This file is part of the following reference

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This file is part of the following reference:

True, James (2004) Massive Porites corals as indicators of environmental changes. PhD thesis,

James Cook University.

Access to this file is available from:

http://eprints.jcu.edu.au/7890

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TITLE PAGE

Massive Porites corals as indicators of environmental changes

Thesis submitted by

James Dominic TRUE, BSc(Hons) JCU in August, 2004

For the degree of Doctor of Philosophy in the Discipline of Marine Biology

within the School of Marine Biology and Aquaculture

James Cook University

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STATEMENT OF ACCESS

I, the undersigned, the author of this thesis, understand that James Cook University will make this thesis available for use within the University Library and, via the Australian Digital Theses network, for use elsewhere.

I understand that, as an unpublished work, a thesis has significant protection under the Copyright Act and;

I wish this work to be embargoed until December 2005

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STATEMENT ON SOURCES DECLARATION

I declare that this thesis is my own work and has not been submitted in any form for another degree or diploma at any university or other institution of tertiary education.

Information derived from the published or unpublished work of others has been acknowledged in the text and a list of references is given.

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Acknowledgements

Little did I know, when I commenced this PhD, how little I knew about how to go about one. This has been a long and particularly frustrating project, beset by hordes of annoying delays, problems, failures and an almost unending supply of bad luck. That I have fmished at last is a tribute to the many people - family, friends, volunteers and scientists - who assisted me throughout the last several years.

Without question, the fIrst on the list is my wife, A, who has never really known me without the dissertation monkey on my back (and may not recognize me when it's gone).

A also provided me with her almost limitless reservoir of manual and mental labour and creative input. Next are my family, who -like A - encouraged me and supported me and (incomprehensibly) believed I could one day finish it. I hope the hundred or so pages following are worthy of their belief.

My supervisors, Bette Willis and Dave Barnes, deserve special mention. Also deserving mention are the staff ofthe Museum of Tropical Queensland, particularly Carden Wallace, who provided me with much support, advice, some taxonomic training and - for a long time inthe middle - a job. Support and fIeld staff at JCU School of Biology and AIMS have been exactly that - supportive - particularly in times when it seemed like nothing could be done... thanks, fell as. Likewise, Prof. Howard Choat, who many times managed to create a Faustian quid pro quo to enable me to carry on or go around a problem. The illustrations of Ch.l & Ch.3 are from drawings made for me by Bronwen Scott.

This project was improved immensely by the support and collaboration of researchers at the ANU Research School of Earth Sciences. Mike Gagan and Malcolm McCulloch have been extraordinarily generous with time, knowledge and resources. Likewise, support staff - notably Joe, Heather & Joan - and research students at ANU-RSES were particularly kind and underS!aE.,,:ng of a zoologist in a geologists' world.

My PhD was supported financially and/or in-kind by grants or contributions from several organizations, namely, the Great Barrier Reef Marine Park Authority, Reef CRC, the Raine Island Corporation, Underwater Explorer and the Linnean Society and AIMS.

Lastly, but in no way the least, the support and companionship of my friends has been a boon to me. I won't list them here - it would run on for a while and I would be mawkish by the end. I hope they know who they are and the debt lowe them. Many of them have been my volunteers - thrashed and tortured by my field schedule; others have been advisors or mentors. Some have simply been there with an open bottle or a table full of food (or the opportunity to create one). All have been invaluable. Thank you all.

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Abstract

Monitoring the responses of corals to environmental change and linking responses to past environmental changes are difficult and rely on correlative proxy techniques. To date, there has been no means to directly measure biologically meaningful effects of environmental changes on corals that could both explain the consequences of sublethal stress and enhance the interpretation of proxy environmental records. Massive Porites are extremely widespread in the Indo-Pacific. While not exceptionally fecund, fast-growing or competitively dominant, they appear to possess a peculiar robustness, often becoming the dominant corals on reefs that have been heavily impacted. The longevity of Porites colonies and the existence of annual density bands in their skeletons, makes them organism of choice for Indo-Pacific researchers interested in the construction of proxy climate records. This project aimed to address the lack of knowledge about the biological responses of Porites to various types of stress and to relate these responses to proxy environmental records derived from the corals' skeletons.

In addition, the project sought to develop a measure of sublethal stress which could be adapted into a general reactive monitoring protocol.

The thickness of the tissue layer (TTL) of a colony of Porites is a product of linear skeletal extension at its upper surface and periodic (up to monthly) uplift of its lower margin. A survey of 20 reefs on the GBR, as well as several reefs in PNG and the Gulf of Thailand indicated that tissue thickness of massive Porites conils varies in space and time. Spatial variation in TTL is mostly a manifestation of local (habitat-level) environmental conditions rather than an indication of broad geographic trends in conditions. Seasonal trends in TTL variation of Porites on the central GBR manifest as summer maxima and winter minima, as reported for calcification and linear extension. SST and insolation are the factors most likely to be responsible for seasonal cycles in TTL. TTL variation is a sensitive indicator of incipient or sublethal stress in massive Porites. Lack of stress-specific responses precludes distinguishing between chronic and acute stress solely from the thickness ofthe tissue layer.

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Continual mobilization of the lower portion of the tissue layer provides a unique mechanism by which massive

Porites

can control its response to stressful conditions. Moreover, tissue thickness and lipid levels appear to be interchangeable indications of the energy level of the polyp under stress, although extreme responses such as bleaching are more closely linked to tissue thickness than lipid levels. The response of corals to environmental impacts is dictated largely by their available energy reserve. Diminishment of a coral's ability to acquire energy leads to a reduction in linear extension as the coral adapts. Reduction of the coral's somatic reserve past a critical point leads to a bleaching response concomitant with shutdown of other functions.

Mass spectroscopic analysis of skeletal cores taken from colonies used in the long term stress experiment revealed that proxy environmental reconstruction techniques based on isotope ratios within the coral skeleton are able to capture stress events in the life of a coral identified by TTL changes. Changes to the amplitude and range of /)

¹⁸

0 and /)

¹³

C cycles during experimental shading suggest that chronic stress changes the way that corals record environmental variation. The sensitivity of isotopic techniques is diminished, however, by previous stress events. Likewise, interpretation of the nature of the stress event from the proxy record is problematic: proximal environmental variation is not recorded, and non- related stress events can leave identical signatures

in

the isotope record.

Skeletal proxy techniques will therefore underestimate the frequency of environmental impacts. These findings shed light on why it has so far been difficult to reconcile proxy records from different studies.

The use of TTL variation as a simple reactive monitoring technique is not readily achievable. Between-colony, habitat and seasonal variation, as well as the need to contextualize measurements to previous history, all place severe constraints on its utility as a simple technique. However, localized spatial gradients in TTL can identify environmental gradients and map their severity. As such, changes in TTL can be used as a broad-scale tool to identify habitats with sub-optimal or impacted environments.

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5.5 Extraction of proxy records from coral skeletons .5-15 5.5. I Corals record stress events as isotope anomalies in their skeletons .5- 15 5.5.2 There are differences between the colonies and species 5- I6 5.5.3 Analysts MUST study more than one core .5- I 8 5.5.4 Identification to species level is vital for comparative studies 5- I9

5.6 Evaluation of TTL as a monitoring tool 5-20

5.6. I Inter-locality, inter-colony, intra-annual and intra-monthly variability

approximates stress-induced variability 5-20

5.6.2 Previous history can influence the sensitivity of the measure 5-21 5.6.3 TTL offers a relative measure of environmental stress gradients

...5-21

5.7 General conclusions __ .5-23

5.8 Publications potentially arising from this research 5-25 Appendix 1

Appendix 2 Appendix 3 Appendix 4 Appendix5 Appendix 6

Spatial survey of TTL: measurement summary from individual colonies Temporal survey of TTL: measurement summary from individual colonies X-ray images of cores used in Chapter 4

Stable isotope traces from cores used in Chapter 4 superimposed over SST Raw data from isotope analyses

Raw data - lipid and tissue thickness values for the colonies undergoing natural bleaching

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List of Figures

Figure Page number

1-1 1-2a

b 1-3 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 3-1 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9 3-10 3-11 3-12

Perforate and imperforate coral skeletons 1-11

Skeletal anatomy ofPorites

I-IS

SEM image ofPorites skeleton 1-15

Tissue/skeleton relationship inPorites 1-19 GBR tissue thickness survey study areas 2-12

Tissue thickness - sampling 2-17

Location map of long-term study colonies in Pioneer Bay,

Orpheus Island, central GBR 2-19

Average TTL ofPorites from the GBR TTL survey and the

Gulf of Thailand 2-24

Average TTL ofPorites colonies in Pioneer Bay 1994-96 2-25 Colony-details TTL variation in Pioneer Bay, 1994-96 2-26

SST in Pioneer Bay, 1994-98 2-29

Idealized drawing of tissue uplift inPorites 2-31 Shade structure used in the light-reduction experiment. 3-8 Shade structurein situ above a colony in Pioneer Bay 3-9 Average incident light reaching colonies below shade

structures during the experiment 3-10

Average TTL of shaded colonies (1994-96) 3-16 TTL in shaded and unshaded colonies during the 1998 mass-

bleaching event 3-17

TTL of shaded colonies during and after the 1998 event 3-19

Visible signs of stress in Porites 3-21

Lipid concentrations in the tissue layers ofPorites colonies

during and after the 1998 event 3-23

Lipid concentrations in shaded and unshaded colonies during

and afterthe bleaching event 3-24

Tissue/lipid relationships during laboratory bleaching 3-26 Tissuellipid relationships of Pioneer Bay colonies during

and afterthe 1998 bleaching event 3-31

Tissue/lipid relationships of Pioneer Bay colonies according

To shading history 3-32

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List of Figures

Figure Page number

4- I

4-2 4-3

4-4

4-5 4-6 4-7 4-8 4-9 4-JO 4- I I

5-1 5-2

Fractured P. lulea core showing fans of corallites

centred on the growth axis 4-17

Detail of sampling procedure used to extract skeletal samples

for isotopic analysis 4- I8

Isotopic analysis of unshaded colony PBOI 4-24

SST in Pioneer Bay, 1994-98 4-25

Record of TTL variation for PBO

J

compared with average

TTL of unshaded colonies in Pioneer Bay, J994-99 4-26 Isotopic analysis of shaded colony PBS04 4-29 Record of TTL variation for shaded colonies, 1994-2000 4-30 Isotopic analysis of shaded colony PBSO I 4-32 Isotope traces of the three cores translated into a time

domain. . .4-35

Mean monthly1)18

0

values for shaded coral PBS04 4-36 Monthly rainfall record from Lucinda Jetty 4-46

Hypothetical tissue uplift mechanisms 5-7

Hypothetical stress-management protocol for corals 5-13

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List of Tables

Table Page number

2-1 Collection sites for tissue thickness spatial survey 2-15 2-2 ANaV A testing for offshorelmidshelf differences

in TTL (northern section) 2-21

2-3 ANaVAtesting for offshorelmidshelf differences

in TTL (southern section) 2-21

2-4 ANaVAtesting latitudinal differences in TTL (N/S) 2-22 2-5a ANaVAtesting latitudinal differences in TTL

(pooled sites within zones) 2-23

b Tukey's LSD identifying significant deviations from

averageTTLwithin zones 2-23

3-1 ANaVA (repeated measures) testing the effects of shading

onTTL 3-15

3-2 ANaVA testing for changes inTTLduring the 1998 mass

bleaching event 3-18

3-3 ANaVA testing for changes in lipid concentrations within

the tissue layer during the 1998 bleaching event 3-22

XI

This file is part of the following reference