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Alaria at Tobago Cays Marine Park |
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Coral reef at Tobago Cays Marine Park |
After Mustique, we sailed south to the drop-dead gorgeous
Tobago Cays Marine Park (“TCMP”). There,
the Park Rangers took us to reefs they have been monitoring for some time. We
spent a week there before we sailed on to Union Island from which we traveled
to Petite St. Vincent again courtesy of the TCMP Rangers and their fast boats. Finally, we sailed to Carriacou in the
country of Grenada. This was our most
southern station where we surveyed the island’s reefs along its windward east
coast and south coast. So after over 170
coral transects and nearly 500 fish transects we had surveyed most of the coral
reefs we had targeted in the eastern Caribbean.
Now, we can consider what, if any, patterns we’ve found.
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The Grenadines with the most extensive coral reefs (right inset) |
Fig. of eastern Caribbean Islands including Grenadines
A “SNAPSHOT” OF THE EASTERN CARIBBEAN CORAL REEFS
Living coral comprised less than 20% of the hard surfaces we
surveyed from Anguilla to Carriacou. This
is a low number but it is comparable with most coral reefs of the Caribbean
today. Nevertheless, three regions --
St. Lucia, Mustique and Tobago Cays -- had higher than average coral cover and
a higher than average abundance of baby corals. Similarly, two of those three regions had
lower than average abundance of harmful seaweed. Grazing fish such as parrotfish and
surgeonfish were most abundant at Mustique but they were either average of
above average at those three regions.
The most prized reef fishes to eat are groupers and they were most
abundant at both Mustique and Tobago Cays.
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The relatively healthy reef at Mustique |
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Relatively healthy reef at Tobago Cays Marine Park |
In short, it appears that all of the reefs with better than
average conditions for coral reef health (abundant coral, baby corals, little
seaweed, many and grazers and relatively abundant predators) were all found in no
fishing “marine reserves” with
effective enforcement. In the larger
view this included St. Maarten, St. Lucia (Soufriere Marine Management Area),
Mustique and Tobago Cays Marine Park.
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Average coral, seaweed and baby coral abundance. The blue horizontal line represents the Antilles average. Note that St. Maarten, St. Lucia, Mustique and Tabago Cays have enforced marine protected areas. |
There are, of course caveats to the pattern that reefs with
less fishing are “healthier”. For
example, it is possible that areas with high coral cover were targeted for
protection. That certainly happened in
St. Lucia and possibly Tobago Cays Marine Park.
However, Mustique’s protection was established with little specific
knowledge of what coral reefs existed there.
Specific reefs within managed sites vary greatly. Sometimes this is due to natural variability
found in any ecosystem. However, in some
places we think we see some patterns that may have caused the local
variations. To address why adjacent reefs
differ, we targeted a few sites for more detailed studies with some more
expertise.
OUR RESEARCH TEAM GROWS!
For help on why reef fishes and seaweed abundances vary so
much among local coral reefs Dr. Peter Mumby (University of Queensland) and Ms.
Natalia Rincón Díaz
(Universidad Nacional
de Colombia) joined our team. Both of
these scientists will spend a month working on these problems from Alaria.
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Dr. Pete Mumby (reef fish ecologist) sailing to our study site on Alaria. |
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Natalia Rincon Diaz (a seaweed expert) joins our group. |
In
the way of introductions, Dr. Peter Mumby is an Australia Research Council,
Laureate Fellow and heads the University of Queensland’s Marine Spatial Ecology
Lab. He is the President of the
Australian Coral Reef Society but most of his research over the past few
decades has been on coral reefs of the Caribbean. He is one of the world’s leading experts on
the ecology of coral reef fishes (Google him if you are curious). Natalia is a masters student at her
university who is studying the relationship between herbivorous fishes and the
algae they eat. I saw this a great
opportunity to help advance her career while helping us with our studies. She will have full access to all of our data to
help her in her masters thesis research.
|
Science discussions intensify during our sunset chats. |
WHY
ARE SOME CORAL REEFS SO DIFFERENT FROM OTHERS NEARBY?
While
it is great that there are areas with higher than average coral cover and fish
abundance, it is also interesting to consider why another reef nearby is
different. We suspect there are two big
factors affecting reefs. One is one is
the variability of reef structure (that is, its habitat architecture), the
other is how fishing pressure changes from place to place. These are by no means the only factors
causing the variability we observed but we think they may be factors
contributing to the differences.
Corals
create the architecture of reefs. This
includes those corals alive today and the skeletons of corals past. This architecture may take centuries to
develop but it provides places for fish and other critters to live or to
hide. The habitat architecture of reefs
increases the surface area on which seaweed can grow and herbivores such as
parrotfish can graze. So, we wondered if
differences in habitat architecture may explain the differences we see among
adjacent and nearby coral reefs.
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A simple and relatively featureless reef in Barbuda. |
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A complex elkhorn coral reef at Tobago Cays Marine Park. |
To examine these questions in greater depth we set out to
measure habitat architecture by measuring the length of coral structure under
each meter along a 10 meter transect.
With our measurements we learn how high and how dense the coral
structures thrust into the overlying water.
We get a sense of how much reef surface area there is in any given
space.
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Bob measuring spatial complexity of the coral reef (photo Pete Mumby). |
We also measure how the topography of the reef is being used
by grazing fishes. We watch for 5 minute
periods and via small video cameras, the bite rates on the reef by parrotfishes
and tangs. As the surface area of reefs
increase, so to does the area on which seaweed can grow. So it may be necessary
in high complexity areas for more parrotfishes grazing just to keep the reef
clean of harmful seaweed.
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Natalia quantifying the rate at which herbivorous parrotfish and tangs bite tops, sides and bottoms of complex reef surfaces. |
Because it is also possible that fish behave differently on
these reefs, Peter Mumby documented the grazing behavior of the dominant
parrotfish including juveniles and adults.
We also deploy video cameras to film fish grazing at sites that range
from high to low complexity
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Pete quantifying bite rates for different size and species of grazing parrotfish. |
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One of several compact GoPro video cameras quantifying fish grazing without a human presence. |
We will need to considerable analyses beyond what I’ve
presented here. However, we are
beginning to see patterns that make sense.
This is also information that reef managers will want to know. In a future blog I’ll describe how we have
been meeting with managers at each of the islands we are studying. All of them are eager to hear what we have
learned.
The beauty of coral reefs today. All these photos happen to be from reef protected areas.
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Elhorn coral in TCMP |
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Neon gobies on a star coral. |
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Sponges in the Soufriere Marine Management Area |
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A green moray in Mustique's Lagoon reef. |
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