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FATE AND EFFECTS OF OIL AND
DISPERSED OIL ON
MANGROVE ECOSYSTEMS IN
AUSTRALIA
Norman C. Duke
Kathryn A. Burns
Australian Institute of Marine Science
and
CRC Reef Research Centre
Final Report
to the
Australian Petroleum Production Exploration Association
12 June 1999
Effects of Oil and Dispersed Oil on Mangroves
An environmental research project with the AUSTRALIAN PETROLEUM PRODUCTION & EXPLORATION
ASSOCIATION L IMITED (APPEA) and the ENERGY RESEARCH AND DEVELOPMENT CORPORATION
(ERDC).
Scientific research conducted under the direction of the COOPERATIVE RESEARCH CENTRE FOR
ECOLOGICALLY S USTAINABLE DEVELOPMENT OF THE GREAT BARRIER REEF (Reef CRC) and the
AUSTRALIAN I NSTITUTE OF MARINE SCIENCE (AIMS).
Contact details:
AIMS (local Australia) — Phone: 07 4753-4444 Fax: 07 4772-5852
(International) — Phone: +617 4753-4444 Fax: +617 4772-5852
N.C. Duke — n.duke@uq.edu.au
K.A. Burns — kburns@aims.gov.au
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Effects of Oil and Dispersed Oil on Mangroves
Project Summary
This three-year project (1995-1998) assessed short and long term effects of commonly transported
oils and dispersed oils on Australian mangrove flora and fauna. Short term studies were conducted in
planthouse and field conditions. Longer term effects were assessed from spill incidents which occurred
over the last 30 years in sites around Australia. Findings from all studies form the basis for improved
guidelines and recommendations for the protection, cleanup, and restoration of oiled mangrove habitat
around Australia, and elsewhere. For example, although there was no difference between oil only and
dispersed oil treatments in field trials where the impact on fauna was catastrophic, the death of mangrove
trees was significantly less in plots treated with dispersed oil. Partial recovery of fauna occurred after
approximately two years, but there was little sign of restoration of trees and damaged forest canopy. For
this reason, dispersion of spilled oil before it reaches mangroves is considered an effective strategy in
reducing the long term impact of oil on mangrove habitat. Such results have established the baseline for
future, on-going assessment of oil damaged sites for both natural recovery, and the application/testing of
remedial/restoration strategies and techniques; particularly for more sensitive and badly affected areas in
Australia.
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Effects of Oil and Dispersed Oil on Mangroves
CONTENTS
FATE AND EFFECTS OF OIL AND DISPERSED OIL ON MANGROVE
ECOSYSTEMS IN AUSTRALIA 232
PROJECT SUMMARY 232
1. INTRODUCTION TO THE PROJECT 236
1.1 Structure of studies undertaken 237
2. SURVEYS OF OIL SPILL INCIDENTS AROUND A USTRALIA – AN ASSESSMENT OF INCIDENTS ,
IMPACTS ON MANGROVES, & RECOVERY OF DEFORESTED AREAS 240
2.1 Summary Points 240
2.2 Introduction 240
2.3 Methods 242
2.3.1 Australia-wide field surveys 242
2.3.2 A standard protocol for site surveys 242
2.3.3 Measurements of tree and seedling condition 244
2.3.4 Sediment sampling and hydrocarbon analyses 244
2.3.5 Prior studies at each site 244
2.4 Results 244
2.4.1 Incidents 244
2.4.2 Impacts on mangroves 245
2.4.3 Status and recovery of deforested mangroves 245
2.5 Discussion 246
3. PLANTHOUSE EXPERIMENT – EFFECT OF OIL & DISPERSED OIL ON MANGROVE SEEDLINGS 248
3.1 Summary points 248
3.2 Introduction 248
3.3 Methods 248
3.3.1 The tidal system and establishment of mangrove seedlings 248
3.3.2 Treatments of oil and dispersed oil 248
3.3.3 Elements in green leaves of treated seedlings 250
3.4 Results 250
3.4.1 Overall effects of oil 251
3.4.2 Overall effects of dispersed oil 252
3.4.3 Species and other seedling variables 252
3.4.3 Elements in leaves of seedlings 252
3.5 Discussion 252
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Effects of Oil and Dispersed Oil on Mangroves
4. GLADSTONE FIELD EXPERIMENT – EXPERIMENTAL SETUP AND METHOD 256
4.1 Summary points 256
4.2 Introduction 256
4.3 Methods 261
4.3.1 The study area and site selection 261
4.3.2 Experimental enclosures and oil treatments 262
4.3.3 Sediment sampling 262
4.4 Results 262
4.4.1 Schedule of research activities 262
4.4.2 Physical description of treatment application 265
4.4.3 Sediment cores 265
4.4.4 Oiled sediment redox levels 267
4.4.5 Sediment nutrients 267
4.5 Discussion 267
5. GLADSTONE FIELD EXPERIMENT – WEATHERING OF HYDROCARBONS 268
5.1 Summary points 268
5.2 Introduction 268
5.3 Methods 270
5.3.1 Experimental design 270
5.3.2 Analysis 270
5.4 Results & Discussion 272
5.4.1 General features 272
5.4.2 Experimental loss rates 275
5.4.3 Mass balance 275
5.4.3 Changes in oil composition at 13 months 275
5.4.5 Further degradation at 22 months 281
5.4.6 Implications for treating oil spills impacting mangroves 281
5.5 Conclusions 281
5.6 Notes on analytical quality assurance 281
6. GLADSTONE FIELD EXPERIMENT – IMPACT, RESPONSE & RECOVERY OF PLANTS 284
6.1 Summary points 284
6.2 Introduction 284
6.3 Methods 284
6.3.1 Surveys of plant condition 284
6.3.2 Shoot observations 286
6.3.3 Litter fall collection 286
6.3.4 Allometric assessment of leaves 286
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Effects of Oil and Dispersed Oil on Mangroves
6.3.5 Derived measures of canopy standing biomass & density 286
6.3.6 Indirect measurement of canopy density 288
6.3.7 Assessment of nutrients in green leaves 288
6.3.8 Seedling and tree demography 288
6.3.9 Tree allometry 288
6.4 Results 288
6.4.1 Impact on forest structure 288
6.4.1.1 Impact on trees 288
6.4.2 Impact on seedlings 290
6.4.3 Canopy condition and growth 290
6.4.3.1 Litter fall 290
6.4.4 Shoot observations 295
6.4.5 Allometric assessment of leaves 297
6.4.6 Litter and shoot derivations 297
6.4.7 Nutrients in leaves 298
6.4.8 Light penetration through the canopy 298
6.5 Discussion 299
7. GLADSTONE FIELD EXPERIMENT – IMPACT, RESPONSE & RECOVERY OF MACROFAUNA 302
7.1 Summary points 302
7.2 Introduction 302
7.3 Methods 302
7.3.1 Canopy herbivory - caterpillars 302
7.3.2 Macrobenthos epifauna - crustaceans 304
7.3.3 Macrobenthos infauna - sipunculids 304
7.4 Results 305
7.4.1 Herbivory of canopy foliage by caterpillars 305
7.4.2 Biomass of crabs and other crustaceans living on the forest floor 306
7.4.3 Leaf removal from the forest floor by crabs 306
7.4.4 Sipunculid worms in mangrove sediments 308
7.5 Discussion 310
8. RECOMMENDATIONS AND GUIDELINES 314
8.1 Summary points 314
8.2 Introduction 314
8.2.1 Management protocol in oil spill response 314
8.3 Before an oil spill incident 315
8.4 During an oil spill – oil mobile phase 315
8.4.1 Oil at sea – a threat to mangrove 315
8.4.2 Oil into mangroves 317
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Effects of Oil and Dispersed Oil on Mangroves
8.5 After an oil spill – oil settled 317
8.6 Observations, recommendations and guidelines 318
9. REFERENCES 320
10. APPENDICES 325
10.1 Appendix 1
Surveys of oil spill incidents which have affected mangrove habitats in Australia: a report on
the incidents, impacts and recovery of affected areas. 325
10.2 Appendix 2
Current policies of key institutions in oil spill response, clean-up and management with
regard to mangroves: the National Plan to Combat Pollution of the Sea by Oil. 361
10.3 Appendix 3
Revised dispersant use guidelines, approved by the GBRMPA on 5 December 1997. 362
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