other end there are two islands,
Trindade and Martin Vaz.
How fish species that live
in shallow environments
move out from the continent
to these distant islands?
Do they jump from one
seamount to another?
The seamounts could be
serving as stepping stones
for continental species
to reach the islands.
Intrigued with the hypothesis
of connectivity by stepping stones,
a group of researchers
from the Federal University of Espírito Santo
went looking for answers.
To do this, we needed to dive
on these seamount summits.
We wanted a boat with autonomy
to stay in the open ocean,
providing security to remain
20-30 days isolated.
Moreover,
the boat had to provide
support for the dives.
We had to be ready to dive
in these conditions.
That is, we had to be prepared
physically, psychologically and technically
to conduct this kind of expedition.
We established partnerships
to execute the expedition and,
later, to analyze its results.
We also aggregated people
able to travel with us
and to provide technical support.
The use of modern techniques
and equipment was necessary
to dive at mesophotic depths
and this was the first utilization
of closed circuit rebreathers
for research in Brazil.
This means that recreational
diving techniques were not adequate.
We could not breathe compressed air
so we needed to breathe a mixture
of oxygen and helium,
at a concentration adapted
to the depth reached.
The common expectation aboard
was to perform diving
in almost untouched places,
where the diversity and abundance
of reef organisms still represented
a significant fraction
of what it was in the past.
In an 18-day expedition in the open sea,
where the depth could reach 5,000 meters,
the team made several dives on the tops
of the five major seamounts
of the Vitória-Trindade Chain,
which are now between 18 and 84 m
below the surface.
During the expedition,
we found that the tops of seamounts
are home to a huge diversity and abundance
of marine organisms.
The rocks that millions of years ago
were steaming lava
are now completely covered
by reefs of calcareous algae and corals,
besides sponges and macroalgae,
which form the basis of the reef environments.
The main goal of our research
is to determine the importance
of the seamounts of the Vitória-Trindade Chain
to maintaining the connectivity between
Trindade and Martin Vaz and the mainland.
One way to do this is using genetic tools.
Two fish species were chosen
to represent different scenarios of connectivity
between islands and coast.
One of these species was a small grouper
popularly known as coney.
The other was the yellowtip damselfish.
In summary,
what is done in the laboratory
is to remove a small piece of muscle
from each individual and extract his DNA.
Then, small parts of the genome
are isolated and the DNA sequence
of each individual is determined.
Then begins the computational analysis.
We determine the DNA composition of
individuals and then we look for
the genetic relationships among them.
Mitochondrial DNA shows that the coney
can maintain a high connectivity from the
coast to Trindade and Martin Vaz.
This means that at each generation
a certain number of larvae
are transported from one population to another,
leading to a homogeneous distribution
of lineages along the chain.
In other hand,
kinship analysis detected that
larvae dispersion occurs mainly between
adjacent populations.
This means that some seamounts,
as Vitória and Davis,
act as stepping stones,
connecting islands and mainland populations.
Thus, the conservation of these environments
is extremely important for the
maintenance of the population size
and the genetic diversity on oceanic islands.
That is,
if seamounts populations are overexploited,
species abundance at Trindade
will probably be affected.
On the other hand,
results for the damselfish were quite different.
While this species is able to maintain
a high connectivity between the coast
and most of the seamounts,
the populations from the islands
are genetically isolated.
Curiously,
two distinct evolutionary lineages
were found at the islands,
both of which coexist at Columbia,
the last seamount of the Vitória-Trindade Chain.
Moreover,
a few individuals at other seamounts
and on the mainland
are closely related to the genetic lineages
endemics to the islands and the Columbia Seamount.
This pattern shows us that the Columbia
is the last, and maybe the main,
stepping stone permitting that species
with short-dispersion larvae
can reach Trindade.
In the same manner,
Columbia allows genetic lineages
that arise in isolation at the islands
to colonize the seamounts,
successively,
until reaching the mainland.
This mechanism contributes to the increase
of the biodiversity of the entire region
along hundred thousands of years.
More than 270 species of fishes
are now known from the islands and seamounts
of the Vitória-Trindade Chain.
Since the first scientific expeditions to Trindade,
still in the early twentieth century,
researchers have found endemic species there,
that is, species that do not exist
anywhere else in the world.
Until recently, six species were considered
endemic to Trindade and Martin Vaz,
with the evolution of these species
attributed to the isolation of their populations.
However, other species were discovered
in the last expeditions
and the number of endemics
has increased to eleven.
An interesting fact is that some
of the species thought to occur
only at Trindade, were also found
on the seamounts but not on the coast.
The presence of these species
on the seamounts
calls attention to the existence of a
possible ecological barrier
distinguishing the coastal environments
from those of the
Vitória-Trindade Chain.
Thus, species can be subjected
to evolutionary processes
not only at the islands
but also at the seamounts.
We also noticed that
while the Vitória-Trindade Chain
harbors an enormous diversity
of environments and species,
the integrity of its ecosystems
is under severe threat.
The uncontrolled fisheries
have led many populations to decline,
especially those of large predators
like sharks and groupers.
These are considered key-species
for the maintenance of reef ecosystems
because they regulate the biomass of their prey
and maintain the balance of the food chain.
While diving in the Vitória-Trindade Chain,
the only shark species sighted was the
nurse shark.
Besides fisheries, another activity
with even greater destructive power
that could quickly endanger the biodiversity
of the Vitória-Trindade Chain
is the mining of carbonate sediments
and rhodolith beds.
Experimental explorations,
through dredging,
were carried between 2009 and 2011
on Davis Seamount,
which is currently
located in international waters.
Despite being built by living organisms,
lime deposits take thousands of years
to be formed and cannot be considered
a renewable resource.
Furthermore,
associated with these environments
there are extremely rich flora and fauna
that are very little known.
These observations
show the need of management and conservation
of the Vitória-Trindade Chain.
Inaction could result in the loss
of a unique biodiversity
and of important goods and services
provided by this volcanic ridge.
This would endanger the continuity
of ecological and evolutionary processes
that occur between the coast
and the eastern tip of Brazil.
Research activities are just
beginning at the Vitória-Trindade Chain.
New expeditions are essential
to improve our knowledge about
the processes of colonization and evolution
as well as the ecology of these
Brazilian oceanic environments.