THE WINSTON CHURCHILL MEMORIAL TRUST OF
AUSTRALIA
Report by Dr Andrew S. Hoey
2011 Churchill Fellow
THE DR DOROTHEA SANDARS AND IRENE LEE CHURCHILL
FELLOWSHIP to study the effect of seaweed chemicals on the
health of reef-building corals
I understand that the Churchill Trust may publish this Report, either in hard copy or
on the internet or both, and consent to such publication.
I indemnify the Churchill Trust against any loss, costs or damages it may suffer
arising out of any claim or proceedings made against the Trust in respect of or
arising out of the publication of any Report submitted to the Trust and which the Trust
places on a website for access over the internet.
I also warrant that my Final Report is original and does not infringe the copyright of
any person, or contain anything which is, or the incorporation of which into the Final
Report is, actionable for defamation, a breach of any privacy law or obligation,
breach of confidence, contempt of court, passing-off or contravention of any other
private right or of any law.
Signed:
Dated: 3rd February, 2011
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INDEX
INTRODUCTION...........................................................................................3
EXECUTIVE SUMMARY...............................................................................4
FELLOWSHIP PROGRAMME.......................................................................5
MAIN BODY………………………...................................................................6
BACKGROUND AND IMPORTANCE……..........................................6
FIJI (15th October – 10th November 2011)….......................................7
Fiji’s local coral reefs.................................................................7
Seaweed chemicals and field techniques in marine chemical
ecology……………………………………………….................8
ATLANTA, GEORGIA (10th – 28th November 2011)….....................14
Laboratory techniques in chemical ecology............................15
CONCLUSIONS AND RECOMMENDATIONS............................................17
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INTRODUCTION
The 2011 award of the DR DOROTHEA SANDARS AND IRENE LEE
CHURCHILL FELLOWSHIP enabled me to travel to Fiji, where I was based at a
marine research facility on the Coral Coast, and to the USA where I was based at
Georgia Institute of Technology, Atlanta to investigate the role of chemicals in
determining the outcomes of competitive interactions among seaweeds and
corals. Coral reefs are in dramatic global decline. Anthropogenic disturbances,
such as overfishing and pollution, are being greatly compounded by climate
change with many reefs being overgrown by seaweeds. The ability of these reefs
to recover is largely dependent on the outcomes of competitive interactions
among coral-seaweed interactions. I was specifically interested in determining
which seaweeds are most damaging to corals and the role of chemicals in
producing these effects, as well as assessing whether herbivorous fishes are
capable of controlling blooms of seaweeds. This research will contribute greatly
to understanding the ecology and functioning of coral reefs worldwide, and
provide the data necessary to manage Australia’s coral reefs in the face of future
climate- and human-induced stressors.
Acknowledgements
I sincerely thank Irene Lee and the late Dr Dorothea Sandars for their generosity
in sponsoring the Churchill Fellowship for the study of an issue in in the field of
marine science. I am extremely grateful to the Winston Churchill Memorial Trust
for providing me with this wonderful opportunity. I would also like to thank the
Votua, Vatualailai, and Namada village elders for granting local research
permissions in Fiji. The Hay Lab at the Georgia Institute of Technology, Atlanta,
USA funded and supported research conducted during my Churchill Fellowship.
I would also like to acknowledge the significant contributions by individuals who
provided detailed instruction, advice, and critical logistical support for this project:
•
Professor Mark Hay, Georgia Institute of Technology, USA
•
Professor Julia Kubanek, Georgia Institute of Technology, USA
•
Dr Roberta Bonaldo, Georgia Institute of Technology, USA
•
Dr Danielle Dixson, Georgia Institute of Technology, USA
•
Dr Sebastian Engel, Georgia Institute of Technology, USA
•
Mr Doug Rasher, Georgia Institute of Technology, USA
•
Associate Professor Henrik Pavia, Göteborg University, Sweden
•
Associate Professor Gunilla Toth, Göteborg University, Sweden
•
Mr Victor Bonito, Reef Explorer Fiji
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EXECUTIVE SUMMARY
Dr Andrew S. Hoey, Postdoctoral Fellow
Red Sea Research Center, KAUST, Saudi Arabia; and
ARC Centre of Excellence for Coral Reef Studies, James Cook University,
Townsville, QLD 4811
Phone: (07) 4781 5979
Email: [email protected]
Project Description
Coral reefs are in global decline, with seaweeds overgrowing corals in many
locations. Despite the potential deleterious effects of seaweeds on coral reefs, we
do not know how the outcome of seaweed-coral competition varies among
species, or the relative importance of chemicals in facilitating seaweed
dominance on degraded reefs. The purpose of this project was to gain an
understanding of chemical extraction methodologies and advanced chemical
ecology techniques to further our understanding of chemically-mediated
competitive interactions between corals and seaweeds. Determining which
seaweeds are most damaging to corals, and the role of chemicals in producing
these effects will contribute greatly to understanding the ecology, functioning and
resilience of coral reefs.
Highlights
The 2011 award of the DR DOROTHEA SANDARS AND IRENE LEE
CHURCHILL FELLOWSHIP enabled me to travel to Fiji and the USA (15th Oct –
30th Nov), where I was hosted by Prof M.E. Hay and the International Cooperative
Biodiversity Group. In Fiji, I worked closely with Prof Hay to gain knowledge and
practical experience in the application of field techniques to extract seaweed
chemicals and directly test the effects of these chemicals on both corals and
herbivorous fishes. In the USA, working closely with Prof Hay, Dr S. Engel, and
Mr D.B. Rasher at the Georgia Institute of Technology, I extended this work and
attained a good appreciation of the practicalities and logistics of advanced
laboratory techniques to partition and isolate various chemical fractions from
seaweeds. While at Georgia Institute of Technology I also gave an invited
seminar, presenting results of my recent research.
Recommendations, Implementation and Dissemination
Advanced chemical ecology techniques represent valuable tools for the study of
coral reef ecosystems. The use of these techniques to isolate and incorporate
various seaweed chemicals into biological and ecological assays (e.g. allelopathy
and herbivore assays) have the potential to greatly advance our understanding of
the role of seaweeds in the dynamics of coral reefs. These techniques have
already been employed in a study of deep-water seaweeds undertaken in
collaboration with Prof Hay. Preliminary findings from this study suggest that
seaweed chemicals were responsible for both suppressing coral health and
deterring herbivore feeding. Results from this study form the basis of a scientific
publication to be submitted to the internationally recognised journal Coral Reefs.
Ongoing research in collaboration with Prof Hay will isolate specific chemical
fractions to determine if the same fractions function as herbivore deterrents and
allelopathic compounds. Research funding is also being sought to expand this
research to the Great Barrier Reef and provide necessary training for graduate
students in this field.
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FELLOWSHIP PROGRAMME
Oct 15th, 2011 – Departed Townsville
Oct 15th, 2011 – Arrived Votua Village, Fiji (via Brisbane and Nadi)
Oct 15th to Nov 10th, 2011 – Hay Lab Marine Research Facility, Votua, Fiji
Oct 16th, 2011. Sevusevu (traditional kava ceremony) with Votua village
elders to discuss research and request permission to work on their reefs,
Votua Village, Vitu Levu, Fiji
Oct 18th, 2011. Group discussion (Prof M Hay, A/Prof H Pavia, A/Prof G
Toth, Dr R Bonaldo, Dr D Dixson) “The role of chemicals in fish-coralseaweed interactions on coral reefs”, Hay Lab Marine Research Facility,
Votua Village, Vitu Levu, Fiji
Oct 18th, 2011. Sevusevu with Namada village elders to discuss the
relevance of our research and request permission to work on their reefs,
Namada Village, Vitu Levu, Fiji
Oct 20th, 2011. Sevusevu with Vatualailai village elders to discuss the
relevance of our research and request permission to work on their reefs,
Vatualailai Village, Vitu Levu, Fiji.
Oct 22nd, 2011. Research presentation by AS Hoey “Herbivorous fishes:
the critical gardeners of coral reefs”, special presentation to the Votua,
Vatualailai, and Namada village elders, Korolevu-iwai district, Vitu Levu,
Fiji
Nov 11th to Nov 28th, 2011 – Georgia Institute of Technology, Atlanta, USA
Nov 15th, 2011. Group discussion (Prof M Hay, Dr Sebastian Engel, Mr
Doug Rasher) “Applications of chemical ecology in tropical marine
research”, Georgia Institute of Technology, Atlanta GA, USA
Nov 18th, 2011. Invited seminar presented by AS Hoey “Biodiversity and
ecosystem function: the role of herbivores on coral reefs”, Biology
Seminar Series, Georgia Institute of Technology, Atlanta GA, USA
Nov 28th, 2011 – Departed Atlanta
Nov 30th, 2011 – Arrived Townsville (via Dallas and Brisbane)
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MAIN BODY
Background and Importance
Coral reefs are one of the world’s most biologically diverse and productive
ecosystems, yet they are also one of the most threatened. The combined effects
of climate change, storms, disease, eutrophication, and overfishing have
significantly changed the structure and functioning of reefs worldwide. Over the
past three decades live coral cover has declined by approximately 80 percent on
Caribbean reefs, and 30 to 50 percent on Indo-Pacific reefs, including the Great
Barrier Reef. These reductions in coral cover are, however, typically
accompanied by increases in other benthic species, in particular fleshy
seaweeds, which rapidly colonise the dead coral skeletons (Figure 1).
Consequently, several reefs around the world have undergone a transition, or
shift, from biologically diverse, topographically-complex coral-dominated
communities to depauperate, topographically-simple communities dominated by
seaweeds.
The ability of reefs to recover from such disturbances is largely dependent
on the rate at which new coral colonies recruit and grow to colonise available
space and/or the regrowth of remnant coral colonies. The proliferation of
seaweed biomass following coral mortality, however, increases the frequency and
duration of competitive interactions between seaweeds and both newly recruited
Figure 1: Changing reef communities on an Indo-Pacific reef. Bleached corals
are rapidly colonized and overgrown by a variety of seaweeds. The ability of
these reefs to recover will be largely dependent on the ability of corals to
outcompete the seaweeds.
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and remnant coral colonies. The limited research to date suggests seaweeds
may influence the survival, growth, and fecundity through physical (e.g., shading,
abrasion) and/or chemical (e.g., water-soluble compounds released into
surrounding water, or lipid-soluble compounds transferred by direct contact)
mechanisms. These interactions may not only decrease the recovery potential of
coral populations, but may also form feedbacks that drive reef decline further.
Despite considerable debate as to whether seaweeds are drivers or
consequences of ecosystem change on coral reefs, the outcomes coral-seaweed
interactions remain poorly understood. The objective of my Churchill Fellowship
was to gain knowledge and experience in the application of techniques to directly
test the effect of seaweed chemicals on corals and reef fishes.
Fiji (15th October – 10th November 2011)
My Churchill Fellowship began at Votua Village on the Coral Coast of Vitu Levu,
Fiji. Here, I spent approximately four weeks working from a small marine research
facility operated by Professor Mark Hay (Georgia Institute of Technology).
Professor Hay heads a research group that is investigating chemical mediation of
biotic interactions on Fijian coral reefs and the roles these interactions play in
affecting the community structure and ecosystem function of these reefs. This is
an important area of research, and perfectly complements my research
examining the role of herbivorous fishes in determining the resilience of coral reef
ecosystems.
Fiji’s local coral reefs
The coral reefs in the Korolevu-iwai district represent the ideal location for the
field component of my fellowship examining the role of seaweed chemicals in
mediating coral-seaweed interactions. The coral reefs in this district are locally
managed and each village has its own no-take marine reserve or marine
protected area (MPA) that is enforced by a village elder. Between each reserve,
the reef is subject to intense artisanal fishing using a variety of methods (e.g.
spears, nets and/or handlines). Despite these no-take marine reserves being
small and relatively young (established 8 to 9 years ago), they have had a
remarkable effect on fish and coral communities. The no-take marine reserves
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are characterized by exceptionally high coral cover, low seaweed cover, and high
fish biomass, while just a couple of hundred metres away the areas open to
fishing are characterized by low coral cover, high seaweed cover, and low fish
biomass (Figure 2). The higher density and biomass of herbivorous (i.e. planteating) fishes within the no-take reserves exerts strong top-down control on the
seaweeds, thereby allowing the coral populations to recover following repeated
disturbances from coral bleaching and outbreaks of the coral-eating crown-ofthorns starfish. This remarkable transition over such a small spatial scale is
unparalleled anywhere else in the world.
Figure 2: The effect of a small no-take marine reserves on reef communities,
Namada Village, Viti Levu, Fiji. A diverse and abundant assemblage of live
corals characterizes the reef within the no-take marine reserve (left). Outside
the no-take marine reserve boundaries the reef is overgrown by seaweeds
(right). Photos courtesy of Dr Joao Krajewski.
Prior to commencing the field research component of my fellowship we had
to seek permission from the respective village elders to enter the water and
conduct research activities on their reefs. This seeking of permission was based
around the traditional Fijian kava ceremony ‘Sevusevu’. The function of the
Sevusevu is firstly to introduce and welcome visitors, and secondly to open up
paths for other discussions and interactions. To initiate a Sevusevu for each
village we made contact with the respective village elders, informed them of our
request to conduct research on their reefs and organized a time to visit their
village and perform the Sevusevu. At the pre-arranged time we were welcomed
into the house of the village elder (usually the village chief) where we sat on the
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floor facing the elders. The ceremony begins when we present the elder with
approximately one kilogram of ‘waka’; a tightly wound buddle of roots from the
kava plant. The elder then accepts the waka and offers a blessing,
acknowledging the presence of their ancestors. We were then welcomed to
village and invited to join the village elders in drinking a round of kava. The kava
is prepared by pounding the waka into powder, mixing it with water and straining
through a piece of cloth (usually an old t-shirt or similar). The kava is then poured
into a large wooden bowl and stirred regularly to keep the powder in suspension.
A cup made from a coconut shell is then filled and offered firstly to the chief, and
then sequentially to each person in the Sevusevu. As the cup was offered, the
recipient must clap their hands once, then accept the cup and drink the kava in
one motion, clap again and pass the cup back. The kava itself looks much like
muddy water and doesn't taste too dissimilar from expectations, except perhaps
for the slight peppery flavour. The volume of kava offered to each person varied
markedly and was quite a source of amusement for the villagers. A cup that was
half filled was referred to as ‘low tide’ and was typically offered to those who had
little experience in drinking kava (i.e., members of Prof Hay’s group and myself).
A cup that was full was referred to as ‘high tide’ and an overflowing cup was aptly
referred to as a ‘tsunami’.
Figure 3: The research group of Prof Mark Hay outside the marine research
facility in Votua Village, Fiji. Pictured from left to right are Prof Mark Hay,
Jessica Hoey, myself, Dr Roberta Bonaldo, and Dr Danielle Dixson.
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During the Sevusevu at each village (Votua Village 16th October; Namada
Village 18th October; and Vatualailai Village 20th October 2011) I not only
described the research that I was proposing to conduct on their reefs during the
next 4-weeks of my Churchill Fellowship, but also the relevance of my previous
research (from the Great Barrier Reef and elsewhere) to their local reefs. This
was a very valuable and rewarding experience that allowed me to describe the
relative importance of certain fish species in maintaining the healthy functioning
of coral reefs. The village elders were very receptive and extremely interested to
hear that some of the fish species they specifically target for food are critically
important to prevent reefs being overgrown by seaweeds and in maintaining and
promoting coral-dominance on coral reefs. Following these discussions we
decided to produce some educational material for the local children so that this
knowledge could be passed on for generations to come. This resulted in two
illustrated short stories (“Super Sivisivi saves the reef” and “Baby fish need
leaves to find their way home”). The first describes the role of sivisivi (the local
name for the blue-spine unicornfish, Naso unicornis) in rescuing the sick reef
from seaweeds that had overtaken the reef. This story also made direct links to
the deleterious effects of pollution and rubbish on reef corals, and the potential
benefits to fish catches of maintaining a healthy coral-dominated reef. The
second book linked the importance of the terrestrial environment to baby fishes.
This was based on the research of Dr Danielle Dixson, a postdoctoral researcher
in Prof Hay’s lab, who showed that some baby fish use the smell of leaves in the
water to find their way back to the reef.
My visit to Fiji also coincided with a larger ceremony, or party, in which Prof
Hay’s lab hosted the local village communities to thank them for allowing the
establishment of the research facility and supporting the continued research
within the Korolevu-iwai district (22nd October 2011). While Prof Hay hosted the
party, the local villagers prepared just about everything from decorating the openair hut to cooking a traditional Fijian feast, or lovo. The lovo is cooked
underground using coals and heated rocks and takes several hours to prepare.
Chicken, fish, taro, potatoes and some local vegetables are wrapped with palm
fronds or placed in coconut shells, covered with banana leaves and buried along
with the coals for a couple of hours to cook. Food cooked in this way is delicious
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with a slightly smoky flavour. Prior to the meal we were all asked to introduce
ourselves and give a presentation of our research. This was another great
opportunity to discuss our research, both past and future, with the wider district
community. The local people take great pride in their reefs and showed great
interest in our research, especially as it related to their reefs. Disseminating
research and conveying the main findings to a range of age groups (i.e. from
children to village elders) was challenging but highly rewarding. The
presentations and dinner were followed by a kava ceremony and several hours of
questions and discussions of our research and how the villages could better
manage their reefs.
Seaweed chemicals and field techniques in marine chemical ecology
Seaweeds, like many plants, produce a range of water-soluble and lipidchemicals (or secondary metabolites). In fact, several thousand secondary
metabolites have been described from marine seaweeds, with over 500
secondary metabolites being recorded from a single genus of red seaweed,
Laurencia (Faulkner 1994). Despite this body of work that has isolated and
identified these compounds, our understanding of the natural function of many
marine secondary metabolites remains limited. Within coral reef ecosystems
seaweeds have been shown to reduce the productivity, growth, survival, and
reproductive output of corals. However the relative importance of chemical and
physical (e.g., shading, abrasion, and pre-emption of space) mechanisms in
influencing these outcomes is currently not known.
My first couple of days in Fiji was spent discussing the potential roles of
seaweed chemicals in the coral reefs processes with Prof Hay. Although these
discussions centred around the potential deleterious effects of seaweeds on
corals we also deliberated on the role of seaweed chemicals in other reef
processes. For example, we discussed at some length the role of seaweed
chemicals in deterring feeding by herbivorous fishes. During this time I gained
extensive knowledge on: (1) the various classes of compounds (e.g., terpenes
and halogenated polyphenolics) produced by different seaweeds groups; (2) the
advantages and disadvantages of various techniques to extract the different
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compounds; and (3) methods to incorporate the extracted chemicals into
biologically meaningful experiments examining the effects of the various
compounds on both corals and fishes. Once I had this knowledge we held a
group discussion with Prof Hay, Dr Roberta Bonaldo, and Dr Danielle Dixson
(Georgia Institute of Technology), A/Prof Henrik Pavia and A/Prof Gunilla Toth
(visiting researchers from Göteborg University, Sweden) and myself on the role of
chemicals in fish-seaweed-coral interactions on coral reefs. This was extremely
valuable as each participant shared their knowledge and experiences, and
consequently gave me considerable insight into the role of seaweed chemicals in
both tropical and temperate marine systems.
Having gained the necessary theoretical background, an understanding of
the various techniques, and permission to work on the local reefs, I was ready to
gain practical experience in the application of these techniques. Several of Prof
Hay’s students were already working on some of the shallow water reef flat
seaweeds. Consequently, we decided to work on a range of deeper water
seaweeds and collected eight species (the red seaweeds: Callophycus densus,
Callophycus serratus, Plocamium sp., Liagora sp., Gelidium sp., Neurymenia sp.,
Melanamansia sp., and the green seaweed Chlorodesmis sp.) from a depth of 20
– 30 m on reef slope. To extract the crude chemicals a volume of the seaweeds
were immersed in methanol and ‘blended’ in a food processor to assist in
breaking down the cell walls. The methanol takes up the chemicals and the
methanolic extract filtered to remove particulate material. A rotovapor is then
used to reduce the methanol from the extract, while continuing to extract the
sample with more methanol. This process is repeated until the methanolic extract
becomes clear, indicating that the majority of the chemicals have been extracted.
Similar volumes of ethyl acetate and distilled water were then added to the
extract to separate the hydrophobic (lipid-soluble) and hydrophilic (water-soluble)
compounds. The water containing the hydrophilic compounds is then removed
using a separation funnel. The ethyl acetate is then removed from the
hydrophobic chemical fraction using a rotary evaporation and the dried extract
sored in a freezer until ready to be used. The production of these crude chemical
extracts is relatively straightforward, however it is time consuming.
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By incorporating these crude extracts into assays we were able to test the
relative effects of these chemicals on both fishes and corals. To examine the
effects of these hydrophobic seaweed chemicals on corals we used allelopathic
bioassays. For these bioassays the crude extract is resuspended in a small
amount (1mL) of the methanol and small amount added to heated Phytagel.
Phytagel is an agar substitute that produces a clear colourless high strength gel
for plant tissue cultures. The Phytagel containing the chemical is then placed in a
mold over nylon fly screen mesh, and allowed to cool, set and bind to the mesh.
The resultant mold is cut into small strips, wrapped around the base of a branch
of coral and secured using a small cable tie. After 24-hours the strip is removed
and the photosynthetic activity of the coral tissue immediately under the strip
measured in situ using pulse-amplitude modulated fluorometry. The majority of
the crude chemical extracts examined resulted in marked declines in the
photosynthetic efficiency of the corals indicating the presence of allelopathic
chemicals.
Having established that many of these chemicals were having adverse
effects on corals we decided to extend this research to determine if the seaweed
chemicals were also acting as a herbivore deterrent. Firstly, we transplanted the
deep water seaweeds together with some shallow water seaweeds that are
known to be palatable to herbivorous fishes and monitored them for several days.
While the shallow water seaweeds were rapidly consumed, all of the deeper
water seaweeds remained untouched after 6-days. Using chemical assays we
were able to determine if this avoidance was related to the chemical or physical
characteristics of the seaweeds. The crude chemical extracts (described above)
were resuspended in a small amount (5mL) of diethyl ether and ‘painted’ onto the
surface of the blades, or leaves, of a palatable seaweed (Padina). As the diethyl
ether evaporated the chemical adhered to the surface of the blades. These
blades were then placed back on the reef. By comparing rates of consumption
between blades with the chemicals to those without we were able to determine
the relative importance of chemical and physical properties of the seaweeds in
deterring feeding by herbivores. While the blades without chemicals were rapidly
consumed, the blades coated with chemicals of seven of the eight seaweed
species were avoided indicating that the chemicals were also deterring feeding by
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herbivores.
Figure 4: Extracting seaweed chemicals for use in herbivore feeding assays.
Clockwise from left: 1 Seaweed immersed in methanol to extract crude
chemicals from the seaweed tissue; 2 Using a rotary evaporator to remove
the solvent (methanol) from the extract; 3 ‘Painting’ the crude chemical extract
onto the blades of the palatable seaweed Padina; 4 Herbivore feeding
bioassays on the reef. The majority of the seaweeds without chemical coating
have been removed (left rope) while those coated with chemicals are still
largely untouched (right rope).
Atlanta, USA (11th – 28th November 2011)
After spending several weeks in Fiji attaining knowledge and practical experience
in the extraction of crude chemicals and their application in field assays I travelled
to the USA to learn some advanced laboratory techniques. In the USA I was
based in the chemical ecology laboratory of Prof Hay and Prof Julia Kubanek at
the Georgia Institute of Technology, Atlanta for 2.5 weeks. The objective of this
component of my Churchill Fellowship was firstly to obtain knowledge in the
available techniques for partitioning crude seaweed extract into various fractions
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or components; and secondly to gain practical experience in the use of these
techniques. The rationale behind this was to allow me to identify the particular
chemical fractions and pure chemical compounds that were influencing coral
health and/or functioning as herbivore deterrents. Consequently, several
kilograms of seaweed collected in Fiji were frozen and brought to the Georgia
Institute of Technology (under permissions from the Fijian and USA
governments).
Arriving in Atlanta on a friday, my first couple of days were spent completing
the necessary paperwork and safety inductions to work in the chemical ecology
laboratory, and orienting myself around the University and the city. Taking
advantage of the weekend I took some time out from the research for my
fellowship and visited many of sites and attractions within the Atlanta area;
including the Georgia Aquarium, the house of Margaret Mitchell (author of Gone
With The Wind) and the Martin Luther King Jr National Historical Site. Despite
having one of the busiest airports in the world, Atlanta is the greenest cities in the
USA with large oak trees lining most streets. The highlight was the Georgia
Aquarium, the largest aquarium in the world. Georgia Aquarium holds over 37
million litres of water and the enormous tanks house a diversity of temperate and
tropical fauna, most notably whale sharks and beluga whales. This is quite a feat
given that the aquarium is located over 400 km from the coast. Consequently, the
millions of litres of water in the aquarium is completely filtered every 6-7 minutes.
Laboratory techniques in marine chemical ecology
My first day in the lab at Georgia Institute of Technology was spent meeting
with the various researchers, postdoctoral fellows and students, and discussing
their current research programs. These discussions proved to be extremely
beneficial in identifying the various techniques they are using and the application
of these techniques to biological, ecological and pharmaceutical studies. The
projects within the lab were highly varied, ranging from ecological studies of
temperate and tropical marine and freshwater ecosystems to the identification of
novel chemical compounds and drug discovery. Interestingly, some of these
projects have isolated and identified chemical compounds from Fijian seaweeds
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that are new to science, with several displaying strong anti-cancer properties.
Following these individual meetings I was invited to join a group discussion on the
‘Applications of chemical ecology in tropical marine research’ with Prof Hay, Dr
Sebastian Engel and Mr Doug Rasher. During this meeting we discussed the
theoretical basis of partitioning chemical fractions, reaffirmed the techniques
available (e.g., positive-phase columns, reverse-phase columns, liquid
chromatography, high-pressure liquid chromatography), and highlighted the
advantages and disadvantages of each technique. These techniques separate
the various chemical fractions of compounds based on their polarity or relative
molecular weights. At the conclusion of the discussion we formulated a project
that I could pursue while in Atlanta, and would lead to real and potentially
significant scientific outputs. This project was aimed at determining if separate
chemical fractions were responsible for allelopathy and deterring herbivores, or if
a single chemical fraction was responsible for both functions.
Before I could begin to partition the various chemical fractions I once again
had to extract the crude chemicals from the seaweeds. This highlighted one of
the advantages of working in a well-equipped laboratory as opposed to a field
laboratory. I was able to process approximately ten times the volume of seaweed
in half the time. The crude chemical extracts were fractioned using a liquid-liquid
partition (a sequence of Hexanes, Chloroform, Ethyl Acetate, and distilled water).
These initial fractions were then further partitioned using vacuum liquid
chromatography (VLC) in which the extracts are loaded onto a resin (HP20SS)
and then eluted with a series of solvents. This process was very labour intensive
and accounted for much of my remaining time in Atlanta. Throughout this time
Prof M. Hay, Dr S. Engel, Mr D Rasher and many other members of the lab were
always on hand to demonstrate the various techniques, provide advice and
answer any questions that had arisen. I plan on going back to Fiji during June
2012 to again work with Prof Hay to test the effects of these chemical fractions on
both coral health and herbivore feeding activities.
While in Atlanta I also delivered an invited seminar: “Biodiversity and
ecosystem function: the role of herbivores on coral reefs”. I described the
research conducted at James Cook University on the role of herbivorous fishes
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and the resilience of coral reefs to ongoing climate- and human-induced
stressors. This body of work not only demonstrated the critical importance of
herbivorous fishes to the health and persistence of coral reefs, but presented
results that question the widely-held view that biodiversity is a source of
ecological stability or insurance. Specifically, I described how critical functions on
one of the world’s most biodiverse and pristine reef systems, Australia’s Great
Barrier Reef, are performed by just one or two species. Reefs may be extremely
susceptible to the loss or overfishing of these species. The seminar was
extremely well attended and stimulated considerable discussion.
CONCLUSIONS AND RECOMMENDATIONS
Chemical ecology has many important applications in the study of coral reef
ecosystems. In particular, the use of both allelopathic and herbivore feeding
assays has real potential to greatly advance our understanding of the role of
seaweeds in the degradation and recovery of reefs worldwide. While the
mechanisms and complexities of coral reef decline are well known, our
understanding of the processes that may facilitate reef recovery is severely
limited. Predicting how reefs respond to increased seaweed cover, and
understanding the role of chemicals in influencing the dynamics of coralseaweed-fish interactions is one of the most significant research gaps in coral
reef science. It is important to recognize however, that bioassays incorporating
chemicals have some limitations. Most notably they are not suited for
investigating the effects of hydrophilic (water-soluble) chemicals. Seaweeds
produce a range of hydrophobic (lipid-soluble) and hydrophilic chemicals. While
hydrophobic compounds are readily incorporated and retained in herbivory and
allelopathy assays, hydrophilic compounds either coated onto palatable
seaweeds or incorporated into gels for allelopathic assays are rapidly lost to the
surrounding water. Therefore these chemical assays should be used in
conjunction with other pre-existing techniques using whole seaweed ‘plants’.
I have already disseminated some of the findings of my Churchill Fellowship
in an invited presentation at an international coral reef conference in Abu Dhabi;
Coral Reef of the Gulf (17th-19th January 2012). My talk, while not focusing on
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Seaweed-coral interactions (2011)
reefs of the region, was extremely well received and generated significant interest
in the use of these techniques from coral reef researchers from across the world.
I am also planning to present the results of my fellowship in the James Cook
University seminar series during early 2012. The results from the research I
conducted in Fiji as part of my fellowship form the basis of a scientific publication
that I am currently preparing to submit to the internationally recognized journal
Coral Reefs. My fellowship has also led to an ongoing collaboration with Prof Hay
to follow on from this research and determine if the certain seaweed chemical
fractions function as both herbivore deterrents and allelopathic compounds. It is
anticipated that this will lead to several more publications in high profile
international journals. Since receiving the 2011 Dr Dorothea Sandars and Irene
Lee Churchill Fellowship I have been actively promoting the Churchill Trust and
encouraging many others in my field of research to apply for a fellowship.
Australia has the necessary infrastructure and capacity to undertake
extensive research in the chemical ecology of coral reefs. Importantly,
incorporating chemical ecology into current research programs on seaweed-coral
and seaweed-fish interactions will greatly advance current understanding of coral
reefs, both in Australia and worldwide, and enhance Australia’s position as a
world-leader in the science and management of coral reefs. I also plan to expand
this research program to examine how changes in water quality effect the
production of seaweed chemicals, and the influence these have on seaweedcoral-fish interactions. Research funding is currently being sought to expand this
research to the Great Barrier Reef and provide necessary training for graduate
students in this field.
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Seaweed-coral interactions (2011)
Figure 5: Diverse seaweed community surrounding corals on an inshore reef of
the Great Barrier Reef. These reefs are subject to increasing eutrophication and
sediment from land-based sources. Determining how the decreased water quality
on these reefs may influence chemically-mediated interactions between
seaweeds, corals and herbivorous fishes will be the focus of my future research.
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